EP4055637A1

EP4055637A1 - N layer having a controlled carbon content in a perovskite-type photovoltaic device

Info

Publication number: EP4055637A1
Application number: EP20800137.0A
Authority: EP
Inventors: Matthieu Manceau; Stéphane Cros; Pia DALLY; Noëlla LEMAITRE
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: 2019-11-05
Filing date: 2020-11-03
Publication date: 2022-09-14
Also published as: WO2021089528A1; FR3102887B1; FR3102887A1

Abstract

The present invention relates to a multilayer stack used to form a photovoltaic device, the stack comprising at least: - an N-type conducting layer; - a P-type conducting layer; and - an active perovskite-type layer interposed between the N-type and P-type conducting layers, wherein the N-type conducting layer is made from individual nanoparticles of N-type metal oxide(s) and has a carbon content of less than or equal to 20 atomic%. The invention also relates to a method for preparing such a multilayer stack.

Description

Title: N LAYER WITH CARBON CONTROLS IN A PEROVSKITE TYPE VOUTAIC PHOTO DEVICE

The present invention relates to the field of photovoltaic devices, in particular photovoltaic cells of the perovskite type. It aims more particularly to propose the formulation of a new conductive layer of type N in the multilayer stacks useful for forming these photovoltaic devices, making it possible to achieve improved performance in terms of photovoltaic conversion efficiency.

Prior art

Photovoltaic devices, and in particular photovoltaic cells, comprise a multilayer stack comprising a photoactive layer, called an “active” layer. This active layer is in contact on both sides with an N-type conductive layer and a P-type conductive layer. This type of multilayer assembly, comprising the superposition of the active layer and the two P-type layers and of type N described above is conventionally called “NIP” or “PIN” according to the order of stacking of the different layers on the substrate. In so-called perovskite-type photovoltaic cells, the active layer consists of a halogenated perovskite-type material, which may be hybrid organic-inorganic or purely inorganic.

For example, a perovskite-type photovoltaic cell of NIP structure comprises a multilayer structure typically comprising, in this stacking order, a transparent substrate, a first transparent electrode also called a lower electrode, an N-type conductive layer, an active layer of perovskite type, a P-type conductive layer and a second electrode, also called an upper electrode made of metal, for example silver or gold.

In this type of perovskite photovoltaic cell, the N-type conductive layer usually consists of an N-type semiconductor oxide, for example ZnO, AZO (zinc oxide doped with aluminum), SnCh or TiO _x (x <2). This layer can be in the so-called mesoporous or planar form. The P-type conductive layer for its part consists, in the majority of cases, of an organic semiconductor material which can be a p-conjugated polymer, such as, for example, poly (3-hexylthiophene) or P3HT. , or even a small molecule like Spiro-MeOTAD (2,2 ', 7,7'-Tetrakis [N, N-di (4-methoxyphenyl) amino] - 9,9'-spirobifluorene).

At present, the best photovoltaic performances are obtained with devices for which a dense conductive layer based on N-type metal oxide (s) is obtained after a heat treatment at high temperature. , typically at temperatures strictly above 200 ° C. Such high temperature heat treatments, in particular at a temperature above 400 ° C, are for example implemented for the preparation of photovoltaic cells where the N layer is formed from a titanium oxide in mesoporous form. This is also the case for the production of N-type layers by the sol-gel route, in particular based on tin oxide (SnC) generated from an SnCT precursor.

The implementation of these heat treatments at high temperature is unfortunately not possible for the production of N layers on the surface of structures that do not withstand these high temperatures, for example for plastic substrates such as polyethylene terephthalate (PET) used. implemented for flexible photovoltaic devices, or even for heteroj unction silicon cells for “tandem” type photovoltaic devices.

To overcome this drawback, alternative methods have already been proposed which proceed with the preparation of the N layer at low temperature, typically at temperatures below 150 ° C. For example, an alternative to prepare a conductive layer of type N at low temperature for a photovoltaic cell in NIP structure, without impacting on the photovoltaic efficiency of the cell, consists in adding a layer of fullerene, for example in PCBM, between the N-type metal oxide and the overlying active layer of perovskite, to facilitate charge extraction. However, such a method is complex to implement, in particular in view of the fact that the thickness of the deposited fullerene layer must be extremely small, typically of the order of a few nanometers.

It has also been proposed, in order to prepare an N-type conductive layer under low temperature conditions, to carry out deposits via vacuum techniques, for example by a process for depositing thin atomic layers ALD (for “Atomic Layer Deposition”). in English terminology) or by evaporation under an electron beam. These techniques nevertheless remain more complex to implement. Consequently, there remains a need to be able to have an easy method of preparing an N-type conductive layer, under low temperature conditions and making it possible to achieve high photovoltaic yields.

