EP4128366A1

EP4128366A1 - Substrate for a two-terminal device

Info

Publication number: EP4128366A1
Application number: EP21716816.0A
Authority: EP
Inventors: Trevor MCARDLE
Original assignee: Power Roll Ltd
Current assignee: Power Roll Ltd
Priority date: 2020-03-27
Filing date: 2021-03-23
Publication date: 2023-02-08
Also published as: GB202004534D0; WO2021191597A1; GB202104071D0; GB2593596A

Abstract

This present invention relates to a substrate for a two-terminal electronic device. In particular, the two-terminal electronic device may be an optoelectronic device. The substrate comprises at least one series of grooves, provided on a first surface of said substrate, each groove comprising first and second opposing groove faces extending between a proximal end and a distal end across a transverse direction of said substrate, and comprising a groove base at a predetermined first depth from said first surface. The substrate also comprises at least one channel, provided on said first surface of said substrate, comprising first and second opposing channel faces, spaced apart by a predetermined channel width at a predetermined second depth from said first surface, and a channel base at a third depth from said first surface, said at least one channel being configured to transect at least one of said at least one series of grooves at a distal end portion or a proximal end portion. Said third depth is greater than said predetermined first depth, and said third depth is determined by a predetermined coating angle relative to an axis normal to said groove base, and said predetermined channel width. A shim for embossing a surface of a UV-curable coating to form a substrate for a two-terminal electronic device, and a method of forming a substrate for a two-terminal electronic device is also disclosed.

Description

SUBSTRATE FOR A TWO-TERMINAL DEVICE

[0001] This present invention relates to a substrate for a two-terminal electronic device. In particular examples, the two-terminal electronic device may be an optoelectronic device. The present invention also relates to shim for embossing a surface of a UV-curable coating to form a substrate for a two-terminal electronic device a method of forming a substrate for a two-terminal electronic device.

BACKGROUND

[0002] A two-terminal device is an electrical component having two terminals, that is, a first terminal and a second terminal. A terminal is generally defined as an area, region or portion of the electrical component that allows the ingress or egress of electrical current to, or from, the electrical component. A two-terminal device includes devices such as a diode, for example a light-emitting diode (LED). A two-terminal device also includes devices such as an optoelectronic device, or photovoltaic device, a phototransistor, a vertical-cavity surface-emitting laser (VCSEL), an energy storage device, or the like. As will be recognised by those skilled in the art, these are simply non-exhaustive examples of two-terminal devices.

[0003] In some examples, such as in optoelectronic technology, otherwise known as photovoltaics, an optoelectronic device produces electricity from light at the junction between two materials that are exposed to the light. Moreover, an optoelectronic device may produce light from the input of electricity. Typically, light used in optoelectronics is sunlight, and therefore photovoltaic is often referred to as solar photovoltaic. It is known to use semiconductors as the two materials. The semiconductor materials used exhibit a photovoltaic effect.

[0004] The semiconductor materials used are usually a p-type semiconductor material and an n-type semiconductor material. When these semiconductor materials are joined together, they form an interface therebetween often referred to as a p-n junction. Another known interface of semiconductor materials is known as a P-i-N, or PIN, junction. The p-n junction is found in most optoelectronic devices that use semiconductors. These optoelectronic devices include photovoltaic cells, solar photovoltaic cells, diodes, light-emitting diodes (LEDs) and transistors. The p-n junction can be thought of as the active site in which the generation or consumption of electrical energy occurs.

[0005] The optoelectronic device may be used as a device for generating electricity for immediate use or for storage purposes. Optoelectronic devices that are used for generating electricity for immediate use typically utilise a p-n junction having a semi-conductor therebetween. Optoelectronic devices that are used for generating electricity for storage are regarded as energy storage devices.

[0006] Existing two-terminal devices, specifically those used in optoelectronic technology, are currently relatively expensive methods of generating electricity. With increasing demands for sources of renewable energy, there is a drive to improve the efficiency of solar photovoltaic cells and to reduce costs associated with the manufacture and running of these devices. Also, existing solar photovoltaic cells remain relatively inefficient in comparison with other methods of generating electricity.

[0007] In an attempt to overcome such problems, grooved substrates have been developed for two-terminal devices, in particular, photovoltaic devices. A number of series of grooves are provided in parallel to one another, and each series of grooves is then connected in series. Such an example is illustrated in Figure 1 , which depicts a prior art device 10 including a first cell 12a, a second cell 12b and a third cell 12c. The first, second and third cells 12a, 12b, 12c may be photovoltaic cells as shown in Figure 1. In this specific example, the first, second and third cells 12a, 12b, 12c include a series of photodiodes, which may be formed as grooves in a substrate of the device 10 as described above. The grooves are first connected in parallel to one another to form respective series of grooves, thus forming cells 12a, 12b, 12c, and then each series of grooves, or each cell 12a, 12b, 12c, is connected in series to one another.

[0008] However, such a configuration provides the disadvantage that, in the event of an unintentional electrical short, a significant impact in the performance of the two-terminal device may be observed. Moreover, in conventional substrates, such as those illustrated in Figure 1, a bypass diode (not shown) is typically needed to provide an electrical pathway around one or more of the cells 12a, 12b, 12c, in case a portion of the photodiodes are shaded, in use, such that the photodiodes in one or more cells 12a, 12b, 12c cannot convert light energy into electrical energy. That is, when a portion of the device is shaded, one or more cells 12a, 12b, 12c may be non-functional. If a portion of the device is shaded, the performance of the whole substrate is degraded and, in some examples, this may also cause damage to the substrate. Thus, bypass diodes are typically provided to mitigate these disadvantages by providing an alternative current path around any non-functional cells 12a, 12b, 12c.

[0009] One solution to this problem is to use an interdigitated grooved arrangement to connect sections of grooves in parallel with each other. However, such a configuration requires that each cell is to be wired together in series to provide a single module, which is commercially undesirable. [0010] In an attempt to provide an improved solution, further grooved substrates for two- terminal devices have been developed. Such grooved substrates provide a number of series of grooves, each groove within a series of grooves being connected in series, and each series of grooves being connected in parallel or in series to one another. The adjacent series of grooves are electrically separated from one another by a delineation feature, such as a channel. The delineation feature typically transects, or intersects, one or more grooves of a first series of grooves at one end of the delineation feature, and one or more grooves of a second series of grooves at the other end of the delineation feature. In this way, once the grooves are coated and filled with appropriate materials to form a two-terminal device, the grooves within a series of grooves are electrically connected in series across the surface of the substrate, thereby allowing voltage addition across the machine direction of the substrate. Thus, by altering the number of grooves in a series of grooves, the output voltage of the two-terminal device can be controlled.

[0011] Moreover, the delineation feature electrically isolates adjacent series of grooves. First and second terminals of the two-terminal device are provided at opposing sides of the substrate, arranged to extract charge from each series of grooves. The first terminal is electrically connected to a first groove of a series of grooves and the second terminal is electrically connected to a last groove of the same series.

[0012] Whilst such two-terminal devices having grooved substrates tend to be more efficient and less expensive to manufacture than other known two-terminal devices, such grooved substrates can be prone to manufacturing defects. In particular, during the manufacture of such grooved devices, the ends of the grooves are coated, adjacent the transecting delineation feature, during a coating process, which allows electrical connectivity between an end of each of the grooves. In this way, an unintentional electrical short may be provided, for example between groove faces. The unintentional electrical short thereby prevents voltage addition across the substrate, thus reducing the efficiency and/or reliability of the two-terminal device. Oftentimes, manufacturers accept such relatively minor losses in efficiency and reliability.

[0013] Alternatively, or additionally, it is also commonplace to unintentionally coat an end of the grooves to the extent that it contacts a material filled within the delineation feature, thereby allowing electrical connectivity between the grooves and the delineation feature. This type of electrical short is highly undesirable, as the efficiency of the device is often dramatically reduced and, in some cases, reduced to the extent that the manufacture of such a device is not commercially viable. In an attempt to overcome such a problem, manufactures seek to mediate the amount of material filled within the delineation feature. However, this can be time consuming, expensive and, oftentimes, unsuccessful. [0014] Therefore, it is an aim of the present invention to provide a substrate for a two- terminal device that mitigates at least one or more of the aforementioned problems. It would also be desirable to provide a two-terminal device having a substrate that mitigate at least one or more of the aforementioned problems.

SUMMARY OF THE INVENTION

[0015] As used herein, the term “groove” is used to describe a depression in a substrate having an elongated length, a width and a depth.

[0016] As used herein, the term “channel” is used to describe a delineation feature, or a structural delineation feature, that serves to electrically isolate adjacent series of grooves. The channel may take the form of a depression in a substrate, have an elongated length, a width and a depth, the depth being greater than a depth of a groove.

[0017] As used herein, the term “transection region” is used to describe the region in which the groove transitions to the channel at an intersection, or at a transection. That is, where a groove and a channel transect, the transection region is the transition from the groove, having groove characteristics such as a groove depth, to the channel, having channel characteristics such as a channel depth.

[0018] As used herein, the term “tends” is used to describe the transition from a first feature to a second feature. In particular, the term “tends” is used to describe the transition between the depth of a groove, that is the depth of a groove base from the substrate surface, and the depth of a channel transecting the groove, that is the depth of a channel base from the substrate surface. In the region in which the groove “tends” to the channel, there may be a variation in depth within the substrate and/or a transition between the profile of the groove and the profile of the channel. For example, a depth of a groove may tend to a depth of a channel in the sense that there is a variation, along an axis, for example in the depth of the groove base, from the depth of the groove to the depth of the channel. For example, a depth of a groove, that is the depth of a groove base, may tend towards, or to, a depth of the channel, that is the depth of a channel base. In other words, the depth of a groove base varies from the depth of the groove towards, or to, the depth of the channel, along an axis formed by the elongate base of the groove.

[0019] As used herein, the term “depth” is used to describe the measurement from a surface to a base of the relevant feature. For example, a depth of a groove refers to the measurement from the surface of the substrate in which it is formed to the base of the groove. For example, a depth of a channel refers to the measurement from the surface of the substrate in which it is formed to the base of the channel. For example, a depth of a transection region refers to the measurement from the surface of the substrate in which it is formed to the base of the groove within the transection region.

[0020] As used herein, the term “aspect ratio” is used to describe a ratio between width and depth of a feature. The aspect ratio is presented as width : depth or width / depth.

[0021] In accordance with one aspect of the present invention, there is provided a substrate for a two terminal device, including: at least one series of grooves, provided on a first surface of said substrate, each groove including first and second opposing groove faces extending between a proximal end and a distal end across a transverse direction of said substrate, and including a groove base at a predetermined first depth from said first surface, and at least one channel, provided on said first surface of said substrate, including first and second opposing channel faces, spaced apart by a predetermined channel width at a predetermined second depth from said first surface, and a channel base at a third depth from said first surface, said at least one channel being configured to transect at least one of said at least one series of grooves at a distal end portion or a proximal end portion, wherein said third depth is greater than said predetermined first depth, and said third depth is determined by a predetermined coating angle relative to an axis normal to said groove base, and said predetermined channel width.

[0022] In certain embodiments, said third depth is determined by the equation: said predetermined channel width said third depth - - - - - - a Tangent function of said predetermined coating angle

[0023] In certain embodiments, said transected distal end portion or said transected proximal end portion of said groove includes a transection region in which said groove base tends towards said channel base forming a transection surface having a first transection depth at a groove end and a second transection depth at a channel end.

[0024] In certain embodiments, said transection surface has a non-linear surface profile between said groove end and said channel end.

[0025] In certain embodiments, said second transection depth is equal to said predetermined second depth.

[0026] In certain embodiments, said transection surface in said transection region is substantially arcuate.

[0027] In certain embodiments, said groove end of said transection surface tends linearly towards said channel end. [0028] In certain embodiments, said groove end of said transection surface tends linearly towards said channel end at an angle that is greater than 0° and less than 90°relative to a longitudinal axis of said groove base.

[0029] Certain aspects of the invention provide the advantage that electrical shorts are prevented at the interface between a series of grooves and the channel. In particular, during manufacture of two-terminal devices using such substrates, a wall of the channel shadows, or shields or masks, at least a portion of the transection region, such that material is not coated within at least a portion of the transection region during manufacture. Thus, an electrical pathway between the ends of grooves, and between an end of a groove and the channel, is prevented.

[0030] Furthermore, electrical shorts are avoided irrespective of the amount of material filled within the channel during the manufacturing process. A two-terminal device manufactured using the substrate described herein is more tolerant of overfill of the channel with material, without being susceptible to an electrical short. Thus, a more efficient and/or reliable two-terminal device may be formed using the substrate described herein. Furthermore, the manufacturing of a two-terminal device using the substrate described herein may be more cost effective and/or less cumbersome.

[0031] In certain embodiments, said first and second opposing groove faces provide a groove width at said first surface of said substrate, and wherein said groove has an aspect ratio of at least 1:1 , preferably at least 1 :1.2.

[0032] In certain embodiments, said at least one channel has an aspect ratio of at least 1 :1.6.

[0033] In certain embodiments, said transection region has an aspect ratio that tends from at least 1:1, preferably 1:1.2, to at least 1 :1.6.

[0034] In certain embodiments, said at least one channel extends across said first surface in first direction to transect at least one of a first series of groove, and wherein said first direction is at an angle of greater than 0° and less than 90° relative to said transverse direction.

[0035] In certain embodiments, said first direction is at an angle relative to the transverse direction either within the range 5° to 85° or within the range -5° to -85°.

[0036] In certain embodiments, said at least one channel is substantially Z-shaped having a predetermined angle.

[0037] Certain aspects of the invention provide the advantage that the shadowing effect, during manufacture of two-terminal devices using such substrates, is increased, thus less material is coated at the interface between a series of grooves and a channel. As discussed above, this prevents electrical shorts and thus improves the efficiency and reliability of the resulting two-terminal device.

[0038] In certain embodiments, a substrate includes a first series of grooves and a second series of grooves, and a at least one channel transecting at least one of said first series of grooves and at least one of said second series of grooves at the respective distal end portions or the respective proximal end portions of each groove.

[0039] In certain embodiments, said at least one channel includes a first channel portion arranged to transect each groove of said first series of grooves at a distal end portion, and a second channel portion arranged to transect each groove of said second series of grooves at a proximal end portion, wherein said first and second channel portions are spaced apart on said first surface by a third channel portion, and wherein said third channel portion includes a plurality of parallelly spaced channel portions.

[0040] In certain embodiments, said first, second and third channel portions are substantially Z-shaped having a predetermined angle

[0041] In certain embodiments, said at least one channel includes a plurality of channels.

[0042] In certain embodiments, each channel of said plurality of channels transects at least one of a first series of grooves and at least one a second series of grooves towards said proximal end of each groove.

[0043] In certain embodiments, each channel of said plurality of channels transects each groove of said first series of grooves and each groove of said second series of grooves towards said proximal end of each groove.

[0044] In certain embodiments, each channel of the plurality of channels is substantially Z-shaped having a predetermined angle.

[0045] In certain embodiments, said predetermined angle is between approximately 0 degrees and approximately 90 degrees, preferably between approximately 30 degrees and approximately 60 degrees. In certain embodiments, the predetermined angle is between approximately 0 degrees and approximately -90 degrees (i.e. minus 90 degrees), preferably between approximately -30 degrees and approximately -60 degrees

[0046] Certain aspects provide the advantage that the electrical pathway across the region between series of grooves is increased, thereby reducing the likelihood of an electrical short across such a region. In particular, a plurality of channels may provide redundancy in the event that one channel becomes filled with a material during manufacture and thus provides an electrical pathway across the same. That is, by having a plurality of channels, the likelihood of providing an electrical pathway across each of the channels is reduced. Typically, the more channels used results in a lower likelihood of an electrical short.

[0047] Certain aspects provide the advantage that the electron transfer path, from the first series of grooves to the second series of grooves, is lengthened, thus increasing the characteristic resistance of the substrate between each series of grooves. Thus, the characteristic resistance of the substrate between the series of grooves may be tuned.

[0048] In accordance with another aspect of the present invention, a two-terminal device, for example an optoelectronic device, is provided which includes at least one of said substrates described herein.

[0049] In accordance with a further aspect of the present invention, there is provided a shim for embossing a surface of UV-curable coating provided on a flexible web, including: at least one series of protrusions, provided on a first surface of said shim, each protrusion including first and second opposing protrusion surfaces extending between a proximal end and a distal end along a first direction of said surface, and including a protrusion apex at a predetermined first distance from said first surface, and at least one elongate projection provided on said first surface of said shim, said at least one elongate projection configured to transect at least one of said at least one series of protrusions at a distal end portion or a proximal end portion, wherein said elongate projection includes first and second opposing projection surfaces spaced apart by a predetermined projection width at a predetermined second distance from said surface, and a ridge apex at a third distance from said first surface, wherein said third distance is greater than said first distance, and wherein said third distance is determined by a predetermined angle relative to a normal to said protrusion apex, and said predetermined ridge width.

[0050] In certain embodiments, said third distance is determined by the equation: said predetermined channel width said third distance - - - - - - a Tangent function of said predetermined coating angle

[0051] In certain embodiments, said second distance is a vertical distance from said first surface of said protrusion apex at said transected distal end portion or said transected proximal end portion.

[0052] In certain embodiments, said at least one elongate projection extends across said first surface of said shim in a second direction to transect at least one of a first series of protrusions, and wherein said second direction is at an angle of greater than 0° and less than 90°relative to said first direction. [0053] In certain embodiments, said second direction is at an angle relative to said first direction either within the range 5° to 85° or within the range -5° to -85°.

[0054] Certain aspects provide the advantage that the transection region that tends from the depth of the groove to the depth of the channel is integrally formed in a single manufacturing process. Thus, the manufacture of such substrates may be more efficient and less expensive.

[0055] Certain aspects provide the advantage that a single stamping process can be used to form the grooves and the channel, thereby improving the efficiency and scalability of the manufacturing of such substrates.

[0056] In accordance with another aspect of the present invention, there is provided a method of forming a substrate for a two-terminal device, including: providing a flexible web, coating a first surface of said flexible web with a UV-curable coating, engaging a shim with said UV-curable coating so that said first surface of said shim embosses said UV-curable coating with said at least one series of protrusions and said at least one elongate protection, at least partially curing said UV-curable coating, and removing said at least one series of protrusions and said at least one elongate protection from said UV-curable coating before said UV-curable coating is fully cured.

[0057] In accordance with a further aspect of the present invention, there is provided a substrate for a two-terminal device, including at least one series of grooves, each groove having a proximal end and a distal end across the transverse direction of the substrate, and at least one channel transecting a portion of the at least one series of grooves towards at least one of the distal end and the proximal end of each groove, and wherein the depth of each groove tends towards the depth of the channel in a transection region towards the respective transected distal end and/or proximal end of each groove.

[0058] In certain embodiments, the substrate includes a first series of grooves and a second series of grooves, the at least one channel, or a channel, transecting a portion of the first series of grooves and a portion of the second series of grooves towards the proximal end of each groove.

