GB2581859A

GB2581859A - Thermoelectric generator

Info

Publication number: GB2581859A
Application number: GB1909136.2A
Authority: GB
Inventors: Mark King Simon; Venugopalan Vijay
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2019-06-25
Filing date: 2019-06-25
Publication date: 2020-09-02
Also published as: GB201909136D0

Abstract

A thermoelectric generator comprising two substrates, each having an electrode, and an electrically insulating material between the substrates, the material including voids for the reduction of thermal conductivity and apertures containing a thermoelectric material. A low energy surface is formed on the apertures to prevent thermoelectric material from entering voids in the material or wicking away from the aperture. The generator provides an increased temperature differential across the device. The insulating material may be a cured thermosetting polymer, an epoxy, an aerogel, polymethyl methacrylate, SU-8, polyethylene naphthalate or a silicone rubber. The thermoelectric material may be organic. Methods for manufacturing the generator are also disclosed. The surface energy of the insulating material may be lowered by adding a layer of another material or by treatment with plasma, ion bombardment or electromagnetic radiation. The insulating material may be patterned by laser patterning, printing, photolithography or photo-patterning. The thermoelectric material may be deposited by solution deposition or printing.

Description

THERMOELECTRIC GENERATOR

BACKGRO UND

Embodiments of the present disclosure relate to a thermoelectric generator and a method for forming the same, and more specifically, but not by way of limitation, to a thermoelectric generator having improved efficiency.

A thermoelectric generator or, equivalently, a thermoelectric device can be used to generate electrical power or for heating or cooling. A thermoelectric generator includes at least one thermoelectric couple. A thermoelectric couple may include an n-type thermoelectric leg electrically coupled by a contact to a p-type thermoelectric leg. The thermoelectric generator may comprise a plurality of alternating n-type thermoelectric legs and p-type thermoelectric legs electrically connected across each leg in series.

The thermoelectric legs may be spaced along a first direction. In use, a temperature difference may be applied across the thermoelectric couple in a second direction that is different to, e.g. orthogonal to, the first direction. The temperature difference may be applied across a contact-thermoelectric couple boundary. In response to the temperature difference a voltage is generated by the thermoelectric elements. This voltage can be used to drive a current through the thermoelectric generator. Alternatively, a current may be driven through the thermoelectric couple to produce a temperature difference across the device, which can be used to heat or cool a thermal load.

Thermal and electrical resistance between the contacts and the thermoelectric couple affects the power efficiency of the thermoelectric couple. By improving the thermal performance of the thermoelectric legs, the thermal efficiency of the thermoelectric couple can be increased. This increase in the thermal efficiency results in a higher power output of the thermoelectric couple for a given temperature differential across the thermoelectric couple. It is desirable to maximise the temperature differential to increase the power output of the thermoelectric generator.

W02009/125317 describes a thermoelectric conversion device using an array of nanowires of conductor or semiconductor material disposed between a pair of electrodes. The space between the nanowires may be filled with a layer of a dielectric material of low thermal conductivity, such as an aerogel or rigid polymeric or foamed material.

US2001/0139207 describes a thermoelectric element for use in a thermoelectric device, the element comprising a porous substrate the pores of which are coated with a thermoelectric material.

US2018/0090659 describes filling air gaps between active material legs in a thermoelectric device with a support material.

US2011/0094556 describes thermal gaps between legs in a thermoelectric device to prevent lateral flow of heat between legs. Thermal gaps may be filled with low conductivity gases.

These references are hereby incorporated into the present disclosure in their respective entireties by reference for any purpose.

SUMMARY

A summary of aspects of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects and/or a combination of aspects that may not be set forth.

A thermoelectric device, when used to generate power, may be provided on apparatus having a surface that is heated when in use, such as electrical equipment, boilers, or hot water pipes in settings such as domestic, office, and industrial settings. The thermoelectric device may for example power a sensor, such as a temperature sensor, or charge a battery.

The present inventors, however, have recognised that, particularly when the thermoelectric device is passively cooled, for example by ambient air, or of thin or flexible construction, the power output may be limited due to a small temperature differential (dT) across the device.

Thermoelectric generators in which the thernmelectric material is deposited from solution generally require a layer of an electrically insulating material to contain the deposited solution until it is dried. This layer may be termed a "bank", and may also provide mechanical support and strength, for example during encapsulation of the device, or when the thermoelectric material is deposited by means other than printing. Bank materials generally have a thermal conductivity that is greater than air and may reduce dT.

Aerogel, foamed materials, or materials that aid in the formation of voids between the substrates may be used as an electrically insulating material to lower heat conductance through non-active regions of a thermoelectric device, thereby raising dT and power efficiency. The use of such porous materials, however, has been problematic in devices in which the thermoelectric material is deposited because of the requirement to contain and support the thermoelectric material until it is dried. Porous materials may wick the thermoelectric material away from its intended position before it is dried.