Summary of the invention

The present invention aims specifically to provide a new method of preparing, at low temperature, a conductive layer based on conductive oxide (s) of type N in a multilayer stack useful for photovoltaic devices of the perovskite type, making it possible to achieve excellent performance, in particular in terms of photovoltaic performance.

Unexpectedly, the inventors have found that it is possible to produce photovoltaic devices, in particular photovoltaic cells of the perovskite type, exhibiting excellent performance, from a multilayer stack incorporating an oxide-based layer (s ) N-type metal (s), prepared at low temperature, subject to controlling the atomic concentration of carbon in said N layer.

More precisely, the present invention relates, according to a first of its aspects, to a multilayer stack useful for forming a photovoltaic device, said stack comprising at least:

- an N-type conductive layer, also called an "electron transport layer";

a P-type conductive layer, also called a “hole transport layer”; and

an active layer from the photovoltaic point of view, called “photo-active layer” or “active layer”, of perovskite type, interposed between said conductive layers of type N and of type P, in which said conductive layer of type N is at based on individualized nanoparticles of N-type metal oxide (s), and has a carbon content of less than or equal to 20 atomic%.

As detailed in the remainder of the text, a multilayer stack according to the invention may have a PIN or PIN structure, preferably a PIN structure. Such a multilayer stack of NIP structure according to the invention can more particularly comprise, in this order of superposition, at least:

a substrate, in particular transparent, flexible or rigid, such as a substrate made of glass or of plastic, for example of PET; a first electrode, called the lower electrode, in particular formed of a transparent conductive layer, in particular of transparent conductive oxide (s);

- an N-type conductive layer as defined above, in the case of a NIP structure, or a P-type conductive layer in the case of a PIN structure;

- an active layer of perovskite type;

- a P-type conductive layer in the case of a NIP structure, or an N-type conductive layer as defined above, in the case of a PIN structure; and

- a second electrode, called the upper electrode.

The invention also relates to a process for preparing such a multilayer stack, comprising at least one step of forming said N-type conductive layer, from a dispersion of nanoparticles of metal oxide (s) of type N in a solvent medium, at a temperature less than or equal to 150 ° C, and under operating conditions adjusted to obtain the desired carbon content in said N layer.

As illustrated in the examples which follow, the control of the carbon content in the N-type layer, formed under conditions of low temperature, makes it possible to access devices exhibiting excellent photovoltaic performance, in particular in terms of efficiency of photo voltaic conversion.

As detailed in the remainder of the text, according to a first alternative embodiment, the carbon content in the N-type layer formed according to the invention can be adjusted by implementing a dispersion of nanoparticles of metal oxide (s). ) exhibiting a reduced content of carbon precursor compounds, such as to make it possible to produce the desired carbon content, less than or equal to 20 atomic%, in the N layer formed. Such dispersions of nanoparticles of metal oxide (s) are, for example, dispersions stabilized via the surface potential of the nanoparticles and having a reduced content of compatibilizing agents.

According to another alternative embodiment, the carbon content in the N-type layer formed according to the invention can be adjusted by subjecting, after deposition of said dispersion of nanoparticles of metal oxide (s) and prior to the deposition of the overlying layer, the N-type layer, to a treatment for removing carbon, in particular by treatment by UV irradiation, by UV-ozone, with ozone and / or by plasma, in particular oxidizing. Furthermore, advantageously, the low temperature conditions, preferably less than or equal to 120 ° C, advantageously less than or equal to 100 ° C, in particular less than or equal to 80 ° C and more particularly less than or equal to 50 ° C, allow the formation of the N layer in stacks of various kinds, in particular at the surface of structures sensitive to high temperatures, for example structures incorporating plastic substrates such as PET.

In particular, the process for preparing an N layer according to the invention at low temperature makes it possible to envisage its formation on the surface of an active layer of perovskite type in the case of a stack in the PIN structure.

As detailed in the remainder of the text, a multilayer stack according to the invention can be intended for perovskite photovoltaic devices, in particular single-junction photovoltaic cells, in a structure known as of the “PIN” or “NIP” type, or else photovoltaic cells of. multi-junction type, in particular tandem type.

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

Other characteristics, variants and advantages of a multilayer stack according to the invention, and of its preparation, will emerge more clearly on reading the description, the examples and figures which follow, given by way of illustration and without limitation of the invention.

Brief description of the drawings

[Fig 1] shows, schematically, in a vertical sectional plane, multilayer stacks according to the invention, of NIP structure (21) or PIN structure (22).

[Fig 2] shows the change in the carbon atomic concentration in an N layer based on AZO nanoparticles as a function of the duration of the UV-ozone treatment, under the conditions of Example 2.

