EP3371838A1

EP3371838A1 - Substrate for conductive ink

Info

Publication number: EP3371838A1
Application number: EP16798100.0A
Authority: EP
Inventors: Matthieu Manceau; Anthony BARBOT
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2015-11-05
Filing date: 2016-11-03
Publication date: 2018-09-12
Also published as: FR3043359A1; WO2017076996A1; FR3043359B1

Abstract

The present invention relates to a multilayer structure (5) comprising an electrically insulating substrate (15) and at least one layer of transparent conductive oxide (20) which is in contact with the substrate and a metal layer (25) and which is partially inserted between the substrate and the metal layer, the metal layer comprising raised fastening elements (55) that are received in corresponding cavities (45) in the layer of transparent conductive oxide.

Description

SUBSTRATE FOR CONDUCTIVE INK

The present invention relates to a multilayer structure, useful in particular for connecting two photovoltaic cells arranged in series. It also relates to a method of manufacturing such a multilayer structure.

The formation of a continuous deposit of a conductive material, in particular a silver layer, on a transparent conductive oxide (TCO) layer is particularly useful for producing electrical contacts within organic electronic devices, for example organic photovoltaic devices (OPV). For example, it intervenes to form the so-called "contact recovery" zone in which the electrical connection between two adjacent cells takes place in an organic photovoltaic module.

In the particular case of an OPV module in so-called "inverse" structure, also called "PIN" structure, where cells are arranged in series as shown diagrammatically in FIG. 1, the contact recovery zone is defined by the superimposition of FIG. upper electrode, typically silver, of the cell (n + 1) of the module with the lower TCO electrode of the cell (n).

The production of a silver layer by printing and drying a silver ink has the advantage of being able to be implemented under easily accessible pressure and temperature conditions.

Unfortunately, it is difficult, because of the respective properties of the majority of the known silver inks and the TCO layer, to form by printing a layer of conductive material on the TCO of sufficient quality.

To overcome this defect, different techniques have already been proposed. A first technique consists in forming a layer, intermediate between the TCO and the silver layer, based on chromium and gold (Perrier et al., Solar Energy Materials and Solar Cells 2012, Volume 101, pages 210 -216). More specifically, a first thin layer of chromium and a second layer of gold, with respective thicknesses of 10 and 40 nm, are formed successively by evaporation in vacuo, defining a transition zone. The deposition of these intermediate layers by evaporation advantageously makes it possible to increase the mobility of the charges in the transition zone (gain electric) and promotes the obtaining of a homogeneous deposit of silver, in particular because of the very low roughness of the gold layer formed by evaporation.

However, this technique has a major disadvantage due to the realization of intermediate layers of chromium and gold under secondary vacuum, which makes it difficult to exploit on an industrial scale.

The second technique consists of a surface treatment of the TCO, for example of the UV-ozone, "Corona" or plasma type (Perrier et al., Solar Energy Materials and Solar Cells 2012, Volume 101, pages 210-216). Such a surface treatment makes it possible to homogenize the surface of the TCO and to make it more hydrophilic, thus promoting a better wettability of the silver.

Unfortunately, these treatments have a tendency, for example in the context of making contact resets in an OPV module, to damage certain layers of the photovoltaic device, in particular the active layer and the semiconductor layer P. Any surface treatment of this type is therefore impossible after deposition of these layers, and must therefore take place at the beginning of the process. However, as the effects of these surface treatments are not permanent, the printing of the re-contacts must take place immediately after their application. Therefore, two printing steps of the upper silver electrode are required: a first print at the beginning of the process after the surface treatment to make the resumption of contact, and a second print at the end of the process to form the electrode higher.

Accordingly, there is a need for a reliable multilayer structure, having electrical properties at least similar to those of the prior art, and can in particular be obtained with a method not having the disadvantages mentioned above.

The present invention seeks to meet this need, and it achieves this through a multilayer structure comprising an electrically insulating substrate, at least one conductive transparent oxide layer in contact with the substrate and with a metal layer and partly interposed between the substrate and the metal layer, the metal layer having attachment reliefs housed in corresponding cavities formed in the transparent conductive oxide layer.

Advantageously, the cavities and the hooking reliefs of the multilayer structure according to the invention improve the adhesion of the metal layer to the layer of transparent conductive oxide. The mechanical and electrical reliability of a device comprising such a multilayer structure is improved. More particularly, the multilayer structure according to the invention is useful for connecting two photovoltaic cells arranged in series, in particular organic photovoltaic cells or perovskites.

In addition, the invention ensures a physical contact between the transparent conductive oxide layer and the metal layer, which makes it possible to ensure electrical contact therebetween and electrical performance adapted to the resumption of contact in many applications, in particular within an organic photovoltaic module in NIP structure.

