EP2839523A1 - Method for preparing a photovoltaic thin film having a heterojunction - Google Patents

Abstract

The present invention relates to a method for preparing a photovoltaic thin film having a heterojunction by depositing a composition, including a first organic electron-donor semiconductor C_P and a second organic electron-acceptor semiconductor C_N, onto a substrate and then carrying out phase segregation, including: a step (E1) of preparing a first mixture M1 including the organic semiconductors C_N and C_P within a solvent medium; and then a step (E2) of adding an additive, having at least one N3 function, to said mixture.

Description

 Process for the preparation of a photovoltaic thin film

 heterojunction

Field of the invention

The present invention relates to a process for the preparation of a heterojunction-type photovoltaic thin film, of the type implementing a deposit on a support of a composition comprising a first organic semiconductor C _P , of the donor type. electron, and a second organic semiconductor C _N , electron acceptor type, then phase segregation. The method of the invention is a particular method of this type, which allows, more specifically, access to a thermal stabilization of the layer produced.

State of the art

Various methods for the preparation of a heterojunction photovoltaic thin film (bulk or bulk heterojunction) are known, in particular based on mixtures of fullerene derivatives and polythiophene derivatives. It is also well known that obtaining good yields with this type of thin layer requires obtaining phase domains of the order of the diffusion length of the excitons which are photogenerated in each of the materials (less than 40 nm typically).

 A recurring problem with this type of thin layer is their instability over time, in particular their thermal instability. Under the effect of heat in particular, the morphology of the layer tends to evolve over time, which generally leads to a growth in the size of the domains, and therefore to a loss of the efficiency of the photovoltaic efficiency. Since photovoltaic cells operate under direct light radiation which is typically sunlight, they are frequently subjected to high temperatures (60 to δΟ 'Ό typically for a solar cell used on a roof) and they see their effectiveness. falling over time, which is one of the major obstacles to the exploitation of organic heterojunction photovoltaic cells.

Presentation of the invention

An object of the present invention is to provide an effective method for thermally stabilizing heterojunction photovoltaic thin films of the aforementioned type. For this purpose, the present invention proposes the use of particular crosslinking agents in the synthesis medium, namely compounds bearing azide functional groups, typically intermolecular crosslinking agents bearing at least two azide functional groups (alternatively, as described above). hereinafter, all or part of the organic semiconductors modified with azide functional groups may be functionalized, in which case the presence of a single azide function by modified semiconductor is sufficient to ensure the crosslinking), and to delay crosslinking effect of the azide functions up to the moment of phase segregation (typically by programming this crosslinking of the azide functions just at the moment when the phase segregation takes place), in particular by employing the crosslinking agents at a sufficiently low temperature beforehand.

More specifically, the subject of the present invention is a process for the preparation of a heterojunction photovoltaic thin film, by deposition on a support of a composition comprising a first organic semiconductor, hereinafter referred to as C _P , of the following type: electron donor, and a second organic semiconductor designated hereinafter by C _N , electron acceptor type, then phase segregation, said method comprising the following steps:

one or more steps are carried out, a mixture M comprising the semiconductors C _P and C _N and crosslinking agents bearing azide groups in a solvent adapted to phase segregation, under conditions of sufficiently low temperature to inhibit the precipitation by crosslinking of one and / or the other of the two organic semiconductors by reaction of the crosslinking agents; then

the mixture M thus produced is deposited on all or part of the surface of a support and the phase segregation is carried out, by raising the temperature during or after this phase segregation and / or by subjecting the reaction medium to UV radiation of wavelength adapted to be placed under conditions where the crosslinking additive reacts to form covalent bonds with at least a portion of the organic semiconductors, whereby a crosslinking within the thin layer is obtained realized photovoltaic. According to a first embodiment, intermolecular crosslinking agents other than the C _P and C _N semiconductors are used according to the invention. In this case, the method of the invention typically comprises the following steps:

(E1) preparing a first mixture M1 comprising organic semiconductors C _N and C _P in a solvent medium; then

(E2) is added to this mixture M1 a crosslinking additive bearing at least two azide functional groups and optionally a solvent, under conditions of sufficiently low temperature to inhibit the precipitation by crosslinking of one and / or the other of the two organic semiconductors with the crosslinking additive during step (E2), so as to form a mixture M comprising the semiconductors C _P and C _N and the additive in a solvent adapted to phase segregation (in step (E2), the temperature is raised and / or the reaction medium is subjected to UV radiation of suitable wavelength during or after the phase segregation, and typically only after the segregation of phase); then

 (E3) the mixture M thus produced is deposited on all or part of the surface of a support and the phase segregation is carried out, by raising the temperature during or after this phase segregation and / or by subjecting the reaction medium to a UV radiation of wavelength adapted to be placed under conditions where the crosslinking additive reacts to form covalent bonds with at least a portion of the organic semiconductors, whereby a crosslinking within the Photovoltaic thin layer realized.