It should be noted that, for reasons of clarity, the various elements in FIG. 1 are shown in free scale, the actual dimensions of the various parts not being respected. In the remainder of the text, the expressions "between ... and ..." and "ranging from ... to ..." and "varying from ... to ..." are equivalent and are intended to mean that the terminals are included, unless otherwise stated.

detailed description

Multilayer stacking

As indicated above, the invention relates, according to a first of its aspects, to a multilayer stack, useful for forming a photovoltaic device, said stack comprising at least:

- an N-type conductive layer;

- a P-type conductive layer; and

- a photovoltaic active layer, called “active layer”, of perovskite type, interposed between said conductive layers of N type and of P type, in which said N type conductive layer is based on individualized nanoparticles of metal oxide (s) (s) of type N, and has a carbon content of less than or equal to 20 atomic%.

N-type conductive layer

An N-type conductive layer according to the invention is more simply referred to in the remainder of the text as "N layer".

An "N-type" material designates a material which allows the transport of electrons (e).

The N layer according to the invention can be more particularly formed of individualized nanoparticles of N-type metal oxide (s).

The N-type metal oxide nanoparticles can in particular be chosen from nanoparticles of zinc oxide ZnO, titanium oxides TiO _x with x between 1 and 2, tin oxide (SnC), doped zinc oxides, e.g. aluminum doped zinc oxide (AZO), indium doped zinc oxide (IZO), gallium doped zinc oxide (GZO), oxides titanium doped, for example titanium oxide doped with nitrogen, phosphorus, iron, tungsten or manganese, and mixtures thereof.

In particular, the N-type conductive layer according to the invention can be formed from nanoparticles of metal oxide (s) chosen from nanoparticles of tin oxide. (S11O2), nanoparticles of doped zinc oxide, in particular zinc oxide doped with aluminum (AZO), and mixtures thereof.

The individualized particles of N-type metal oxide (s) of the N-type conductive layer in a multilayer stack according to the invention may have an average particle size of between 2 to 100 nm, in particular between 5 to 50 nm, in particular between 5 and 20 nm and more particularly between 8 and 15 nm.

Particle size can be assessed by transmission electron microscopy.

In the case of particles of spherical or generally spherical shape, the average particle size refers to the diameter of the particle. If the particles are irregularly shaped, the particle size refers to the equivalent diameter of the particle. By equivalent diameter is meant the diameter of a spherical particle that exhibits the same physical property when determining the particle size as the irregularly shaped particle measured.

The nanoparticles of N-type metal oxide (s) can in particular be of spherical shape. By "spherical particle" is meant particles having the shape or substantially the shape of a sphere.

In particular, spherical particles have a coefficient of sphericity greater than or equal to 0.75, in particular greater than or equal to 0.8, in particular greater than or equal to 0.9 and more particularly greater than or equal to 0.95.

The coefficient of sphericity of a particle is the ratio of the smallest diameter of the particle to the largest diameter of the particle. For a perfect sphere, this ratio is equal to 1.

By "individualized" nanoparticles is meant that the particles retain their state of individual particles within the N layer of the multilayer stack according to the invention, in particular that they are not fused.

In particular, less than 10% of the nanoparticles of N-type metal oxide (s) in said N layer are fused, preferably less than 5%, or even less than 1%.

This can be clearly visualized for example by observation of the N layer by electron microscopy. An N layer based on individualized N-type metal oxide (s) nanoparticles is distinguished in particular from sintered layers, in which the particles have fused to each other. An N layer according to the invention is thus an unsintered layer.

The structuring of the N-type layer in a stack according to the invention testifies in particular to the fact that its preparation, as detailed in the remainder of the text, does not involve any step of heat treatment at high temperature, typically at a strictly higher temperature. at 150 ° C, especially above 200 ° C.

The presence of individualized N-type metal oxide (s) particles, in other words non-fused, at the N-type layer according to the invention can also be manifested by a surface roughness of said layer of type. N, measured before formation of the overlying layer, greater than that obtained for example for a sintered layer.

In particular, an N layer according to the invention may have an average RMS roughness value greater than or equal to 3 nm, in particular between 5 and 10 nm.

Surface roughness can be measured by mechanical profilometry.

An N-type conductive layer according to the invention is also characterized by a low carbon content (atomic carbon concentration), in particular less than or equal to 20 atomic%.

Preferably, an N layer according to the invention has a carbon content of less than or equal to 17 atomic%, preferably less than or equal to 15 atomic%, in particular between 0 and 15 atomic%.

The carbon content of an N layer according to the invention can be determined by X-ray induced photoelectron spectrometry (XPS for "X-Ray photoelectron spectrometry").