The invention also relates to a method of manufacturing a multilayer structure comprising the following successive steps consisting of:

a) having an electrically insulating substrate covered with at least one transparent conductive oxide layer,

b) forming cavities on the surface of the conductive transparent oxide layer, c) forming a partially superposed metal layer and in contact with the transparent conductive oxide layer, under conditions such that the material constituting the metal layer fills less partially, preferably completely, the cavities of the transparent conductive oxide layer, so as to define attachment reliefs.

As will become more apparent later, the process according to the invention is particularly versatile. In particular, it authorizes the deposition of a wider range of precursors of the metal layer compared to the methods of the prior art, in particular in the case of deposition of the metal layer by silver ink printing.

In a particularly preferred manner, the process according to the invention is suitable for the manufacture of a multilayer structure according to the invention. In particular, it will be clear to those skilled in the art how to adapt the parameters of the method according to the invention to obtain a multilayer structure according to the invention, from the detailed description of the invention which follows.

Furthermore, the invention also relates to a device chosen from a photo-organic diode, an organic photovoltaic module or perovskite, an organic light-emitting diode, an electrical circuit, the device comprising a structure multilayer according to the invention or obtained from a process according to the invention. More particularly, it relates to an organic photovoltaic module or perovskite, comprising a substrate, first and second organic photovoltaic cells or perovskites which respectively comprise at least one transparent conductive oxide layer and a metal layer arranged to form with the substrate a multilayer structure according to the invention.

Other characteristics, variants and advantages of the invention will emerge more clearly on reading the detailed description and the examples which follow, given by way of illustration and not limitation, and on examining the appended drawing, in which:

FIG. 1 is a side view of a photovoltaic module in reverse structure,

FIGS. 2a and 2b illustrate in cross section and in enlargement multilayer structures according to the invention,

FIG. 3 represents the cavities in normal view on the upper face of the transparent conductive oxide layer, according to plane (I)

FIG. 4 illustrates the electrical properties of the conductive transparent oxide layer,

FIGS. 5a to 5c and 6a to 6e show photographs of silver layers for different cavity surface densities and obtained from different silver inks,

FIG. 7 is a graph illustrating the electrical properties of the multilayer structure according to the invention, and

FIG. 8 is a three-dimensional perspective representation of a particular mode of implementation of the method according to the invention.

It should be noted that for the sake of clarity, the various elements of Figures 1 to 3 are represented in free scale, their actual dimensions and real proportions not being respected.

In the remainder of the text, the expressions "between ... and ...", "ranging from ... to ..." and "varying from ... to ..." are equivalent and mean to mean that terminals are included unless otherwise stated. Unless otherwise indicated, the expression "comprising / including / including a" shall be understood as "comprising / including / including at least one" respectively. MULTILAYER STRUCTURE

FIG. 1 represents a multilayer structure 5 disposed within a photovoltaic module 10.

The multilayer structure comprises a substrate 15, a conductive transparent oxide layer 20 and a metal layer 25.

The substrate is in the form of a film, this form being however not restrictive. It can also be in the form of a plate. It consists of an electrically insulating material. It is preferably selected from glass, polyethylene terephthalate PET, polyethylene naphthalate PEN, polycarbonate PC and mixtures thereof. Preferably, it is poly (ethylene terephthalate) PET. As will be detailed later, in the case where the metal layer is deposited by printing and drying an ink, these preferred constituent materials of the substrate exhibit good wettability with the ink. Thus, the metal layer, where it is in contact with the substrate, adheres surely and is distributed homogeneously. Furthermore, these preferred substrate materials are suitable for depositing a transparent conductive oxide layer.

The constituent material of the substrate may be adapted as a function of the electronic device, for example a light-emitting diode, in which the multilayer structure according to the invention is integrated and / or of the materials constituting the transparent conductive oxide layer and / or the metallic layer. .

The conductive transparent oxide layer is carried by the substrate. It has a lower face 30 in contact with the substrate, and an upper face 35, in particular in contact with the metal layer.

As illustrated in FIG. 1, the contact with the substrate takes place on the whole of the lower face. The contact with the metal layer takes place on only a part of the upper face of the transparent conductive oxide layer, thus defining a contact surface 40. Preferably the area of the contact surface represents less than 10% of the area of the upper surface of the transparent conductive oxide layer.

The transparent conductive oxide layer may have a thickness of between 50 nm and 1000 nm, in particular between 100 and 500 nm.

Preferably, the conductive transparent oxide layer is made of a material chosen from tin-doped indium oxide (commonly known as ITO for the English name "Indium Tin Oxide"), doped indium oxide. zinc (commonly known as IZO for the English name "Indium Zinc Oxide"), zinc oxide, preferably doped, and mixtures thereof. Preferably, the doped zinc oxide is doped with a dopant selected from tin, aluminum, gallium and mixtures thereof. Zinc oxide doped with tin, aluminum, gallium is respectively commonly known as ZTO (for the English name "Zinc Tin Oxide"), AZO (for the English name "Aluminum doped Zinc Oxide") , GZO (for the English name "Gallium doped Zinc Oxide").