It was therefore not to be expected by a skilled artisan that such materials would be suitable for solution deposited thermoelectric materials. Although such materials have been used to fill the space between pre-formed legs of thermoelectric generators, they have not heretofore been known in solution deposited thermoelectric generators for the above-mentioned reasons.

The present inventors have surprisingly found that lowering the surface energy of the electrically insulating material where the electrically insulating material contacts a solution deposited thermoelectric material is effective to prevent wicking of the thermoelectric material even though the surface energy of the bulk of the electrically insulating material may remain unchanged.

This surprising finding enables solution deposition of thermoelectric material and preferred low thermal conductivity electrically insulating materials to be combined in thermoelectric devices for the first time. It further enables the production of thin and flexible thermoelectric devices where the difficulties of maintaining high dT are greater.

According to some embodiments of the present disclosure, there is provided a thermoelectric device (100) having first and a second substrates (102,106) having one or more electrodes (104,108). An electrically insulating material is disposed between the substrates. The electrically insulating material (110) includes at least one void (112), or one or both substrates and the electrically insulating material together form at least one void. The electrically insulating material also has at least one aperture (114) extending between the substrates, which is formed from a low energy surface (116) of the material. A thermoelectric material (118) is disposed in the aperture between the electrodes.

The use of voids in the present embodiments is further advantageous in reducing the amount of electrically insulating material that is required, reducing costs and any environmental concerns associated with the use of the electrically conductive material.

In some embodiments the electrically insulating material includes a cured thermosetting polymer, an epoxy, an aerogel, a polymethyl methacrylate, SU-8 (commercially available from Microchem. Corp.), a polyimide, a polyethylene naphthalate, or a silicon rubber.

In another embodiment the electrically insulating material includes an aerogel, which may be supported by a polymer backing.

In some embodiments the low energy surface includes a polytetrafluoroethylene, a silicon polymer, a UV/acid treated polymer. In other embodiments the low energy surface is formed by plasma treatment, ion bombardment, or electromagnetic radiation.

In some embodiments the thermoelectric material is a printable thermoelectric material.

In some embodiments the electrically insulating material is a layer of electrically insulating material having a thickness of less than about lmm. In further embodiments the layer has a thickness of less than about 200µm.

In yet other embodiments the thermoelectric device may have a plurality of thermoelectric couples. Each couple may have an n-type and a p-type thermoelectric leg located between the first electrode and second electrode. In further embodiments the first and second electrodes may be patterned electrodes, and the n-type and p-type thermoelectric legs may include an n-doped and a p-doped organic or composite semiconductor, respectively.

In certain embodiments there is provided a sensor system in which a thermoelectric device according to the present disclosure is coupled to a sensor that is powered by the thermoelectric 20 device.

The present inventors have found that embodiments of the thermoelectric device of the present disclosure can be made by an improved and simplified method that may include one or more lamination steps. In certain embodiments the method is advantageous because the cost and complexity of photopatterning of printed banks can be avoided. In other embodiments, the bank material can be prepared prior to lamination to a substrate by inexpensive processes, for example without requiring the use of a clean room for certain steps.

According to some embodiments, the method includes patterning a sheet of an electrically insulating material to include an aperture, and treating at least the surface of the aperture to lower its surface energy. The method also includes prior to, in-between, or after these processes, laminating the sheet to a first substrate. The method further includes depositing a thermoelectric material in the aperture, and laminating a second substrate on the thermoelectric material. Optionally, further thermoelectric material may be applied to the second substrate prior to lamination.

In further embodiments, the method includes forming a layer of an electrically insulating material on a first substrate, patterning the layer to form an aperture having a surface, treating at least the surface of the aperture to reduce the energy of the surface, depositing a thermoelectric material in the aperture, and laminating a second substrate on the thermoelectric material.

In other embodiments, the patterning may be a laser patterning.

In other embodiments, the thermoelectric material comprises a printable thermoelectric material.

In yet further embodiments, depositing of the thermoelectric material is by solution deposition.

DRAWINGS

The present disclosure is described in conjunction with the appended figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

In the appended figures, similar components and/or features may have the same reference label.

