Perovskite / P-type or N-type material composite layer in a photovoltaic device

Abstract

Perovskite / P-type or N-type material composite layer in a photovoltaic device The present invention relates to a multilayer stack, useful for forming a photovoltaic device, of NIP or PIN structure, said stack comprising at least:- a semiconducting layer, called the lower semiconducting layer, of type N (13) in the case of a NIP structure, or of type P (15) in the case of a PIN structure;and- a composite layer, superimposed on said lower semiconducting layer, comprising at least one perovskite material and at least one P-type material in the case of a NIP structure (17) or N-type material in the case of a PIN structure (18), and having a gradient of the mass ratio P material / perovskite material in the case of a NIP structure or N-type material / perovskite material in the case of a PIN structure, in the direction of the interface between said composite layer and said lower semiconducting layer towards the opposite face of said composite layer.;

Description

Title of the invention: Perovskite / P-type or N-type material composite layer in a photovoltaic device Technical field

[0001] The present invention relates to the field of photovoltaic devices, in particular photovoltaic cells based on perovskite-type materials. It aims more particularly to propose the formulation of a composite layer, in the multilayer stacks useful for forming these photovoltaic devices, integrating a perovskite-type material and a semiconductor material, of P type in the case of a NIP structure and of N type in the case of a PIN structure, while retaining the desired performance in terms of photovoltaic conversion efficiency. Prior art

[0002] Photovoltaic devices, and in particular photovoltaic cells, include take a multilayer stack comprising a photoactive layer, called the "active" layer. This active layer is in contact on both sides with an N-type semiconductor layer and a P-type semiconductor layer. This type of multilayer assembly, comprising the superposition of the active layer and the two P-type and N-type layers described above, is conventionally called "NIP" or "PIN" depending on the order of stacking of the different layers on the substrate. In so-called perovskite-type photovoltaic cells, the active layer is made of a halogenated perovskite-type material, which may be organic-inorganic hybrid or purely inorganic.

[0003] For example, a perovskite-type photovoltaic cell with a NIP structure comprises a multilayer structure typically comprising, in this stacking order, a transparent substrate, a first transparent electrode also called the lower electrode, an N-type semiconductor layer, a perovskite-type active layer, a P-type semiconductor layer and a second electrode, also called the upper electrode (which may be made of metal, for example silver or gold).

[0004] In this type of perovskite photovoltaic cell, the N-type semiconductor layer is generally made of an N-type semiconductor oxide, for example ZnO, AZO (aluminum-doped zinc oxide), SnO2 or TiOx (x<2). This layer can be in a so-called mesoporous or planar form. The P-type semiconductor layer is made, in the majority of cases, of an organic semiconductor material which can be an ir-conjugated polymer, such as for example poly(3-hexylthiophene) or P3HT, or a small molecule such as Spiro- MeOTAD (2,2',7,7'-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene).

[0005] Currently, devices are typically made by successive deposition of layers one after the other. In the case where these deposits are made using a solvent method, for example by spin-coating, the problem arises of choosing the solvent(s) to be used, to prevent the deposited layer from causing degradation of the underlying layer.

[0006] The problem arises more particularly for the deposition of the upper semiconductor layer, of type P in the case of a NIP type structure, and of type N in the case of a PIN structure, on the surface of the perovskite. The upper semiconductor layer is thus generally formed from a solution or a dispersion of said semiconductor material(s) in one or more apolar solvent(s), so as not to damage the perovskite, soluble in polar solvents. The adhesion between the perovskite and the overlying semiconductor layer thus formed is therefore particularly weak, which can pose problems in terms of stability, in particular mechanical stability, of the structure thus formed. Summary of the invention

[0007] The present invention aims precisely to propose a new multilayer stacking structure, of NIP or PIN structure, useful for forming a photovoltaic device, making it possible to overcome the aforementioned problems, in terms of compatibility of the formulation implemented to form the upper semi-conductor layer with an underlying active layer of perovskite type.

[0008] The inventors have thus shown that it is possible to produce photovoltaic devices, in particular perovskite-type photovoltaic cells, exhibiting excellent performance, from a multilayer stack integrating, on the surface of the lower semi-conductor layer, of N type in the case of the development of a NIP structure and of P type in the case of the development of a PIN structure, a composite layer, combining the perovskite material and the material of the upper semi-conductor layer, of P type in the case of a NIP structure and of N type in the case of a PIN structure.

[0009] More specifically, the present invention relates, according to a first of its aspects, to a multilayer stack, useful for forming a photovoltaic device, of NIP or PIN structure, said stack comprising at least: - a semiconductor layer, called the lower semiconductor layer, of N type in the case of a NIP structure, or of P type in the case of a PIN structure; and - a composite layer, superimposed on said lower semiconductor layer, comprising at least one perovskite material and at least one P type material in the case of a NIP structure or N-type in the case of a PIN structure, and having a gradient of the mass ratio of P material / perovskite material in the case of a NIP structure or N material / perovskite material in the case of a PIN structure, in the direction of the interface between said composite layer and said lower semiconductor layer towards the opposite face of said composite layer.

[0010] The composite layer thus has an inhomogeneous distribution of perovskite and P-type (or N-type) materials. The distribution of perovskite and P-type (or N-type) materials is such that the mass ratio of perovskite material / P material in the case of a NIP structure or perovskite material / N material in the case of a PIN structure is higher in the vicinity of the interface of said composite layer with the underlying semiconductor layer and lower in the vicinity of the opposite face of said composite layer.

[0011] In particular, as detailed more particularly in the remainder of the text, the perovskite material and the P-type (or N-type) material form within the composite layer according to the invention, over a thickness of at least 10 nm, in particular over a thickness of 10 to 150 nm, an interpenetrating structure.