The conductive transparent oxide layer may consist of a stack of underlays. Each sub-layer of the stack may in particular be one of the constituent materials as described in the previous paragraph, different from the constituent materials of the other sub-layers which constitute the transparent conductive oxide layer.

Alternatively, the conductive transparent oxide layer may be constituted by a single underlayer, in particular consisting of a mixture of constituent materials as described above.

The transparent conductive oxide layer comprises cavities 45. By "cavity" is meant a hole having at least one opening 46 and at least one lateral face 47. Such a hole may be blind or through.

As illustrated in Figures 2a and 2b, the cavities have an opening 50 opening on the upper surface of the transparent conductive oxide layer.

The openings of the cavities may have contours 50 of polygonal shape, for example rectangular or square, or of ellipsoidal shape, or preferably of circular shape, as illustrated in FIG. The cavities may have a frustoconical or prismatic shape, or preferably a cylindrical shape, preferably of revolution.

In particular, the diameter Φ of a cavity may be between 5 μιη and 30 μιη, preferably between 15 μιη and 25 μιη. The "diameter" of a cavity is defined as the diameter of the circle circumscribing the contour of the opening of the cavity.

As will be detailed later, the cavities may in particular be obtained by laser ablation. They then have a cylinder shape of revolution whose axis preferably extends according to the thickness of the transparent conductive oxide layer, with a circular opening.

Alternatively they can be obtained by etching.

In an alternative embodiment of the invention illustrated in Figure 2a, the cavities are blind holes that do not open on the underside of the transparent conductive oxide layer. Preferably, however, more than 80%, preferably more than 90%, or even more than 99% by number, or all the blind cavities have a ratio of the depth P, measured between the opening and the bottom of the cavity according to the thickness e of the conductive transparent oxide layer on said thickness, greater than 0.3, preferably greater than 0.5, or even greater than 0.7. Thus, the attachment of the metal layer on the transparent conductive oxide layer is improved.

In another particularly preferred variant and illustrated in FIG. 2b, at least 80%, preferably 90%, more preferably 99% by number, or all the cavities pass through the transparent conductive oxide layer from one side to the other thickness of the conductive transparent oxide layer and the corresponding hooking reliefs 55 are in contact with the substrate. Thus, a particularly reliable bonding of the metal layer on the conductive transparent oxide layer and on the substrate by means of the attachment reliefs is obtained, as well as a particularly homogeneous distribution of the metal layer on the transparent oxide layer. conductor during the manufacture of the multilayer structure. This embodiment is particularly preferred in the case where the metal layer consists of a material deposited in solution in a solvent, said solution having wettability properties of the transparent conductive oxide layer such as a metal layer would be distributed from heterogeneously at the outer surface of the transparent conductive oxide layer if the cavities do not open onto the substrate. Preferably, the apertures of at least 90% by number, preferably at least 99% by number, or even all the cavities opening onto the outer surface of the conductive transparent oxide layer are covered by the metal layer.

On the other hand, the density in number of cavities may be greater than 450 mm.sup.- ² It is defined as the number of cavities occupying the contact surface between the transparent conductive oxide layer and the metal layer, divided by the area of the contact surface. preferably, it is greater than 900 mm ^"2, or even greater than 1000 ^{mm" 2,} or even greater than 1200 mm ^".

The number density of the cavities can be calculated according to one of the two following techniques. According to a first technique, on a part, for example on an area of 1 mm ² , or even on the entire contact surface, the number of cavities is counted manually or using a suitable computer tool. According to a second technique, in the case where the cavities form a periodic lattice in two directions of space, an elementary mesh of the periodic lattice, as well as the number of cavities present on the elementary mesh are determined. For example, a square elementary mesh contains a single cavity, while a hexagonal mesh contains two. By dividing the number of cavities of the elementary cell by the area of the unit cell, for example measured from a photograph obtained by optical or electronic microscopy, the density in number of cavities is thus obtained.

The surface density of cavities may be greater than 0.1. It is defined as the area occupied by the openings of the cavities on the contact surface between the conductive transparent oxide layer and the metal layer, divided by the area of the contact surface. Preferably it is greater than or equal to 0.2, preferably greater than 0.25. The surface density of cavities, expressed in percent is also called structuration rate. The surface density of the cavities is obtained by multiplying the number density of the cavities by the area of a cavity. The area of a cavity is for example measured from a photograph obtained by optical or electronic microscopy.