Further, various components of the same type may be distinguished by following the reference label by a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

Figure 1 is a schematic illustration of a thermoelectric apparatus according to an embodiment; Figure 2 is a schematic illustration of a thermoelectric apparatus according to a further embodiment; Figure 3 shows an arrangement of the electrically insulating layer of a thermoelectric apparatus embodiment comprising a plurality thermoelectric legs; Figure 4 show a sensor system according to an embodiment; Figure 5 is a flow diagram of an embodiment of a method of making a thermoelectric device; Figure 6 is a flow diagram of a further embodiment of a method of making a thermoelectric device; Figure 7 is a photomicrograph showing a solution of a thermoelectric active material applied to the surface (left panel) and aperture (right panel) of surface-treated aerogel; Figure 8 is a photomicrograph of a patterned polymer electrically insulating material of an embodiment; Figure 9 shows the thickness normalized thermal resistance of exemplary embodiments and comparative examples; Figurel0 shows thickness normalized dT of exemplary embodiments and comparative

examples;

Figure 11 shows thickness normalized thermal resistance of exemplary aerogel embodiments and comparative examples; Figure 12 shows device performance of an aerogel containing thermoelectric generator embodiment; and Figure 13 shows thickness normalized dT of an aerogel containing thermoelectric generator embodiment.

DESCRIPTION

The ensuing description above provides preferred exemplary embodiment(s) only, and is not intended to limit the scope, applicability or configuration of the invention. Rather, the ensuing description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements, including combinations of features from different embodiments, without departing from the scope of the invention.

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." As used herein, the terms "connected," "coupled," or any variant thereof means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, electromagnetic, or a combination thereof Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or," in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

The terms "thermoelectric generator" and "thermoelectric device" should not be construed as being limited to the production of electricity. All other applications of such structures, including without limitation temperature sensing and the generation of a temperature difference by application of an electrical current, are to be considered as being within the scope of these terms. Thus, the two terms should not be construed as having different scopes.

The term "void" herein represents a volume or space capable of containing a gas but not required to contain a gas.

The term "low energy surface" herein represents a surface formed by a treatment of a material that exhibits a lower surface energy than a surface of the same material in untreated form.

The present disclosure is directed to improved thermoelectric devices and to methods for making them. The inventors have found that surface treatment of certain porous or wicking materials, or other materials comprising voids, to reduce surface energy can surprisingly provide suitable banks for solution processed and otherwise formed thermoelectric devices, such that wicking of thermoelectric material, or other problem, is avoided even where only a thin surface is treated and the bulk material remains untreated.

This surprising finding enables the use of low thermal conductivity insulating materials and configurations previously considered incompatible with solution processed devices, and further provides improved methods for making such devices.

Figure 1, which is not drawn to scale, schematically illustrates a thermoelectric device according to an embodiment. As shown in Figure 1, a thermoelectric device (100) comprises a first substrate (102) comprising a first electrode (104), and a second substrate (106) comprising a second electrode (108). The substrates can be made, for example, of a polymer.

The substrates (102,106) may be arranged substantially parallel with the electrodes arranged on opposing surfaces of the respective substrates. Disposed between the substrates (102,106) is an electrically insulating material (110), for example an aerogel. Within the electrically insulating material is one or more voids (112), either disposed within the material as, for example, in aerogel, or formed by the material and one or both substrates, including the electrode portions thereof The void or voids lower the thermal conductivity of the material compared to such material without voids. The material further comprises one or more apertures (114) that are formed by a low energy surface (116) of the material (110). The low energy surface may be formed, for example, by treatment with a solution of PTFE in perfluorohexane. The aperture (114) extends between the first and second substrates. A thermoelectric material is disposed within the aperture and can be, for example, an n-type organic semiconductor (118a) or a p-type organic semiconductor (118b). In use, one substrate may be at a relatively higher temperature and the other substrate may be at a relatively lower temperature.

The thermoelectric device (100) comprises at least one thermoelectric couple, the or each thermoelectric couple comprising a p-type thermoelectric leg (118b) and a n-type thermoelectric leg (118a), the thermoelectric legs being electrically coupled by an electrode (108).

For simplicity, Fig. 1 illustrates a device having only one thermoelectric couple. It will, however, be appreciated that the thermoelectric device may comprise only one thermoelectric couple, or two or a larger number connected, for example, in an array. The thermoelectric couples may be connected to one another in series, parallel, or a combination thereof The substrate may comprise an electrically insulating polymer layer. The materials used for the first and second substrates (102,106) may be suitably selected by the skilled artisan from substrate materials known in the art. Examples thereof include, but are not limited to glass, ceramics and plastics (e.g. polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyimide (PI), polycarbonate (PC), polyethersulphone (PES), polymethyl methacrylate (PM MA), polydimethylsiloxane (PDMS), polyurethane (PU), acryl ate based polymers, and the like. The substrates may comprise a single layer or may comprise two or more layers of different materials. The substrate may be flexible or rigid. The thickness of the substrate is not particularly limited. Thinner substrates may be preferred in some embodiments to facilitate heat flow to and from the surroundings and the thermoelectric material, or for flexibility, and the substrates of some embodiments may have a thickness of less than about 20 um.