[0012] This interpenetrating structure is identifiable by analysis by time-of-flight secondary ion mass spectrometry (ToF-SIMS). More particularly, this interpenetrating structure is composed of crystallized perovskite domains incorporated in a matrix based on said P-type (or N-type) material(s).

[0013] Said perovskite / material P (or material N) composite layer as defined above will be referred to more simply in the remainder of the text as “composite layer”.

[0014] A multilayer stack according to the invention more particularly has a so-called “planar” architecture. By “planar” architecture, it is meant that each of the layers of the multilayer stack according to the invention is compact. In particular, a multilayer stack according to the invention differs from structures with a so-called “mesoporous” architecture, as presented for example in the publication Rong et al. [1]. So-called “mesoporous” architectures implement a mesoporous layer within which the perovskite is partially infiltrated. Generally speaking, in this type of structure, the perovskite is interpenetrated with the lower semiconductor layer, of the N type in the case of a NIP structure or of the P type in the case of a PIN structure.

[0015] Thus, advantageously, the multilayer stack of NIP or PIN structure according to the invention does not use a layer based on a mesoporous material.

[0016] In particular, the interface between the composite layer according to the invention and the underlying semiconductor layer forms a planar junction.

[0017] As illustrated in the following example, a composite layer according to the invention leads to performances of the photovoltaic cell, in particular in terms of photovoltaic conversion efficiency, similar to those which can be obtained via the implementation of separate superimposed layers active layer / P-type (or N-type) layer.

[0018] Advantageously, the preparation of a multilayer stack according to the invention makes it possible to overcome the compatibility problems encountered during the formation of conventional multilayer stacks with planar architecture, between the formulation used for the formation of the upper semiconductor layer and the underlying crystallized perovskite active layer, and the risk of deterioration of the latter.

[0019] According to another of its aspects, the invention relates to a method for preparing a multilayer stack according to the invention comprising at least the following consecutive steps: (a) having a structure having, on the surface, an N-type semiconductor layer, in the case of the formation of a NIP structure stack, or a P-type semiconductor layer in the case of the formation of a PIN structure stack, (b) forming, on the surface of said N-type or P-type semiconductor layer, a wet film from a solution of precursors of the perovskite material in one or more solvents; (c) adding to said wet film of step (b) at least one P-type material in the case of the formation of a NIP stack, and an N-type material in the case of a PIN stack; and (d) subjecting the assembly to a heat treatment conducive to the elimination of solvents and the crystallization of the perovskite material.

[0020] Advantageously, the composite layer according to the invention is formed by a wet process and, preferably, comprises, in step (c), the deposition, on the surface of said wet film of step (b), of a formulation of at least one P-type material in the case of the formation of a PIN stack, also called "P-type ink" (or N-type in the case of the formation of a PIN stack, also called "N-type ink"), in one or more solvents, called "anti-solvents", in which the perovskite precursors are not soluble.

[0021] According to a particular embodiment, as detailed more precisely in the rest of the text, steps (b) and (c) can be carried out by solvent means, more particularly by spin coating or centrifugal coating, better known by the Anglo-Saxon term “spin-coating”.

[0022] Advantageously, the deposition of the P-type or N-type ink in step (c) of the method of the invention, preferably by spin-coating, simultaneously operates the “quenching” of the perovskite.

[0023] As presented for example in the publication Xiao et al. [2], in the context of the preparation of a perovskite active layer, the method known as “solvent quenching” consists more particularly in dripping onto the wet film of precursors of the perovskite active layer, during spin-coating, a quantity of anti-solvent, for example toluene and chlorobenzene, to induce rapid crystallization of the perovskite. The addition of an anti-solvent, by rapidly reducing the solubility of the perovskite precursors in the solvent medium, advantageously makes it possible to promote rapid nucleation and growth of the perovskite crystals. It has been shown that such a “quenching” operation advantageously makes it possible to improve the crystallinity of the perovskite material, at the end of the thermal annealing, and thus the quality of the resulting perovskite active layer.

[0024] Thus, advantageously, the invention proposes a simplified method for producing a multilayer stack for photovoltaic devices, in which the steps of “solvent quenching” the perovskite and of forming the upper semiconductor layer are advantageously combined before proceeding with the crystallization of the perovskite. The method of the invention thus makes it possible to reduce the number of steps necessary for the preparation of the multilayer stack.

[0025] As detailed in the remainder of the text, a multilayer stack according to the invention may be intended for perovskite photovoltaic devices, in particular single-junction photovoltaic cells, in so-called “PIN” or “NIP” type structure, or even multijunction type photovoltaic cells, in particular tandem type.

[0026] The invention thus relates, according to another of its aspects, to a photovoltaic device, in particular a perovskite type photovoltaic cell, comprising a multilayer stack as defined previously or obtained by a method as defined previously.

[0027] Other characteristics, variants and advantages of a composite layer according to the invention, and of its preparation, will emerge more clearly on reading the description, examples and figures which follow, given by way of illustration and not limitation of the invention. Brief description of the drawings

[0028] [fig. 1] schematically represents, in a vertical section plane, conventional multilayer stacks, of NIP 21 structure or PIN 22 structure.

[0029] [fig.2] schematically represents, in a vertical section plane, em multilayer stacks according to the invention, of NIP 23 structure or PIN 24 structure, integrating a composite perovskite / P 17 type material layer in the case of a NIP 23 structure, and perovskite / N-type material 18 in the case of a PIN structure.

[0030] [fig.3] schematically represents, in a vertical section plane, silicon-perovskite tandem cells, comprising a conventional multilayer stack 25 (left figure) or comprising a stack 26 according to the invention (right figure).

[0031] It should be noted that, for reasons of clarity, the various elements in the figures are represented in free scale, the actual dimensions of the various parts not being respected.