[0059] That is to say, in one particular aspect of the present invention, there is provided a substrate for a two-terminal device, including a first series of grooves and a second series of grooves, each groove having a proximal end and a distal end across the transverse direction of the substrate, and a channel transecting a portion of the first series of grooves and a portion of the second series of grooves towards the proximal end of each groove, and wherein the depth of each groove tends towards the depth of the channel in a transection region towards the proximal end of each groove.

[0060] That is, each groove of the substrate includes a proximal end and a distal end across the transverse direction of the substrate. The proximal end may be proximal to a first edge of the substrate. The distal end may be distal to the first edge of the substrate. Each groove of the first series of grooves and each groove of the second series of grooves may include a proximal end and a distal end.

[0061] The channel transects one or more, that is a portion, of both the first series of grooves and the second series of grooves. The channel transects each groove, of the series of grooves in which it transects, towards the proximal end of each transected groove. The channel may transect each groove substantially towards, that is near to, or at the proximal end of each groove.

[0062] The channel may transect a portion, that is part of, the first series of grooves and the second series of grooves. The channel may transect a majority, that is most of, the first series of grooves and the second series of grooves. The channel may transect each of, that is the entirety of, the first series of grooves and the second series of grooves.

[0063] The depth of each groove, that is each groove of the first series of grooves and the second series of grooves that transects the channel, also referred to as a transected groove, tends towards the depth of the channel in a transection region towards the proximal end of each groove. That is, there may be provided a groove region, a transection region and a channel region. The groove region is the portion of the transected groove that is not yet transected, that is, the portion at which the transected grove has a depth equal to the groove depth. The transection region is the portion of the transected groove that is transected, that is, the portion at which the depth of the groove tends towards the depth of the channel. The channel region is the portion of the channel that is not transected, that is, the portion at which the channel has a depth equal to the channel depth. The transection region is generally provided towards, that is near to or at, the proximal end of each groove that is transected.

[0064] During the manufacture of two-terminal devices making use of such substrates, an off-axis directional coating process is often used, in which one face of the grooves, and the delineation feature, for example the channel, is selectively coated. This is particularly useful for roll-to-roll manufacture of such two-terminal devices, as the manufacturing process can be carried out as a continuous process, rather than a batch process. In such cases, the opposing face of the grooves casts a shadow onto the face to be coated, such that only a portion of the face to be coated can be coated by the incoming material. This is known as the “shadowing effect”. Thus, the shadowing effect governs the amount of material deposited on a face of the grooves. The shadowing effect can be modified by increasing or decreasing the angle of the off-axis directional coating.

[0065] The substrate, such as a flexible substrate, may be provided as a length of continuous flexible substrate. In some examples, the length of continuous flexible substrate is provided on a roll or a roll core. This provides roll-to-roll continuous manufacture, which provides a more cost and labour efficient manufacturing process. In some particular examples, the length of the continuous flexible substrate is up to 6000m, that is less than or equal to 6000m.

[0066] Thus, certain aspects of the invention provide the advantage that electrical shorts are prevented at the interface between a series of grooves and the channel. In particular, during manufacture of two-terminal devices using such substrates, a wall of the channel shadows, or shields or masks, at least a portion of the transection region, such that material is not coated within at least a portion of the transection region during manufacture. Thus, an electrical pathway between the ends of grooves, and between an end of a groove and the channel, is prevented.

[0067] Furthermore, electrical shorts are avoided irrespective of the amount of material filled within the channel during the manufacturing process. A two-terminal device manufactured using the substrate described herein is more tolerant of overfill of the channel with material, without being susceptible to an electrical short. Thus, a more efficient and/or reliable two-terminal device may be formed using the substrate described herein. Furthermore, the manufacturing of a two-terminal device using the substrate described herein may be more cost effective and/or less cumbersome.

[0068] In certain embodiments, the depth of each groove tends non-linearly towards the depth of the channel.

[0069] In certain embodiments, the depth of each groove tends in a non-linear manner towards the depth of the channel. That is, in certain embodiments, the transection region has a variable depth that tends from the groove depth to the channel depth in a non-linear manner. That is, in certain embodiments, the depth of each groove tends variably towards the depth of the channel.

[0070] In certain embodiments, the depth of each groove tends gradually towards the depth of the channel.

[0071] That is, in certain embodiments, the depth of each groove tends at a constant rate from the groove depth to the channel depth. That is, in certain embodiments, the transection region may tend from the groove depth to the channel depth at a constant rate. [0072] In certain embodiments, the depth of each groove tends gradually and non-linearly towards the depth of the channel.

[0073] In certain embodiments, the transection region is substantially arcuate.

[0074] That is, in certain embodiments, the transection region forms a substantially arc shaped region.

[0075] In certain embodiments, each groove tends linearly towards the depth of the channel.

[0076] In certain embodiments, the depth of each groove tends in a linear manner towards the depth of the channel. That is, in certain embodiments, the transection region has a constant slope from the depth of the groove to the depth of the channel.

[0077] In certain embodiments, the depth of each groove tends linearly towards the depth of the channel at an angle of between 0 degrees and 90 degrees, excluding 0 degrees and 90 degrees, formed with respect to an axis extending along the elongate base of each groove.

[0078] In certain embodiments, an angle is formed between an imaginary axis extending along the entirety of the elongate base of each groove, and the transection region. Such an angle may be formed between 0 degrees and 90 degrees, that is excluding 0 degrees and 90 degrees. The angle may be formed between 10 degrees and 80 degrees. The angle may be formed between 20 degrees and 70 degrees. The angle may be formed between 30 degrees and 60 degrees. The angle may be formed between 40 degrees and 50 degrees. The angle may be formed at substantially 45 degrees. The lower limit of the angle may be 1 degree, 5 degrees, 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 85 degrees or any integer therebetween. The upper limit of the angle may be 5 degrees, 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 85 degrees, 89 degrees or any integer therebetween. As will be recognised by the person skilled in the art, any combination of lower limit and upper limit may be used, as well as, the angle polarity.

[0079] In certain embodiments, the channel is substantially Z-shaped having a predetermined angle.

[0080] That is, in certain embodiments, the channel may form a substantial Z-shape, for example, when viewed from above. In some embodiments, the channel may include a first region and a second region in parallel and each connected to a third region extending therebetween. The first region may transect a portion of the first series of grooves, and the second region may transect a portion of the second series of grooves. The predetermined angle may be formed between the first region and the third region, or between the second region and the third region. That is, there may be a first predetermined angle formed between the first region and the third region, and a second predetermined angle between the second region and the third region. In other embodiments, the first predetermined angle and the second predetermined angle are equal, that is, there is a predetermined angle formed between the first region and the third region, and the second region and the third region. The first region, the second region or both the first region and the second region may extend along the machine direction of the substrate. The third region may extend along the transverse direction of the substrate.

[0081] In certain embodiments, the predetermined angle is, or the first and the second predetermined angles independently are, in the range of 0 degrees to 90 degrees, excluding 0 degrees and excluding 90 degrees. In other embodiments, the predetermined angle is, or the first and the second predetermined angle independently are, in the range of 0 degrees to 180 degrees, excluding 0 degrees and 180 degrees. In some embodiments, the predetermined angle is, or the first and the second predetermined angles independently are, between 0 degrees and 90 degrees, that is, excluding 0 degrees and 90 degrees. In some embodiments, the predetermined angle is, or the first and the second predetermined angles independently are, in the range of 30 degrees to 60 degrees, including 30 degrees or 60 degrees or including 30 degrees and 60 degrees. In some embodiments, the predetermined angle is, or the first and the second predetermined angles independently are, between 30 degrees and 60 degrees, that is excluding 30 degrees and 60 degrees. In some embodiments, the predetermined angle is, or the first and the second predetermined angles independently are, in the range of 40 degrees to 50 degrees, including 40 degrees or 50 degrees or including 40 degrees and 50 degrees. In some embodiments, the predetermined angle is, or the first and the second predetermined angles independently are, between 40 degrees and 50 degrees, that is excluding 40 degrees and 50 degrees. It may be preferable that the predetermined angle is, or the first and the second predetermined angles independently are, approximately 45 degrees

[0082] In certain embodiments, the predetermined angle, or the first and the second predetermined angles independently, may have a lower limit of 1 degree, 5 degrees, 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, 150 degrees, 155 degrees, 160 degrees, 165 degrees, 170 degrees, 175 degrees, or any integer therebetween. The upper limit of the predetermined angle, or the first and the second predetermined angles independently, may be 5 degrees, 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 85 degrees, 90 degrees, 95 degrees, 100 degrees, 105 degrees, 110 degrees, 115 degrees, 120 degrees, 125 degrees, 130 degrees, 135 degrees, 140 degrees, 145 degrees, 150 degrees, 155 degrees, 160 degrees, 165 degrees, 170 degrees, 175 degrees, 179 degrees or any integer therebetween. As will be recognised by the person skilled in the art, any combination of lower limit and upper limit may be used.

[0083] In certain embodiments, the predetermined angle, or the first and the second predetermined angles independently, may have an upper limit of greater than 90 degrees.

[0084] Certain aspects provide the advantage that the shadowing effect, during manufacture of two-terminal devices using such substrates, is increased, thus less material is coated at the interface between a series of grooves and a channel. As discussed above, this prevents electrical shorts and thus improves the efficiency and reliability of the resulting two-terminal device.

[0085] In certain embodiments, each groove has an aspect ratio of at least 1 :1 , preferably at least 1 :1.2 [along the length of the groove] from the distal end to the proximal end, excluding the transection region. In certain embodiments the groove aspect ratio from distal end to proximal end is adapted to provide shadowing of the base of the groove. That is, the groove aspect ratio is adapted such that the groove base is shaded by one or both sides of the groove. In these ways, the groove aspect ratio is adapted such that incoming coating material for a wide range of coating angles cannot be deposited on the groove face at, or in proximity to the groove base.

[0086] That is, in certain embodiments, an aspect ratio of each groove is at least 1:1. It may be preferable that the aspect ratio is at least 1 :1.2. That is, in certain embodiments, the aspect ratio of each groove is 1:1 or greater, and it may be preferably that the aspect ratio of each groove is 1 : 1.2 or greater.

[0087] Aspect ratio refers to the ratio between the width of the groove, that is the width of the groove at the substrate surface measured from a first face to a second, opposing, face, to the depth of the groove, that is the depth of the groove from the surface of the substrate to the base of the groove. That is, the aspect ratio of each groove may be regarded as width:depth of each groove. That is, the aspect ratio of the groove is measured along the elongate length of the groove from the distal end to the proximal end, excluding the transection region. That is, the aspect ratio of the groove is measured from the distal end of each groove up until the transection region of each groove. The aspect ratio between the distal end of each groove to the proximal end, excluding the transection region, may be substantially constant. In some examples, it may be preferable that the depth of each groove is greater than the width of each groove.

[0088] In certain embodiments, the channel has an aspect ratio of at least 1 :1.6.

[0089] That is, in certain embodiments, an aspect ratio of the channel is at least 1 :1.6. That is, in some embodiments, the aspect ratio of the channel is 1 : 1.6 or greater. It may be preferable that the depth of the channel is greater than the depth of the groove.

[0090] Aspect ratio refers to the ratio between the width of the channel, that is the width of the channel measured from a first face to a second, opposing, face, to the depth of the channel, that is the depth of the channel from the surface of the substrate to the base of the channel. That is, the aspect ratio of the channel may be regarded as width:depth (i.e. width divided by depth) of the channel. That is, the aspect ratio of the channel is measured along the elongate length of the channel. It may be preferable that the depth of the channel is greater, or much greater, than the depth of each groove.

[0091] In certain embodiments, the transection region has an aspect ratio that tends from at least 1:1 , preferably 1 : 1.2, to at least 1 :1.6.

[0092] That is, in certain embodiments, an aspect ratio of the transection region tends from at least 1 :1, or from 1 :1, preferably from at least, or from, 1 :1.2, to at least 1 :1.6 or to 1 :1.6. The aspect ratio of the transection region may tend from greater than 1 :1 to 1 : 1.6. The aspect ratio of the transection region may tend from 1:1 to greater than 1 :1.6.

[0093] Aspect ratio refers to the ratio between the width of each groove within the transection region, that is the width of each groove measured from a first face to a second, opposing, face, to the depth of each groove within the transection region, that is the depth of each groove from the surface of the substrate to the base of each groove. That is, the aspect ratio of each groove within the transection region may be regarded as width:depth of each groove within the transection region. That is, the aspect ratio of each groove is measured along the elongate length of the transection region.

[0094] In certain embodiments, the channel transects each groove of the first series of grooves and/or the second series of grooves.

[0095] That is, in certain embodiments, the channel transects each groove of the first series of grooves, or each groove of the second series of grooves, or each groove of the first series of grooves and each groove of the second series of grooves.

[0096] In certain embodiments, the substrate includes a plurality of channels. [0097] That is, in certain embodiments, the substrate includes more than one channel, or two or more channels. Any number of channels may be used.

[0098] Certain aspects provide the advantage that the electrical pathway across the region between series of grooves is increased, thereby reducing the likelihood of an electrical short across such a region. In particular, a plurality of channels may provide redundancy in the event that one channel becomes filled with a material during manufacture and thus provides an electrical pathway across the same. That is, by having a plurality of channels, the likelihood of providing an electrical pathway across each of the channels is reduced. Typically, the more channels used results in a lower likelihood of an electrical short.

[0099] In certain embodiments, each channel of the plurality of channels transects a portion of the first series of grooves and a portion of the second series of grooves towards the proximal end of each groove.

[00100] That is, in certain embodiments, each channel of the plurality of channels transects one or more, that is a portion of, the first series of grooves and one or more, that is a portion of, the second series of groves. The portion of the first series of grooves is transected towards, that is at or near, the proximal end of each groove of the first series of grooves. The portion of the second series of grooves is transected towards, that is at or near, the proximal end of each groove of the second series of grooves.

[00101] In certain embodiments, each channel of the plurality of channels transects each groove of the first series of grooves and each groove of the second series of grooves towards the proximal end of each groove.

[00102] That is, in certain embodiments, each channel of the plurality of channels transects the entirety of, that is all of, the grooves of the first series of grooves and the entirety of, that is all of, the grooves of the second series of grooves. Each groove of the first series of grooves is transected towards, that is at or near, the proximal end of each groove of the first series of grooves. Each groove of the second series of grooves is transected towards, that is at or near, the proximal end of each groove of the second series of grooves.

[00103] In certain embodiments, each channel of the plurality of channels transects a portion of the first series of grooves and each groove of the second series of grooves towards a proximal end of each groove. That is, in some embodiments, each channel of the plurality of channels transects one or more of, that is a portion of, the first series of grooves and the entirety of, that is all of, of the grooves of the second series of grooves. In some embodiments, each channel of the plurality of channels transects each groove of the first series of grooves and a portion of the second series of grooves towards a proximal end of each groove. That is, in some embodiments, each channel of the plurality of channels transects the entirety of, that is all of, the first series of grooves and one or more of, that is a portion of, the second series of grooves.

[00104] In certain embodiments, each channel of the plurality of channels is substantially Z-shaped having a predetermined angle.

[00105] That is, in certain embodiments, each channel of the plurality of channels may form a substantial Z-shape, for example, when viewed from above. In some embodiments, each channel may include a first region and a second region in parallel and each connected to a third region extending therebetween. The first region may transect a portion of the first series of grooves, and the second region may transect a portion of the second series of grooves. The predetermined angle may be formed between the first region and the third region, or between the second region and the third region. That is, there may be a first predetermined angle formed between the first region and the third region, and a second predetermined angle between the second region and the third region. In other embodiments, the first predetermined angle and the second predetermined angle are equal, that is, there is a predetermined angle formed between the first region and the third region, and the second region and the third region. The first region, the second region or both the first region and the second region may extend along the machine direction of the substrate. The third region may extend along the transverse direction of the substrate. The substantially Z-shaped channel(s) formed may include any of the features described above in relation to Z-shaped channels, including predetermined angles.

[00106] In certain embodiments, each Z-shaped channel of the plurality of channels may extend through the substrate in parallel to one another. That is, each Z-shaped channel of the plurality of channels may be off-set. In some examples, the first region of each channel runs in parallel, the second region of each channel runs in parallel, and the third region of each channel runs in parallel.

[00107] In certain embodiments, one or more of the channels of the plurality of channels is or are substantially Z-shaped. The remaining channels of the plurality of channels may not be Z-shaped.

[00108] Certain embodiments provide the advantage that the shadowing effect, during manufacture of two-terminal devices using such substrates, is increased, thus less material is coated at the interface between a series of grooves and a channel. As discussed above, this prevents electrical shorts and thus improves the efficiency and/or reliability of the resulting two-terminal device.

[00109] In certain embodiments, the substrate further includes a first transection channel transecting each channel of the plurality of channels at their distal ends, the first transection channel transecting the entirety the first series of grooves towards the proximal end of each groove; and a second transection channel transecting each channel of the plurality of channels at their proximal ends, the second transection channel transecting the entirety of the second series of grooves towards the proximal end of each groove.

[00110] That is, in certain embodiments, there is provided a plurality of channels, each channel having a distal end and a proximal end across the transverse direction of the substrate. The distal end of each channel may be distal to a first edge of the substrate.

The proximal end of each channel may be proximal to the first edge of the substrate. Each channel may be transected by a first transection channel at the distal end. Each channel may be transected by a second transection channel at the proximal end. The first transection channel may further transect the entirety, that is all, of the first series of grooves. In other examples, the first transection channel may further transect at least a portion or a portion, that is some, of the first series of grooves. The second transection channel may further transect the entirety, that is all, of the second series of grooves. In other examples, the second transection channel may further transect at least a portion or a portion, that is some, of the second series of grooves.

[00111] In certain embodiments, the first transection channel is parallel to the second transection channel. In some embodiments, the first transection channel and the second transection channel run along the web direction, i.e. the longitudinal or machine direction, of the substrate. In some embodiments, each channel of the plurality of channels runs substantially along the transverse direction of the substrate.

[00112] Certain embodiments provide the advantage that the electrical pathway across the region between series of grooves is increased, thereby reducing the likelihood of an electrical short across such a region. In particular, a plurality of channels may provide redundancy in the event that one channel becomes filled with material during manufacture and thus provides an electrical pathway across the same. That is, by having a plurality of channels, the likelihood of providing an electrical pathway across each of the channels is reduced. Typically, the more channels used results in a lower likelihood of an electrical short. Furthermore, the arrangement of transection channels and a plurality of channels therebetween may increase the ease of manufacture of such substrates.

[00113] In certain embodiments, the first transection channel, the plurality of channels, and the second transection channel substantially form a Z-shape having a predetermined angle.