The first and second electrodes (104,108) may each form a pattern of a plurality of conducting pads connecting the legs of thermoelectric materials (118a,b). In some embodiments, the first and second electrodes are each in the form of a patterned layer defining a plurality of conductive pads. The electrodes may consist of a single conductive material or may comprise two or more materials, and may be deposited or laminated onto the substrate. In some embodiments, the conductive materials are preferably selected from metals and conductive metal compounds, for example conductive metal oxides, optionally including non-conductive materials, or a mixture thereof (e.g. Al/A1203). Exemplary metals are copper, aluminium and gold. In some embodiments, the first and second electrodes may optionally each independently have a thickness in the range of about 1-10 nm.

The substrates (102,106) comprising the electrode (104,108) may be arranged substantially parallel. Commercially available thermoelectric generators are usually found in one of two configurations, one being a vertical configuration which comprises a plurality of thermoelectric legs connected in series and sandwiched between a thermally conductive hot plate and a cold plate. Such thermoelectric legs comprise a p-type leg and an n-type leg connected in series, each of which may consist of a series configuration of multiple materials selected to maximise efficiency. A second type of thermoelectric generator is the lateral configuration, which follows the same principle as the vertical type, the main difference being that the heat source and sink are located to the sides of the generator. The substrates in both configurations are generally substantially parallel.

An electrically insulating material (110) is disposed between the substrates (102,106). The electrically insulating material advantageously provides a support for the thermoelectric materials on the first and/or second substrates, enables a more regular thermoelectric leg spacing for an enhanced contact area, and may enable an increased fill factor. the latter being defined as the ratio of the total cross-section area of thermoelectric material (of the thermoelectric legs) to the total surface area of the substrate. The electrically insulating materials are not particularly limited and may be selected by the skilled artisan from materials known in the art. Preferred electrically insulating materials also exhibit thermally insulating properties.

In some embodiments, the electrically insulating material (110) may be a polymer, such as thermosetting polymer and/or a photoresist, for example a negative or positive photoresist, and may be formed and patterned as described herein. The material may, in some embodiments, also be referred to as a bank material. The polymer may be an epoxy polymer. In some embodiments, the electrically insulating material may be a polymethyl methacrylate, SU-8, a polyimide, a polyethylene naphthal ate, or a silicon rubber.

In some embodiments, the electrically insulating material comprises an aerogel or other porous or microporous solid in which the dispersed phase may be a gas, for example a microporous silica, microporous glass, carbon-based aerogel, or metal oxide (e.g. alumina) or zeolite based aerogel, which may be prepared, for example, by supercritical drying of a gel. In certain embodiments, the electrically insulating material consists of an aerogel, while in other embodiments the aerogel may be backed by a polymer backing, for example a thin polyimide backing. Further details of aerogels, their properties and preparation may be found in Aerogels Handbook, Aegerter & Prassas (Eds.), Springer, 2011, the contents of which are incorporated herein by reference for all purposes.

Within the electrically insulating material is/are one or more voids (112). Voids in the electrically insulating material may advantageously lower the thermal conductivity of the thermoelectric device in regions of the device between the substrate not occupied by thermoelectric material. Voids (112) may be formed within the electrically insulating material, for example by the use of porous materials as in, for example, aerogels (Fig.1), or voids may be formed by cooperation of the electrically insulating material and one or both substrates. Fig. 2 shows an embodiment in which a void (112) is formed by cooperation of electrically insulating material (112) with a substrate (102) and/or an electrode (104). Preferably, voids may be positioned in any location between the substrates and may be selected as to size, position, and number so as to reduce the thermal conductivity in regions of the device between the substrate not occupied by thermoelectric material, while retaining one or more of the advantages of supporting the thermoelectric materials, enabling a more regular thermoelectric leg spacing, and increasing the fill factor. Voids may be formed within the electrically insulating material, for example, by supercritical drying of a gel, or by selective deposition, for example by vapour deposition or ink-jet printing, or by a patterning technique such as, for example, laser patterning or photolithography.

The electrically insulating material comprises a low energy surface that defines at least one aperture (114), the aperture extending between the first and second substrates. The means by which the low energy surface of the electrically insulating material is formed is not particularly limited, and may be selected for example from plasma treatment (e.g. SF6-), ion bombardment, UV-VIS treatment, X-ray treatment, acid etching, or a coating treatment such as coating with PTFE, Teflon, a silicone polymer, or the like. Without thereby being limited by theory, the low energy surface may provide a high contact angle with a liquid comprising a thermoelectric material deposited on the surface, whereby wicking away of the liquid is reduced and/or penetration of the liquid into pores in the material is inhibited. The low energy surface may therefore aid in confining a liquid comprising a thermoelectric material within the aperture.