[0032] In the rest of the text, the expressions “between ... and ...” and “ranging from ... to ...” and “varying from ... to ...” are equivalent and are intended to mean that the limits are included, unless otherwise stated. Detailed description MULTILAYER STACKING

[0033] As indicated previously, the invention relates, according to a first of its aspects, to a multilayer stack, useful for forming a photovoltaic device, of NIP or PIN structure, said stack comprising at least: - a lower N-type semiconductor layer in the case of a NIP structure, or P-type in the case of a PIN structure; and - a composite layer, superimposed on said lower semiconductor layer, comprising at least one perovskite material and at least one P-type material in the case of a NIP structure, or N-type material in the case of a PIN structure, and having a gradient of the mass ratio P material / perovskite material in the case of a NIP structure or N material / perovskite material in the case of a PIN structure, in the direction of the interface between said composite layer and said lower semiconductor layer towards the opposite face of said composite layer.

[0034] Perovskite / P or N type material composite layer

[0035] A composite layer according to the invention comprises, or is formed from, at least one perovskite material and at least one P-type material in the case of a NIP structure stack, or at least one N-type material in the case of a PIN structure stack.

[0036] The composite layer according to the invention is in direct contact with the underlying N-type semiconductor layer in a NIP structure and P-type in a PIN structure.

[0037] Advantageously, the perovskite is a material comprising 1, 2 or 3 cations and anions, for example halides, in particular Cl, Br, I and their mixtures.

[0038] The perovskite material of a composite layer according to the invention may more particularly be a material of general formula ABX3, with: . A representing a cation or a combination of metallic or organic cations; . B representing one or more metallic elements, such as lead (Pb), tin (Sn), bismuth (Bi) and antimony (Sb); and . X representing one or more anions, in particular one or more halides, and more particularly chosen from chloride, bromide, iodide and their mixtures.

[0039] Such perovskite materials are notably described in document WO 2015 / 080990.

[0040] As an example of perovskite materials, mention may in particular be made of organic-inorganic hybrid perovskites. These hybrid perovskite materials may more particularly be of the aforementioned formula ABX3, in which A comprises one or more organic or inorganic cations.

[0041] The organic cation can be chosen from organoammonium cations such as: - alkyl-ammonium cations of general formula RiR2R3R4N+, with Ri R2 R3 and R4 being independently of each other a hydrogen atom or a C1-C5 alkyl radical, such as for example a methyl-ammonium (MA) type cation and - formamidinium cations (FA) of formula [RiNCHNRi]+, with Ri being able to represent a hydrogen atom or a C1-C5 alkyl radical.

[0042] The organic cation(s) of the hybrid perovskite material may optionally be associated with one or more metal cations, for example cesium.

[0043] As examples of hybrid perovskite materials, we can more particularly cite perovskites of formula ABX3, with: - A representing an organoammonium cation, for example of the methylammonium type (MA+), a formamidinium cation (FA+) or a mixture of these two cations, possibly associated with cesium (Cs+); - B being chosen from lead, tin, bismuth, antimony and their mixtures; and - X being chosen from chloride, bromide, iodide and their mixtures.

[0044] The perovskite material can be in particular CH3NH3PbI3, also called PK with the lead being able to be replaced by tin or germanium and the iodine being able to be replaced by chlorine or bromine.

[0045] The perovskite material can also be a compound of formula CsxFAi xPb(Ii yBr y)3 with x < 0.17; 0 < y < 1 and FA symbolizing the formamidinium cation.

[0046] In the case of a NIP structure stack, the composite layer according to the invention comprises at least one P-type material.

[0047] A “P-type” material designates a material allowing the transport of holes (h+).

[0048] The P-type material may for example be chosen from Nafion, WO3, MoO3, V2 O5 and NiO, ir-conjugated semiconducting polymers, optionally doped, and mixtures thereof. Preferably, the P-type material is chosen from ir-conjugated semiconducting polymers, optionally doped.

[0049] By way of illustration of the ir-conjugated semiconducting polymers, optionally doped, mention may in particular be made of poly(3-hexylthiophene) or P3HT, poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2',r,3'-benzothiadiazo le or PCDTBT, poly[2,l,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,lb:3,4-b' ]dithiophene-2,6-diyl]] or PCPDTBT, poly(benzo[1,2-b:4,5-b']dithiophene-alt-thieno[3,4-c]pyrrole-4,6-dione) or PBDTTPD, poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] or PTB7, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] or PT AA.

[0050] The ir-conjugated semiconducting polymers may advantageously be doped with one or more P-type dopants, such as a lithium salt, for example lithium bis(trifluoromethane)sulfonide (LiTFSI), and / or 4-tert-butylpyridine (t-BP).

[0051] Also suitable as a P-type material is a PEDOT-type conductive material in a form combined with a counter-anion, such as PEDOT:PSS.

[0052] A preferred P-type material is a mixture of PEDOT and PSS, or PT AA, preferably doped, in particular with a lithium salt, such as lithium bis(trifluoromethane)sulfonide (LiTFSI) and / or 4-tert-butylpyridine.

[0053] The P-type material can also be chosen from P-type semiconductor molecules such as: - porphyrin; - the: 7,7'-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b 2]dithiophene-2,6-diyl)bis(6-fluoro-4-(5'-hexyl-[2,2'-bithiophen]-5-yl)benzo[c][1,2,5]t hiadiazole): p-DTS(FBTTh2)2; - boron-dipyromethenes (BODIPY); and - molecules with a triphenylamine nucleus (TPA).

[0054] In the case of a PIN structure stack, the composite layer according to the invention comprises at least one N-type material.