According to a second embodiment, the azide functions inducing the crosslinking are carried by all or part of the semiconductors C _P and C _N , the azide functions preferably being carried by the semiconductors C _N , the acceptor character of which they do not modify. According to this embodiment, it is generally not necessary to employ intermolecular crosslinking agents of the type used in the first variant, but the implementation of such agents is not however excluded in the second embodiment according to the invention. certain particular variants. In its second embodiment, the method of the invention typically comprises the following steps:

(E1) preparing a first mixture M1 comprising only part of the organic semiconductors C _N and C _P in a solvent medium; then

(E2) is added to this mixture M the remainder of organic semiconductors, previously modified by grafting azide functions and optionally a solvent, under conditions of sufficiently low temperature to inhibit the precipitation by crosslinking of one and / or the other of the two organic semiconductors with the crosslinking additive during step (E2), so as to forming a mixture M comprising the semiconductors C _P and C _N , part of which is modified by azide functions in a solvent adapted to phase segregation; then

(E3) the mixture M thus produced is deposited on all or part of the surface of a support and the phase segregation is carried out; and, during or after this phase segregation, and typically only after the phase segregation, the temperature is raised and / or the reaction medium is subjected to UV radiation of wavelength adapted so as to be placed in conditions where the crosslinking additive reacts to form covalent bonds with at least a part of the organic semiconductors, whereby a crosslinking is obtained within the photovoltaic thin film produced. In this second embodiment, the steps (E1) and (E2) are generally distinct, but the process may alternatively comprise the steps (E1) and (E2) fused in a single step of preparing the mixture M by mixing the semiconductor assembly (functionalized and non-functionalized) in a suitable solvent. According to the second embodiment mentioned above, whether or not the steps (E1) and (E2) are merged, the organic semiconductors, previously modified by grafting azide functional groups, act as crosslinking agents in the step (E3). ). These organic semiconductors previously modified by grafting azide functional groups are preferably organic C _n semiconductors functionalized with at least one group carrying at least one azide function. Typically, the mixture M1 used in the step (E1) comprises only part of the organic semiconductors C _N and all the organic semiconductors C _P and is added during the step (E2) the rest of the organic semiconductors C _N , previously functionalized with at least one group carrying at least one azide function, to form the mixture M.

According to this embodiment, the functionalization of the organic semiconductors by at least one azide group can be carried out according to any means known per se. In particular, it can be carried out starting from semiconductors bearing ester functions -COOAlk where Alk represents an alkyl group, for example the PCBM ([6,6] -phenyl-C ₆ i-methyl butyrate, described in more detail below) by hydrolysis of the ester function and esterification of the acid function obtained at the end of the hydrolysis with a compound of formula HO-AN ₃ , where A is a hydrocarbon chain, typically an alkylene group of formula - (CH ₂ ) _m - where m is typically from 2 to 6, whereby a -COO-AN ₃ type group is formed typically a -COO- (CH ₂ ) mN _{3 group} on organic semiconductors.

By way of example, compounds known as [60] PCB-C3-N3 or [60] PCB-C6-N3 obtained by hydrolysis of PCBM to the corresponding acid PCBA can be used as semiconductors carrying azide groups (for English "[6,6] -phenyl-C ₆ -butyric acid"), especially according to the procedure described in J. Org. Chem. 60, pp. 532-538 (1995), then esterification of the PCBA obtained respectively with HO- (CH ₂ ) ₃ -N ₃ or with HO- (CH ₂ ) ₆ -N ₃ , typically according to the routes described below:

By "azide" is meant within the meaning of the present invention a group of formula -N = N ⁺ = N ^" (denoted more simply -N ₃ , for conciseness purposes).