Referring now to Figure 3, there is shown (300) an arrangement of the electrically insulating material in sheet form in an embodiment comprising multiple thermoelectric legs in an array. In this embodiment, the electrically insulating material is patterned to form an array of apertures (114), the regions adjacent each aperture being patterned to form (in cooperation with the substrates, not shown) voids (112a). To further reduce thermal conductivity in regions peripheral to the apertures, additional voids (112b) may be introduced.

The thermoelectric material (118) may be organic, inorganic, or a combination thereof. Exemplary thermoelectric materials are described in J. Mater. Chem. C., 2015, 3, 10362 and Chem. Soc. Rev., 2016, 45, 6147-6164, the contents of which are incorporated herein by reference for all purposes.

The material for the p-type legs used in this configuration is not particularly limited and may be selected from known organic and inorganic p-type semiconducting thermoelectric materials, including, but not limited to p-doped conductive polymers (e.g., polypyrroles, polyaniline (PANI), polythiophene and their derivatives (e.g., poly(3-hexylthiophene-2,5-diyl (P3HT) and poly(3,4-ethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS)), inorganic p-doped materials (e.g., mechanical alloyed metals including elemental bismuth, antimony, and tellurium, doped with tellurium, bismuth or selenium), and combinations thereof (e.g., carbon nanoparticles in polymeric matrices).

The material for the n-type legs is likewise not particularly limited and may be selected from known organic and inorganic n-type semiconducting thermoelectric materials, including, but not limited to, n-type organic small molecules (e. g. n-type dopants based on 4-(2,3-Dihydro1,3-dimethy1-1H-benzimidazol-2-y1)-N,N-dimethylbenzenamine (N-DMBI) precursor, such as 2-(2-NIethoxypheny1)-1,3-dimethy1-1H-benzoimidazol-3-ium iodide), n-doped fullerene and/or fullerene derivatives, perylenediimides, n-doped conductive polymers (e.g. naphthalenediimide-based polymers and derivatives thereof), organometallic coordination polymers, and n-doped inorganic materials.

Preferred materials for n-type legs include printable n-doped inorganic materials (e.g., alloys based on bismuth in combinations with antimony, tellurium or selenium, such as Bi2Te3; or alloys based on zinc and antimony) and n-doped fullerene and/or fullerene derivatives (such as a functionalized fullerene, and preferably a PCBM-type fullerene derivative). Such derivatives include [6,6]-phenyl-C61-butyric acid methyl ester (C6OPCBM), [6,6]-phenyl-C71-butyric acid methyl ester (C7OPCBM), [6,6]-phenyl-C85-butyric acid methyl ester (C84PCBM), and mixtures and adducts thereof, for example. Further preferably, the PCBM-type fullerene derivative is [6,6]-phenyl-C61-butyric acid methyl ester (C6OPCBM). Preferably, the n-type dopant is selected from the group of non-polymeric electron donors and/or reducing agents.

As preferred examples thereof in terms of stability under ambient conditions, imidazole derivatives and tetraalkylammonium salts (e.g. tetrabutylammonium fluoride) may be mentioned. N-type dopants based on imidazole derivative precursors are further preferred n-type dopants, and benzoimidazole derivatives are especially preferable in view of an excellent solution processability. Specific examples ofbenzoimidazole derivative precursors include, but are not limited to DMBI derivatives, such as e.g. (4-(1,3-dimethy1-2,3-dihydro-IH- benzoimidazole-2-y1)-pheny1)-dimethyl-amine (N-DMB I), 2-(2,4-dichloropheny1)-1,3- dimethy1-2,3-dihydro-1H-benzoimidazole 2-(1,3 -dimethy1-2,3-dihydro-1H-benzoimi dazol -2-y1)-phen ol (OH-DMBI), and 1,2,3-trim ethyl -2-phenyl -2,3 -di hydro-1 H -benzoimidazole (TMB1). In an especially preferred embodiment, the n-type dopant is based on the precursor N-DMBI.

It is understood that the n-and p-type semiconducting legs may comprise additional materials (including additional polymers, conductive particles, antioxidants, light or resistance enhancing agents, plasticizers etc.). The thermoelectric material is disposed in the aperture between the first and second electrodes.

Referring now to Fig. 4, an embodiment of a sensor system (400) is shown. The sensor system comprises a thermoelectric device (402) electrically connected to a sensor (404) whereby the sensor may be powered by the thermoelectric device. In this embodiment, the sensor may be, for example, an environmental sensor such as for example a temperature, humidity or gas sensor, or a biomedical sensor, such as for example a glucose, pH, pulse, blood pressure, blood analyte, or temperature sensor.

It will be readily understood that the sensor system (400) may further comprise communication elements such as RFID, wireless, 1R, or visible light means of communicating with and/or controlling the operation of the sensor.