[00114] That is, in certain embodiments, the first transection channel and the second transection channel are parallel, and the plurality of channels extend therebetween. [00115] That is, in certain embodiments, the first transection region, the plurality of channels and the second transection region may form a substantial Z-shape, for example, when viewed from above. In some embodiments, the predetermined angle may be formed between the first transection channel and each channel of the plurality of channels, or between the second transection channel and each channel of the plurality of channels. That is, there may be a first predetermined angle formed between the first transection channel and each channel of the plurality of channels, and a second predetermined angle between the second transection channel and each channel of the plurality of channels. In other embodiments, the first predetermined angle and the second predetermined angle are equal, that is, there is a predetermined angle formed between the first transection channel and each channel of the plurality of channels, and the second transection channel and each channel of the plurality of channels. The first transection channel, the second transection channel or both the first transection channel and the second transection channel may extend along the machine direction of the substrate. Each channel of the plurality of channels may extend along the transverse direction of the substrate. The substantially Z-shaped channel(s) formed may include any of the features described above in relation to Z-shaped channels, including predetermined angles.

[00116] In certain embodiments, the channel, or one or more of the plurality of channels, includes a rutted-base, a rutted-wall and/or a non-conductive electrical insulator material therein.

[00117] That is, in certain embodiments, the channel, or one of more of the plurality of channels, may include a rutted-bottom or a rutted base. That is, the bottom, or the base, of the channel, or one or more of the plurality of channels, may be rutted in that the bottom, or the base, is jagged, uneven, undulated or the like.

[00118] Additionally, or alternatively, the channel, or one or more of the plurality of channels, may include a rutted-wall. That is, the wall of the channel, or one or more of the plurality of channels, may be rutted in that the wall is jagged, uneven, undulated or the like.

[00119] Additionally, or alternatively, the channel, or one or more of the plurality of channels, may include a non-conductive electrical insulator material within the channel or one or more of the plurality of channels. The non-conductive electrical insulator may partially, mostly, or entirely fill the channel or one or more of the plurality of channels.

[00120] Certain aspects provide the advantage that a characteristic resistance of the channel may be increased. Thus, the characteristic resistance of a portion of the substrate between he first series of grooves and the second series of grooves may be tuned. [00121] In certain embodiments, the channel, or one or more of the plurality of channels, has an aspect ratio of at least 1:1.6

[00122] That is, in certain embodiments, the channel, or one or more of the plurality of channels, has an aspect ratio that may be 1 :1.6 or greater than 1:1.6, for example, 1 :1.8, 1 :1.9, 1 :2.0 or the like. The term aspect ratio is used to define a ratio between the width and the depth. Thus, an aspect ratio of at least 1:1.6 may be regarded as a ratio of 1 :1.6, referring to the width:depth of the channel or one or more of the plurality of channels, or greater. That is, the depth of the channel or one or more of the plurality of channels may be greater than the width of the channel.

[00123] Certain aspects provide the advantage that the electron transfer path, from the first series of grooves to the second series of grooves, is lengthened, thus increasing the characteristic resistance of the substrate between each series of grooves. Thus, the characteristic resistance of the substrate between the series of grooves may be tuned.

[00124] In certain embodiments, the channel, or one or more of the plurality of channels, has an aspect ratio of at least 1.6:1.

[00125] Certain aspects provide the advantage that the electron transfer path, across the width of the channel or one or more of the plurality of channels, is increased, thus reducing the likelihood that an electron may “hop” across the gap formed by the respective channel, thus reducing the likelihood of electrical shorts.

[00126] In certain embodiments, the substrate includes a peak, a discontinuous non insulating coating and/or a rutted portion. In some embodiments, the peak, the discontinuous non-insulating coating and/or the rutted portion may be adjacent to the channel, or one or more of the plurality of channels. In some embodiments, the peak, the discontinuous non insulating coating and/or the rutted portion may be between the first series of groove and the second series of grooves.

[00127] That is, in certain embodiments, the substrate may include, may include or may be formed of one or more peaks of the substrate, that is, one or more projections, protrusions or the like formed in the substrate.

[00128] Alternatively, or additionally, the substrate may include, may include or may be formed of a discontinuous non-insulating coating of the substrate. That is, a non-insulating coating may be deposited on the substrate to provide one or more resistive elements. The non-insulating coating may be discontinuous in that there is discontinuity across the substrate in the web direction. The non-insulating coating may be formed by etching, or removing, a portion of another coating of the substrate to expose a non-insulating coating. The non-insulating coating may be discontinuous in that there is discontinuity across the substrate in the web direction. In some embodiments, the discontinuous non-insulating coating may be formed by masking of a region of the connecting portion during manufacture. Thus, a region of the connecting portion may be devoid of conductive material.

[00129] Alternatively, or additionally, the substrate may include, may include or may be formed of a rutted portion of the substrate. That is, in certain embodiments, the substrate may have one or more rutted portions or regions. A rutted-potion may be defined as a jagged, uneven, undulated surface or the like.

[00130] Further, as described below, any of the features contemplated herein may be combined. For example, the disclosed transection region, tending from a groove depth to a channel depth, may be used in combination with one channel, a plurality of channels, channels having rutted-walls, rutted-bases and/or non-insulating electrical material therein, channels having aspect ratios of at least 1 : 1.6 or at least 1.6:1, and/or portions of the substrate including one or more peaks, discontinuous non-insulating electrical coatings and/or rutted portions. Thus, the transection region may prevent electrical shorting across an end of each groove, in combination with the abovementioned features to prevent electrical shorting across the or each channel, i.e. from the first series of grooves to the second series of grooves.

[00131] In another aspect according to the present invention, there is provided a two- terminal device includes a substrate as described herein.

[00132] In certain embodiments, the two-terminal device is an optoelectronic device.

[00133] In certain embodiments, the optoelectronic device is a solar photovoltaic device.

[00134] In certain embodiments, the solar photovoltaic device is an energy storage device.

[00135] In another aspect according to the present invention, there is provided a method of forming a substrate for a two-terminal device, including: providing a web of flexible material; forming at least one series of grooves within the web of flexible material; forming a channel within the web of flexible material, the channel transecting a portion of the at least one series of grooves towards at least one of a distal end and a proximal end of each groove, wherein the step of forming a channel includes forming a transection region in which the depth of each groove that tends towards the depth of the channel at the respective transected distal end and/or proximal end of each groove.

[00136] In certain embodiments the step of forming at least one series of grooves within the web of flexible material includes: forming a first series of grooves within the web of flexible material, and forming a second series of grooves within the web of flexible material; the step of forming a channel within the web of flexible material includes: forming a channel within the web of flexible material, the channel transecting a portion of the first and second series of grooves towards a proximal end of each groove; and the step of forming a channel includes forming a depth of each groove that tends towards the depth of the channel at the proximal end of each groove.

[00137] That is to say, in one particular aspect, there is provided a method of forming a substrate for a two-terminal device, including: providing a web of flexible material; forming a first series of grooves within the web of flexible material; forming a second series of grooves within the web of flexible material; forming a channel between the first series of grooves and the second series of grooves within the web of flexible material, the channel transecting a portion of the first and second series of grooves towards a proximal end of each groove, wherein the step of forming a channel includes forming a transection region in which the depth of each groove that tends towards the depth of the channel at the proximal end of each groove.

[00138] Certain aspects provide the advantage that electrical shorts are prevented at the interface between a series of grooves and the channel. In particular, during manufacture of two-terminal devices using such substrates, a wall of the channel shadows, or shields or masks, at least a portion of the transection region, such that material is not coated within at least a portion of the transection region. Thus, an electrical pathway between the ends of grooves, and between an end of a groove and the channel, is prevented.

[00139] Furthermore, electrical shorts are avoided irrespective of the amount of material filled within the channel during the manufacturing process. A two-terminal device manufactured using the substrate described herein is more tolerant of overfill of the channel with material, without being susceptible to an electrical short. Thus, a more efficient and/or reliable two-terminal device may be formed using the substrate described herein. Furthermore, the manufacturing of a two-terminal device using the substrate described herein may be more cost effective and/or less cumbersome.

[00140] In certain embodiments, the first series of grooves, the second series of grooves and the channel are formed as a unitary step.

[00141] That is, in some embodiments, the steps of forming a first series of grooves, forming a second series of grooves, and forming a channel between the first series of grooves and the second series of grooves occur simultaneously or concurrently. [00142] In certain embodiments, the first series of grooves, the second series of grooves and the channel are formed in discrete, or separate, steps. In some embodiments, the method includes a series of ordered steps, preferably as outlined above.

[00143] Certain aspects provide the advantage that the manufacturing process is more efficient and less expensive.

[00144] In certain embodiments, the step of forming a first series of grooves within the web of flexible material includes embossing the web of flexible material to form the first series of grooves.

[00145] That is, in some embodiments, the step of forming a first series of grooves within the web of flexible material may be embossing a first series of grooves into the web of flexible material.

[00146] Certain aspects provide the advantage that the manufacturing process is more efficient and less expensive.

[00147] In certain embodiments, the step of forming a second series of grooves within the web of flexible material includes embossing the web of flexible material to form the second series of grooves.

[00148] That is, in some embodiments, the step of forming a second series of grooves within the web of flexible material may be embossing a second series of grooves into the web of flexible material.

[00149] This provides the advantage that the manufacturing process is more efficient and less expensive.

[00150] In certain embodiments, the step of forming a channel within the web of flexible material includes embossing the web of material to form the channel.

[00151] That is, in some embodiments, the step of forming a channel within the web of flexible material may be embossing a channel into the web of flexible material.

[00152] In certain embodiments, the steps of embossing a first series of grooves, a second series of grooves, and a channel occur simultaneously or concurrently.

[00153] In certain embodiments, the steps of embossing a first series of grooves, a second series of grooves and a channel occur in discrete, or separate, steps. In some embodiments, the method, including the steps of embossing, includes a series of ordered steps, preferably as outlined above.

[00154] Certain aspects provide the advantage that the manufacturing process is more efficient and less expensive. [00155] In certain embodiments, the step of embossing includes: providing one or more shims having at least one protrusion corresponding to at least one of the first series of grooves, the second series of grooves and the channel; coating a surface of the web of flexible material with a UV-curable coating; engaging the at least one protrusion of the or each shim with the coated web of flexible material; at least partially UV curing the UV-curable coating; and removing the at least one protrusion of the or each shim from the coated web of flexible material before the UV-curable coating has fully cured.

[00156] That is, in some embodiments, the step of embossing includes providing one or more shims, each shim having at least one protrusion. The at least one protrusion may correspond to the first series of grooves, or the second series of grooves, or the channel, or the first series of grooves and the second series of grooves, or the first series of grooves and the channel, or the second series of grooves and the channel, or the first series of grooves, the second series of grooves and the channel. In other embodiments, there may be provided a plurality of shims. In some examples, the plurality of shims include a first shim including one or more protrusions corresponding to the first series of grooves, a second shim including one or more protrusions corresponding to the second series of grooves, and a third shim including one or more protrusion corresponding to the channel.

[00157] That is, in some embodiments, the web of flexible material may be partially, mostly, of fully coated with a UV-curable composition. The web of flexible material may be coated on a single face. The web of flexible material may be coated on a plurality of faces, for example, a first or upper face and a second or lower face. In other examples, the web of flexible material may be dipped into a UV-curable composition, thereby coating the entirety of the web of flexible material.

[00158] That is, in some embodiments, the at least one protrusion of the or each shim is engaged with, or pressed into, the coated web of flexible material. In some examples, where there is a plurality of protrusions on a single shim, the single shim may be engaged with, or pressed into, the coated web of flexible material in a sequential manner to provide the first series of grooves, the second series of grooves and the channel. In some examples, where there are a plurality of shims having protrusions corresponding to the first series of grooves, the second series of grooves and the channel, each shim of the plurality of shims may sequentially engage with, or press into, the coated web of flexible material. Alternatively, each shim of the plurality of shims may be engaged with, or pressed into, the coated web of flexible material simultaneously or concurrently. [00159] That is, in some embodiments, the UV-curable coating is at least partially UV cured. That is, in some embodiments, the UV-curable coating is partially, mostly or fully UV cured. It may be preferable for the UV-curable coating to be partially UV cured. In this respect, partially UV cured refers to a curing that is less than fully cured.

[00160] Certain aspects provide the advantage that the transection region that tends from the depth of the groove to the depth of the channel is integrally formed in a single manufacturing process. Thus, the manufacture of such substrates may be more efficient and less expensive.

[00161] In certain embodiments, the shim is a master shim including at least one protrusion corresponding to the first series of grooves, at least one protrusion corresponding to the second series of grooves, and at least one protrusion corresponding to the channel.

[00162] That is, in some embodiments, the shim may be a master shim, that is a single shim having the relevant protrusions for forming the first series of grooves, the second series of grooves and the channel. The master shim may include at least one or a plurality of protrusions corresponding to the first series of grooves. The master shim may include at least one or a plurality of protrusions corresponding to the second series of grooves. The master shim may include at least one or a plurality of protrusions corresponding to the channel, or each channel of a plurality of channels. That is, the protrusions may be shaped such that they provide their respective grooves or channel.

[00163] Certain aspects provide the advantage that a single stamping process can be used to form the grooves and the channel, thereby improving the efficiency and scalability of the manufacturing of such substrates.

[00164] In certain embodiments, the master shim is a metal-plated master shim.

[00165] In certain embodiments, the master shim is a Nickel-plated master shim.

[00166] That is, in some embodiments, the master shim may be Nickel-plated. The master shim may include a Nickel-plated metal. The master shim may include a Nickel-plated polymer. The master shim may include a Nickel-plated silicone.

[00167] In certain embodiments, the or each shim is formed as a cylindrical stamping roll.

[00168] That is, in some embodiments, the or each shim may be formed as a substantially cylindrical shim configured and arranged to stamp the web of flexible material, in use. That is, in use, the cylindrical stamping roll may be rolled across the flexible web of material, along the machine direction, such that the first series of grooves, the second series of grooves and the channel are stamped into the web of flexible material. There may be one or more cylindrical stamping rolls. For example, there may be a master cylindrical stamping roll including at least one protrusion corresponding to the first series of grooves, at least one protrusion corresponding to the second series of grooves, and at least one protrusion corresponding to the channel. In other examples, there may be a plurality of cylindrical stamping rolls, each stamping roll having at least one protrusion corresponding to the first series of grooves, the second series of grooves, or the channel.

[00169] In some embodiments, there may be a first cylindrical stamping roll having at least one first protrusion corresponding to the first series of grooves, a second cylindrical stamping roll having at least one second protrusion corresponding to the second series of grooves, and a third cylindrical stamping roll having at least one third protrusion corresponding to the channel.

[00170] Certain aspects provide the advantage that a roll-to-roll process can be achieved, thus improving the efficiency and scalability of the manufacturing of such substrates.

[00171] In certain embodiments, the or each shim is formed as a stamping plate.

[00172] That is, in some embodiments, the or each shim may be formed as a plate that is configured and arranged to stamp the web of flexible material, in use. That is, in use, the stamping plate may stamp, or otherwise engage with, the surface of the web of flexible material, such that the first series of grooves, the second series of grooves and the channel are stamped into the web of flexible material. The stamping plate may be formed as a pressing plate that presses, or stamps, at least one surface of the web of flexible material. The stamping plate, or pressing plate, and the at least one surface of the web of flexible material may be in face-to-face engagement during the stamping process. There may be one or more stamping plates. For example, there may be a master stamping plate including at least one protrusion corresponding to the first series of grooves, at least one protrusion corresponding to the second series of grooves, and at least one protrusion corresponding to the channel. In other examples, there may be a plurality of stamping plates, each stamping plate having at least one protrusion corresponding to the first series of grooves, the second series of grooves, or the channel.

[00173] In some embodiments, there may be a first stamping plate having at least one first protrusion corresponding to the first series of grooves, a second stamping plate having at least one second protrusion corresponding to the second series of grooves, and a third stamping plate having at least one third protrusion corresponding to the channel.

[00174] Certain aspects provide the advantage that the manufacturing process can be tuned according to a specific design specification.

[00175] In another aspect according to the present invention, there is provided a method of forming a two-terminal device, including: forming a substrate as described herein; coating a first face of each groove of the first series of grooves, each groove of the second series of grooves, and the channel with at least one first material; coating a second opposing face of the first series of grooves, the second series of grooves, and the channel with at least one second material; and at least partially filling the channel with a third material.

[00176] That is, each groove of the first series of grooves may have a first face and a second, opposing, face. Each groove of the second series of grooves may have a first face and a second, opposing, face. The channel, or each channel, may have a first face and a second, opposing, face. The first faces are coated with at least one first material. The second faces are coated with at least one second material.

[00177] This provides the advantage that electrical shorts are prevented at the interface between a series of grooves and the channel. In particular, during manufacture of two- terminal devices, a wall of the channel shadows, or shields or masks, at least a portion of the transection region, such that material is not coated within at least a portion of the transection region. Thus, an electrical pathway between the ends of grooves, and between an end of a groove and the channel, is prevented.

[00178] Furthermore, electrical shorts are avoided irrespective of the amount of material filled within the channel during the manufacturing process. A two-terminal device manufactured is thus more tolerant of overfill or underfill of the channel with material during manufacture, without being susceptible to an electrical short. Thus, a more efficient and/or reliable two-terminal device may be formed. Furthermore, the manufacturing of a two- terminal device may be more cost effective and/or less cumbersome.

[00179] In certain embodiments, the step of coating the first face with the at least one first material and coating the second face with the at least one second material is before the step of at least partially filling the channel with the third material.

[00180] That is, the method described herein may include a series of ordered steps, in that the first face is coated, the second face is coated either before, after or at the same time as the first face is coated, and then the channel is filled with the third material.

[00181] In some embodiments, the method further includes the step of at least partially filling each groove of the first series of grooves with the third material.

[00182] In some embodiments, the method further includes the step of at least partially filling each groove of the second series of grooves with the third material.

[00183] In some embodiments, each groove of the first series of grooves, each groove of the second series of grooves, and the channel are at least partially filled with the third material. In some examples, each groove of the first series of grooves is at least partially filled with the third material, then the channel is at least partially filled with the third material, and then each groove of the second series of grooves is at least partially filled with the third material. That is, in some examples, the grooves and the channel are sequentially filled in the order described above. In other examples, each groove of the first series of grooves, the channel, and each groove of the second series of grooves are at least partially filled with the third material simultaneously or concurrently.

[00184] In some embodiments, the step of coating the first face with the at least one first material and coating the second face with the at least one second material is before the step of at least partially filling each groove of the first series of grooves, each groove of the second series of grooves, and the channel.

[00185] In certain embodiments, the step of coating the first face with the at least one first material includes an off-axis directional coating process. Advantageously, in some embodiments, the step of coating the second face with the at least one second material includes an off-axis directional coating process. Advantageously, in some embodiments, the step of coating the first face with the at least one first material and the step of coating the second face with the at least one second material includes an off-axis directional coating process.

[00186] That is, the step of coating the first face with the at least one first material, the step of coating the second face with the at least one second material, or coating both the first face with the at least one first material and the second face with the at least one second material includes an off-axis directional coating process.

[00187] In some embodiments, the off-axis directional coating process only coats a single face, either the first face or the second face, at one time.