In the context of the present invention, the inventors have now demonstrated that the crosslinking additive used in steps (E2) and (E3) makes it possible to ensure a thermal stabilization of the photovoltaic properties of the thin layer. In particular, it turns out that the use of the additive under the conditions of steps (E2) and (E3) makes it possible to reduce or even inhibit the formation of crystals (microcrystals of PCBM, typically) that the it is observed otherwise when the photovoltaic layer is subjected to high temperatures, typically above 100 ° C., for example around 150 ° C. The crosslinking additive used according to the invention allows more generally to avoid the degradation of the photovoltaic properties of the thin layer when it is subjected to high temperatures of the aforementioned type. In some cases, the additive even allows, on the contrary, an improvement of the photovoltaic properties when it is subjected to a heat treatment, as is illustrated in the examples given at the end of the present description. Without wishing to be bound to a particular theory, it seems possible to be argued that this stabilization is explained by the fact that the crosslinking agent fixes, in a way, the structure obtained by phase segregation.

 The method of the invention leads in particular to a stabilization of the photovoltaic efficiency of the coating, which is reflected in particular by an increase in the power conversion efficiency (PCE) and the fill factor (FF, namely "FUI Factor" in English) photovoltaic devices implementing a photovoltaic coating as obtained according to the invention The values of PCE and FF are characteristic quantities of photovoltaic devices which are commonly used and which are defined in particular in the article "Conjugated Polymer-Based Organic Solar Cells" published in Chemical Reviews, 107, (4), pp. 1324-1338 (2007) For the record, they are measured by implementing the Photovoltaic device comprising the material to be tested as a photovoltaic diode The value of the ECP corresponds to the ratio of the maximum power delivered by the report material é to the power of the luminous flux illuminating it. The filling factor (between 0 and 1) reflects the more or less distant nature of the material from that of an ideal diode (a filling factor of 1 corresponding to the case of an ideal diode).

 The method of the present invention can be used with a very large number of organic semiconductors.

 Thus, it can especially be used as a semiconductor organic compound

C _N any electron acceptor material known to have such properties, which may for example be selected from the following compounds:

fullerenes and fullerene derivatives, such as C60, C70, PCBM (also called "PC ₆₀ BM" or, more precisely, PC61 BM, of formula [6,6] -phenyl-C ₆ methyl butyrate) ), and PC ₇₁ BM (of formula [6,6] -phenyl-C ₇ methylbutyrate, which is sometimes referred to, more improperly, as "PC ₇₀ BM");

 polymers of the polyfluorene type;

PCNEPV (poly [oxa-1,4-phenylene- (1-cyano-1,2-vinylene) - (2-methoxy-5- (3,7-dimethyloctyloxy) -1,4-phenylene) -1,2 - (2-cyanovinylene) -1,4-phenylene); and poly (styrene sulfonate) (PSS). The derivatives of fullerenes, in particular PC _6- BM ([6,6] -phenyl-C ₆ -methylbutyrate), or the PC ₇₁ BM ([6,6] -phenyl-C ₇ methylbutyrate) above, are particularly suitable as the semiconductor organic compound C _N according to the present invention. These derivatives are particularly well crosslinked in the context of the process of the invention, which prevents their subsequent recrystallization, which results in increased thermal stability compared to photovoltaic coatings based on unstabilized fullerenes according to the present invention.

As organic semiconductor compound C _P , it is possible to use, in the context of the present invention, any material known to have a P type semiconductor character. Advantageously, the organic semiconductor compound C _P is an organic polymer. conjugate preferably selected from the following compounds:

 polythiophene derivatives, such as P3HT (Poly [3-hexylthiophene-2,5-diyl]);

- Tetracene;

 anthracene;

 derivatives of PPV (polyphenylenevinylene) such as MDMO-PPV (poly [2-methoxy-5- (3,7-dimethyloctyloxy) -1,4-phenylenevinylene]) and MEH-PPV (poly [2-methoxy-5- (2-ethylhexyloxy) -1,4-phenylenevinylene]); and

 polymers called "low bandgap", also called third-generation semiconductor polymers, including derivatives known as "push-pu / structure, such as PCDTBT.