Referring now to Fig. 5, there is shown flow diagram of an embodiment of a method (500) of making a thermoelectric device. The method comprises patterning (502) a sheet of an electrically insulating material comprising at least one void, including forming at least one aperture in the layer and treating (504) at least the surface defining the aperture to lower its surface energy. The method further comprises laminating (506) the sheet on a first substrate, the laminating occurring either before patterning, between patterning and treating, or after treating the sheet. The method further comprises depositing (508) a thermoelectric material in the aperture, and laminating (510) a second substrate on the thermoelectric material.

The method of patterning (502) the sheet is not particularly limited and may be suitably selected by the skilled artisan from patterning methods known in the art, including laser patterning using, for example, a CO2 laser, stamping, cutting or machining.

The method of depositing (508) the thermoelectric material is not particularly limited and may be suitably selected by the skilled artisan from deposition methods known in the art, including coating and printing methods, including without limitation, roll coating, spray coating, doctor blading, slit coating, ink jet printing, screen printing, dispense printing, gravure printing and flexographic printing. The thermoelectric material may be suspended or dissolved in a solvent.

The solvent or solvents may comprise or consist of, for example: one or more polar aprotic solvents such as N-methylpyrrolidone, dimethylformamide, propylene carbonate, and dimethylsulfoxide; one or more polar protic solvents such as water or Ci.6 alcohols; benzene substituted with one or more C hie alkyl or alkoxy groups, e.g. ani sole, and ketones, e.g. methyl isobutyl ketone. In some embodiments, ink formulations preferably further comprise a polymeric binder. Alternatively, deposition may be by extrusion of a paste, placement of solid material, or 3D printing. The deposited ink may be dried or cured prior to lamination.

Referring now to Fig. 6, there is shown a flow diagram of another embodiment of a method (600) of making a thermoelectric device. The method comprises forming (602) a layer of an electrically insulating material on a first substrate and patterning (604) the layer to form at least one aperture and at least one void. The method further comprises treating (606) the surface defining the aperture to lower its surface energy, depositing (608) a thermoelectric material in the aperture, and laminating (610) a second substrate on the thermoelectric material.

The method of forming (602) the layer is not particularly limited and may be suitably selected by the skilled artisan from methods known in the art, including solution deposition, photolithography, vapour deposition, and the like. The layer may be deposited in a patterned form, e.g. using a mask, or patterning may follow deposition, e.g. by laser patterning or etching.

Referring now to Fig.7, there is shown a photomicrograph illustrating the effect of surface treating an aerogel with PTFE/perfluorohexane. Left panel: printed thermoelectric material on a surface treated aerogel. Right panel: printed thermoelectric ink inside an approximately square aperture. On drying, the thermoelectric material filled the aperture completely and did not percolate into the aerogel from the side-walls of the aperture. The surface treatment therefore prevented entry of the thermoelectric material into the voids in the aerogel even though only the surface and not the interior of the aerogel was surface treated.

In use, the thermoelectric device of the present invention may be placed between a heat source and a heat sink and used to generate electricity with improved efficiency. For example, the device may be placed on a warm body such as pipe carrying a heated material, a heated building, an electrical apparatus, a warm part of a vehicle, or worn on the human body, and the second surface cooled by ambient air. Alternatively, the device may be used to produce a thermal gradient by the passage of current, whereby the device exhibits a warm side and a cool side. Alternatively, the device may be used to sense a temperature difference between its substrates from the current or voltage thereby produced. The thermoelectric device herein exhibits several advantages over prior devices including, independently and without limitation: enabling the use of porous electrically insulating materials of low thermal conductivity, reducing the amount of required electrically insulating material, and enhancement of the temperature differential (DT) achieved across the device, which is of particular benefit for passively cooled (e.g. ambient air-cooled) devices and for thin and flexible devices.

The method of making the device herein also exhibits advantages of prior methods of making including, independently and without limitation, a simplified method that may include one or more lamination steps. In certain embodiments the method is advantageous because the cost and complexity of photo-patterning of printed banks, or of the cost of stamps or dies, can be avoided. In other embodiments, the bank material can be prepared prior to lamination to a substrate by inexpensive processes, for example without requiring the use of a clean room.

The increased thermoelectric efficiency due to the enhanced temperature differential (DT) of the present devices helps to enable sensor systems according to the present disclosure, in which the sensor is powered by the thermoelectric device, thus enabling smaller, lighter and less expensive systems.