Preferably, the surface density of cavities is less than 0.35, preferably less than 0.3. Beyond a surface density of cavities of 0.35, the electrical properties of the multilayer structure are degraded and are unsuitable for application in an organic photovoltaic module in reverse structure. A conductive transparent oxide layer having a cavity number density and / or a cavity density thus preferred during the manufacture of the multilayer structure significantly improves the homogeneity of the metal layer, especially when the metal layer is obtained by printing and drying an ink in a single pass.

The cavities are spaced apart from each other. Preferably, the distance Δ between two adjacent closer cavities is greater than 20 μιη and less than 50 μιη. The distance is measured between the centers 60 ₁ , 60 ₂ of the cavity openings on the contact surface 40 between the conductive transparent oxide layer and the metal layer. By center of a cavity is meant the center of the circle circumscribing the contour of the opening of a cavity. First and second cavities are closer together, since among all the cavities with the exception of the first cavity, the distance separating the second cavity from the first cavity is the shortest. Such a distance between adjacent closer cavities promotes a hooking of the metal layer while maintaining good electrical properties of the multilayer structure.

With regard to the distribution of the cavities on the contact area between the conductive transparent oxide layer and the metal layer, it may be random, or preferably ordered.

In particular, the cavities may be arranged periodically with a period of between 20 μιη and 50 μιη along at least one guideline d _r . More particularly, the cavities may form a two-dimensional network, in particular of diamond mesh, preferably of square mesh. Such an arrangement of the cavities within the conductive transparent oxide layer is particularly simple to manufacture.

In particular, as is observed in FIG. 3 according to a view normal to the upper face of the transparent conductive oxide layer, the cavities are arranged in a square mesh, the center-to-center distance of the cavities being between 20 μιη and 50 μιη.

Furthermore, the conductive transparent oxide layer may have a surface resistance, measured from the four-point resistivity measurement technique on the contact surface, of between 5 Ω / sq and 100 Ω / sq, preferably less than 20 Ω / sq. Thus, the transparent conductive oxide layer is adapted so that the transfer of electrical charges within the multilayer structure can be carried out optimally.

The metal layer partially overlies the conductive transparent oxide layer. Moreover, as illustrated in Figure 1, it may be in contact with the substrate, the contact being established by the lower surface 65 of the metal layer. Preferably the area of the contact surface is less than 10% of the area of the lower surface of the metal layer.

The metal layer is of a material chosen for example from silver, gold, copper, aluminum and their mixtures. According to a preferred embodiment, it is made of silver and can in particular be deposited, as will be described later, by inkjet printing. A poly (ethylene terephthalate) substrate is then preferred, the silver ink and polyethylene terephthalate having good adhesion properties therebetween.

The metal layer, in particular when it is silver, has a thickness of between 100 nm and 2000 nm, preferably between 200 nm and 1000 nm.

Preferably, it has a uniform thickness. By thickness of the metal layer, the distance is considered in a direction normal to the lower and upper faces of the metal layer, connecting said faces, in the parts of said layer which are free of attachment reliefs.

By homogeneous thickness of a layer, it is understood that the thickness variation over the entire layer is less than 20%, preferably 10%.

Preferably, the metal layer covers more than 70%, preferably more than 80%, preferably more than 90%, or even more than 99%, indeed the totality of the area of the surface defined by the enveloping envelope 70 enveloping all the cavities on the upper surface of the transparent conductive oxide layer. Optimal contact is thus ensured between the conductive transparent oxide layer and the metal layer favoring the electrical properties to make contact recovery.

DEVICE

The invention relates to a device chosen from a photo-organic diode, an organic photovoltaic module or perovskite, an organic light-emitting diode, an electrical circuit, the device comprising a multilayer structure according to the invention. or obtained from a process according to the invention. In particular, the device can be an organic photovoltaic module or perovskite.

As illustrated in Figure 1, the organic photovoltaic module or perovskite comprises first 75 and second 80 photovoltaic cells electrically connected in series and carried by the substrate. The succession of layers constituting each of the first and second cells is identical.

A photovoltaic cell illustrated in FIG. 1 comprises:

a lower electrode layer 851, 85 ₂ , on which are stacked successively,

an electron-conducting semiconductor layer 90i, 90 ₂ , also called "ETL" layer (or for the acronym "Electron Transport Layer") or N-layer,

an active layer made of organic material or perovskite 951, 95 ₂ ,

a semiconducting layer carrying holes 100i, 100 ₂ , also called "HTL" layer (for the acronym "Hole Transport Layer") or layer P,

and an upper electrode layer 105i, 105 ₂ .

The lower electrode layer 851 of the first photovoltaic cell 75 is a transparent conductive oxide layer and the upper electrode layer 105 ₂ of the second photovoltaic cell 80 is a metal layer.

In other words, the lower electrode layer 851 of the first photovoltaic cell 75, the upper electrode layer 105 ₂ of the second photovoltaic cell 80 form a multilayer structure according to the invention.