[00188] In some embodiments, the off-axis directional coating process may include spraying the at least one first material, the at least one second material, or both the at least one first material and the at least one second material at an angle relative to the plane of the substrate. Thus, the at least one first material, the at least one second material, or both the at least one first material and the at least one second material are sprayed at an angle relative to the plane of the substrate. In this way, only the first or second face of the grooves and the channel are coated at one time. This is typically because the coating is substantially restricted by viewing angle to only one of the first face or the second face.

[00189] In some embodiments, the off-axis directional coating process may include using a shield to restrict the coating of the at least one first material, the at least one second material or both the at least one first material and the at least one second material onto the first face, the second face, or both the first face and the second face of each groove of the first series of grooves and the second series of grooves. In some embodiments, the off-axis directional coating process may include using a shield to restrict the coating of the at least one first material, the at least one second material or both the at least one first material and the at least one second material onto the first face, the second face, or both the first face and the second face of the channel.

[00190] In some embodiments, the off-axis directional coating is repeated one or more times. In some embodiments, the off-axis directional coating is repeated one or more times with different material, for example, a fourth material and a fifth material. In some examples, the fourth material may be provided over the at least one first material on the first face, and the fifth material may be provided over the at least one second material on the second face.

[00191] In some embodiments, the step of at least partially filling the channel with a third material includes a uniform coating process. In some embodiments, the step of at least partially filling the channel with a third material includes a directional coating process.

[00192] In certain embodiments, the step of at least partially filling the channel with a third material includes printing the third material over the substrate. In some examples, the step of printing the third material over the substrate includes rolling a cylindrical roller over the substrate, the cylindrical roller including the third material. In this way, as the third material is printed over the substrate, the third material is partially or fully printed into the, or each, groove.

[00193] In certain embodiments, the at least one first material includes a non-insulating material.

[00194] In some embodiments, the at least one first material includes a conductor material, a semiconductor material and electron transport layer, carbon-60 (Ceo, also known as Buckminsterfullerene) or a combination thereof. In some examples, the semiconductor material includes a metal oxide. In some examples, the metal oxide includes or tin oxide, that is tin (IV) oxide, SnC>2_, or Nb₂0s that is Niobium oxide

[00195] In certain embodiments, the at least one second material includes a non-insulating material.

[00196] In some embodiments, the at least one second material includes a conductor material, a semiconductor material or a hole transport layer, or a combination thereof. In some examples, the semiconductor material includes a metal oxide. In some examples, the metal oxide includes nickel oxide, that is nickel (II) oxide or NiO, or copper oxide, that is copper (I) oxide or CU2O. [00197] In certain embodiments, the at least one third material includes a capacitor material, a supercapacitor material, or a perovskite structured material.

[00198] It may be preferable that the third material includes a perovskite structured material. A perovskite structured material is a material having a crystal structure corresponding to calcium titanium oxide, CaTiC>3, that is, having a general chemical structure of ABX3, for example ^XMA^{2+ VI}B⁴⁺ X^2_3, where A and B are two different cations of different sizes, and X is an anion that chemically bonds to both A and B.

[00199] In some examples, the perovskite structured material is provided in the form of a perovskite ink.

[00200] In preferred examples, the perovskite structured material has an optical bandgap between 1.1 eV and 2.5 eV.

[00201] In preferred examples, the perovskite structured material includes an organic lead trihalide, such as methylammonium lead trichloride, tribromide or triiodide, formamidinium lead trihalide, such as formamidinium lead trichloride, tribromide or triiodide, caesium tin trihalide, such as caesium tin triiodide, or another like organic lead or tin halide combination with the general chemical structure ABX3 as outlined above.

[00202] In another aspect according to the present invention, there is provided a substrate, for a two-terminal device, obtainable by the method as described herein.

[00203] In another aspect according to the present invention, there is provided a two- terminal device obtainable by the method as described herein.

[00204] Certain terminology is used in the following description for convenience only and is not limiting. The words ‘right’, ‘left’, ‘lower’, ‘upper’, ‘front’, ‘rear’, ‘upward’, ‘down’ and ‘downward’ designate directions in the drawings to which reference is made and are with respect to the described component when assembled and mounted. The words ‘inner’, ‘inwardly¹ and ‘outer’, ‘outwardly’ refer to directions toward and away from, respectively, a designated centreline or a geometric centre of an element being described (e.g. central axis), the particular meaning being readily apparent from the context of the description.

[00205] Further, as used herein, the terms ‘connected¹, ‘attached’, ‘coupled’, ‘mounted’ are intended to include direct connections between two members without any other members interposed therebetween, as well as, indirect connections between members in which one or more other members are interposed therebetween. The terminology includes the words specifically mentioned above, derivatives thereof, and words of similar import.

[00206] Further, unless otherwise specified, the use of ordinal adjectives, such as, “first”, “second”, “third” etc. merely indicate that different instances of like objects are being referred to and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking or in any other manner.

[00207] Below, there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment or aspect described herein, provided that they are not mutually incompatible. In particular, any one of examples 1 to 40 can be combined with any one of examples 41 to 96, provided that they are not mutually incompatible.

[00208] Example 1 : A substrate for a two-terminal device, comprising: a first series of grooves and a second series of grooves, each groove having a proximal end and a distal end across the transverse direction of the substrate, and a channel transecting a portion of the first series of grooves and a portion of the second series of grooves towards the proximal end of each groove, and wherein the depth of each groove tends towards the depth of the channel in a transection region towards the proximal end of each groove.

[00209] Example 2: A substrate according to example 1 , wherein the depth of each groove tends non-linearly towards the depth of the channel.

[00210] Example 3: A substrate according to example 2, wherein the depth of each groove tends gradually towards the depth of the channel.

[00211] Example 4: A substrate according to example 2 or example 3, wherein the transection region is substantially arcuate.

[00212] Example 5: A substrate according to example 1, wherein each groove tends linearly towards the depth of the channel.

[00213] Example 6: A substrate according to example 5, wherein the depth of each groove tends linearly towards the depth of the channel at an angle of between 0° and 90°, excluding 0° and 90°, formed with respect to an axis extending along the elongate base of each groove.

[00214] Example 7: A substrate according to any preceding example, wherein the channel is substantially Z-shaped having a predetermined angle.

[00215] Example 8: A substrate according to any preceding example, wherein each groove has an aspect ratio of at least 1 :1 , preferably at least 1 :1.2, from the distal end to the proximal end, excluding the transection region. [00216] Example 9: A substrate according to any preceding example, wherein the channel has an aspect ratio of at least 1 :1.6.

[00217] Example 10: A substrate according to any preceding example, wherein the transection region has an aspect ratio that tends from at least 1 :1 , preferably 1 :1.2, to at least 1:1.6.

[00218] Example 11 : A substrate according to any preceding example, wherein the channel transects each groove of the first series of grooves and/or the second series of grooves.

[00219] Example 12: A substrate according to any preceding example, comprising a plurality of channels.

[00220] Example 13: A substrate according to example 12, wherein each channel of the plurality of channels transects a portion of the first series of grooves and a portion of the second series of grooves towards the proximal end of each groove.

[00221] Example 14: A substrate according to example 12, wherein each channel of the plurality of channels transects each groove of the first series of grooves and each groove of the second series of grooves towards the proximal end of each groove.

[00222] Example 15: A substrate according to any one of examples 12 to 14, wherein each channel of the plurality of channels is substantially Z-shaped having a predetermined angle.

[00223] Example 16: A substrate according to example 12, further comprising: a first transection channel transecting each channel of the plurality of channels at their distal ends, the first transection channel transecting the entirety the first series set of grooves towards the proximal end of each groove; and a second transection channel transecting each channel of the plurality of channels at their proximal ends, the second transection channel transecting the entirety of the second series of grooves towards the proximal end of each groove.

[00224] Example 17: A substrate according to example 16, wherein the first transection channel, the plurality of channels, and the second transection channel substantially form a Z-shape having a predetermined angle.

[00225] Example 18: A substrate according to example 7, example 15 or example 17, wherein the predetermined angle is between approximately 0 degrees and approximately 90 degrees, preferably between approximately 30 degrees and approximately 60 degrees. [00226] Example 19: A substrate according to example 18, wherein the predetermined angle is between approximately 40 degrees and approximately 50 degrees, preferably approximately 45 degrees.

[00227] Example 20: A two-terminal device comprising the substrate of any preceding example.

[00228] Example 21: A two-terminal device according to example 20, wherein the two- terminal device is an optoelectronic device.

[00229] Example 22: A method of forming a substrate for a two-terminal device, comprising: providing a web of flexible material; and forming a first series of grooves within the web of flexible material; forming a second series of grooves within the web of flexible material; forming a channel between the first series of grooves and the second series of grooves within the web of flexible material, the channel transecting a portion of the first and second series of grooves towards a proximal end of each groove, wherein the step of forming a channel includes forming a depth of each groove that tends towards the depth of the channel at the proximal end of each groove.

[00230] Example 23: A method according to example 22, wherein the first series of grooves, the second series of grooves and the channel are formed as a unitary step.

[00231] Example 24: A method according to example 22 or example 23, wherein the step of forming a first series of grooves within the web of flexible material comprises embossing the web of flexible material to form the first series of grooves.

[00232] Example 25: A method according to any one of examples 22 to 24, wherein the step of forming a second series of grooves within the web of flexible material comprises embossing the web of flexible material to form the second series of grooves.

[00233] Example 26: A method according to any one of examples 22 to 25 wherein the step of forming a channel within the web of flexible material comprises embossing the web of material to form the channel.

[00234] Example 27: A method according to any one of examples 24 to 26, wherein the step of embossing comprises: providing one or more shims having at least one protrusion corresponding to at least one of the first series of grooves, the second series of grooves and the channel; coating a surface of the web of flexible material with a UV-curable coating; engaging the at least one protrusion of the or each shim with the coated web of flexible material; at least partially UV curing the UV-curable coating; and removing the at least one protrusion of the or each shim from the coated web of flexible material before the UV-curable coating has fully cured.

[00235] Example 28: A method according to example 27, wherein the shim is a master shim comprising at least one protrusion corresponding to the first series of grooves, at least one protrusion corresponding to the second series of grooves, and at least one protrusion corresponding to the channel.

[00236] Example 29: A method according to example 28, wherein the master shim is a Nickel-plated master shim.

[00237] Example 30: A method according to any one of examples 27 to 29, wherein the or each shim is formed as a cylindrical stamping roll.

[00238] Example 31 : A method according to any one of examples 27 to 30, wherein the or each shim is formed as a stamping plate.

[00239] Example 32: A method of forming a two-terminal device, comprising: forming a substrate according to a method of any one of examples 22 to 31 ; coating a first face of first series of grooves, the second series of grooves and the channel with at least one first material; coating a second opposing face of the first series of grooves, the second series of grooves and the channel with at least one second material; and at least partially filling the channel with a third material.

[00240] Example 33: A method according to example 32, wherein the step of coating the first face with the at least one first material and coating the second face with the at least one second material is before the step of at least partially filling the channel with the third material.

[00241] Example 34: A method according to example 32 or example 33, wherein the step of coating the first face with at least one first material and/or coating the second face with at least one second material comprises an off-axis directional coating process. [00242] Example 35: A method according to any one of examples 32 to 34, wherein the step of at least partially filling the channel with a third material comprises printing the third material over the substrate.

[00243] Example 36: A method according to any one of examples 32 to 35, wherein the at least one first material comprises a non-insulating material.

[00244] Example 37: A method according to any one of examples 32 to 36, wherein the at least one second material comprises a non-insulating material.

[00245] Example 38: A method according to any one of examples 32 to 37, wherein the third material comprises a capacitor material, a supercapacitor material, or a perovskite.

[00246] Example 39: A substrate obtainable by the method of any one of examples 22 to 31.

[00247] Example 40: A two-terminal device obtainable by the method of any one of examples 32 to 38.

[00248] Example 41. A two-terminal device, including a substrate comprising: a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; a first terminal and a second terminal, each terminal being formed towards or at opposing edges of the substrate across the transverse direction, and each terminal being in electrical communication with the first cell and the second cell; a connecting portion, between the first cell and the second cell, the connecting portion having a third characteristic resistance; wherein the third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extractable from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer from the first cell to the second cell across the connecting portion.

[00249] Example 42. A two-terminal device according to example 41, wherein the third characteristic resistance is greater than at least one of the first characteristic resistance and the second characteristic resistance. [00250] Example 43. A two-terminal device according to example 42, wherein the third characteristic resistance is at least two times, preferably at least five times, most preferably at least ten times, greater than at least one of the first characteristic resistance and the second characteristic resistance.

[00251] Example 44. A two-terminal device according to any one of examples 41 to 43, wherein the connecting portion comprises at least one resistive element.

[00252] Example 45. A two-terminal device according to example 44, wherein the at least one resistive element comprises a peak of the substrate, a discontinuous non-insulating coating of the substrate, and/or a rutted portion of the substrate.

[00253] Example 46. A two-terminal device according to example 44 or 45, wherein the at least one resistive element comprises a channel in the substrate.

[00254] Example 47. A two-terminal device according to example 46, wherein the channel comprises a rutted-base, a rutted-wall and/or a non-conductive electrical insulator material therein.

[00255] Example 48. A two-terminal device according to example 46 or 47, wherein the channel has an aspect ratio of at least 1:1.6.

[00256] Example 49. A two-terminal device according to example 46 or 47, wherein the channel has an aspect ratio of at least 1:2.

[00257] Example 50. A two-terminal device according to any one of examples 41 to 49, wherein the first cell comprises at least one first groove and/or the second cell comprises at least one second groove.

[00258] Example 51. A two-terminal device according to example 50, wherein the first cell comprises a first series of grooves and/or the second cell comprises a second series of grooves.

[00259] Example 52. A two-terminal device according to example 50, when dependent upon any one of examples 46 to 49, wherein the channel transects a portion of the at least one first groove and/or a portion of the at least one second groove.

[00260] Example 53. A two-terminal device according to example 51, when dependent upon example 50 and any one of examples 46 to 49, wherein the channel transects a portion of the first series of grooves and/or a portion of the second series of grooves.

[00261] Example 54. A two-terminal device according to example 53, wherein the channel transects the entirety of the first series of grooves and/or the entirety of the second series of grooves. [00262] Example 55. A two-terminal device according to example 53 or example 54, wherein the channel transects the first series of grooves and/or the second series of grooves towards an end of each groove.

[00263] Example 56. A two-terminal device according to any one of examples 46 to 55, wherein the channel is substantially Z-shaped having a predetermined angle.

[00264] Example 57. A two-terminal device according to example 44, wherein the at least one resistive element comprises a plurality of channels in the substrate.

[00265] Example 58. A two-terminal device according to example 57, wherein one or more of the plurality of channels comprises a rutted-base, a rutted-wall and/or a non- conductive electrical insulator therein.

[00266] Example 59. A two-terminal device according to example 57 or 58, wherein one or more of the plurality of channels has an aspect ratio of at least 1:1.6.

[00267] Example 60. A two-terminal device according to example 57 or 58, wherein one or more of the plurality of channels has an aspect ratio of at least 1 :2.

[00268] Example 61. A two-terminal device according to any one of examples 57 to 60, wherein the first cell comprises at least one first groove and/or the second cell comprises at least one second groove.

[00269] Example 62. A two-terminal device according to example 61, wherein the first cell comprises a first series of grooves and/or the second cell comprises a second series of grooves.

[00270] Example 63. A two-terminal device according to example 61, when dependent upon any one of examples 57 to 60, wherein each channel transects the at least one first groove and/or the at least one second groove.

[00271] Example 64. A two-terminal device according to example 62, when dependent upon example 61 and any one of examples 57 to 60, wherein each channel transects a portion of the first series of grooves and/or a portion of the second series of grooves.

[00272] Example 65. A two-terminal device according to example 64, wherein each channel transects the entirety of the first series of grooves and/or the entirety of the second series of grooves.

[00273] Example 66. A two-terminal device according to example 64 or example 65, wherein each channel transects the first series of grooves and/or the second series of grooves towards an end of each groove. [00274] Example 67. A two-terminal device according to any one of examples 57 to 66, wherein the plurality of channels comprises a first channel, having a first channel characteristic resistance, and a second channel, having a second channel characteristic resistance, wherein the first channel characteristic resistance and the second channel characteristic resistance provide substantially all of the third characteristic resistance.

[00275] Example 68. A two-terminal device according to example 67, wherein the plurality of channels further comprises a third channel, having a third channel characteristic resistance, wherein the first channel characteristic resistance, the second channel characteristic resistance and the third channel characteristic resistance provide substantially all of the third characteristic resistance.

[00276] Example 69. A two-terminal device according to any one of examples 57 to 68, wherein each channel of the plurality of channels is substantially Z-shaped having a predetermined angle.

[00277] Example 70. A two-terminal device according to example 61, further comprising: a first transection channel that transects each channel of the plurality of channels at their distal ends and transects the at least one first groove; a second transection channel that transects each channel of the plurality of channels at their proximal ends and transects the at least one second groove.

[00278] Example 71. A two-terminal device according to example 62, further comprising: a first transection channel that transects each channel of the plurality of channels at their distal ends and transects a portion of the first series of grooves; and a second transection channel that transects each channel of the plurality of channels at their proximal ends and transects a portion of the second series of grooves.

[00279] Example 72. A two-terminal device according to example 61, wherein the first transection channel transects the entirety of the first series of grooves, and wherein the second transection channel transects the entirety of the second series of grooves.

[00280] Example 73. A two-terminal device according to example 71 or example 72, wherein the first transection channel and/or the second transection channel transect the grooves towards an end of each groove.

[00281] Example 74. A two-terminal device according to any one of examples 70 to 73, wherein the plurality of channels comprise a first channel and a second channel, wherein the first transection channel transects the first channel and the second channel at their distal ends, and wherein the second transection channel transects the first channel and the second channel at their proximal ends.

[00282] Example 75. A two-terminal device according to example 74, wherein the plurality of channels further comprises a third channel, wherein the first transection channel further transects the third channel at its distal end, and wherein the second transection channel further transects the third channel at its proximal end.

[00283] Example 76. A two-terminal device according to any one of examples 70 to 75, wherein each channel, the first transection channel and the second transection channel form a substantial Z-shape having a predetermined angle.

[00284] Example 77. A two-terminal device according to any one of examples 41 to 76, wherein the two-terminal device is an optoelectronic device.

[00285] Example 78. A method of forming a two-terminal device, comprising: providing a substrate; forming a first cell within the substrate, the first cell having a first characteristic resistance; forming a second cell within the substrate, spaced apart from the first cell along the web direction of the substrate, the second cell having a second characteristic resistance; forming a connecting portion, between the first cell and the second cell, the connecting portion having a third characteristic resistance; wherein the third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer from the first cell to the second cell across the connecting portion.

[00286] Example 79. A method according to example 78, wherein the step of forming a first cell comprises forming at least one first groove within the substrate.

[00287] Example 80. A method according to example 79, wherein the step of forming at least one first groove comprises forming a first series of grooves within the substrate.