EXAMPLES 5 Example 1

A layer of electrically insulating material in the form of a polyimide sheet was patterned using a 30W CO2 laser to form the pattern shown in Fig.3 including the voids and apertures as illustrated in Fig. 8C and Fig.8D. The apertures formed in the sheet had an approximately square cross-section of dimensions 1.5mm x 1.5mm. The patterned layer was then laminated to a polymer substrate comprising pre-positioned metal film electrodes. The surface of the patterned layer was then treated to reduce its surface energy by spin coating with a solution of 1% by weight PTFE in perfluorohexane to form a uniform coating on the surface. Solutions of thermoelectric n-type and p-type organic semiconductor material were then solution deposited by dispense printing into the apertures (Fig.8E) of some of the patterned layers and dried, while in other identically patterned layers no thermoelectric material was deposited in order to facilitate comparison of the thermal resistance of the device attributable to the layer of electrically insulating material in the presence and absence of thermoelectric material. A second polymer substrate comprising pre-positioned metal film electrodes was then laminated onto the thermoelectric material.

Example 2

Thermoelectric devices otherwise identical to those of Example 1 were prepared in which the apertures formed in the sheet had an approximately square cross-section of dimensions 2.0mm x 2.0mm, the voids about the periphery of the active area as shown in Fig.8D were not formed, but the voids between the apertures (Fig.8C) were formed. The number of apertures in the device of Example 2 was the same as the number in Example 1, whereby the area of thermoelectric material in Example 2 was increased relative to Example 1.

Comparative Example 1 A device otherwise identical to the device of Example 1 was prepared in which the voids as shown in Figs.8C and 8D were not formed. The patterning of the apertures was as shown in 30 Fig.8B.

Comparative Example 2 A device otherwise identical to the device of Example 2 was prepared in which the voids as shown in Fig.8C were not formed. The patterning of the apertures was as shown in Fig.8A.

Fig.9 compares the thickness normalised thermal resistance of the banks of Examples 1 and 2, and Comparative Examples 1 and 2, in the absence of thermoelectric material. The presence of air gaps significantly increased the thermal resistance of the Example devices compared the otherwise equivalent Comparative devices.

Fig.] 0 illustrates the improvement in the thickness normalised dT of Example 1 compared to Comparative Examples 1 and 2. Decreasing the active area (2mm squares to 1.5mm squares) decreased the active area from 23% to 13% and increased the bank area from 72% to 82%. However, the dT was improved. Reducing the active area and introducing air gaps provided a significant increase in DT.

Example 3

An aerogel sheet (125pm thick) comprising a 25p.m thick polyimide backing sheet was patterned using a 30W CO2 laser to form the pattern of apertures shown in Fig.3 without added voids. Devices were then prepared as in Example 1.

Example 4

Devices were prepared as in Example 3, except that the backing sheet was polyethylene naphthalate.

Comparative Example 3 Devices were prepared as in Example 3, except that the bank material was polyimide sheet of thickness 150pm patterned to comprise apertures but not voids.

Comparative Example 4 Devices were prepared as in Example 3, except that the bank material was SU-8 of thickness 125pm patterned to comprise apertures but not voids.

Fig.11 compares the thickness normalised thermal resistance of the banks of Examples 3 and 4, and Comparative Examples 3 and 4, in the absence of thermoelectric material. The use of aerogel significantly increased the thermal resistance of the Example devices compared the otherwise equivalent Comparative devices using a polymer.

F g.12 illustrates the voltage, current and power output of the device of Example 3.

Fig. 13 compares the thickness normalised dT of Example 3 and Comparative Example 3. The use of aerogel significantly enhances DT.

The teachings of the technology provided herein can be applied to other systems, not necessarily the system described below. The elements and acts of the various examples described below can be combined to provide further implementations of the technology. Some alternative implementations of the technology may include not only additional elements to those implementations noted below, but also may include fewer elements.

These and other changes can be made to the technology in light of the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. Details of the system may vary considerably in its specific implementation, while still being encompassed by the technology disclosed herein. As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed in the specification, unless the Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims.

To reduce the number of claims, certain aspects of the technology are presented below in certain claim forms, but the applicant contemplates the various aspects of the technology in any number of claim forms. For example, while some aspect of the technology may be recited as a computer-readable medium claim, other aspects may likewise be embodied as a computer-readable medium claim, or in other forms, such as being embodied in a means-plus-function claim.

In the description above, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of implementations of the disclosed technology.

It will be apparent, however, to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details.

The techniques introduced herein can be embodied as special-purpose hardware (e.g., circuitry), as programmable circuitry appropriately programmed with software and/or firmware, or as a combination of special-purpose and programmable circuitry. Hence, embodiments may include a machine-readable medium having stored thereon instructions which may be used to program a computer (or other electronic devices) to perform a process.