The contact recovery zone 5 is the electrical connection zone between the first 75 and second 80 adjacent photovoltaic cells.

Of course, the invention is not limited to the reverse structure photovoltaic module described above, and other applications of the multilayer structure according to the invention can be envisaged.

MANUFACTURING PROCESS

The invention relates to a method of manufacturing a multilayer structure comprising the following successive steps consisting of: a) having an electrically insulating substrate covered with at least one transparent conductive oxide layer,

b) forming cavities on the surface of the conductive transparent oxide layer, c) forming a partially superposed metal layer and in contact with the transparent conductive oxide layer, under conditions such that the material constituting the metal layer fills less partially, preferably completely, the cavities of the transparent conductive oxide layer, so as to define attachment reliefs. In a particularly preferred manner, the process according to the invention is suitable for manufacturing a multilayer structure according to the invention.

In step a), the conductive transparent oxide layer may be formed by physical vapor deposition (PVD) or by chemical vapor deposition (CVD).

These techniques are well known to the skilled person, who knows how to choose a suitable substrate, for example as described above, to achieve such a deposit.

The formation of cavities in the transparent conductive oxide layer made in step b) is also referred to as "structuring" and the conductive transparent oxide layer having cavities is also referred to as the "structured" conductive transparent oxide layer.

Any technique for selectively eroding the constituent material of the transparent conductive oxide layer can be implemented.

In particular, according to a first variant, the formation of the cavities in step b) can be performed by laser ablation.

Laser ablation of a layer is a technique well known to those skilled in the art which consists in selectively irradiating the layer, that is to say on a defined surface, for a period of time adapted so as to erode the constituent material of the layer. Once the irradiation is complete, a cavity remains in place of the area below the irradiated surface.

Preferably, the laser source is a picosecond or femtosecond laser source.

The parameters of the laser source depend in particular on the thickness and the constituent material of the conductive transparent oxide layer to be eroded. The wavelength of the laser source may be 355 nm, or may be 532 nm, or may be 1064 nm. Preferably, it is equal to 532 nm or equal to 1064 nm.

The ablation power of the laser source is preferably between 0.4 W and 2 W.

Furthermore, the laser beam may be movable relative to the transparent conductive oxide layer. The laser beam can in particular move along a rectilinear direction d _r , preferably with a constant speed. The firing frequency of the laser, that is to say the frequency at which the emission of the laser beam starts can be set at a constant value between 5 kHz and 200 kHz, in particular equal to 200 kHz. Thus, cavities are formed periodically along the rectilinear direction. The laser beam can then be moved in an oblique direction, preferably normal, to the rectilinear direction, a distance corresponding to that traveled by the laser beam in the rectilinear direction between two successive shots. Then the laser beam is moved in a direction parallel to the rectilinear direction under conditions of movement speed and firing frequency identical to those to travel in the rectilinear direction. Thus, the cavities form a diamond-shaped network, preferably of square shape.

By jointly modifying the firing frequency and the moving speed of the laser source, the cavity number density and the surface density of cavities can be determined.

According to a particular embodiment, illustrated in FIG. 8, the laser ablation can be implemented to form the cavities in step b) and to form a space 110, free of transparent conductive oxide and splitting the transparent conductive oxide in two separate parts 85 ₁ , 85 ₂ . The space 110 may be formed by laser ablation before or on the contrary after formation of the cavities. In this way, the space 110 between the two distinct parts of the layer 851, 85 ₂ defines an electrical insulation zone useful for forming a device according to the invention.

According to a second variant, in step b), the formation of the cavities can be carried out by acid etching according to the succession of the following steps consisting of:

i. depositing on the conductive transparent oxide layer, in particular by screen printing, an inert masking resin capable of attacking the material forming the conductive transparent oxide layer, so as to form a masking layer having recesses passing through the masking layer in its thickness and opening on the transparent conductive oxide layer,

ii. filling the recesses with an acid capable of etching the transparent conductive oxide layer, so as to form the cavities in the transparent conductive oxide layer under the corresponding recesses, after etching of the transparent conductive oxide layer material by the 'acid

iii. optionally, removing the masking layer by chemical washing, iv. optionally, washing the assembly formed by the substrate and the transparent conductive oxide layer.

In particular, the masking resin may be a photosensitive or thermosensitive resin, for example based on polyimide, and the acid may be hydrochloric acid, especially when the transparent conductive oxide layer is indium oxide and 'tin.

In step c), preferably a solution comprising the constituent material of the metal layer is deposited on the conductive transparent oxide layer to form the metal layer.

In particular, the solution may comprise the material forming the metal layer in solution in a solvent. For the case where the material forming the metal layer is silver, the solvent may be an alcohol or a glycol, preferably chosen from ethanediol, propanediol, glycerol, butanol, isopropanol, ethanol and their mixtures.