[0055] An “N-type” material designates a material which allows the transport of electrons (e). It may be more particularly chosen from metal oxides. The metal oxides may be present, for example, in the form of metal oxide nanoparticles.

[0056] The N-type metal oxides may in particular be chosen from zinc oxide ZnO, titanium oxides TiOx with x between 1 and 2, tin oxide (SnO2), doped zinc oxides, for example aluminum-doped zinc oxide (AZO), indium-doped zinc oxide (IZO), gallium-doped zinc oxide (GZO), doped titanium oxides, for example titanium oxide doped with nitrogen, phosphorus, iron, tungsten or manganese, tin oxides doped with for example fluorine, and mixtures thereof.

[0057] In particular, the N-type material of the composite layer according to the invention may be chosen from tin oxide (SnO2), doped zinc oxides, in particular aluminum-doped zinc oxide (AZO) and mixtures thereof.

[0058] According to an alternative embodiment, the multilayer stack according to the invention is of the NIP type, and said composite layer comprises, or is formed from, at least one perovskite material and at least one P-type material, in particular as defined previously.

[0059] According to a particular embodiment, a composite layer according to the invention comprises, or is even formed: . of a perovskite material of formula ABX3 as defined previously, in particular of formula CsxFAi xPb(Ii yBry)3 with x < 0.17; 0 < y < 1 and FA symbolizing the formamidinium cation; and . of a P-type material, as defined above, in particular chosen from ir-conjugated semiconducting polymers, optionally doped, and in particular PT AA, optionally doped with a lithium salt and / or 4-tert-butylpyridine.

[0060] A composite layer according to the invention preferably has a thickness less than or equal to 1 μm, in particular between 200 and 800 nm and more particularly between 300 and 600 nm.

[0061] As mentioned previously, a composite layer according to the invention has an inhomogeneous distribution of perovskite and P-type (or N-type) materials.

[0062] More specifically, the composite layer has a gradient of the P (or N) material / perovskite material mass ratio, in the direction of the interface between said composite layer and the underlying semiconductor layer, towards the opposite face of said composite layer. By "gradient of the P (or N) material / perovskite material mass ratio", is meant a P (or N) material / perovskite material mass ratio increasing in the direction indicated by the gradient, in other words increasing according to the invention from the interface between said composite layer and the underlying semiconductor layer to the opposite face of said composite layer.

[0063] In other words, the perovskite material / P (or N) material mass ratio is higher in the vicinity of the interface between said composite layer and the underlying semiconductor layer than in the vicinity of the opposite face.

[0064] In particular, the distribution of perovskite and P-type (or N-type) materials is such that in the vicinity of the interface between said composite layer and the underlying semiconductor layer, the composite layer according to the invention is formed mainly, or even exclusively, of the perovskite material; while in the vicinity of the face of said composite layer, opposite the interface between the composite layer and the underlying semiconductor layer, in other words, in the vicinity of the interface between the composite layer and the upper electrode, the composite layer according to the invention is formed mainly of P-type material in the case of a NIP structure or N-type material in the case of a PIN structure, in other words is locally P-type or N-type.

[0065] A composite layer according to the invention more particularly comprises a zone in which the perovskite material and the P-type (or N-type) material form an interpenetrating structure. In particular, the composite layer according to the invention comprises a zone in which said perovskite and P-type (or N-type) materials are mixed at the submicron scale.

[0066] More particularly, this interpenetrated zone extends over a thickness of at least 10 nm, in particular over a thickness of between 10 and 150 nm, of the composite layer according to the invention.

[0067] In particular, at this interpenetrated zone, the crystallized perovskite domains are included in a matrix based on said P-type (or N-type) material. In other words, the perovskite domains are covered by the P-type (or N-type) material. This structure can be identified by analysis of said composite layer by scanning electron microscopy (SEM), combined with energy dispersive X-ray microanalysis (EDX).

[0068] The crystallized perovskite domains may have an average size greater than 100 nm, in particular greater than 200 nm and preferably greater than 300 nm. By size is meant the largest dimension of the perovskite domains, for example the diameter for grains of generally spherical shape.

[0069] The average size of crystallized perovskite domains can be measured by optical microscopy or scanning electron microscope.

[0070] Thus, a composite layer according to the invention may more particularly have, in the direction of the interface between said composite layer and the underlying semi-conductor layer towards the face of said composite layer, opposite the interface between the composite layer and the underlying semi-conductor layer, in other words, towards the interface between the composite layer and the upper electrode: - a first zone formed mainly of perovskite-type material, or even exclusively made up of perovskite-type material; - an area comprising a mixture of perovskite and P-type materials in the case of a NIP structure or N-type materials in the case of a PIN structure; and - an area formed mainly, or even exclusively, of P-type material in the case of a NIP structure or N-type material in the case of a PIN structure.

[0071] As mentioned above, the stack according to the invention advantageously has a so-called “planar” structure. In particular, a composite layer according to the invention is a compact, non-porous layer. It thus differs from so-called mesoporous structures, in which a material is incorporated into the pores of another material.

[0072] Other layers of the multilayer stack

[0073] The lower semiconductor layer, underlying the composite layer according to the invention, of N type in a NIP structure, or of P type in a PIN structure, can be formed from one or more N type materials, respectively of P type, as described previously for the composition of the composite layer.

[0074] It can typically have a total thickness of between 100 nm and 2 μm, in particular between 400 and 800 nm.

[0075] As indicated previously, a multilayer stack according to the invention may be intended for a photovoltaic device, in particular a perovskite photovoltaic cell, in a NIP or PIN type structure, or even a tandem type.

[0076] Preferably, the multilayer stack according to the invention is in a so-called NIP structure. Such a stack may comprise the following layers, adjoining each other and in this order of superposition: - an N-type semiconductor layer, and - a composite perovskite / P material layer, as defined previously.