An N-type conductive layer according to the invention may have a thickness of between 10 and 80 nm, in particular between 30 and 50 nm.

The thickness can be measured with a profilometer, for example of the trade name KLA Tencor or else with an AFM atomic force microscope, for example of the trade name VEECO / INNOVA. Other layers of the multilayer stack

Active Layer of Perovskite Type As indicated above, a multilayer stack according to the invention comprises at least one active photovoltaic layer of perovskite type.

This active layer is formed from a perovskite material, and more particularly 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 halogens, and more particularly chosen from chlorine, bromine, iodine and mixtures thereof.

Such perovskite materials are described in particular in document WO 2015/080990. By way of example of perovskite materials, mention may in particular be made of organic-inorganic hybrid perovskites. These hybrid perovskite materials can be more particularly of the abovementioned formula ABX3, in which A comprises one or more organic or non-organic cations.

The organic cation can be chosen from organo-ammonium cations such as:

- alkylammonium cations of general formula RIR2R3R4N ⁺ , with Ri _, R2 _, R3 and R4 being, independently of one another, a hydrogen atom or a C1-C5 alkyl radical, such as for example a cation of the type methyl ammonium (MA) and

- formamidinium cations (FA) of formula [RiNCHNRi] ⁺ , with Ri possibly representing a hydrogen atom or a C1-C5 alkyl radical.

The organic cation (s) of the hybrid perovskite material may optionally be combined with one or more metal cations, for example cesium and / or rubidium.

As examples of hybrid perovskite materials, mention may more particularly be made of perovskites of formula ABX3, with:

- A representing an organo-ammonium cation, for example of methylammonium (MA) type, a formamidinium (FA) cation or a mixture of these two cations, optionally combined with cesium;

- B being chosen from lead, tin, bismuth, antimony and their mixtures; and

- X being chosen from chlorine, bromine, iodine and their mixtures. The perovskite material can in particular be CH3NH3PM3, 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.

The perovskite material may also be a compound of the formula Cs _x _FAI-x Pb (II Br _y _y) 3 with x <0.17; 0 <y <1 and FA symbolizing the formamidinium cation.

P-type conductive layer

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

The P-type material can be chosen, for example, from Nafion, WO3, M0O3, V2O5 and NiO, p-conjugated semiconductor polymers, optionally doped, and mixtures thereof. By way of illustration of p-conjugated semiconductor polymers, optionally doped, mention may in particular be made of poly (3,4-ethylenedioxythiophene) (PEDOT), preferably PEDOT: PSS; poly (3-hexylthiophene) or P3HT, poly [N-9'-heptadecanyl-2,7-carbazole-alt-5,5- (4,7-di-2-thienyl-2 ', l', 3 '-benzothiadiazole 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 [l, 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.

A preferred P-type material is a mixture of PEDOT and PSS, or alternatively PT AA, optionally doped with a lithium salt.

The P-type material can also be chosen from P-type semiconductor molecules such as:

- porphyrin;

- les: 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] thiadiazole): p-DTS (FBTTh2) 2;

- boron-dipyromethenes (BODIPY);

- molecules with a triphenylamine nucleus (TPA).

As indicated above, a multilayer stack according to the invention may be intended for a photovoltaic device, in particular a perovskite photovoltaic cell, in a PIN or NIP type structure, or else of the tandem type. The “PIN” or “PIN” structure reflects the order of superposition of the different layers in the multilayer stack.

Preferably, the multilayer stack according to the invention is in a so-called NIP structure. Such a stack comprises, in this order of superposition:

- an N-type conductive layer as defined above,

- an active layer of perovskite type, and

- a P-type conductive layer.

Alternatively, in the case of a so-called PIN structure, a multilayer stack according to the invention comprises, in this order of superposition, the following layers:

- a P-type conductive layer,

- an active layer of perovskite type, and

- an N-type conductive layer as defined above.

A stack according to the invention, in particular intended for a photovoltaic cell, of the perovskite type, in the NIP or PIN structure, may more particularly include, as shown in FIG. 1, in this order of superposition at least:

- a substrate 11, in particular transparent, flexible or rigid, such as a substrate made of glass or of plastic, in particular of PET;

- a first electrode, called the lower electrode 12;

- a conductive layer of type N 13 in the case of a NIP structure or of type P 15 in the case of a PIN structure;

an active layer of perovskite type 14;

- A conductive layer of type P 15 in the case of a NIP structure or of type N 13 in the case of a PIN structure; and

- a second electrode, called the upper electrode 16; said layers of N type, of type P, and said active layer of perovskite type being in particular as described above.

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.