[00288] Example 81. A method according to any one of examples 78 to 80, wherein the step of forming a second cell comprises forming at least one second groove within the substrate. [00289] Example 82. A method according to example 81, wherein the step of forming at least one second groove comprises forming a second series of grooves within the substrate

[00290] Example 83. A method according to any one of examples 78 to 82, wherein the step of forming a connecting portion further comprises the step of forming at least one resistive element within the connecting portion between the first cell and the second cell, the at least one resistive element providing the third characteristic resistance.

[00291] Example 84. A method according to example 83, wherein the at least one resistive element comprises at least one channel.

[00292] Example 85. A method according to example 84, when dependent upon examples 80, 82 and 83, further comprising: coating a first face of each groove of the first series of grooves, each groove of the second series of grooves and the or each channel with a first material; coating a second face of each groove of the first series of grooves, each groove of the second series of grooves and the or each channel with a second material; and at least partially filling each groove of the first series of grooves, each groove of the second series of grooves and the or each channel with a third material.

[00293] Example 86. A method according to example 85, wherein the step of coating the first face with the first material and/or coating the second face with the second material comprises an off-axis directional coating process.

[00294] Example 87. A method according to example 85 or 86, wherein the step of at least partially filling the grooves and the or each channel with the third material comprises printing the third material over the substrate.

[00295] Example 88. A method according to any one of examples 85 to 87, wherein the step of at least partially filling each groove of the first series of grooves and the second series of grooves comprises filling each groove with the third material thereby providing an electrical connection across each groove of the first series of grooves, and an electrical connection across each groove of the second series of grooves.

[00296] Example 89. A method according to any one of examples 85 to 88, wherein the step of at least partially filling the or each channel comprises filling the or each channel with the third material thereby providing an electrical connection across the or each channel. [00297] Example 90: A two-terminal device obtainable according to any one of examples 78 to 89.

[00298] Example 91 : An optoelectronic device obtainable according to any one of examples 78 to 89.

[00299] Example 92. A two-terminal device, including a substrate comprising: a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; a connecting portion, between the first cell and the second cell, comprising a channel, the connecting portion having a third characteristic resistance; wherein the channel has an aspect ratio of at least 1:1.6 such that third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer from the first cell to the second cell across the connecting portion.

[00300] Example 93. A two-terminal device, including a substrate comprising: at least one first groove having a terminal groove or a terminal portion, the at least one groove having a first characteristic resistance, and at least one second groove having a terminal groove or a terminal portion, spaced apart from the at least one first groove along the web direction of the substrate, having a second characteristic resistance; a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; a connecting portion, between the terminal groove or terminal portion of the at least one first groove and the terminal groove or terminal portion of the at least one second groove, comprising a channel, the connecting portion having a third characteristic resistance; wherein the channel has an aspect ratio that greater than, preferably between 20% and 50% greater than, an aspect ratio of at least one of the terminal groove or terminal portion of the at least one first groove and the terminal groove or terminal portion of the at least one second groove, such that the third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the at least one first groove and the at least one second groove at the first terminal and the second terminal in preference to electrical charge transfer from the terminal groove or terminal portion of the at least one first groove to the terminal groove or terminal portion of the at least one second groove across the connecting portion.

[00301] Example 94. A two-terminal device, including a substrate comprising: a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; a connecting portion, between the first cell and the second cell, comprising a channel, the connecting portion having a third characteristic resistance; wherein the channel includes a rutted-base, a rutted-wall and/or a non-conductive electrical insulator therein, such that the third characteristic resistance is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer from the first cell to the second cell across the connecting portion.

[00302] Example 95. A two-terminal device, including a substrate comprising: a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; a connecting portion, between the first cell and the second cell, comprising a plurality of channels, wherein the plurality of channels each have a channel resistance, a combination of the channel resistances forming a third characteristic resistance; wherein the third characteristic resistance that is greater than or equal to at least one of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer from the first cell to the second cell across the connecting portion.

[00303] Example 96. A two-terminal device, including a substrate comprising: a first cell having a first characteristic resistance, and a second cell, spaced apart from the first cell along the web direction of the substrate, having a second characteristic resistance; a first terminal and a second terminal, each terminal being formed towards or at opposing edges along the transverse direction of the substrate; a connecting portion, between the first cell and the second cell, comprising a plurality of channels, wherein the plurality of channels each have a channel resistance, a combination of the channel resistances forming a third characteristic resistance; wherein the third characteristic resistance is equal to one of the first characteristic resistance or the second characteristic resistance, and greater than the other of the first characteristic resistance and the second characteristic resistance, such that electrical charge is extracted from the first cell and the second cell at the first terminal and the second terminal in preference to electrical charge transfer from the first cell to the second cell across the connecting portion.

[00304] Other examples will be apparent from the aforementioned summary of invention and the detailed description noted below.

BRIEF DESCRIPTION OF THE DRAWINGS

[00305] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 illustrates an electrical diagram of a two-terminal device in accordance with the prior art;

Figure 2 illustrates (a) an electrical diagram of a two-terminal device in accordance with the invention and (b) an enlarged view of a portion of the electrical diagram of (a);

Figure 3 illustrates a plan view of a substrate in accordance with one embodiment of the invention;

Figure 4 illustrates a plan view of a substrate in accordance with one embodiment of the invention; Figure 5 illustrates a plan view of a substrate in accordance with one embodiment of the invention;

Figure 6 illustrates a plan view of a substrate in accordance with one embodiment of the invention;

Figure 7 illustrates (a) a plan view of a substrate in accordance with one embodiment of the invention and (b) a plan view of another substrate in accordance with one embodiment of the invention;

Figure 8 illustrates (a) an enlarged top view of the substrate of Figure 5, (b) an enlarged perspective view of the substrate of Figure 5, (c) another enlarged top view of the substrate of Figure 5, and (d) an enlarged perspective view of the transection region of the substrate of Figure 5;

Figure 9 illustrates (a) an enlarged perspective view of the substrate of Figure 7(a), and (b) an enlarged perspective view of the transection region of the substrate of Figure 7(a);

Figure 10 illustrates a cross-sectional view of a groove, a transection region and a channel of a substrate in accordance with one embodiment of the invention;

Figure 11 illustrates a cross-sectional view of a groove, a transection region and a channel of a substrate in accordance with one embodiment of the invention;

Figure 12 illustrates a method of forming a substrate in accordance with one embodiment of the invention;

Figure 13 illustrates a method of forming a substrate in accordance with one embodiment of the invention;

Figure 14 illustrates a method of forming a two-terminal device in accordance with one embodiment of the invention;

Figure 15 illustrates a coating process of the method of Figure 14;

Figure 16 illustrates a two-terminal device in accordance with one embodiment of the invention;

Figure 17 illustrates a cross-section view of a two-terminal device according to one embodiment of the present invention;

Figure 18 illustrates a cross-section view of a two-terminal device according to another embodiment of the present invention; Figure 19 illustrates a cross-section view of a two-terminal device according to a further embodiment of the present invention;

Figure 20 illustrates a cross-section view of a two-terminal device according to another embodiment of the present invention;

Figure 21 illustrates a cross-section view of a two-terminal device according to a still further embodiment of the present invention;

Figure 22 illustrates a cross-section view of a two-terminal device according to another embodiment of the present invention;

Figure 23 illustrates a graph comparing the performances of the two-terminal device of Figure 1 with the two-terminal device of Figures 2(a) and 3;

Figure 24 illustrates a graph depicting the performance of a two-terminal device as described herein; and

Figure 25 illustrates yet another graph depicting the performance of a two-terminal device as described herein.

DETAILED DESCRIPTION

[00306] Like reference numerals are used to depict like features throughout.

[00307] Various modifications to the detailed designs are described above are envisaged. For example, any number of grooves within any number of series of grooves may be used. Equally, any number of delineation features, such as channels, transection channels or the like may be used. Moreover, any combination of such delineation features may be used.

[00308] It will be clear to a person skilled in the art that features described in relation to any of the embodiments described above can be application interchangeably between the different embodiments. The embodiments described above are examples to illustrate various features of the invention.

[00309] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Through the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[00310] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect embodiment, or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract or drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[00311] The reader’s attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[00312] Figures 2(a) and 2(b) illustrate an example of a two-terminal device 50 having a substrate, in accordance with the present invention. The substrate includes a first cell 54a, a second cell 54b and a third cell 54c. The first, second and third cells 54a, 54b, 54c may be photovoltaic cells as shown in Figures 2(a) and 2(b). In this specific example, the first, second and third cells 54a, 54b, 54c are formed as a first series of grooves 54a, a second series of grooves 54b and a third series of grooves 54c. Each series of grooves 54a, 54b, 54c includes a plurality of grooves.

[00313] As shown in Figures 2(a) and 2(b), grooves are connected in series with one another to form a first series of grooves 54a. Likewise, grooves are connected in series to form a second series of grooves 54b, and further grooves are connected in series to form a third series of grooves 54c. In this way, the grooves of a respective series of grooves 54a, 54b, 54c is first connected in series to form each of the respective series of grooves 54a, 54b, 54c, and then each series of grooves 54a, 54b, 54c is connected in parallel to one another. Thus, the two-terminal device 50 of Figures 2(a) and 2(b) differs from that of the prior art as illustrated in Figure 1.

[00314] The two-terminal device 50 of Figures 2(a) and 2(b) provides the advantage that bypass diodes, which are typically required in conventional substrates such as those illustrated in Figure 1, are not necessary. Instead, grooves are placed in series relatively close to one another, in some examples with a spacing of approximately 0.1mm or less between each groove, such that each groove within a series of grooves 54a, 54b, 54c experiences substantially, or exactly, the same lighting conditions, in use. Moreover, since each series of grooves 54a, 54b, 54c is connected in parallel, shading of grooves of an individual series of grooves 54a, 54b, 54c has a less significant impact on the overall performance of the device. Thus, the prerequisite of bypass diodes is negated in the present invention.

[00315] Furthermore, as shown in Figures 2(a) and 2(b), the two-terminal device 50 includes a first connecting portion including a first delineation feature 56a and a second connecting portion including a second delineation feature 56b. The first delineation feature 56a is provided between the first series of grooves 54a and the second series of grooves 54b. the second delineation feature 54b is provided between the second series of grooves 54b and the third series of grooves 54c. Any number of grooves may be present in any number of series of grooves 54a, 54b, 54c having any number of delineation features 56a, 56b therebetween, as described herein. Further, the delineation feature 56a, 56b may take any appropriate form as discussed further herein.

[00316] Each series of grooves 54a, 54b, 54c provides an electrical connection between a first electrical connection 58 and a second electrical connection 60. The first electrical connection 58 is a positive electrical connection and the second electrical connection 60 is a negative electrical connection in the depicted embodiment. Alternatively, the first electrical connection 58 may be a negative electrical connection and the second electrical connection 60 may be a positive electrical connection. The positive and negative electrical connections 58, 60 may be connected to respective terminals, for example, positive and negative busbars 62, 64 of the two-terminal device 50. In this way, positive electrical charge is carried to the positive busbar 62 and negative electrical charge is carried to the opposing negative busbar 64. The busbars 62, 64 may be connected to another electrical element, such as a capacitor or the like.

[00317] As described herein, the delineation features typically serve to provide an electrical disconnection, or provide electrical isolation, between adjacent series of grooves. However, as described herein, this is oftentimes not possible, and so an electrical short occurs across one or more of the delineation features during manufacture of such devices. In this case, the inventors have surprisingly found that conductive delineation features 56a, 56b, that is delineation features that provide an electrical connection thereacross, can be modelled upon a resistor in parallel with a reverse-biased diode, as shown in Figure 2(a).

In this way, each delineation feature 56a, 56b provides a resistance such that the electrical pathway from a terminal groove of a series of grooves 54a, 54b, 54c to its adjacent electrical connection 58, 60 is favoured over the electrical pathway across the delineation feature 56a, 56b. Thus, electrical charge is extractable at positive and negative busbars 62, 64 in preference to electrical charge transfer across the delineation feature 56a, 56b, that is, a short circuit across the delineation feature 56a, 56b. [00318] Furthermore, the inventors have surprisingly found that if the delineation feature 56a, 56b is conductive, said delineation feature 56a, 56b provides charge blocking and substantive electrical isolation between adjacent series of grooves simultaneously. That is, the delineation feature 56a, 56b provides charge blocking in the same orientation that would be used for a bypass diode. In this way, a conductive delineation feature 56a, 56b protects the adjacent series of grooves 54a, 54b, 54c from reverse bias damage, that is, from electrical charge flowing in a direction that is opposite to the flow of electrical charge across each groove within the series of grooves 54a, 54b, 54c. For example, referring to Figure 2(b), the delineation feature 56a prevents electrical charge flowing from positive electrical connection 58, connected to positive busbar 62, through the delineation feature 56a and towards the grooves and the negative electrical connection 60, connected to the negative busbar 64. Thus, it has been found, much to the surprise of the inventors, that not only does a conductive delineation feature 56a, 56b allow for charge extraction as in non- conductive delineation features, but also that a conductive delineation feature 56a, 56b can provide protection against reverse bias damage.

[00319] Figure 3 illustrates a plan view of a two-terminal device 100 comprising a substrate 102. The substrate 102 has a surface comprising a plurality of series of grooves 104a - 104d. In particular, the substrate 102 comprises a first series of grooves 104a, a second series of grooves 104b, a third series of grooves 104c and a fourth series of grooves 104d. Further series of grooves may be provided in the machine direction MD of the substrate 102. Each groove of the series of grooves 104a - 104d generally run in parallel to one another across the transverse direction TD of the substrate 102, extending from a proximal end, for example, proximal to a first terminal 112 as described below, to a distal end, for example, distal to the first terminal 112 as described below. A channel 106 is provided between each series of grooves 104a - 104d.

[00320] The two-terminal device 100 may be an optoelectronic device, such as a solar photovoltaic cell. Such a two-terminal device 100 includes a mixture of interdigitated (parallel connected) and cascaded (series connected) grooves 104a - 104d. The operating voltage of such a two-terminal device 100 can be controlled by changing the number of series of grooves 104a - 104d. Increasing the number of series of grooves 104a - 104d increases the operating voltage of the two-terminal device 100. Such a two-terminal device 100 can be operated in parallel or a combination of series and parallel arrangement. It may be an advantage of the two-terminal device 100 that this removes the need for extra process steps to be used to connect the cascaded groove structures in series to achieve the desired output voltage. [00321] The channel 106 physically separates the cascaded (series connected) grooves 104a - 104d. The channel 106 enables the cascaded grooves 104a-104d to be connected in parallel via electrical connection to first and second terminals 112, 114. In this way, it is possible to extract the desired electric charge generated at the voltage designed by the number of cascaded groove structures 104a - 104d.

[00322] The channel 106, also referred to as the delineation or structural delineation feature, first crosses the first series of grooves 104a towards one end of the substrate 102 and then crosses a spacer 108 between the first series of grooves 104a and the second series of grooves 104b, and subsequently crosses the second series of grooves 104b towards the opposite edge of the substrate 102. Since many of these channels 106 are used, each series of grooves, 104a, 104b for example, are crossed toward each edge by elements of two successive individual channels 106, as shown in Figure 3. The channel 106 crosses towards an end of each groove of the series of grooves 104a, 104b, 104c, 104d. However, in other embodiments, the channel 106 may terminate an end, i.e. cross at an end, of each groove of the series of grooves 104a, 104b, 104c, 104d.

[00323] Together, the spacers 108 and channels 106 divide the substrate 102 into a first area 110a and a second area 110b. The first area 110a carries a positive charge and the second area 110b carries a negative charge. The first area 110a terminates at a first or positive terminal 112 at one edge of the substrate 102, and the second area 110b terminates at a second or negative terminal 114 at the other, opposite, edge of the substrate 102, referring to the transverse direction TD. The first area 110a provides an electrical connection of the first groove of each series of grooves 104a-104d to the first terminal 112. The second area 110b provides an electrical connection of the last groove of each series of grooves 104a-104d to the second terminal 114. Thus, a two-terminal device 100 having a first terminal 112 and a second terminal 114 is formed.

[00324] Figure 4 illustrates a plan view of another two-terminal device 200 comprising a substrate 202. The substrate 202 has a surface comprising a plurality of series of grooves 204a - 204d. In particular, the substrate 202 comprises a first series of grooves 204a, a second series of grooves 204b, a third series of grooves 204c and a fourth series of grooves 204d. Further series of grooves may be provided in the machine direction MD of the substrate 202. Each groove of the series of grooves 204a - 204d generally run in parallel to one another across the transverse direction TD of the substrate 202, extending from a proximal end, for example, proximal to a first terminal 212 as described below, to a distal end, for example, distal to the first terminal 212 as described below. A channel 206, in this case a plurality of channels 206a - 206c, is provided between each series of grooves 204a - 204d. [00325] The two-terminal device 200 may be an optoelectronic device, such as a solar photovoltaic cell. Such a two-terminal device 200 includes a mixture of interdigitated (parallel connected) and cascaded (series connected) grooves 204a - 204d. The operating voltage of such a two-terminal device 200 can be controlled by changing the number of series of grooves 204a - 204d. Increasing the number of series of grooves 204a - 204d increases the operating voltage of the two-terminal device 200. Such a two-terminal device 200 can be operated in parallel or a combination of series and parallel arrangement. It may be an advantage of the two-terminal device 200 that this removes the need for extra process steps to be used to connect the cascaded groove structures in series to achieve the desired output voltage.

[00326] Each channel of the plurality of channels 206a-206c physically separates the cascaded (series connected) grooves 204a-204d. Each of the plurality of channels 206a- 206c enables the cascaded (series connected) grooves 204a - 204d to be electrically connected in parallel to the first and second terminals 212, 214. In this way, it is possible to extract the desired electric charge generated at the voltage designed by the number of cascaded groove structures 204a - 204d.

[00327] The first channel 206a, also referred to as the first delineation or structural delineation feature, first crosses the first series of grooves 204a towards one end of the substrate 202 and then crosses a space 208 between the first series of grooves 204a and the second series of grooves 204b, and subsequently crosses the second series of grooves 204b towards the opposite edge of the substrate 202. Since many of these channels are used, each series of grooves, 204a, 204b for example, are crossed toward each edge by elements of two successive individual channels, as shown in Figure 4. The first channel 206a crosses towards an end of each groove of the series of grooves 204a, 204b, 204c, 204d. However, in other embodiments, the first channel 206a may terminate an end, i.e. cross at an end, of each groove of the series of grooves 204a, 204b, 204c, 204d.

[00328] The second channel 206b, like the first channel 206a, first crosses the first series of grooves 204a towards one end of the substrate 202 and then crosses a spacer 208 between the first series of grooves 204a and the second series of grooves 204b, and subsequently crosses the second series of grooves 204b towards the opposite edge of the substrate 202. The third channel 206c crosses the first series of grooves 204a, the spacer 208, and the second series of grooves 204b, in the same manner as the first channel 206a and the second channel 206b.