[0077] Alternatively, in the case of a PIN structure, a multilayer stack according to the invention may comprise the following layers, adjoining each other and in this order of superposition: - a P-type semiconductor layer, and - a composite perovskite / N material layer, as defined previously.

[0078] As shown in [fig.2], a photovoltaic device, in particular a perovskite photovoltaic cell in NIP 23 or PIN 24 structure, may more particularly comprise, in this order of superposition, at least: - a substrate 11, in particular transparent, flexible or rigid, such as a glass or plastic substrate, in particular PET; - a first electrode, called the lower electrode 12; - a lower semiconductor layer, of type N 13 in the case of a NIP structure or of type P 15 in the case of a PIN structure, in particular as defined previously; - a composite layer, as defined above, of perovskite / material P 17 type in the case of a NIP structure or of perovskite / material N 18 type in the case of a PIN structure; and - a second electrode, called the upper electrode 16.

[0079] Preferably, a multilayer stack according to the invention is intended for a photovoltaic device, in particular a photovoltaic cell, of the perovskite type in NIP structure.

[0080] The substrate 11 implemented in a photovoltaic device, in particular a photovoltaic cell, comprising a multilayer stack according to the invention, refers to a solid base structure, on one of the faces of which the lower electrode is formed. It can be in the form of a plate. It can be flexible or rigid.

[0081] It can be of various natures, for example made of glass or plastic, in particular polyester, preferably polyethylene terephthalate (PET), polyethylene naphthalate (PEN) or polycarbonates.

[0082] This may in particular be a glass plate.

[0083] The lower electrode 12, in contact with the support, may be formed from a transparent semi-conducting layer, for example made of transparent conducting oxide(s) (TCO) such as tin-doped indium oxide (ITO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), indium-doped zinc oxide (IZO) and mixtures thereof, or may be formed from a multi-layer assembly, for example AZO / Ag / AZO.

[0084] It can also be formed by a network of nanowires, in particular in silver.

[0085] The upper electrode 16 may for example be formed by a layer of gold, silver, or by a network of nanowires, preferably silver. It may also be made of aluminum or transparent conductive oxide.

[0086] According to yet another variant embodiment, a multilayer stack according to the invention may be intended for a photovoltaic cell of the multijunction type, in particular of the “tandem” or double junction type, of which at least one of the active materials is a perovskite material.

[0087] Such tandem type cells typically comprise two multi-layer assemblies stacked on top of each other, the respective active layers of which generally have different light absorption spectra. In these tandem type cells, photons not absorbed by the first active layer can be absorbed by the second. The quantity of photons recovered by all the active layers of the cell is thus increased and the electrical efficiency of the latter is improved.

[0088] A tandem type photovoltaic device according to the invention may comprise a stack according to the invention, in NIP or PIN structure, preferably in NIP structure, as described previously.

[0089] This may be, for example, a silicon-perovskite tandem cell 26 as shown schematically in [fig.3].

[0090] A tandem type photovoltaic device according to the invention can more par- liment comprise a first sub-cell, for example based on crystalline silicon, on which is stacked a perovskite-based sub-cell comprising a multilayer stack according to the invention, and more particularly, comprising, in this order of superposition, as represented in [fig.3], at least: - a lower N-type semiconductor layer 13 in the case of a NIP structure or P-type in the case of a PIN structure; - a composite layer according to the invention, of perovskite / material P 17 type in the case of a NIP structure or of perovskite / material N type in the case of a PIN structure, and - a transparent upper electrode, in particular made of transparent conducting oxide (TCO).

[0091] In the case of the development of tandem type photovoltaic cells, the implementation of a composite layer according to the invention proves to be particularly advantageous from the optical point of view. Indeed, in such a structure, the illumination is done via the upper face, as shown schematically in [fig.3], and must therefore pass through the interface semiconductor layer (of type P 15 in a NIP structure as shown in [fig.3]; of type N in a PIN structure), before reaching the active perovskite layer.

[0092] On the other hand, in a structure implementing a composite layer according to the invention, for example a perovskite / P 17 layer composite layer as shown in [fig.3], the filter effect due to the upper interface layer is advantageously reduced. Also, the possible losses by reflections at the perovskite / interface layer interface are advantageously reduced.

[0093] The photovoltaic device may further comprise electrical connection means, in particular contact connections, which make it possible to connect the electrodes to supply current to an electrical circuit.

[0094] METHOD FOR PREPARING A STACK ACCORDING TO THE INVENTION

[0095] The invention also relates to a method for preparing a stack according to the invention in which a composite layer as defined above is formed by successive deposition of perovskite and P-type (or N-type) materials, preferably by wet method, before crystallization of the perovskite.

[0096] More particularly, the method of the invention implements at least the following consecutive steps: (a) having a structure having, on the surface, an N-type semiconductor layer, in the case of the formation of a NIP structure stack, or a P-type semiconductor layer in the case of the formation of a PIN structure stack, (b) forming, on the surface of said N-type or P-type semiconductor layer, a wet film from a solution of precursors of the perovskite material in one or more solvents; (c) adding to said wet film of step (b) at least one P-type material in the case of the formation of a NIP stack, and an N-type material in the case of a PIN stack; and (d) subjecting the assembly to a heat treatment conducive to the elimination of solvents and the crystallization of the perovskite material.

[0097] Preferably, a composite layer according to the invention is formed by the wet method, that is to say by a technique involving the deposition of liquid solutions or dispersions.