The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, compact disc read-only memories (CD-ROMs), magneto-optical disks, ROMs, random access memories (RAMs), erasable programmable read-only memories (EPROMs), electrically erasable programmable read-only memories (EEPROMs), magnetic or optical cards, flash memory, or other type of media / machine-readable medium suitable for storing electronic instructions. The machine-readable medium includes non-transitory medium, where non-transitory excludes propagation signals. For example, a processor can be connected to a non-transitory computer-readable medium that stores instructions for executing instructions by the processor.

REFERENCE NUMERALS

100, 200 thermoelectric device 102 first substrate 104 first electrode 106 second substrate 108 second electrode electrically insulating material 112, 112a, 1126 void 114 aperture 116 low energy surface 118a n-type thermoelectric material 118b p-type thermoelectric material 400 sensor system 402 thermoelectric device 404 sensor 500 method of making a thermoelectric device 502 patterning sheet of electrically insulating material 504 treating surface 506 laminating sheet 508 depositing thermoelectric material 510 laminating second substrate 600 another method of making a thermoelectric device 602 forming layer of an electrically insulating material 604 patterning layer 606 treating surface 608 depositing thermoelectric material 610 laminating second substrate

Claims

What is claimed is: 1. A thermoelectric device comprising: a first substrate comprising a first electrode and a second substrate comprising a second electrode; an electrically insulating material disposed between the substrates, the material comprising at least one void or the material together with one or both substrates forming at least one void, the material further comprising a low energy surface forming at least one aperture between the first and second substrates; and a thermoelectric material disposed in the aperture between the first and second electrodes.
2. The thermoelectric device according to claim 1 in which the electrically insulating material comprises a cured thermosetting polymer, an epoxy, an aerogel, a polymethyl methacryl ate, SU-8, a polyimi de, a polyethylene naphthalate, or a silicon rubber.
3. The thermoelectric device according to claim 2 in which the electrically insulating material comprises an aerogel and a polymer backing.
4. The thermoelectric device according to claim 1 in which the low energy surface comprises a polytetrafluoroethylene, a silicon polymer, a UV/acid treated polymer, or is formed by plasma treatment, ion bombardment, or electromagnetic radiation.
5. The thermoelectric device according to any preceding claim in which the thermoelectric material is a printable thermoelectric material.
6. The thermoelectric device according to any preceding claim in which the electrically insulating material is a layer having a thickness of less than about lmm.
7. The thermoelectric device according to claim 6 in which the layer has a thickness of less than about 200pm
8. The thermoelectric device according to any preceding claim in which the thermoelectric device comprises a plurality of thermoelectric couples comprising n-type and p-type thermoelectric legs between the first electrode and second electrode and in which the first and second electrode are patterned electrodes.
9. The thermoelectric device according to claim 8 in which the n-type and p-type thermoelectric legs comprise an n-doped and a p-doped organic semiconductor, respectively.
10. A sensor system comprising the thermoelectric device according to any one of the preceding claims and a sensor electrically connected to the thermoelectric device.
11. A method of making a thermoelectric device, the method comprising: a. patterning a sheet of an electrically insulating material comprising at least one void, including forming at least one aperture in the layer, the aperture defined by a surface of the sheet; b. treating the surface to lower its surface energy; c. before (a), between (a) and (b), or after (b), laminating the sheet on a first substrate; d. depositing a thermoelectric material in the aperture; and e. laminating a second substrate on the thermoelectric material.
12. A method of making a thermoelectric device, the method comprising the steps of: a. forming a layer of an electrically insulating material on a first substrate; b. patterning the layer, including forming at least one aperture and at least one void in the layer, the aperture defined by a surface of the sheet; c. treating the surface to lower its surface energy; d. depositing a thermoelectric material in the at least one aperture; and e. laminating a second substrate on the thermoelectric material.
13 The method according to one of claims 11 or 12, in which the electrically insulating material comprises a cured thermosetting polymer, an epoxy, an aerogel, a polymethyl methacrylate, SU-8, a polyimide, a polyethylene naphthalate, or a silicon rubber.
14 The method according to claim 13 in which the electrically insulating material comprises an aerogel and a polymer backing.
The method according to one of claims 11 or 12 in which treating the surface to lower its surface energy comprises depositing a polytetrafluoroethylene, a silicon polymer, a UV/acid treated polymer, or is by plasma treatment, ion bombardment, or electromagnetic radiation.
16. The method according to one of claims 11 to 15 in which the thermoelectric material is an organic semiconductor.
17 The method according to claim 11 in which the patterning is by laser patterning.
18. The method according to claim 12 in which the forming a layer of the electrically insulating material is by printing.
19 The method according to one of claim 18 in which the patterning of the layer is by photolithography.
20. The method according to claim 12 in which the patterning a layer of the electrically insulating material is by photo-patterning.
21 The method according to one of claims 11 or 12 in which the depositing of the thermoelectric material is by solution deposition.