Such a multilayer structure is shown schematically in FIG. 1. A multilayer stack in NIP structure according to the invention 21 more particularly comprises, in this order of superposition, at least:

- a substrate 11, in particular transparent;

- a lower electrode 12;

- An N-type conductive layer according to the invention as defined above 13;

an active layer of perovskite type 14;

a P-type conductive layer 15; and

- an upper electrode 16.

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

Such tandem-type cells have two multilayer assemblies stacked on top of each other, and the respective active layers of which generally exhibit different light absorption spectra. In these tandem cells, photons not absorbed by the first active layer may 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.

A tandem type photovoltaic device according to the invention may include a stack according to the invention, in a PIN or PIN structure, preferably in a PIN structure, as described above.

It may be, for example, a perovskite silicon tandem cell.

The substrate 11 implemented in a multilayer stack according to the invention as described above, for example, for a photovoltaic cell of the perovskite type, refers to a solid base structure, on one of the faces of which the electrode is formed. lower. It can come in the form of a plaque. It can be soft (flexible) or rigid.

It can be of various kinds, for example glass or plastic, in particular polyester, preferably polyethylene terephthalate (PET), polyethylene naphthalate (PEN) or polycarbonates. It may in particular be a glass plate.

The lower electrode 12, in contact with the support, may be formed of a transparent conductive layer, for example of transparent conductive oxide (s) (TCO) such as indium oxide doped with l 'tin (ITO), zinc oxide doped with aluminum (AZO), zinc oxide doped with gallium (GZO), zinc oxide doped with indium (IZO) and mixtures thereof, or still be formed of a multilayer assembly, for example AZO / Ag / AZO.

It can also be formed by an array of nanowires, in particular made of silver.

The upper electrode 16 can, for example, be formed by a layer of gold, of silver, or of an array of nanowires, preferably of silver. It can also be in aluminum or in transparent conductive oxide.

PROCESS FOR PREPARING A STACK ACCORDING TO THE INVENTION

As indicated above, the process for preparing a stack according to the invention comprises at least one step of forming an N-type conductive layer according to the invention, at low temperature, in particular at a temperature less than or equal to 150 ° C, preferably less than or equal to 100 ° C and more preferably less than or equal to 80 ° C, from a dispersion of nanoparticles of N-type metal oxide (s) in a solvent medium and in operating conditions adjusted to obtain the desired reduced carbon content in the N layer formed.

Said N-type conductive layer can advantageously be formed under temperature conditions less than or equal to 120 ° C, in particular less than or equal to 100 ° C, in particular less than or equal to 80 ° C, preferably less than or equal to 50 ° C, and more particularly at room temperature

It is understood that, according to the NIP or PIN structure of the multilayer stack according to the invention, the N-type layer according to the invention is formed on the surface of the lower electrode or, alternatively, on the surface of an active layer of perovskite type, as described above. In the case of the formation of an N-type layer according to the invention in a multilayer stack of NIP-type structure according to the invention, the method according to the invention can more particularly comprise at least the steps consisting in:

(a) have a first electrode 12, called the lower electrode, supported by a substrate 11;

(b) forming, on the surface of said lower electrode 12, an N-type conductive layer 13 according to the invention, at a temperature less than or equal to 150 ° C, preferably less than or equal to 100 ° C and more preferably less, or equal to 80 ° C, from a dispersion of nanoparticles of N-type metal oxide (s) in a solvent medium, under operating conditions adjusted to obtain a level of carbon in the N layer that is less than or equal at 20 atomic%; and

(c) successively forming, on the surface of said N-type conductive layer 13 formed at the end of step (b), in this order of superposition: an active layer 14 of perovskite type, a conductive layer 15 of the type P and a second electrode 16, called the upper electrode, in particular as defined above.

More particularly, the formation of said N-type layer by the solvent route according to the invention involves the deposition of said dispersion of nanoparticles of metal oxide (s), followed by the elimination of said solvent or solvents.

The dispersion can be deposited by means of any technique known to those skilled in the art, for example chosen from spin coating or centrifugal coating (“spin coating”), deposition with a scraper, blade coating, ultrasonic spray deposition, G slot-die coating, inkjet printing, gravure printing, flexography and screen printing. Preferably, the deposition is carried out by spin-coating.

The solvent medium for said dispersion of nanoparticles of metal oxide (s) can comprise one or more solvents chosen from polar solvents, such as water and / or alcohols, or of ether type (for example alkyl ethers and glycol ethers) or esters (acetate, benzoate or lactones for example). It may for example consist of water and / or an alcohol, such as butanol. Of course, the nature of the solvent (s) is chosen with regard to the nature of the underlying layer on the surface of which said N-type conductive layer is formed.