[0098] According to a particular embodiment, the formation of a multilayer stack integrating a composite layer according to the invention can thus be more particularly carried out via at least the following steps: (a) having a structure having, on the surface, an N-type semiconductor layer in the case of preparing a NIP structure stack, or a P-type semiconductor layer in the case of preparing a PIN structure stack; (b) depositing, on the surface of said N-type or P-type semiconductor layer, a solution of precursors of the perovskite material in one or more solvents; (c) depositing, on the surface of the wet film formed in step (b), a formulation of at least one P-type material in the case of a NIP stack, or N-type material in the case of a PIN stack, in one or more solvents, called “anti-solvents”, in which the precursors of the perovskite material are not soluble; and (d) subjecting the assembly to a heat treatment conducive to the elimination of solvents and the crystallization of the perovskite material.

[0099] It is understood that the starting structure, having on the surface an N-type (or P-type) semiconductor layer, implemented in step (a) of the method of the invention, is suitable for the photovoltaic device for which the multilayer stack according to the invention is intended.

[0100] It can more particularly comprise, in the context of the preparation of a perovskite photovoltaic cell in NIP or PIN structure, as shown schematically in [fig.2], in this order of superposition: - a substrate 11 as defined previously; - a first electrode 12, called the lower electrode, in particular as defined previously; - said N-type 13 (or P-type 15) semiconductor layer.

[0101] In the case of the development of a tandem type photovoltaic cell, for example of the silicon-perovskite type, as shown schematically in [fig.3], the structure having on the surface an N-type (or P-type) semi-conductor layer may include the following stacking: - a first sub-cell, for example based on silicon 19, - a so-called recombination layer, for example formed from a transparent conductive oxide, in particular chosen from the transparent conductive oxides indicated previously for the lower electrode; and - said N-type 13 (or P-type) semiconductor layer.

[0102] The term "ink" commonly refers to a solution, dispersion or suspension of material(s) used to produce layers for a multi-layer stack useful for forming a photovoltaic device.

[0103] The inks generally comprise a solvent, one or more materials constituting the layer, and optionally one or more additives, for example a plasticizer and / or a binder and / or a dispersant.

[0104] The solution of precursors of the perovskite material, referred to more simply in the remainder of the text as “perovskite ink”, may typically comprise the precursors of the perovskite material in one or more solvents. A person skilled in the art is able to choose the nature and proportions of perovskite precursors to be used to obtain the desired perovskite material.

[0105] Said solvent(s) are chosen with regard to the nature of the perovskite precursor(s), so as to allow their solubilization. The solvents are conventionally chosen from polar organic solvents, in particular chosen from dimethylformamide (DMF), dimethylsulfoxide (DMSO), gamma-butyrolactone (GBL), and mixtures thereof.

[0106] Preferably, said solvent(s) of the perovskite ink are chosen from DMF, DMSO and mixtures thereof.

[0107] The formulation based on P-type (or N-type) material, referred to in the remainder of the text as “P-type ink” (respectively “N-type ink”), typically comprises said P-type (respectively N-type) material(s) in one or more “anti-solvents”.

[0108] Said solvent(s), called “anti-solvents”, are solvents called “orthogonal” with respect to the precursors of the perovskite material. By “orthogonal” solvent with respect to the precursors of the perovskite material, is meant a solvent not capable of dissolving said precursors of the perovskite material. It is understood that the nature of said anti-solvent(s) is chosen with regard to the nature of the precursors of the perovskite material.

[0109] As mentioned above, anti-solvents are conventionally used when producing a crystallized layer of perovskite, to carry out the so-called “quenching” phase, subsequent to the deposition of the perovskite precursor solution. Such anti-solvents are for example described in the publication Paek et al. [3].

[0110] The anti-solvents are typically chosen from diethyl ether; dichloromethane; aromatic compounds with one, two or three rings, substituted, in particular substituted by one or more alkyl groups, in particular methyl, and / or halogen, in particular chlorine, such as toluene, chlorobenzene, xylene, methylnaphthalene; and mixtures thereof.

[0111] Preferably, the anti-solvent is chlorobenzene.

[0112] The concentration of P-type (or N-type) material(s) in the P-type (or N-type) ink used may be between 2 g / L and 30 g / L, preferably between 4 g / L and 20 g / L.

[0113] The concentrations of perovskite precursors and P-type or N-type material(s) in the deposited inks are adjusted in particular with regard to the final thickness of the desired composite layer.

[0114] The deposition of the inks during the process for preparing a composite layer according to the invention can be carried out by means of a solvent deposition technique chosen from spin-coating, scraper deposition, blade-coating, ultrasonic spray deposition, slot-die coating, dip-coating, inkjet printing, gravure printing, flexography and screen printing.

[0115] According to an alternative embodiment, the perovskite ink and / or the P-type (or N-type) ink is (are) deposited by spin-coating.

[0116] Preferably, the perovskite ink and the P-type (or N-type) ink are deposited by the same deposition technique, advantageously by spin-coating.

[0117] It is within the skill of the person skilled in the art to adjust the conditions for deposition of said P-type (or N-type) ink, on the wet film of perovskite precursor solution, to obtain, after thermal annealing, said desired composite layer, as described above.

[0118] By "wet film" is meant that the film on which the P-type (or N-type) ink is deposited comprises one or more solvents. In other words, the deposition of the P-type (or N-type) ink is carried out before the total removal of said solvent(s) from the previously deposited perovskite ink film.

[0119] According to a particular embodiment, steps (b) and (c) of the method of the invention can be carried out consecutively, by spin-coating, step (c) being carried out without stopping the rotation of the rotating plate of the spin-coating device.

[0120] More particularly, according to this embodiment variant, the structure having on the surface an N-type (or P-type) semiconductor layer is fixed on the sample holder of the spin-coating device. The perovskite precursor solution is then deposited on the surface of said N-type (or P-type) layer, then the substrate is rotated rapidly by the spinner, to form a thin and regular film of the perovskite ink. The formulation of P-type (or N-type) material(s) in one or more anti-solvent(s) is then dripped onto the surface of the wet film of the perovskite ink, without stopping the rotation.