Preferably, the ratio expressed as a percentage of the mass of material forming the metal layer in the solution to the mass of the solution is between 5% and 50%, preferably between 10% and 30%.

Preferably, the solution is chosen so as to have good wettability with the transparent conductive oxide layer, especially in the case where more than 90% by number, or all the cavities intended to be covered by the solution are blind holes . In addition, or alternatively, the solution is preferably chosen so as to have good wettability with the substrate, in particular in the case where more than 90% by number, or all the cavities intended to be covered by the solution are through holes and open on the substrate. In particular, the wettability of the solution on the conductive transparent oxide layer and / or on the substrate may be adapted to deposit a metal layer of uniform thickness.

By "good wettability" with respect to a support, is meant within the meaning of the invention the ability of the liquid medium to be deposited in the form of drops on the surface of the support, forming a contact angle, said further wetting angle, less than 90 °.

The determination of the contact angle is made, in a manner known to those skilled in the art, by measuring the angle Θ between the tangent to the drop deposited on the support at the point of contact with the support and the flat surface of the support on which the drop is deposited.

Those skilled in the art are able to choose adequately the nature of the solution with regard to the nature of the transparent conductive oxide layer and / or the substrate.

The solution may be deposited by ink jet printing, in particular in the form of drops, arranged for example regularly in a square mesh pattern on the surface of the transparent conductive oxide layer. Preferably, the distance between two successive drops is chosen so that the drops coalesce with each other to form a fluid layer. We speak of "coalescence" of the drops when the drops deposited side by side, spreading, meet because of the particular surface tension of the drops and possibly their mobility on the substrate on which they are deposited.

The ink jet printing operation is then followed by a drying operation of the solution, preferably of between 0.5 minutes and 10 minutes and at a temperature of between 120 ° C. and 150 ° C. ° C. In the case where the substrate is glass, the drying temperature of the solution may be greater than 150 ° C, while remaining below 300 ° C. Thus, the solvent is evaporated from the liquid layer and the metal layer is formed.

The metal layer may be deposited in several passes, for example by successively performing several sequences of inkjet printing operations and drying of sub-layers and overlays. For example, in the case where the surface density of cavities is less than 0.25, or even less than 0.20, or even less than 0.15, or even less than 0.10, a deposit in several passes is particularly advantageous. In in such a case, the surface density of cavities may be too low to obtain a homogeneous metal layer in a single pass. By performing at least one additional pass, the underlay deposited during the first pass facilitates the attachment of an overlayer, thus resulting in a metal layer of uniform thickness.

The process according to the invention is particularly versatile in that it makes it possible to adapt the formation parameters of the cavities as a function of the properties of the solutions comprising the material constituting the metal layer. In particular, the number density and / or the surface density of cavities may be modified depending on the wettability properties of the solution on the conductive transparent oxide layer and / or the substrate. In particular, it is preferable that the density of cavities be high in the case where a transparent conductive oxide of low surface energy is chosen to manufacture the multilayer structure according to the invention. On the other hand, in the case where the cavities are blind holes, the cavities improve the wettability of the silver solution on the transparent conductive oxide layer.

It is thus possible to use a range of liquid solutions, for example silver inks, wider than that which can be implemented for example in the case where the surface of the transparent conductive oxide layer is functionalized. by a surface treatment as described above.

Of course, the formation of cavities in step b) is not limited to the implementation of laser ablation or chemical etching. Similarly, the deposition of the metal layer in step c) is not limited to the technique of ink jet printing.

EXAMPLES

In all the examples that follow, the samples have the following stack:

PET / Conductive Transparent Oxide (TCO) substrate: tin doped indium oxide (ITO) 300 nm thick / silver layer.

Sample preparation follows the following order:

(1) laser ablation of a TCO layer previously deposited on a substrate to form cavities;

(2) printing the silver layer by inkjet; and

(3) drying the silver layer. No surface treatment is performed on the PET / conductive oxide substrate.

Cavities formation

The structuring of the TCO layer is carried out using a picosecond laser source emitting at 532 nm. The ablation power chosen is 1.1 W. Thus sharp ablations, of circular shape, of constant diameter and not having excess thickness at the edges, are obtained and the resulting cavities have opening diameters between 16 μιη and 18 μιη, are all through and open on the PET substrate.

Printing and drying of the silver layer

The silver layer is printed by inkjet, with a Fujifilm Dimatix printer equipped with a 16-nozzle ink cartridge, delivering drops of nominal volume of 10 μl. The printing is carried out at a temperature of 25 ° C and at atmospheric pressure.

The drops are arranged on the TCO layer in a square mesh.

The inks used for the examples consist of silver nanoparticles dispersed in a solvent. The wettability properties of inks are here characterized by their surface tension. A low surface tension reflects a high wettability, for the same surface energy of the TCO layer.