Polythiophene derivatives, such as P3HT (Poly [3-hexylthiophene-2,5-diyl]), P3BT (Poly [3-butylthiophene-2,5-diyl]), P30T (Poly [3-octylthiophene] 2,5-diyl]) or else P3DT (Poly [3-decylthiophene-2,5-diyl]) are particularly suitable as the semiconductor organic compound C _P in the process of the present invention. The organic semiconductor compounds (C _N and C _P ) which are used in the context of the present invention may also be chosen from conjugated aromatic molecules containing at least three aromatic nuclei, optionally fused. Organic semiconductor compounds of this type may for example comprise 5, 6 or 7 conjugated aromatic rings, preferably 5 or 6. These compounds may be monomers as well as oligomers or polymers.

The aromatic nuclei present on the organic semiconductors of the aforementioned type can comprise one or more heteroatoms chosen from Se, Te, P, Si, B, As, N, O or S, preferably from N, O or S. They can moreover, they are bound by conjugated linking groups, such as -C (T1) = C (T2) -, -C≡C-, -N (Rc) -, -N = N- groups, -N = C (R ') -, where T1 and T2 are, for example, independently, H, Cl, F, or a C1-C6 alkyl group (i.e. having 1 to 6 carbon atoms), preferentially C4 and Rc represent H, optionally substituted alkyl or optionally substituted aryl.

These aromatic rings may also be optionally substituted with one or more groups selected from alkyl, alkoxy, polyalkoxy, thioalkyl, acyl, aryl or substituted aryl, halogen (in particular -F or Cl, preferably F), cyano, nitro, and optionally substituted secondary or tertiary amines (preferably amines of formula -NRaRb where each of Ra and Rb is, independently, H, or an optionally substituted (and optionally fluorinated or even perfluorinated) alkyl group) optionally substituted aryl (e.g., fluorinated), alkoxy or polyalkoxy.

More generally, organic semiconductor compounds (C _N and C _P ) that can be used according to the present invention include compounds and polymers chosen from conjugated hydrocarbon polymers and oligomers such as polyacenes, polyphenylenes, polyphenylene vinylenes), polyfluorenes, condensed aromatic hydrocarbons such as tetracene, chrysene, pentacene, pyrene, coronene, and more preferably soluble derivatives of these compounds, such as p-substituted phenylenes, for example p-substituted phenylenes; quaterphenyl (p-4P), p-quinquephenyl (p-5P), p-sexiphenyl (p-6P), or substituted derivatives thereof such as poly (3-substituted thiophene), poly (3,4-disubstituted thiophene), polybenzothiophenes, polyisothianaphthenes, β-substituted poly (pyrrole), poly (3-substituted poly (pyrrole), poly (3,4-disubstituted pyrrole), polyfurans, polypyridines, poly-1,3,4- oxadiazoles, the po lyisothianaphthenes, poly (substituted 1-aniline), poly (2- substituted anilines), poly (3-substituted poly) anilines, poly (2,3-disubstituted anilines), polyazulenes, polypyrenes, compounds of the pyrazoline, polyselenophenes, polybenzofurans, polyindoles, polypyridazines, benzidine compounds, stilbene compounds, triazines, porphines, phthalocyanines, fluorophthalocyanines, naphthalocyanines or fluoronaphthalocyanines, optionally metallated, fullerenes and their derivatives, diphenoquinones 1,3,4-oxadiazoles, 1,1,1,12,12-tetracyanonaptho-2,6-quinodimethane, [alpha], [alpha] '- bis (dithieno [3,2-b]', 3'-dithiophene), substituted anthradithiophenes and 2,2'-bibenzo [1,2-b: 4,5-b '] dithiophene. The invention is particularly well suited to the specific case of the pair of semiconductor organic compounds according to:

C _N = PCBM ([6,6] -phenyl-C ₆ methylbutyrate, and

C _P = P3HT (poly (3-hexylthiophene)),

which corresponds to a typical pair of polymers in the context of the preparation of organic photovoltaic compositions, described for example in Advanced Materials, vol. 23, pp. 3597-3602 (201 1).

The invention is also well adapted to the particular pair of semiconductor organic compounds according to:

C _N = PCBM ([6,6] -phenyl-C ₇ methylbutyrate, and

C _P = P3HT (poly (3-hexylthiophene)).