It is understood that the removal of said solvent (s) is carried out under temperature conditions less than or equal to 150 ° C, in particular less than or equal to 120 ° C, preferably less than or equal to 100 ° C and more preferably less than or equal to 80 ° C. The drying of the N layer can for example be carried out at room temperature. By "ambient temperature" is meant a temperature of 20 ° C ± 5 ° C.

According to a first variant embodiment, the level of carbon in the N-type conductive layer is adjusted by controlling the content of carbon precursor compounds in the dispersion of nanoparticles of metal oxide (s) used.

In other words, the N-type layer according to the invention can be formed by depositing a dispersion of nanoparticles of metal oxide (s) having a content of carbon precursor compounds such that the resulting N layer exhibits the rate of desired residual carbon, less than 20 atomic%.

The dispersions of nanoparticles of metal oxide (s) having a reduced content of carbon precursor compounds are in particular dispersions having a low content of compatibilizing agents. Such dispersions more particularly comprise less than 5% by mass, in particular less than 1% by mass, of compatibilizing agent (s), relative to the total mass of the dispersion.

Such dispersions are in particular dispersions of nanoparticles stabilized via the surface potential (zeta potential) of the particles, more precisely by the use of counterions.

Such colloidal dispersions of nanoparticles of metal oxide (s) may, for example, be commercially available.

According to another variant embodiment, the carbon content in the N layer formed can be adjusted, after depositing the dispersion of nanoparticles of metal oxide (s) and prior to depositing the overlying layer in the multilayer stack, for example prior to the deposition of the active perovskite layer in the case of a stack multilayer in NIP structure, by subjecting the N-type layer to a carbon removal treatment.

It is understood that the carbon removal treatment is carried out under low temperature conditions, in particular at a temperature less than or equal to 150 ° C, in particular less than or equal to 120 ° C, in particular less than or equal to 100 ° C, preferably less than or equal to 80 ° C, and more particularly less than or equal to 50 ° C. Advantageously, the carbon removal treatment is carried out at room temperature. Such a carbon removal treatment can more particularly be a treatment by UV irradiation, by UV-ozone, with ozone and / or by plasma, in particular an oxidizing one.

As part of the implementation of such a carbon removal treatment, it is possible to obtain said N-type conductive layer, having the desired carbon content of less than 20 atomic%, from any dispersion of nanoparticles of metal oxide (s), regardless of the carbon content of said dispersion.

Of course, in a particular embodiment of a multilayer stack according to the invention, it is possible to combine the two aforementioned variants to achieve the desired carbon content in the N-type conductive layer formed.

Those skilled in the art are able to adjust the operating conditions for carrying out the carbon removal treatment, in particular the duration of exposure of the free surface of said N layer to UV, UV-ozone, to l. ozone or a plasma, in particular an oxidizer, to achieve the desired reduced carbon content according to the invention.

The treatment under UV radiation can more particularly consist in irradiating the free surface of said N layer formed by UV light of two wavelengths, for example 185 and 256 nm.

Any UV light source making it possible to irradiate the surface of said N layer can be used for such irradiation. One example is a mercury vapor lamp.

The treatment of said layer by UV irradiation can be carried out for a period ranging from 5 to 60 minutes, in particular from 10 to 30 minutes.

As indicated above, it is operated under low temperature conditions. Preferably, the UV irradiation is carried out at a temperature less than or equal to 150 ° C, in particular less than or equal to 100 ° C, preferably less than or equal to 80 ° C, and more particularly less than or equal to 50 ° C. More particularly, the UV irradiation is carried out at room temperature.

The UV irradiation treatment can be carried out in a vacuum or in a gas.

The UV irradiation treatment can in particular be carried out in an ambient atmosphere, the UV radiation then transforming the oxygen in the air into ozone; we speak in this case of UV-ozone treatment.

The UV irradiation treatment can also be carried out under an inert gas such as nitrogen.

According to another particular embodiment, the carbon removal treatment can be an ozone treatment (in the absence of UV irradiation).

Such ozone treatment can be carried out, for example, by bringing the free surface of the N layer into contact with an atmosphere containing ozone generated by UV irradiation, the sample being placed behind a filter protecting it from said radiation.

According to yet another variant embodiment, the elimination of carbon can be carried out by plasma treatment, in particular with an oxidizing plasma.

Oxidizing plasma is, for example, a plasma comprising oxygen or a plasma of a mixture of oxygen and argon. Preferably, the treatment is carried out with an oxygen plasma. A person skilled in the art is able to use the equipment necessary to generate such a plasma.

The other layers of the multilayer stack according to the invention can be made by techniques known to those skilled in the art. Advantageously, they are carried out wet, by conventional deposition techniques, that is to say by techniques implementing the deposition of an ink in the liquid state.