[00329] It may be advantageous to use a plurality of channels 206a - 206c to mitigate the likelihood of an electrical short forming across the interface between the first series of grooves 204a and the second series of grooves 204b, that is, across the plurality of channels 206a-206c. Thus, a plurality of channels 206a-206c ensure a more efficient and reliable two-terminal device 200.

[00330] Together, the spacers 208 and channels 206 divide the substrate 202 into a first area 210a and a second area 210b. The first area 210a carries a positive charge and the second area 210b carries a negative charge. The first area 210a terminates at a first or positive terminal 212 at one edge of the substrate 202, and the second area 210b terminates at a second or negative terminal 214 at the other, opposite, edge of the substrate 202, referring to the transverse direction TD. The first area 210a provides an electrical connection of the first groove of each series of grooves 204a-204d to the first terminal 212. The second area 210b provides an electrical connection of the last groove of each series of grooves 204a-204d to the second terminal 214. Thus, a two-terminal device 200 having a first terminal 212 and a second terminal 214 is formed.

[00331] Figure 5 illustrates a plan view of yet another two-terminal device 300 comprising a substrate 302. The substrate 302 has a surface comprising a plurality of series of grooves 304a - 304d. In particular, the substrate 302 comprises a first series of grooves 304a, a second series of grooves 304b, a third series of grooves 304c and a fourth series of grooves 304d. Further series of grooves may be provided in the machine direction MD of the substrate 302. Each groove of the series of grooves 304a - 304d generally run in parallel to one another across the transverse direction TD of the substrate 302, extending from a proximal end, for example, proximal to the first terminal 312 as described below, to a distal end, for example, distal to the first terminal 312 as described below. A delineation feature (306a, 306b, 306c, 316, 318) is provided between each series of grooves 304a - 304d.

[00332] The two-terminal device 300 may be an optoelectronic device, such as a solar photovoltaic cell. Such a two-terminal device 300 includes a mixture of interdigitated (parallel connected) and cascaded (series connected) grooves 304a - 304d. The operating voltage of such a two-terminal device 300 can be controlled by changing the number of series of grooves 304a - 304d. Increasing the number of series of grooves 304a - 304d increases the operating voltage of the two-terminal device 300. Such a two-terminal device 300 can be operated in parallel or a combination of series and parallel arrangement. It may be an advantage of the two-terminal device 300 that this removes the need for extra process steps to be used to connect the cascaded groove structures in series to achieve the desired output voltage.

[00333] The delineation features (306a, 306b, 306c, 316, 318) physically separates the cascaded (series connected) grooves 304a-304d. The delineation features enable the cascaded (series connected) grooves 304a - 304d to be connected in parallel via electrical connection to the first and second terminals 312, 314. In this way it is possible to extract the desired electric charge generated at the voltage designed by the number of cascaded groove structures 304a - 304d.

[00334] The delineation feature comprises a plurality of channels, specifically a first channel 306a, a second channel 306b and a third channel 306c. Each channel 306a - 306c is connected at their distal ends to a first transection channel 316, and connected at their proximal ends to a second transection channel 318. The first and second transection channels 316, 318 form part of the delineation feature and may be substantially channel like, or may be further channels. The first and second transection channels 316, 318 generally connect to each channel 306a - 306c perpendicularly at their respective ends. The first transection channel 316 first crosses the first series of grooves 304a towards one end of the substrate 302 and then crosses a spacer 308 between the first series of grooves 304a and the second series of grooves 304b, and subsequently crosses the second series of grooves 304b towards the opposite edge of the substrate 302. Since many of these delineation features are used, each series of grooves, 304a, 304b for example, are crossed toward each edge by elements of two successive transection channels 316, 318, as shown in Figure 5. The delineation feature, specifically transection channels 316, 218 crosses towards an end of each groove of the series of grooves 304a, 304b, 304c, 304d. However, in other embodiments, the transection channels 316, 318 may terminate an end, i.e. cross at an end, of each groove of the series of grooves 304a, 304b, 304c, 304d.

[00335] It may be advantageous to use a plurality of channels 306a - 306c between the series of grooves to mitigate the likelihood of an electrical short forming across the interface between the first series of grooves 304a and the second series of grooves 304b, that is, across the delineation feature. Furthermore, the described arrangement, specifically of transection channels 316, 318 at each end of each channel 306a - 306c, may provide for an easier manufacture of such efficient and reliable substrates.

[00336] Together, the spacers 308 and the plurality of channels 306a-306c divide the substrate 302 into a first area 310a and a second area 310b. The first area 310a carries a positive charge and the second area 310b carries a negative charge. The first area 310a terminates at a first or positive terminal 312 at one edge of the substrate 302, and the second area 310b terminates at a second or negative terminal 314 at the other, opposite, edge of the substrate 302, referring to the transverse direction TD. The first area 310a provides an electrical connection of the first groove of each series of grooves 304a-304d to the first terminal 312. The second area 310b provides an electrical connection of the last groove of each series of grooves 304a-304d to the second terminal 314. Thus, a two- terminal device 300 having a first terminal 312 and a second terminal 314 is formed.

[00337] Figure 6 illustrates a plan view of yet another two-terminal device 400 comprising a substrate 402. The substrate 402 has a surface comprising a plurality of series of grooves 404a - 404c. In particular, the substrate 402 comprises a first series of grooves 404a, a second series of grooves 404b, and a third series of grooves 404c. Further series of grooves may be provided in the machine direction MD of the substrate 402. Each groove of the series of grooves 404a - 404c generally run in parallel to one another across the transverse direction TD of the substrate 402, extending from a proximal end, for example, proximal to a first terminal 412 as described below, to a distal end, for example, distal to the first terminal 412 as described below. A channel 406 is provided between each series of grooves 404a - 404c.

[00338] The two-terminal device 400 may be an optoelectronic device, such as a solar photovoltaic cell. Such a two-terminal device 400 includes a mixture of interdigitated (parallel connected) and cascaded (series connected) grooves 404a - 404c. The operating voltage of such a two-terminal device 400 can be controlled by changing the number of series of grooves 404a - 404c. Increasing the number of series of grooves 404a - 404c increases the operating voltage of the two-terminal device 400. Such a two-terminal device 400 can be operated in parallel or a combination of series and parallel arrangement. It may be an advantage of the two-terminal device 400 that this removes the need for extra process steps to be used to connect the cascaded groove structures in series to achieve the desired output voltage.

[00339] The channel 406 physically separates the cascaded (series connected) grooves 404a - 404c. The channel 406 enables the cascaded grooves 404a-404c to be connected in parallel via electrical connection to the first and second terminals 412, 414. In this way, it is possible to extract the desired electric charge generated at the voltage designed by the number of cascaded groove structures 404a - 404c.

[00340] The channel 406, also referred to as a delineation feature or structural delineation feature, comprises first region, extending along the machine direction MD, a second region extending along the machine direction MD and substantially parallel to the first region, and a third region therebetween extending along the transverse direction TD and connecting the first region to the second region. The channel 406 first crosses the first series of grooves 404a towards one end of the substrate 402 and then crosses a spacer 408 between the first series of grooves 404a and the second series of grooves 404b, and subsequently crosses the second series of grooves 404b towards the opposite edge of the substrate 402. Since many of these channels 406 are used, each series of grooves, 404a, 404b for example, are crossed toward each edge by elements of two successive channels 406, as shown in Figure 6. The channel 406 terminates, i.e. crosses at, an end of each groove of the series of grooves 404a, 404b, 404c. However, in other embodiments, the channel 406 may cross towards an end, i.e. it may not terminate an end, of each groove of the series of grooves 404a, 404b, 404c.

[00341] Moreover, the channel 406 are substantially Z-shaped in the depicted embodiment. As shown in Figure 6, a first predetermined angle, a, is formed between the first region of the channel 406 and the third region of the channel 406. A second predetermined angle, b, is formed between the second region of the channel 406 and the third region of the channel 406. In this example, a = b, however, in other examples, a ¹ b. In this specific example, a and b are approximately 70 degrees a and b may have a different value in other examples, for example, any value between 1 degree and 179 degrees.

[00342] It may be desirable to use a Z-shaped channel 406 as this can be advantageous during the manufacture of such substrates. As described further below, such substrates are coated using off-axis directional coating methods. Thus, by providing an angle between the various regions of the channel 406, the shadowing effect is increased, thereby providing regions of the channel 406 that are not coated with material. In this way, the likelihood of a short circuit across the channel 406 is mitigated, as described further below.

[00343] Together, the spacers 408 and the channels 406 divide the substrate 402 into a first area 410a and a second area 410b. The first area 410a carries a positive charge and the second area 410b carries a negative charge. The first area 410a terminates at a first or positive terminal 412 at one edge of the substrate 402, and the second area 410b terminates at a second or negative terminal 414 at the other, opposite, edge of the substrate 402, referring to the transverse direction TD. The first area 410a provides an electrical connection of the first groove of each series of grooves 404a-404c to the first terminal 412. The second area 410b provides an electrical connection of the last groove of each series of grooves 404a-404c to the second terminal 414. Thus, a two-terminal device 400 having a first terminal 412 and a second terminal 414 is formed.

[00344] Figures 7(a) and 7(b) illustrates a plan view of yet another two-terminal device 500 comprising a substrate 502. The two-terminal device 500 of Figures 7(a) and 7(b) is similar in construction to the two-terminal device of Figure 6. That is, the two-terminal device 500 includes a substrate 502, a plurality of series of grooves 504a - 504d, a channel 506, a spacer 508, a first area 510a carrying a positive charge, a second area 510b carrying a negative charge, and first and second terminals 512, 514. These features are described in relation to Figure 6 and are not discussed further here.

[00345] The two-terminal device 500 of Figures 7(a) and 7(b) differs from Figure 6 in that the first and second predetermined angles a, b are formed differently. In Figure 6, the third region of the channel 406 is angled and the first and second regions are substantially perpendicular to the series of grooves 404a - 404c. However, as shown in Figure 7(a), in the present example of the two-terminal device 500, the third region of the channel 506 extends substantially in parallel to the series of grooves 504a - 504d, and the first and second regions are formed at an angle with respect to the third region. In the depicted example, a = b, however, in other examples, a ¹ b. In this specific example, a and b are approximately 45 degrees. In some examples (not shown), a and b may be greater than 90 degrees, for example, up to, but not including, 180 degrees. As shown in Figure 7(b), the delineation feature may take any shape, having any angle, disposed in any appropriate manner on the substrate.

[00346] It may be desirable to use a Z-shaped channel 506 as this can be advantageous during the manufacture of such substrates. As described further below, such substrates are coated using off-axis directional coating methods. Thus, by providing an angle between the various regions of the channel 506, the shadowing effect is increased, thereby providing regions of the channel 506 that are not coated with material. In this way, the likelihood of a short circuit across the channel 506 is mitigated, as described further below. Moreover, the Z-shaped channel 506 may be preferred as it allows for a more efficient use of space between the series of grooves 504a - 504d.

[00347] Figures 8(a) to 8(d) illustrate various views of the two terminal device 300 as shown in Figure 5. Like numerals denote like features in Figures 8(a) to 8(d). As best shown in Figures 8(c) and 8(d), the two-terminal device 300 includes a series of grooves 304, each groove having first and second opposing groove faces, and a groove base 350. The groove extends between a proximal end and a distal end. The groove base is provided at a groove depth from the substrate surface.

[00348] The delineation feature, specifically the transection channels 316, 318 of the delineation feature, each includes first and second opposing channel faces, and a channel base 354. The channel faces are spaced apart by a channel width. As can be seen in Figures 8(a) to 8(d), and with further reference to Figures 10 and 11 as discussed below, the groove base 350 has a substantially constant groove depth from the substrate surface across the elongate width of the grooves 304. Additionally, the groove base 350 tends towards the channel base 354 in a transection region 352. That is, the depth of each groove base of the grooves 304 tends towards the depth of the delineation feature, or channel, in this example the transection channels 316, 318, within a transection region 352. This is described in further detail below, with reference to Figures 10 and 11.

[00349] Figures 9(a) and 9(b) illustrate various views of the two-terminal device 500 as shown in Figure 7(a). Like numerals denote like features in Figures 9(a) and 9(b). The two- terminal device 500 includes a series of grooves 504, each groove having a groove base 550. The delineation feature, specifically the channel 506, includes a channel base 554. As best shown in Figure 9(b), and with further reference to Figures 10 and 11 as discussed below, the groove base 550 has a substantially constant depth across the elongate width of the grooves 504. Additionally, the groove base 550 tends towards the channel base 554 in a transection region 552. That is, the depth of each groove of the grooves 504 tends towards the depth of the delineation feature, in this example, the channel 506, within a transection region 552. This is described in further detail below, with reference to Figures 10 and 11.

[00350] Figure 10 illustrates a cross-sectional view of one example of a transection region between a groove and a channel that can be applied to any of the examples discussed herein. Specifically, Figure 10 shows a substrate 602 having a groove 604, of a series of grooves, and a channel 606. The channel 606 transects the groove 604 at its proximal end. The groove 604 includes a groove base 650, and the channel 606 includes a channel base 654.

[00351] The groove 604, specifically the groove base 650, tends towards the channel 606, specifically the channel base 654, in a transection region 652. The transection region 652 has a transection region base 656 that is substantially arcuate in the example shown. That is, the transection region base 656 has a variable depth as it tends from the groove base 650 to the channel base 654. The variable depth is non-linear in the depicted example.

[00352] The channel 606 has a channel width. The channel width varies over the depth of the channel 604 so that there is a first channel width at the surface of the substrate 602, as well as a second channel width within the channel. That is the first and second opposing channel faces may be spaced apart by a first channel width at the substrate surface and spaced apart with a second channel width at a predetermined depth in the channel. The first and second channel widths may be the same or may differ.

[00353] In the example shown in Figure 10, the second channel width corresponds to the channel width at a depth corresponding to the depth of the groove base 650 where the groove is transected by the channel. That is, the second channel width corresponds to the channel width at a depth corresponding to the depth of groove base 650 at the channel end of the transection region 656. [00354] Figure 11 illustrates another example of a transection region between a groove and a channel that can be applied to any of the examples discussed herein. Specifically, Figure 11 shows a substrate 702 having a groove 704, of a series of grooves, and a channel 706. The channel 706 transects the groove 704 at its proximal end. The groove 704 includes a groove base 750, and the channel 706 includes a channel base 754.

[00355] The groove 704, specifically the groove base 750, tends towards the channel 706, specifically the channel base 754, in a transection region 752. The transection region 752 has a transection region base 756 that is substantially linear, or straight, in the example shown. That is, the transection region base 756 has a variable depth as it tends from the groove base 750 to the channel base 754. The variable depth is linear in the depicted example.

[00356] The channel 706 has a channel width. As with the example shown in Figure 10, the channel width of the example shown in Figure 11 varies over the depth of the groove 704 so that there is a first channel width at the surface of the substrate 702, as well as a second channel width within the channel. The first and second channel widths may be the same or may differ.

[00357] In the example shown in Figure 11, the second channel width corresponds to the channel width at a depth corresponding to the depth of the groove base 650 where the groove is transected by the channel. That is, the second channel width corresponds to the channel width at a depth corresponding to the depth of groove base 650 at the channel end of the transection region 656.

[00358] As shown in Figure 11, the linear transection region 752 forms an angle g with respect to an imaginary axis, formed as a continuation of the groove base 750. The angle Y is shown as approximately 45 degrees in the depicted example. However, other angles may be used.

[00359] Figure 12 illustrates a method 800 of forming a substrate as described herein.

The method 800 includes the step of providing 810 a web of flexible material, forming 820 a first series of grooves within the web of flexible material, forming 830 a second series of grooves within the web of flexible material, and forming 840 a channel between the first series of grooves and the second series of grooves within the web of flexible material.

[00360] The respective steps 810, 820, 830, 840 may be carried out sequentially, that is in an order. For example, the steps 810, 820, 830, 840 may be carried out in the order as described in Figure 12. Alternatively, the steps 810, 820, 830, 840 may be carried out in any other order. For example, the step of forming 840 the channel may take place between forming 820 the first series of grooves and forming 830 the second series of grooves. Further, two or more, or all, of steps 810, 820, 830, 840 may be carried out simultaneously, or concurrently, that is at the same time. For example, the steps of forming 820 the first series of grooves, forming 830 the second series of grooves, and forming 840 the channel may all take place simultaneously.

[00361] The step of forming 840 the channel further includes forming the channel such that the channel transects a portion of the first series of grooves and the second series of grooves towards a proximal end of each groove. Furthermore, the step of forming 840 the channel includes forming a depth of each groove that tends towards the depth of the channel at the proximal end of each groove.

[00362] In some examples, one or more of the steps of forming 820 a first series of grooves, forming 830 a second series of grooves and forming 840 a channel therebetween includes an embossing process, as described in relation to Figure 13.

[00363] Figure 13 illustrates a specific method 900 of forming a substrate as described herein. The method 900 may be a specific example of the method 800 of Figure 12, for example, the method 900 may represent an embossing process. The method 900 starts by providing 910 a web of flexible material 902. The method 900 also includes the step of coating 920 the web of flexible material 902 with a UV-curable composition, thereby forming a UV-curable coating 904 on at least one surface of the web of flexible material 902. The method may also include the step of engaging 930 the coated web of flexible material (902, 904) with a shim, shown in this particular example as a master shim being a cylindrical stamping roll 906. In other examples, there may be a plurality of shims, a single master shim, or a stamping plate formed as one or more of the plurality of shims or as the single master shim. That is, the skilled person would recognise that the shim need not be a master shim, nor need it be a cylindrical stamping roll 906. In the example shown, the cylindrical stamping roll 906 includes a series of protrusions 908. The protrusions 908 correspond to the first series of grooves, the second series of grooves and the channel, as described further below.

[00364] As the protrusions 908 engage the coated web of flexible material (902, 904), the UV-curable coating 904 is at least partially UV-cured 940 during the engagement step 930. The protrusions 908 are then removed 950 from the coated web of flexible material (902, 904). As the protrusions 908 are removed 950, the coated web of flexible material (902, 904) is caused to be drawn towards the protrusions 908 of the cylindrical stamping roll 906 as they are removed 950, due to the partial UV-curing of the UV-curable coating 904. However, since the UV-curable coating 904 is only partially UV-cured, that is not fully cured, the coated web of flexible material (902, 904) then relaxes as the protrusions 908 of the cylindrical stamping roll 906 are fully removed. In this way, the transection region between the first series of grooves or the second series of grooves and the channel is first caused to be drawn upwardly, towards the cylindrical stamping roll 906, and then relaxes, such that the transection region is formed in a manner such that the depth of the grooves tends towards the depth of the channel, as described above.

[00365] The cylindrical stamping roll 906 is continually rolled 960 across the machine direction MD of the coated web of flexible material (902, 904). Thus, the process is repeated along the machine direction MD. It may also be desirable to cut the formed substrate at various intervals along the machine direction MD. In such cases, the method 900 may optionally include the step of cutting the master substrate into a plurality of substrates.