In particular, without any specific surface treatment, neither of these two inks wets the TCO layer correctly and the silver layer obtained is not homogeneous.

After deposition, the liquid silver solution layer is dried at 140 ° C for 1 minute.

Table 1 below summarizes the properties of the inks used for the examples. In the table, the ratio R corresponds to the ratio of the mass of the silver particles to the total mass of solution, expressed in percentages. Particle size Voltage

Ink R (%) Solvent

silver (nm) surface (mN / m) ethanediol mixture and

El <50 30 26

isopropanol

ethanediol mixture and

E2 <150 20 28

ethanol

Table 1

Moreover, Table 2 indicates, for the laser ablation parameters used for the examples, the density of cavities in number and the surface density of cavities.

Table 2

FIG. 4 illustrates the increase of the surface resistance of the TCO layer in the portion of the TCO layer comprising the cavities for different values of cavity surface density, expressed in percent (also called structuring rate). However, this increase is limited and does not represent a handicap for the formation of a contact recovery for an organic photovoltaic module in reverse structure.

Example 1 - El Silver Ink

As illustrated in FIG. 5a, the silver ink El 120 does not wet the surface of the cavity-free TCO layer 125. In particular, it forms isolated islands. An increase in the amount of money does not prevent this phenomenon.

For a surface density of cavities of 0.21, as illustrated in FIG. 5b, the silver layer 135 obtained, after drying, is not continuous. However, the homogeneity of the silver layer is improved compared to the case for which the TCO layer has no cavity, illustrated in Figure 5a. In particular, the TCO layer is not covered by islands.

A homogeneous silver layer 135 is obtained for a surface density of 0.36, as can be seen in FIG. 5c, which illustrates a multilayer structure comprising a silver layer deposited on a TCO layer having such a surface density of cavities.

Example 2 - E2 Silver Ink

As illustrated in FIG. 6a, the silver ink E2 140, although not forming islands, does not wet the surface of the TCO layer 125 correctly when it is free of cavities, some parts of the surface of the TCO layer not being wet.

For a surface density of cavities of 0.21, as illustrated in FIG. 6b, the silver layer 145 obtained, after drying, is not continuous. Nevertheless, the homogeneity of the silver layer is improved with respect to the case for which the TCO layer has no cavity, illustrated in FIG. 6a.

A homogeneous silver layer is obtained for a surface density of at least 0.25, as can be seen in FIGS. 6c to 6e, where multilayer structures comprising layers of silver deposited on TCO layers having a density 0.25, 0.30 and 0.36 respectively are illustrated.

For a surface density of cavities of at least 0.25, the thickness of the measured silver layer is at least 200 nm, or even 400 nm.

Moreover, the electrical properties of the multilayer structure obtained for this silver ink E2 are illustrated in FIG. 7, where the resistance of a 5 cm silver line is measured as a function of the surface density of cavities. By way of comparison, the electrical resistance of a multilayer structure of the prior art comprising a chromium and gold contact layer obtained by evaporation and sandwiched between the TCO layer and the silver layer is presented.

It is observed that the structuring of the TCO layer makes it possible to obtain a multilayer structure whose electrical properties are very close to the electrical properties of a multilayer structure obtained by evaporation, and well above those of a multilayer structure obtained by printing a silver ink on a TCO layer free of cavities.

More specifically, for the process conditions envisaged in this example, it is observed that the resistance is substantially constant for a surface density of cavities of between 0.25 and 0.35. Without being bound by any theory, the inventors consider, at least in this area density range, that the decrease in electrical conductivity related to a laser ablation of a greater quantity of material of the TCO layer is compensated by an increase in wettability. of the silver layer on the layer

TCO. The silver layer thus obtained is of excellent quality. For a lower cavity density, less than 0.25, the standard deviation of the resistance measurement is higher, which seems to confirm the effect of a lower homogeneity of the thickness of the coating layer. 'money.

For examples with a surface density of cavities less than

0.25, it is possible to obtain a layer of silver of uniform thickness to the adapted electrical resistance by depositing an overlay of silver on that already deposited on the layer

TCO.

Of course, the invention is not limited to an embodiment described and shown. In particular, the multilayer structure according to the invention can be useful for applications other than an organic photovoltaic module. In particular, it is particularly suitable for photovoltaic modules of the perovskite type, preferably in the NIP type structure.

Claims

1) multilayer structure (5) comprising an electrically insulating substrate (15), at least one conductive transparent oxide layer (20) in contact with the substrate and with a metal layer (25) and partially interposed between the substrate and the substrate; metal layer, the metal layer having attachment reliefs (55) housed in corresponding cavities (45) formed in the transparent conductive oxide layer.

2) multilayer structure according to claim 1, wherein at least 80% by number of the cavities pass through the transparent conductive oxide layer from one side to the thickness (e) of the transparent conductive oxide layer and the reliefs d corresponding snaps are in contact with the substrate.