[0121] The spin-coating deposition in steps (b) and (c) can be carried out for example with a rotation speed of between 500 and 8000 rpm. The P-type (or N-type) ink can be for example deposited on the surface of the wet film of perovskite precursor solution between 5 and 35 seconds, in particular between 5 and 20 seconds before the end of the deposition program of the perovskite precursor solution.

[0122] It is up to the person skilled in the art to adjust the deposition parameters, in particular in terms of the time elapsed between the deposition of the perovskite precursor solution by spin-coating and the deposition of the P-type or N-type ink, to access, after annealing, a composite layer according to the invention. In particular, the P-type or N-type ink is deposited after formation, on the surface of the lower semiconductor layer, of a wet film of perovskite precursor solution (perovskite ink), of homogeneous thickness, and before evaporation of the solvent(s) of the deposited perovskite ink.

[0123] Total removal of solvents can be achieved conventionally, for example by thermal drying.

[0124] The assembly is then heated to crystallize the perovskite material. It is up to the person skilled in the art to adjust the thermal annealing conditions to obtain the desired perovskite material. The thermal annealing may in particular be carried out at a temperature between 60 and 150°C, in particular between 80 and 120°C. The duration of the annealing may be between 5 and 120 minutes, in particular between 15 and 90 minutes and more particularly between 30 and 60 minutes.

[0125] The invention will now be described by means of the following examples, given of course by way of illustration and not limitation of the invention. Examples

[0126] Formulation of a composite layer of perovskite + P material

[0127] The P-type material is poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine].

[0128] From a commercial PTAA powder (Mw of approximately 14500 g / mol), a PTAA formulation is prepared at a concentration of 12 g / L in anhydrous toluene.

[0129] This PTAA formulation is completed by the addition, for 1.5 mL of the PTAA solution in toluene, of 15.75 pL of a 170 g / L Li-TFSI solution in acetonitrile and 8.4 pL of 4-tert-butylpyridine (t-BP).

[0130] A 1.1 mm thick glass substrate 11, covered with a layer of ITO forming the lower electrode, is covered with a layer N of tin oxide (SnO2). The layer N is formed by spin-coating.

[0131] A perovskite ink, formed from the precursors Pbl2, PbBr2, Csl and FAI in a mixture of DMF and DMSO, is deposited on the surface of the SnO2 layer by spin-coating. Without stopping the rotation of the structure, the PT AA solution, prepared above (250-350 pL) is deposited on the surface of the structure.

[0132] The PT AA solution thus serves as a “quenching” formulation for the perovskite. The “quenched” film is then annealed for one hour at 100 °C to form the composite perovskite layer CsoxjsFAo^PKIo^BrojvVPTAA.

[0133] The perovskite + PTAA composite layer has a thickness of approximately 400 nm.

[0134] Analysis of the composite layer by ToF-SIMS analysis makes it possible to identify an increasing concentration of the perovskite material and a decreasing concentration of the P-type material, from the free surface of the formed composite layer to the interface between the composite layer and the underlying N-layer. In particular, three zones can be distinguished, from the interface between the formed composite layer and the underlying N-layer to the free surface of the composite layer: a first zone formed mainly of the perovskite material, a zone comprising a mixture of the perovskite material and the P-type material and a zone formed mainly of the P-type material.

[0135] Evaluation of the performance of the device

[0136] An upper electrode (gold layer, 100 nm thick) is then evaporated on the surface of the perovskite+PTAA composite layer.

[0137] The entire device is produced in a glove box under internal atmosphere. The active surface area of ​​the NIP type device thus formed, with a Glass / ITO / N layer / perovskite+PTAA / Au composite structure, is 0.33 cm2.

[0138] The photovoltaic performances of the device were measured at 25°C under standard lighting conditions (1000 W.m2, AM 1.5 G).

[0139] The characteristic parameters of the operation of the device (open circuit voltage Voc, short-circuit current density Jsc, form factor FF and conversion efficiency PCE) are determined from these curves.

[0140] The results obtained are presented in the following table 1.

[0141] [Tables 1] Device Voc (mV) Jsc (mA / cm2) FF (%) PCE (%) In accordance with the invention (with a composite layer pero v skite+PT AA) 1048 19.7 69.7 14.4 List of cited documents

[0142] [1] Rong et al.. Science 361, 1214 (2018) ;

[0143] [2] Xiao et al., Angew. Chem. 2014, 126, 1-7 ;

[0144] [3] Paek et al., Chem. Mater. 2017, 29, 3490-3498.

Claims

Claims

1. Multilayer stack, useful for forming a photovoltaic device, of NIP or PIN structure, said stack comprising at least: - a semiconductor layer, called lower semiconductor layer, of N type (13) in the case of a NIP structure, or of P type (15) in the case of a PIN structure; and - a composite layer, superimposed on said lower conductive layer, comprising at least one perovskite material and at least one P type material in the case of a NIP structure (17) or of N type in the case of a PIN structure (18), and having a gradient of the P material / perovskite material mass ratio in the case of a NIP structure or N material / perovskite material in the case of a PIN structure, in the direction of the interface between said composite layer and said lower semiconductor layer towards the opposite face of said composite layer; said stack having a planar architecture.

2. Multilayer stack according to the preceding claim, in which said perovskite material and said P-type or N-type material form within the composite layer according to the invention, over a thickness of at least 10 nm, in particular over a thickness of between 10 and 150 nm, an interpenetrating structure, said interpenetrating structure being more particularly formed from a matrix based on said P-type or N-type material, in which domains of crystallized perovskite are incorporated.