In particular, the deposition of a solution during the manufacturing process, in particular to form a conductive layer of type P and an active layer of perovskite type, can be carried out by means of a technique as described above for the preparation. an N-type conductive layer. In particular, all the layers formed during the process steps can be carried out using a single technique chosen from those described above.

The photovoltaic device may also include electrical connection means, in particular contact points, which make it possible to connect the electrodes in order to supply an electrical circuit with current.

The invention will now be described by means of the following examples, given of course by way of illustration and not limiting the invention.

Example

In the following examples, different N layers are tested in a stack of a perovskite-type photovoltaic cell, in "NIP" structure, as shown schematically in Figure 1.

- The support 11 is a 1.1 mm thick glass substrate covered with a layer of ITO conductive oxide forming the lower electrode 12.

- Two types of perovskite materials are tested: of the CH3NH3PM3 type (also noted MAPbL) or of the “double cation” perovskite type Cs _x FAi- _x Pb (I _y Bri- _y ) 3, FA symbolizing the formamidinium cation.

- The N-type layer 13 is formed as described below.

- The P-type layer 15 is composed of PT AA doped with a lithium salt, 80 nm thick.

- The upper electrode 16 is a layer of gold, 100 nm thick.

The active surface of the devices is 0.28 cm ² and their performance was measured at 25 ° C. under standard lighting conditions (1000 W / m ² , AM 1.5G).

The photovoltaic performances of the cells are more particularly measured by recording the current-voltage characteristics of the devices on a Keithley ^® SMU 2600 device under AM 1.5G illumination at a power of 1000 Wm ² .

The cell under test is illuminated through the Glass / ITO face using an Oriel simulator. A mono-crystalline silicon cell calibrated at the Fraunhofer ISE (Friborg, Germany) is used as a reference to ensure that the light power delivered by the simulator is indeed equal to 1000 Wm ² .

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

Example 1 ink containing a controlled carbon content

Different N tin oxide (SnCh) layers are tested in a stack as described above.

The N layers, approximately 50 nm thick, are formed by spin-coating, operated at room temperature, from separate commercial solutions (called "inks") of SnCL nanoparticles:

- two dispersions of SnCh particles in water (Disp 1 and Disp 2), stabilized via the surface charge of the particles, and which differ from each other in the nature of the counterions; and

- a dispersion (denoted Disp 3) of SnCL particles in a mixture of butanols.

For these three dispersions, the particle size of SnCh is in the range of 10-15 nm.

Dispersions 1 and 2 contain a reduced content of compatibilizers, a source of carbon, compared to dispersion 3.

Dispersions 1 and 2 lead, after application by spin-coating, to layers of SnCh nanoparticles containing approximately 15 atomic% of carbon, while dispersion 3 results in a layer of SnCL containing approximately 40 atomic% of carbon. The carbon content (atomic concentration) is determined by X-ray induced photoelectron spectrometry (XPS for “X-Ray photoelectron spectrometry”).

No post-deposition treatment of the N layers thus formed is carried out.

Results The carbon content for each of the N layers formed, as well as the performances of the various photovoltaic cells formed with a multilayer stack integrating each of these N layers, are presented in Table 1 below.

[Table 1]

Example 2

Formation of the N-type conductive layer with control of the carbon content by post-deposition treatment of carbon removal

Different N layers of zinc oxide doped with aluminum (AZO) and tin oxide (SnC) are tested in a stack as described above, comprising a perovskite layer of MAPbL type.

The N layers, with a thickness of about 50 nm, are formed at room temperature, by spin-coating from separate commercial solutions of AZO or SnCh nanoparticles, if necessary followed by an elimination treatment. carbon, by UV irradiation, by UV-ozone or by ozone, as detailed below.

Dispersion 4 (Disp 4) is a dispersion of particles of ZnO doped Al or AZO, of average size 12 nm, in 2-propanol.

The UV irradiation treatment of the N layer, after depositing the dispersion by spin coating, is carried out for 30 minutes, at a wavelength of 185 nm and 256 nm, under an inert atmosphere and room temperature.

The UV-ozone treatment is carried out by exposure to UV radiation generating ozone of the surface of the N layer, after deposition of the dispersion by spin-coating, under ambient atmosphere and temperature, for 30 minutes in equipment for the JetLight brand. The ozone treatment is carried out in the same JetLight equipment and under the same conditions, except that the sample is placed behind a filter avoiding exposure to UV radiation but suitable for exposure to ozone generated during 30 minutes.

The different treatments (UV irradiation, UV-ozone, ozone) make it possible to reduce the carbon content of the deposited layer. By way of example, FIG. 2 represents the evolution of the carbon content in an N layer based on AZO nanoparticles as a function of the duration of the UV-ozone treatment.