3) Multilayer structure according to any one of the preceding claims, wherein the density in number of cavities is greater than 900 mm ^"2 , the density in number of cavities being defined as the number of cavities occupying the contact surface (40) between the layer of transparent conductive oxide and the metal layer, divided by the area of the contact surface.

4) multilayer structure according to any one of the preceding claims, wherein the surface density of cavities is greater than or equal to 0.1, preferably greater than 0.25, the surface density of cavities being defined as the area occupied by the openings of the cavities on the contact surface between the conductive transparent oxide layer and the metal layer, divided by the area of the contact surface.

5) Multilayer structure according to any one of the preceding claims, wherein the surface density of cavities is less than 0.35, preferably less than 0.30, the density of cavities being defined as the area occupied by the openings. cavities on the contact surface between the conductive transparent oxide layer and the metal layer, divided by the area of the contact surface.

6) Multilayer structure according to any one of the preceding claims, wherein the diameter (Φ) of a cavity is between 5 μιη and 30 μιη, preferably between 15 μιη and 25 μιη.

7) Multilayer structure according to any one of the preceding claims, wherein the distance (Δ) between two adjacent closer cavities is greater than 20 μηι and less than 50 μηι, the distance being measured between the centers of the openings of the cavities on the contact surface between the transparent conductive oxide layer and the metal layer.

8) Multilayer structure according to any one of the preceding claims, wherein the cavities are arranged periodically with a period between 20 μιη and 50 μιη along at least one guideline (d _r ).

9) multilayer structure according to any one of the preceding claims, wherein the conductive transparent oxide layer has a surface resistance, measured on the contact surface, of between 5 and 100 Ω / sq, preferably less than 20 Ω / sq.

Multilayer structure according to any one of the preceding claims, wherein the substrate is made of a material selected from the group consisting of glass, polyethylene terephthalate PET, polyethylene naphthalate PEN, PC polycarbonate and mixtures thereof, preferably polyethylene terephthalate PET.

11) multilayer structure according to any one of the preceding claims, wherein the conductive transparent oxide layer is made of a material selected from indium oxide doped with tin, zinc doped indium oxide, preferably doped zinc oxide, and mixtures thereof, the doped zinc oxide being preferably doped with a dopant selected from tin, gallium, aluminum, and mixtures thereof.

12) multilayer structure according to any one of the preceding claims, wherein the metal layer is of a material selected from silver, copper, aluminum and mixtures thereof and mixtures thereof, preferably is silver.

13) A method of manufacturing a multilayer structure comprising the following successive steps of:

b) forming cavities on the surface of the conductive transparent oxide layer, c) forming a partially superposed metal layer and in contact with the transparent conductive oxide layer, under conditions such that the material constituting the metal layer fills less partially, preferably completely, the cavities of the conductive transparent oxide layer, so as to define relief hooking.

14) Method according to the preceding claim, wherein step b) consists in forming cavities passing through the transparent conductive oxide layer from one side to the other according to the thickness of the transparent conductive oxide layer.

15) Method according to any one of claims 13 and 14, wherein the formation of the cavities in step b) is performed by laser ablation.

16) A method according to any of claims 13 to 15, wherein the formation of the cavities in step b) is carried out by acid etching according to the succession of the following steps consisting of:

i. depositing on the conductive transparent oxide layer, in particular by screen printing, an inert masking resin capable of attacking the material forming the transparent conductive oxide layer, so as to form a masking layer comprising recesses passing through the masking layer in its thickness and opening on the transparent conductive oxide layer, ii. filling the recesses with an acid capable of etching the transparent conductive oxide layer, so as to form the cavities in the transparent conductive oxide layer under the corresponding recesses, after etching of the transparent conductive oxide layer material by the 'acid

iii. optionally, removing the masking layer by chemical washing,

iv. optionally, washing the assembly formed by the substrate and the transparent conductive oxide layer.

17) Method according to any one of claims 13 to 16, wherein in step c), a solution comprising the material constituting the metal layer is deposited at least in part on the transparent conductive oxide layer to form the metal layer.

18) The method of claim 17, the solution being deposited by ink jet printing, followed by a drying operation of the solution to form the metal layer. 19) Device chosen from a photo-organic diode, an organic photovoltaic module or perovskite, an organic light-emitting diode, an electrical circuit, the device comprising a multilayer structure according to any one of claims 1 to 12 or obtained from a process according to any one of claims 13 to 18.

20) Device according to the preceding claim being an organic photovoltaic module (10) or perovskite, comprising a substrate (15), first and second organic photovoltaic cells or perovskites (75; 80) which respectively comprise at least one transparent oxide layer conductor (20) and a metal layer (25) arranged to form with the substrate a multilayer structure (5) according to any one of claims 1 to 12.