3. Multilayer stack according to claim 1 or 2, wherein said composite layer has, in the direction of the interface between said composite layer and the underlying semiconductor layer towards the face of said composite layer, opposite the interface between the composite layer and the underlying semiconductor layer: - a first zone formed mainly of the perovskite type material, or even exclusively of the perovskite type material; - a zone comprising a mixture of perovskite and P-type materials in the case of a NIP structure or N-type materials in the case of a PIN structure; and - a zone formed mainly, or even exclusively of the

4.

5.

6. P-type material in the case of a NIP structure or N-type material in the case of a PIN structure. Multilayer stack according to any one of the preceding claims, in which said composite layer has a thickness less than or equal to 1 μm, in particular between 200 and 800 nm and more particularly between 300 and 600 nm. Multilayer stack according to any one of the preceding claims, wherein the perovskite material of said composite layer is of formula ABX3, with: . A representing a cation or a combination of metallic or organic cations; . B representing one or more metallic elements, such as lead, tin, bismuth and antimony; and . X representing one or more anions, in particular one or more halides, and more particularly chosen from chloride, bromide, iodide and their mixtures; said perovskite material being in particular of formula CsxFAi xPb(Ii y Bry)3 with x < 0.17; 0 < y < 1 and FA symbolizing the forma-midinium cation. Multilayer stack according to any one of the preceding claims, said stack being: - of NIP structure, in which the P-type material of said composite layer is chosen from ji-conjugated semiconducting polymers, optionally doped, and PEDOT-type conductive polymers in a form combined with a counter-anion, such as PEDOT:PSS; in particular, said P-type material is chosen from a mixture of PEDOT and PSS and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), optionally doped with a lithium salt and / or 4-tert-butylpyridine;or - of PIN structure, in which the N-type material of said composite layer is chosen from N-type metal oxide(s), in particular chosen from zinc oxide ZnO, titanium oxides TiOx with x between 1 and 2, tin oxide (SnO2), doped zinc oxides, for example aluminum-doped zinc oxide (AZO), indium-doped zinc oxide (IZO), gallium-doped zinc oxide (GZO), doped titanium oxides, for example nitrogen-doped, phosphorus-doped, iron-doped, tungsten-doped or manganese-doped titanium oxide, tin oxides doped for example with fluorine, and mixtures thereof; and more particularly; among tin oxide (SnO2), doped zinc oxides, in particular aluminum-doped zinc oxide (AZO) and mixtures thereof.

7. A method for preparing a multilayer stack as defined according to any one of claims 1 to 6, comprising at least the following consecutive steps: (a) providing a structure having, on the surface, an N-type semiconductor layer, in the case of the formation of a NIP structure stack, or a P-type semiconductor layer in the case of the formation of a PIN structure stack, (b) forming, on the surface of said N-type or P-type conductive layer, a wet film from a solution of precursors of the perovskite material in one or more solvents; (c) adding to said wet film of step (b) at least one P-type material in the case of the formation of a NIP stack, and an N-type material in the case of a PIN stack; and (d) subjecting the assembly to a heat treatment conducive to the removal of the solvents and the crystallization of the perovskite material.

8. Method according to the preceding claim, in which step (c) is carried out by depositing, on the surface of said wet film of step (b), a formulation of at least one P-type material in the case of the formation of a PIN stack, also called "P-type ink", or N-type material in the case of the formation of a PIN stack, also called "N-type ink", in one or more solvents, called "anti-solvents", in which the perovskite precursors are not soluble.

9. A method according to claim 7 or 8, wherein steps (b) and (c) are carried out by spin coating, preferably step (c) being carried out without stopping the rotation of the turntable of the spin-coating device.

10. A method according to any one of claims 7 to 9, wherein said solvent(s) of the perovskite precursor solution are selected from dimethylformamide, dimethylsulfoxide, gamma-butyrolactone and mixtures thereof.

11. Method according to any one of claims 8 to 10, in which the said anti-solvent(s) of the P-type or N-type ink are chosen from diethyl ether; dichloromethane; aromatic compounds with one, two or three rings, substituted, in particular substituted by one or more alkyl groups, in particular methyl, and / or halogen, in particular chlorine, such as toluene, chlorobenzene, xylene, me- ethylnaphthalene; and mixtures thereof.

12. Method according to any one of claims 7 to 11, in which step (d) is carried out by thermal annealing at a temperature between 60 and 150°C, in particular between 80 and 120°C, in particular for a duration between 5 and 120 minutes, in particular between 15 and 90 minutes and more particularly between 30 and 60 minutes.

13. Photovoltaic device comprising at least one multi-layer stack as defined according to any one of claims 1 to 6 or obtained by a method as defined according to any one of claims 7 to 12.

14. Photovoltaic device according to the preceding claim, said device being a perovskite photovoltaic cell in NIP or PIN structure, preferably in NIP structure, or a multijunction type photovoltaic cell, in particular of tandem type.

15. Photovoltaic device according to the preceding claim, said device being a perovskite photovoltaic cell in NIP (23) or PIN (24) structure, and comprising in this order of superposition, at least: - a substrate (11), in particular transparent, flexible or rigid, such as a substrate made of glass or plastic, in particular PET; - a first electrode, called the lower electrode (12); - a multilayer stack as defined according to any one of claims 1 to 6, formed from said lower semiconducting layer and said composite layer; and - a second electrode, called the upper electrode (16).

16. Photovoltaic device according to claim 13, said device being a tandem type photovoltaic cell (26), comprising a first sub-cell, in particular based on crystalline silicon, on which is stacked a perovskite-based sub-cell comprising, in this order of superposition, at least: - a multilayer stack as defined according to any one of claims 1 to 6, formed of said lower semi-conductor layer and said composite layer; and - a transparent upper electrode, in particular made of transparent conductive oxide (TCO).

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