Results The carbon content for each of the N layers thus formed, after the carbon removal treatment, as well as the performance of the various photovoltaic cells formed from the multilayer stacks integrating each of these N-type conductive layers, are presented in the table 2 below. [Table 2]

Claims

1. Multilayer stack useful for forming a photovoltaic device, said stack comprising at least:

- an N-type conductive layer (13);

- a P-type conductive layer (15); and

an active layer from the photovoltaic point of view (14), called an active layer, of perovskite type, interposed between said conductive layers of N type and of P type, in which said N type conductive layer is based on individualized nanoparticles of N-type metal oxide (s) and has a carbon content of less than or equal to 20 atomic%; said nanoparticles of metal oxide (s) having an average particle size of between 5 and 20 nm.

2. Multilayer stack according to the preceding claim, wherein said nanoparticles of N-type metal oxide (s) are chosen from nanoparticles of zinc oxide ZnO, titanium oxides TiO _x with x between 1 and 2, tin oxide SnCh, doped zinc oxides, eg zinc oxide doped with aluminum AZO, zinc oxide doped with indium IZO, doped zinc oxide with gallium GZO, doped titanium oxides, for example titanium oxide doped with nitrogen, phosphorus, iron, tungsten or manganese; and their mixtures; in particular from nanoparticles of tin oxide SnCh, nanoparticles of doped zinc oxide, in particular of zinc oxide doped with AZO aluminum, and mixtures thereof.

3. A multilayer stack according to any one of the preceding claims, wherein said nanoparticles of metal oxide (s) have an average particle size of between 8 and 15 nm.

4. Multilayer stack according to any one of the preceding claims, in which said N-type conductive layer has a carbon content of less than or equal to 17 atomic%, preferably less than or equal to 15 atomic%, in particular between 0 and 15% atomic.

5. A multilayer stack according to any one of the preceding claims, wherein said perovskite-like active layer is formed of a perovskite material 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

6. Multilayer stack according to any one of the preceding claims, said stack being of NIP or PIN structure, in particular 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 of plastic, in particular of polyethylene terephthalate;

- a first electrode (12), called the lower electrode, in particular formed of a transparent conductive layer, in particular of transparent conductive oxide (s);

- said N-type conductive layer (13) in the case of a NIP structure or of P-type (15) in the case of a PIN structure;

- said active layer of perovskite type (14);

- said P-type conductive layer (15) in the case of a NIP structure or of N-type (13) in the case of a PIN structure; and

- a second electrode (16), called the upper electrode.

7. A method of preparing a multilayer stack as defined according to any one of claims 1 to 6, comprising at least one step of forming said N-type conductive layer from a dispersion of oxide nanoparticles ( s) N-type metal (s) in a solvent medium, at a temperature less than or equal to 150 ° C, and under operating conditions adjusted to obtain the desired carbon content in said N layer.

8. Method according to the preceding claim, wherein said N-type conductive layer is formed at a temperature less than or equal to 120 ° C, in particular less than or equal to 100 ° C, in particular less than or equal to 80 ° C, preferably. less than or equal to 50 ° C, and more particularly at room temperature.

9. The method of claim 7 or 8, wherein the level of carbon in said N-type conductive layer is controlled by adjusting the content of carbon precursor compounds of the dispersion of nanoparticles of metal oxide (s) placed. implementation, in particular by using a dispersion of nanoparticles of metal oxide (s) stabilized via the surface potential of the nanoparticles.

10. A method according to any one of claims 7 to 9, wherein the level of carbon in said N-type conductive layer is controlled, by subjecting, after deposition of said dispersion of nanoparticles of metal oxide (s) (s) and prior to the deposition of the overlying layer, the N-type layer undergoes a carbon removal treatment, in particular by UV irradiation, by UV-ozone, with ozone and / or by plasma, in particular oxidizing; preferably by treatment with UV irradiation, UV-ozone and / or ozone.

11. A method according to any one of claims 7 to 10, for the preparation of a multilayer stack of NIP structure, said method comprising at least the steps consisting in: (a) having a first electrode (12), said lower electrode, supported by a substrate (11);

(b) forming, on the surface of said lower electrode (12), said N-type conductive layer (13); and

(c) forming, successively, on the surface of said N-type conductive layer (13) formed in step (b), in this order of superposition: an active layer (14) of perovskite type, a conductive layer (15) of type P and a second electrode (16) called the upper electrode.

12. Photovoltaic device comprising at least one multilayer stack as defined in any one of claims 1 to 6 or obtained by a process as defined in any one of claims 7 to 11.

13. 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 multi-junction type photovoltaic cell, in particular of the tandem type.