[00366] Figure 14 illustrates a method 1000 of forming a two-terminal device having a substrate as described herein. The method 1000 may be a continuation of method 800 of Figure 12 or method 900 of Figure 13. The method 1000 starts by providing, or forming, 1010 a substrate 1001 as described herein. The method 1000 may also include coating 1020 a first face 1002 of a first series of grooves 1006, a second series of grooves 1008 and a channel 1011 with a first material 1012. The method 1000 may also include coating 1040 a second face 1004 of the first series of grooves 1006, the second series of grooves 1008 and the channel 1010 with a second material 1014. The first material 1012 and the second 1014 may be different.

[00367] The coating steps 1020, 1040 may comprise an off-axis directional coating as best shown in Figures 14, and 15(a) to 15(c). That is, the coating steps 1020, 1040 may comprise coating at an angle formed with respect to the plane of the substrate 1001. As shown in Figure 15, such an angle d may be in the range of 30 to 70 degrees, for example approximately 45 degrees.

[00368] Figures 15(a) and 15(b) illustrate a coating process, of the substrates shown in Figures 10 and 11, respectively. Figure 15(c) further illustrates a comparison coating process without having the transection regions of Figures 10 and 11 as described. Figures 15(a) and 15(b) illustrate a coating process having an incident coating angle d. The arrow C illustrates the incoming coating of a material. As shown, the transection region 652, 752, in which the groove base tends from the groove depth 650, 750 to the channel depth 654, 754, as described above, ensures that a large proportion of the transection region 652, 752, that is the region connecting the grooves 604, 704 to the channel 606, 706, is shadowed, indicated by the region below arrow C, by the wall W of the channel 606, 706 during the coating process. In this way, during the coating process, a large proportion of the transection region 652, 752 is not coated with an incoming material. Thus, once the grooves 604, 704 and the channel 606, 706 are filled with a material that allows for an electrical pathway, as described below, the lack of coated material in the transection region 652, 752 ensures that there is no electrical connection between the grooves 604, 704 and the channel 606, 706.

[00369] In comparison, referring to Figure 15(c), without the transection regions 652, 752 in which the groove base tends from the groove depth to the channel depth as described, the interface between an adjacent series of grooves 780 and the channel 790 is coated with material at the same incident coating angle d as in Figures 15(a) and 15(b). That is, in the example of Figure 15(c), the creation of an electrical short during manufacture is solely dependent upon the amount of material to be filled in the grooves 780 and the channel 790. This is known to be difficult to control. Whereas, electrical shorts are mitigated through the use of a transection region in which the groove depth tends to the channel depth, thus increasing the shadowing of the region between the grooves and the channel during manufacture.

[00370] The method 1000 further includes the step of at least partially filling 1060 the channel 1010 with a third material 1016. The third material 1016 may be different to the first material 1012 and the second material 1014. In some examples, the step of at least partially filling 1060 the channel 1010 may comprise a printing process. In addition to the channel 1010 being filled with a third material 1016, the first series of grooves 1006, the second series of grooves 1008, or both the first and second series of grooves 1006, 1008 may be at least partially filled with the same third material 1016, as shown in Figure 14. Figure 14 illustrates an embodiment in which the channel 1004 is filled, or completely filled, with the third material 1016.

[00371] The first material 1012, the second material 1014 and the third material 1016 vary depending on the intended use of the two-terminal device that is to be formed. For example, in some cases it may be desirable to produce a solar photovoltaic device that can supply electricity to a device. In this example, the first material 1012 may be a non insulating material, such as a conductor or a semiconductor, the second material 1014 may be a non-insulating material, such as a conductor or a semiconductor, and the third material 1016 may be a perovskite structured material. As would be recognised by the person skilled in the art, the two-terminal device can be produced with the appropriate coatings that are suitable for the intended final use of the two-terminal device to be produced.

[00372] Figure 16 illustrates a two-terminal device 1100 including a substrate 1102 as described herein. The substrate 1102 includes a first series of grooves 1104, a second series of grooves 1106 and a channel 1108 therebetween. The channel 1108 may have a greater depth than that of the grooves 1104, 1106, as shown. [00373] The first series of grooves 1104 include a first face 1104a, a second, opposing, face 1104b, and a cavity 1104c therebetween. The second series of grooves 1106 include a first face 1106a, a second, opposing, face 1106b, and a cavity 1106c therebetween. The channel 1108 includes a first face 1108a, a second, opposing, face 1108b, and a cavity 1108c therebetween. The first faces 1104a, 1106a, 1108a are coated with a first material 1110. The second face 1104b, 1106b, 1108b are coated with a second material 1112. Additionally, a third material 1114 is provided within the cavities 1104c, 1106c, 1108c. As shown in Figure 16, the cavities 1104c, 1106c of the first and second series of grooves 1104, 1106 are filled to the extent that the first material 1110 and the second material 1112 on opposing faces (1104a, 1104b and 1106a, 1106b) are in contact with the third material 1114. In this way, an electrical pathway is formed across the first series of grooves 1104 and the second series of grooves 1106.

[00374] As can be seen in Figure 16, the cavity 1108c of the channel 1108 is filled with the third material 1114 such that the third material 1114 is in contact with the first material 1110 on the first face 1108a or the second material 1112 on the second face 1108b. Thus, an electrical pathway is provided. However, due to the nature of the substrate described herein and the methods of formation thereof, the cavity 1108c of the channel 1108 could also be filled with the third material 1114 to a lesser extent. Thus, even if the cavity 1108c is filled to a large extent as shown, it would not make contact with the first material 1110 or the second material 1112 within the transection region in which the grooves 1104, 1106 meet with the channel 1108. In this way, an electrical pathway, and thus an electrical short, is prevented across the channel 1108, whilst allowing for a more simple manufacturing process.

[00375] Figure 17 illustrates a two-terminal device 1200. The two-terminal device 1200 includes a substrate 1202. The substrate 1202 has a first cell and a second cell that is spaced apart from the first cell. The second cell is spaced from the first cell along the substrate 1202 along the web direction of the substrate 1202. The first cell is provided with a first series of grooves 1204. Each groove of the first series of grooves 1204 include a first face 1204a, a second, opposing, face 1204b, and a cavity 1204c therebetween. The second cell is provided with a second series of grooves 1206. Each groove of the second series of grooves 1206 include a first face 1206a, a second, opposing, face 1206b, and a cavity 1206c therebetween. A connecting portion including a first channel 1208 and a second channel 1209 is provided between the first cell and the second cell. The first channel 1208 has a first face 1208a, a second, opposing, face 1208b, and a cavity 1208c therebetween. The second channel 1209 is provided between the first channel 1208 and the second cell. The second channel 1209 has a first face 1209a, a second, opposing, face 1209b, and a cavity 1209c therebetween. In other examples, one channel 1208 is provided between the first cell and the second cell. In other additional examples, more than two channels 1208, 1209 are provided between the first cell and the second cell. The substrate 1202 is provided with a first terminal and a second terminal. The first and second terminals are formed at opposing edges of the substrate 1202 across the transverse direction of the substrate 1202. The first and second terminals are electrically connected to the first cell and the second cell in a manner similar to that described in relation to Figures 3 to 7. That is, the first and second terminals are in electrical communication with each of the first cell and the second cell.

[00376] The first faces 1204a, 1206a, 1208a, 1209a are coated with a first material 1210. The second faces 1204b, 1206b, 1208b, 1209b are coated with a second material 1212. Additionally, a third material 1214 is provided within the cavities 1204c, 1206c, 1208c, 1209c. The cavities 1204c, 1206c of the first and second series of grooves 1204, 1206 are filled to the extent that the first material 1210 and the second material 1212 on opposing faces (1204a, 1204b and 1206a, 1206b) are in contact with the third material 1214. This forms an electrical pathway across the first series of grooves 1204 of the first cell, and between the second series of grooves 1206 of the second cell.

[00377] The cavity 1208c of the first channel 1208 is partially filled with the third material 1214 such that the third material 1214 in the cavity 1208c does not contact the first material 1210 on the first face 1208a and the second material 1212 on the second face 1208b. No electrical pathway is provided between the third material 1214 and the first material 1210 on the first face 1208a. No electrical pathway is provided between the third material 1214 and the second material 1212 on the second face 1208b. The cavity 1209c of the second channel 1209 is partially filled with the third material 1214 such that the third material 1214 in the cavity 1209c does not contact the first material 1210 on the first face 1209a and the second material 1212 on the second face 1209b. No electrical pathway is provided between the third material 1214 and the first material 1210 on the first face 1209a. No electrical pathway is provided between the third material 1214 and the second material 1212 on the second face 1209b. The first and second channels 1208, 1209 ensure there is an electrical resistance from one side of the connecting portion to the other. In some examples, one, or both, of the cavities 1208c, 1209c may be filled to the extent that the third material 1214 within those cavities 1208c, 1209c contact the first material 1210 and the second material 1212 to provide an electrical connection thereacross. However, due to the combined resistance of the channels 1208, 1209, as discussed further below, charge from the first or second cell is extracted at the first and second terminals of the device rather than being transferred across the connecting portions 1208, 1209.

[00378] In use, the combined resistance across the first and second channels 1208, 1209 that is the resistance across the connecting portion is greater than the resistance across the first cell. The combined resistance across the first and second channels 1208, 1209 is greater than the resistance across the second cell. More specifically, the first cell has a first characteristic resistance. The second cell has a second characteristic resistance. The combined resistance across the first and second channels 1208, 1209 is a third characteristic resistance that is greater than the first characteristic resistance across the first cell. The third characteristic resistance is greater than the second characteristic resistance across the second cell. By having a combined resistance across the first and second channels 1208, 1209 that is greater than the resistance across the first cell and the second cell, charge is extracted from the first and second terminals, rather than being transferred across between the first cell and the second cell, across the connecting portions. In this particular example, the resistance value of the first characteristic resistance and the value of the second characteristic resistance are the same. It is envisaged that in some examples, the third characteristic resistance across the connecting portions 1208, 1029 is equal to at least one of the first characteristic resistance and the second characteristic resistance. It is envisaged that more than two connecting portions may be provided between the first cell and the second cell. By providing multiple channels 1208, 1209 between the first cell and the second cell, the combined resistance is increased with the number of channels 1208, 1209. The space between the channels may be increased to further increase the combined resistance across the connecting portion. In this particular example, the combined resistance across the connecting portion is five times the resistance across the first cell. In this particular example, the resistance across the connecting portion is also five times the resistance across the second cell. The resistance across the first cell and across the second cell are the same in this particular example.

[00379] Figure 18 illustrates a two-terminal device 1300. The two-terminal device 1300 includes a substrate 1302. The substrate 1302 has a first cell 1304, a second cell 1306, a first terminal and a second terminal as previous described with reference to Figure 17 and thus will not be described again in detail. Like numerals apply with respect to Figure 17, except in that in Figure 18 they begin with the digits “13” instead of “12”. A connecting portion is provided between the first cell 1304 and the second cell 1306. The connecting portion includes a number of channels. In this particular example, the connecting portion is provided with two channels 1308, 1309 that are filled with the third material 1314 as described in relation to Figure 17. As will be noted, Figure 18 is identical to that of Figure 17, except in that the channels within the connecting portion are filled, such that an electrical connection is made between the first material 1310 on one side of each channel, and the second material 1312 on the other side of each channel. Thus, an electrical pathway is formed thereacross.

[00380] In use, the resistance across the connecting portion is greater than the resistance across the first cell 1304. The resistance across the connecting portion is also greater than the resistance across the second cell 1306. More specifically, the first cell has a first characteristic resistance. The second cell has a second characteristic resistance. The resistance across the connecting portion is a third characteristic resistance that is greater than the first characteristic resistance across the first cell 1304. The third characteristic resistance is also greater than the second characteristic resistance across the second cell 1306. By having an arrangement where the resistance across the connecting portion is greater than the first characteristic resistance across the first cell 1304 and greater than the second characteristic resistance across the second cell 1306, charge is extracted from the first and second terminals, rather than being transferred across the first and second terminals. In this particular example, the third characteristic resistance is three times the first characteristic resistance across the first cell 1304. The third characteristic resistance is there times the second characteristic resistance across the second cell 1306. In some examples, the connecting portion is additionally provided with a resistive element (not shown) that increases the resistance across the connecting portion.

[00381] Figure 19 illustrates a two-terminal device 1400. The two-terminal device 1400 includes a substrate 1402 that has a first cell 1404 and a second cell 1406 substantially as previously described with reference to Figure 17, and therefore will not be described here again in detail. Substrate 1402 is provided with a first terminal and a second terminal substantially as previously described with reference to Figure 17, and therefore will not be described here again in detail. A connecting portion 1408 is provided between the first cell 1404 and the second cell 1406. In this particular example, the connecting portion 1408 is a planar element extending from and between the first series of grooves forming the first cell 1404 and the second series of groves forming the second cell 1406. The connecting portion 1408 extends between the first cell 1404 and the second cell 1406 in the direction along the web direction of the substrate 1402. The first series of grooves include a first face 1404a, a second, opposing, face 1404b, and a cavity 1404c therebetween. The second series of grooves include a first face 1406a, a second, opposing, face 1406b, and a cavity 1406c therebetween. The first faces 1404a, 1406a are coated with a first material 1410. The second faces 1404b, 1406b are coated with a second material 1412. The second material 1412 coating the second face 1404b of the groove 1404 proximal the connecting portion 1408 partially coats the connecting portion 1408.

[00382] The first material 1410 coating the first face 1406a of the groove 1404 proximal the connecting portion 1408 partially coats the connecting portion 1408. In this way, the connecting portion 1408 provided between the first cell 1404 and the second cell 1406 is partially coated with a second material 1412 on the end of the connecting portion 1408 proximal the first cell 1404. The connecting portion 1408 provided between the first cell 1404 and the second cell 1406 is partially coated with a first material 1410 on the end of the connecting portion 1408 proximal the second cell 1406. The connecting portion 1408 is therefore provided between the first cell 1404 and the second cell 1406, partially coated with a second material 1412 on a first end proximal the first cell 1404, and is partially coated with a first material 1410 on a second end proximal the second cell 1406. The first material 1410 and the second material 1412 partially coating the connecting portion 1408 are electrically separated from one another. The connecting portion 1408 ensures an electrical resistance from one side to the other.

[00383] In use, the resistance across the connecting portion 1408 is greater than the resistance across the first cell 1404. The resistance across the connecting portion 1408 is greater than the resistance across the second cell 1406. The first cell 1404 has a first characteristic resistance. The second cell 1406 has a second characteristic resistance.

The resistance across the connecting portion 1408 is a third characteristic resistance that is greater than the first characteristic resistance across the first cell 1404. The third characteristic resistance is greater than the second characteristic resistance across the second cell 1406. The arrangement of having a greater resistance across the connecting portion 1408 between the first cell 1404 and the second cell 1406 allows charge from the first or second cell 1404, 1406 to be extracted from the first and second terminals, rather than being transferred between the first cell 1404 and the second cell 1406, across the connecting portion 1408.

[00384] Figure 20 illustrates a two-terminal device 1500. The two-terminal device 1500 includes a substrate 1502. The substrate 1502 has a first cell 1504 and a second cell 1504 spaced apart from the first cell 1504 along the substrate 1502 along the web direction of the substrate 1502. The first cell 1504 and the second cell 1506 are as previously described with reference to Figure 17, and therefore will not be described here again in detail. The substrate 1502 is provided with a first terminal and a second terminal as described with reference to Figure 17, and therefore will also not be described here again in detail. A connecting portion is provided between the first cell 1504 and the second cell 1506. The connecting portion includes a channel 1508 provided with a first face 1508a, a second, opposing, face 1508b, and a cavity 1508c therebetween. The channel 1508 has a depth that is greater than the grooves of each of the first cell 1504 and the second cell 1506.

[00385] The first faces 1504a, 1506a, 1508a are coated with a first material 1510. The second faces 1504b, 1506b, 1508b are coated with a second material 1512. Additionally, a third material 1514 is provided within the cavities 1504c, 1506c, 1508c. The cavities 1504c, 1506c of the first cell 1504 and second cell 1506 respectively are filled to the extent that the first material 1510 and the second material 1512 on opposing faces (1504a, 1504b and 1506a, 1506b) are in contact with the third material 1514. This forms an electrical pathway across the first cell 1504, and across the second cell 1506.

[00386] Unlike the two-terminal device shown in Figure 14, in which the cavity is fully filled by a material 1016, the walls, formed by faces 1508a, 1508b, of the cavity 1508c are coated with the third material 1514. The coating of the cavity 1508c is such that the third material 1514 in the cavity 1508c is electrically connected to the first material 1510 on the first face 1508a, and the second material 1512 on the second face 1508b. An electrical pathway is therefore provided between the first material 1510 on the first face 1508a of the channel 1508, and the second material 1512 on the second face 1508b of the channel 1508. The channel 1508 creates an electrical connection from one side to the other. That is, the channel 1508 electrically connects one side, proximal the first cell 1504, to the other side, proximal the second cell 1506.

[00387] In use, the resistance across the connecting portion is greater than the resistance across the first cell 1504. The resistance across the connecting portion is greater than the resistance across the second cell 1506. The first cell 1504 has a first characteristic resistance. The second cell 1506 has a second characteristic resistance. The resistance across the connecting portion is a third characteristic resistance that is greater than the first characteristic resistance across the first cell 1504. The third characteristic resistance is greater than the second characteristic resistance across the second cell 1506. This arrangement allows charge from the first or second cell to be extracted from the first and second terminals, rather than being transferred between the first cell 1504 and the second cell 1506, across the connecting portion.

[00388] Figure 21 illustrates a two-terminal device 1600. The two-terminal device 1600 includes a substrate 1602 having a first cell 1604, a second cell 1606, a first terminal and a second terminal, as hereinbefore described with reference to Figure 20, and therefore will not be described here again in detail. A connecting portion including a channel 1608 is provided between the first cell 1604 and the second cell 1606. The channel 1608 is provided with a first face 1608a proximal the first cell 1604, and a second, opposing face 1608b proximal the second cell 1606. The channel 1608 is provided with a cavity 1608c between the first face 1608a and the second face 1608b. The first face 1608a of the channel 1608 and the second face 1608b of the channel 1608 extend a depth into the substrate 1602 greater than the depth of the grooves of the first cell 1604 and second cell 1606. In this particular example, the channel 1608 is substantially U-shaped, having the first face 1608a, the second face 1608b, and a bottom rutted portion. In this example, the bottom rutted portion is formed of eight undulations. The cavity 1608c of the channel 1608 is larger in size in comparison to the cavities 1604c, 1606c of the first cell 1604 and the second cell 1606 respectively. The greater size and the depth of the channel 1608 in comparison with the grooves of the first cell 1604 and the second 1606 provide a greater resistance across the connecting portion relative to the resistance across the first cell 1604 and the second cell 1606 respectively.

[00389] The first faces 1604a, 1606a, 1608a are coated with a first material 1610. The second faces 1604b, 1606b, 1608b are coated with a second material 1612. Additionally, a third material 1614 is provided within the cavities 1604c, 1606c, 1608c. The cavities 1604c, 1606c of the first cell 1604 and the second cell 1606 respectively, are filled to the extent that the first material 1610 and the second material 1612 on opposing faces (1604a, 1604b and 1606a, 1606b) are in contact with the third material 1614. This forms an electrical pathway across the grooves of the first cell 1604, and between the grooves of the second cell 1606.

[00390] In this particular example, each of the grooves of the bottom rutted portion, forming the cavity 1608c, is partially filled, for example coated, with the third material 1614. In this way, the third material 1614 forms a coating, or a conformed coating or a film, of the third material 1614 within the undulations of the channel 1608. Thus, the third material 1614 is in contact with the first material 1610 on the first face 1608a. The third material 1614 also contacts the second material 1612 on the second face 1608b. An electrical pathway is provided between the third material 1614 and the first material 1610 on the first face 1608a. An electrical pathway is provided between the third material 1614 and the second material 1612 on the second face 1608b. The connecting portion provides an electrical connection from one side to the other. That is, the connecting portion provides an electrical connection from one side of the connecting portion proximal the first cell 1604, to the other side of the connecting portion 1608 proximal the second cell 1606.

[00391] In use, the resistance across the connecting portion 1608 is greater than the resistance across the first cell 1604. The resistance across the connecting portion is also greater than the resistance across the second cell 1606. The first cell 1604 has a first characteristic resistance. The second cell 1606 has a second characteristic resistance. The resistance across the connecting portion has a third characteristic resistance that is greater than the first characteristic resistance across the first cell 1604. The third characteristic resistance across the connecting portion is greater than the second characteristic resistance across the second cell 1606. By having a resistance across the connecting portion 1608 that is greater than the resistance across the first cell 1604 and the second cell 1606, charge from the first or second cell 1604, 1606 is extracted from the first and second terminals, rather than being transferred across between the first cell 1604 and the second cell 1606.

[00392] Figure 22 illustrates a two-terminal device 1700. The two-terminal device 1700 includes a substrate 1702. The substrate 1702 has a first cell 1704 and a second cell 1706 spaced apart from the first cell 1704 along the substrate 1702 along the web direction of the substrate 1702. The first cell 1704 and the second cell 1706 are as previously described with reference to Figure 20, and therefore will not be described here again in detail. The substrate 1702 is provided with a first terminal and a second terminal. The first and second terminals are formed at opposing edges of the substrate 1702 across the transverse direction of the substrate 1702. The first and second terminals are electrically connected to the first cell 1704 and the second cell 1706. That is, the first and second terminals are in electrical communication with each of the first cell 1704 and the second cell 1706.

[00393] A connecting portion, including a peak 1708 of the substrate 1702, is provided between the first cell 1704 and the second cell 1706. The peak 1708 is provided with a first face 1708a and a second, opposing, face 1708b. In this example, the peak 1708 is directed upwards, in a direction opposite to the direction of the grooves of the first cell 1704 and the second cell 1706. The first face 1708a of the peak 1708 is provided on a side proximal the first cell 1704. The second face 1708b of the peak 1708 is provided on a side proximal the second cell 1706. The peak 1708 has a height that is greater than the depth of the grooves of each of the first cell 1704 and the second cell 1706. In this particular example, the peak 1708 is formed from a block material having a first material disposed on the first face 1708a and a second material disposed on the second face 1708b. This first and second materials disposed thereon may be the same as the first and second material 1710, 1712 disposed on the faces 1704a, 1704b, 1706a, 1706b of the cells 1704, 1706 as described below. In particular, the first face 1708a may be coated with non-insulating material, such as a conductor. In particular, the second face 1708b may be coated with non-insulating material, such as a conductor. There may be a region between the first face 1708a, 1708b in which no material is provided, such as a gap. This may be provided by removing a portion of the materials provided on the first face 1708a and the second face 1708b. Alternatively, such a portion may be masked during manufacturing. Further, in other embodiments, the upper portion of the block material may be removed after coating the first face 1708a and the second face 1708b, thereby providing an electrical resistance between the respective faces. In this example, the connecting portion does not have a cavity. The connecting portion includes a peak at an end distal the grooves of the first cell 1704 and the second cell 1706.

[00394] The first faces 1704a, 1706a of the first cell 1704 and second cell 1706 respectively, are coated with a first material 1710. The second faces 1704b, 1706b of the first cell 1704 and second cell 1706 respectively, are coated with a second material 1712. Additionally, a third material 1714 is provided within the cavities 1704c, 1706c of the first cell 1704 and second cell 1706 respectively. The cavities 1704c, 1706c are filled to the extent that the first material 1710 and the second material 1712 on opposing faces (1704a, 1704b and 1706a, 1706b) are in contact with the third material 1714. This forms an electrical pathway across the first cell 1704, and across the second cell 1706.

[00395] In use, the resistance across the connecting portion is greater than the resistance across the first cell 1704. The resistance across the connecting portion is greater than the resistance across the second cell 1706. The first cell 1704 has a first characteristic resistance and the second cell 1706 has a second characteristic resistance. The resistance across the connecting portion is a third characteristic resistance that is greater than the first characteristic resistance across the first cell 1704. The third characteristic resistance is greater than the second characteristic resistance across the second cell 1706. This arrangement allows charge from the first or second cell 1704, 1706 to be extracted from the first and second terminals, rather than being transferred between the first cell 1704 and the second cell 1706, across the connecting portion.

[00396] Figure 23 illustrates a comparison between the two-terminal device described in relation to Figure 1 (“parallel first”) and the two-terminal device described in relation to Figures 2(a) and 3 (“series first (with delin)”). Figure 23 illustrates the performance of each device as a function of electrical short probability per groove section. The performance of a device is defined as a percentage or a fraction of incoming light energy converted into electrical energy (PCE). As can be seen in Figure 23, the performance of the two-terminal device described in Figures 2(a) and 3 is far superior to that of the two-terminal device described in Figure 1. In particular, the device of Figures 2(a) and 3 remains at a high operational performance even at high short probabilities per groove section. On the other hand, the operational performance of the device of Figure 1 rapidly decreases with an increasing short probability per groove section. In this way, the two-terminal device as described herein has a superior performance over the prior art. [00397] Figure 24 illustrates the performance, specifically the fraction of optimal performance with respect to a two-terminal device without a delineation feature, as a function of the resistance of the delineation feature, specifically measured as a multiple of the characteristic resistance of the delineation feature with respect to the characteristic resistance of the adjacent grooves, for a two-terminal device described herein. As shown in Figure 24, as the characteristic resistance of the delineation feature, that is the connecting portion, is increased with respect to the characteristic resistance of the adjacent grooves, the performance of the device tends towards the expected ideal performance.

[00398] Figure 25 illustrates the performance, specifically the fraction of optimal performance with respect to a two-terminal device without a delineation feature, as a function of the delineation short-circuit current, as a fraction of the current within a series of grooves. In particular, as described herein, the delineation feature acts as a reverse biased diode, and so the open-circuit voltage created is unimportant, as the operating voltage flows in the opposite direction. This is shown by the linear relationship between these functions, as demonstrated in Figure 25.

[00399] It will be appreciated by persons skilled in the art that the above embodiment(s) have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departing from the scope of the invention as defined by the appended claims. Various modifications to the detailed designs as described above are possible, for example, variations may exist in number, shape, size, arrangement, assembly or the like. For example, any number of grooves and any number of series of grooves may be used, any number of channels, or delineation features, may be used. Further, the channel(s) may intersect the grooves at any appropriate angle and may be shaped in any appropriate way. Further, various grooves, channels, connecting portions or the like may be partially filled, filled, completely filled, or coating, as described herein. Mere reference to coating or filling in one embodiment does not preclude the possibility of filling or coating, respectively, the feature of said embodiment.

[00400] Further embodiments of the invention are set out in the following clauses in which there is provided:

1. A substrate for a two-terminal device, comprising: at least one series of grooves, each groove having a proximal end and a distal end across the transverse direction of the substrate, and at least one channel transecting a portion of the at least one series of grooves towards at least one of the distal end and the proximal end of each groove, and wherein the depth of each groove tends towards the depth of the channel in a transection region towards the respective transected distal end and/or proximal end of each groove.

2. A substrate according to clause 1 , comprising a first series of grooves and a second series of grooves, and a channel transecting a portion of the first series of grooves and a portion of the second series of grooves towards the proximal end of each groove.

3. A substrate according to clause 1 or clause 2, wherein the depth of each groove tends non-linearly towards the depth of the at least one channel.

4. A substrate according to clause 3, wherein the depth of each groove tends gradually towards the depth of the at least one channel.

5. A substrate according to clause 3 or clause 4, wherein the transection region is substantially arcuate.

6. A substrate according to clause 1 or clause 2, wherein each groove tends linearly towards the depth of the at least one channel.

7. A substrate according to clause 6, wherein the depth of each groove tends linearly towards the depth of the at least one channel at an angle of between 0° and 90°, excluding 0° and 90°, formed with respect to an axis extending along the elongate base of each groove.

8. A substrate according to any preceding clause, wherein the at least one channel is substantially Z-shaped having a predetermined angle.

9. A substrate according to any preceding clause, wherein each groove has an aspect ratio of at least 1:1, preferably at least 1:1.2, from the distal end to the proximal end, excluding the transection region.

10. A substrate according to any preceding clause, wherein the at least one channel has an aspect ratio of at least 1 :1.6.

11. A substrate according to any preceding clause, wherein the transection region has an aspect ratio that tends from at least 1 :1, preferably 1 : 1.2, to at least 1:1.6.

12. A substrate according to any preceding clause, comprising a plurality of channels. 13. A substrate according to clause 12, when dependent upon any one of clauses 2 to 11 , wherein each channel of the plurality of channels transects a portion of the first series of grooves and a portion of the second series of grooves towards the proximal end of each groove.

14. A substrate according to clause 12, when dependent upon any one of clauses 2 to 11 , wherein each channel of the plurality of channels transects each groove of the first series of grooves and each groove of the second series of grooves towards the proximal end of each groove.

15. A substrate according to any one of clauses 12 to 14, wherein each channel of the plurality of channels is substantially Z-shaped having a predetermined angle.

16. A substrate according to clause 12, when dependent upon any one of clauses 2 to 11, further comprising: a first transection channel transecting each channel of the plurality of channels at their distal ends, the first transection channel transecting the entirety the first series set of grooves towards the proximal end of each groove; and a second transection channel transecting each channel of the plurality of channels at their proximal ends, the second transection channel transecting the entirety of the second series of grooves towards the proximal end of each groove.

17. A substrate according to clause 16, wherein the first transection channel, the plurality of channels, and the second transection channel substantially form a Z-shape having a predetermined angle.

18. A substrate according to clause 8, clause 15 or clause 17, wherein the predetermined angle is between approximately 0 degrees and approximately 90 degrees, preferably between approximately 30 degrees and approximately 60 degrees.

19. A two-terminal device, for example an optoelectronic device, comprising the substrate of any preceding clause.

20. A method of forming a substrate for a two-terminal device, comprising: providing a web of flexible material; and forming at least one series of grooves within the web of flexible material; forming a channel within the web of flexible material, the channel transecting a portion of the at least one series of grooves towards at least one of a distal end and a proximal end of each groove, wherein the step of forming a channel includes forming a depth of each groove that tends towards the depth of the channel at the respective transected distal end and/or proximal end of each groove.

21. A method according to clause 20, wherein: the step of forming at least one series of grooves within the web of flexible material comprises: forming a first series of grooves within the web of flexible material, and forming a second series of grooves within the web of flexible material; the step of forming a channel within the web of flexible material comprises: forming a channel within the web of flexible material, the channel transecting a portion of the first and second series of grooves towards a proximal end of each groove; and the step of forming a channel includes forming a depth of each groove that tends towards the depth of the channel at the proximal end of each groove.

22. A method according to clause 21 , wherein at least one of the steps of forming a first series of grooves within the web of flexible material, forming a second series of grooves within the web of flexible material, and forming a channel within the web of flexible material, comprises embossing the web of flexible material to form at least one of the first series of grooves, the second series of grooves, and the channel.

23. A method according to clause 22, wherein the step of embossing comprises: providing one or more shims having at least one protrusion corresponding to at least one of the first series of grooves, the second series of grooves and the channel; coating a surface of the web of flexible material with a UV-curable coating; engaging the at least one protrusion of the or each shim with the coated web of flexible material; at least partially UV curing the UV-curable coating; and removing the at least one protrusion of the or each shim from the coated web of flexible material before the UV-curable coating has fully cured.

24. A method according to clause 23, wherein the shim is a master shim comprising at least one protrusion corresponding to the first series of grooves, at least one protrusion corresponding to the second series of grooves, and at least one protrusion corresponding to the channel.

25. A method of forming a two-terminal device, comprising: - forming a substrate according to a method of any one of clauses 21 to 24; coating a first face of first series of grooves, the second series of grooves and the channel with at least one first material; coating a second opposing face of the first series of grooves, the second series of grooves and the channel with at least one second material; and - at least partially filling the channel with a third material.

Claims

1. A substrate for a two terminal device, comprising: at least one series of grooves, provided on a first surface of said substrate, each groove comprising first and second opposing groove faces extending between a proximal end and a distal end across a transverse direction of said substrate, and comprising a groove base at a predetermined first depth from said first surface, and at least one channel, provided on said first surface of said substrate, comprising first and second opposing channel faces, spaced apart by a predetermined channel width at a predetermined second depth from said first surface, and a channel base at a third depth from said first surface, said at least one channel being configured to transect at least one of said at least one series of grooves at a distal end portion or a proximal end portion, wherein said third depth is greater than said predetermined first depth, and said third depth is determined by a predetermined coating angle relative to an axis normal to said groove base, and said predetermined channel width.

2. A substrate according to claim 1, wherein said third depth is determined by the equation: said predetermined channel width said third depth - - - - - - a Tangent function of said predetermined coating angle

3. A substrate according to claim 1 or claim 2, wherein in said transected distal end portion or said transected proximal end portion of said groove comprises a transection region in which said groove base tends towards said channel base forming a transection surface having a first transection depth at a groove end and a second transection depth at a channel end.

4. A substrate according to claim 3, wherein said transection surface has a non-linear surface profile between said groove end and said channel end.

5. A substrate according to claim 3 or claim 4, wherein said second transection depth is equal to said predetermined second depth.

6. A substrate according to any one of claims 3 to 5, wherein said transection surface in said transection region is substantially arcuate.

7. A substrate according to any one of claims 3, 5 or 6, wherein said groove end of said transection surface tends linearly towards said channel end.

8. A substrate according to claim 7, said groove end of said transection surface tends linearly towards said channel end at an angle that is greater than 0° and less than 90°relative to a longitudinal axis of said groove base.

9. A substrate according to any preceding claim, wherein said first and second opposing groove faces provide a groove width at said first surface of said substrate, and wherein said groove has an aspect ratio of at least 1 :1, preferably at least 1 :1.2.

10. A substrate according to any preceding claim, wherein said at least one channel has an aspect ratio of at least 1 :1.6.

11. A substrate according to any one of claims 3 to 10, wherein said transection region has an aspect ratio that tends from at least 1 :1, preferably 1 : 1.2, to at least 1 :1.6.

12. A substrate according to any preceding claim, wherein said at least one channel extends across said first surface in first direction to transect at least one of a first series of groove, and wherein said first direction is at an angle of greater than 0° and less than 90° relative to said transverse direction.

13. A substrate according to claim 12, wherein said first direction is at an angle relative to the transverse direction either within the range 5° to 85° or within the range -5° to -85°.

14. A substrate according to any preceding claim, wherein said at least one channel is substantially Z-shaped having a predetermined angle.

15. A substrate according to any preceding claim, comprising a first series of grooves and a second series of grooves, and a at least one channel transecting at least one of said first series of grooves and at least one of said second series of grooves at the respective distal end portions or the respective proximal end portions of each groove.

16. A substrate according to claim 15, wherein said at least one channel comprises a first channel portion arranged to transect each groove of said first series of grooves at a distal end portion, and a second channel portion arranged to transect each groove of said second series of grooves at a proximal end portion, wherein said first and second channel portions are spaced apart on said first surface by a third channel portion, and wherein said third channel portion comprises a plurality of parallelly spaced channel portions.

17. A substrate according to claim 16, wherein said first, second and third channel portions are substantially Z-shaped having a predetermined angle

18. A substrate according to any preceding claim, wherein said at least one channel comprises a plurality of channels.

19. A substrate according to claim 18, wherein each channel of said plurality of channels transects at least one of a first series of grooves and at least one a second series of grooves towards said proximal end of each groove.

20. A substrate according to claim 18, wherein each channel of said plurality of channels transects each groove of said first series of grooves and each groove of said second series of grooves towards said proximal end of each groove.

21. A substrate according to any one of claims 18 to 20, wherein each channel of the plurality of channels is substantially Z-shaped having a predetermined angle.

22. A substrate according to claim 14, claim 17 or claim 21 , wherein said predetermined angle is between approximately 0 degrees and approximately 90 degrees, preferably between approximately 30 degrees and approximately 60 degrees.

23. A two-terminal device, for example an optoelectronic device, comprising said substrate of any preceding claim.

24. A shim for embossing a surface of UV-curable coating provided on a flexible web to form a substrate for a two-terminal electronic device, comprising: at least one series of protrusions, provided on a first surface of said shim, each protrusion comprising first and second opposing protrusion surfaces extending between a proximal end and a distal end along a first direction of said surface, and comprising a protrusion apex at a predetermined first distance from said first surface, and at least one elongate projection provided on said first surface of said shim, said at least one elongate projection configured to transect at least one of said at least one series of protrusions at a distal end portion or a proximal end portion, wherein said elongate projection comprises first and second opposing projection surfaces spaced apart by a predetermined projection width at a predetermined second distance from said surface, and a ridge apex at a third distance from said first surface, wherein said third distance is greater than said first distance, and wherein said third distance is determined by a predetermined angle relative to a normal to said protrusion apex, and said predetermined ridge width.

25. A shim according to claim 24, wherein said third distance is determined by the equation: said predetermined channel width said third distance - - - - - - a Tangent function of said predetermined coating angle

26. A shim according to claim 24 or claim 25, wherein said second distance is a vertical distance from said first surface of said protrusion apex at said transected distal end portion or said transected proximal end portion.

27. A shim according to any one of claims 24 to 26, wherein said at least one elongate projection extends across said first surface of said shim in a second direction to transect at least one of a first series of protrusions, and wherein said second direction is at an angle of greater than 0° and less than 90°relative to said first direction.

28. A shim according to claim 27, wherein said second direction is at an angle relative to said first direction either within the range 5° to 85° or within the range 95° to 175°.

29. A method of forming a substrate for a two-terminal device, comprising: providing a flexible web, coating a first surface of said flexible web with a UV-curable coating, engaging a shim according to any one of claims 24 to 28 with said UV-curable coating so that said first surface of said shim embosses said UV-curable coating with said at least one series of protrusions and said at least one elongate protection, at least partially curing said UV-curable coating, and removing said at least one series of protrusions and said at least one elongate protection from said UV-curable coating before said UV-curable coating is fully cured.