For these particular C _N / C _P couples (and more generally for all fullerene derivative / polythiophene derivative pairs), the use of the crosslinking agent according to the invention generally makes it possible to crosslink the compound of type C _N (PCBM or similar) during step (E3), which makes it possible to achieve a particularly effective stabilization of the photovoltaic properties of the thin layer produced (this crosslinking in particular inhibits the natural tendency that fullerenes have and their derivatives to crystallize).

In particular, when employing semiconductor C _N type fullerene derivative compounds, it is advantageous that the molar ratio of crosslinking agent / semiconductor C _N is less than 2, more preferably less than 1, in particular less than 0.5, for example less than or equal to 0.25. The inventors have demonstrated that with a low ratio in these ranges, the thermal stabilization effect is particularly pronounced and inhibits the recrystallization phenomena of fullerenes which take place in the absence of crosslinking agent. Moreover, the inventors have demonstrated that the introduction of the crosslinker does not affect the photovoltaic performance of the thin layer, and this particularly with a ratio in the aforementioned ranges.

Depending on the nature of the semiconductor compounds C _N and C _P used in the process of the invention, the exact nature of the solvent medium of step (E1) is to be adapted to obtain the desired phase segregation. The principles of phase segregation and the rules governing the choice of suitable solvents have in particular been described in Adv. Funct. Mater, vol. 18, pp. 1783-1789 (2008). By way of example, when a fullerene derivative of the PCBM type is used as a C _N semiconductor and a polythiophene derivative such as P3HT as a C _P semiconductor, it can for example be used in the step (E1) one or more solvents selected from chlorobenzene, dichlorobenzene (o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene), trichlorobenzene, benzene, toluene, chloroform, dichloromethane, dichloroethane, xylenes (especially ortho-xylene), Γα, α, α-trichlorotoluene, methylnaphthalene (1-methylnaphthalene and / or 2-methylnaphthalene), chloronaphthalene (1-chloronaphthalene and / or 2-chloronaphthalene). The crosslinking agent may be introduced into step (E2) in the form of a solution in one of these solvents which is prepared before introduction into the M1 mixture.

According to an advantageous embodiment, the solvent employed in step (E1) (and, where appropriate in step (E2)) comprises at least one or more xylene (s), for example ortho-xylene .

In the most general case, the concentration of semiconductor C _N in the mixture M1 of step (E1) and in the medium obtained at the end of step (E2) is preferably between 5 and 50 mg / ml, more preferably between 10 and 30 mg / ml, for example between 15 and 25 mg / ml. The concentration of semiconductor C _P in the mixture M1 of step (E1) and in the medium obtained at the end of step (E2) is similarly preferably between 5 and 50 mg / ml, more preferably between 10 and 30 mg / ml, for example between 15 and 25 mg / ml.

The crosslinking agent is typically introduced during step (E2) in the form of a solution, in a solvent that is identical or different to that of the mixture M1 prepared in step (E1). The term "solvent" as used in the present description with reference to steps (E1) and (E2) denotes a single solvent or, most often, a mixture of several solvents (also called "solvent system").

In the step (E3), the phase segregation can be obtained by any means known per se, for example by a heat treatment (by annealing for example) and / or drying, in particular under solvent vapor (which allows slow down the kinetics of drying to allow the mixture to relax), for example according to the method known as "solvent annealing".

According to a particular variant, the steps (E1), (E2) and (E3) are conducted under the following conditions: (E1) preparing the first mixture M1 comprising, in the solvent medium S1, the organic semiconductor C _P and the second organic semiconductor C _N ,

 (E2) is added to this mixture M1 the crosslinking additive in the form of a mixture M2 comprising the additive in a second solvent medium S2, whereby a mixture M is obtained comprising a solvent S including the solvent S1 and the optional solvent S2, where the solvent S of the mixture M is constituted by a mixture of:

a first fraction F1 consisting of a solvent or mixture of solvents having a boiling point lower than that of compounds C _P and C _N and which is capable of solvating the two compounds C _P or C _N ;

a second fraction F2, miscible with the first fraction, consisting of a solvent or mixture of solvents which has a boiling point greater than that of fraction F1 and less than that of compounds C _P and C _N and which is capable of to selectively solvate one of the compounds C _P or C _N but not the other (ie incapable of solvating respectively C _N or C _P ), this addition being operated under conditions of sufficiently low temperature to inhibit the crosslinking of the one and / or of the other of the two organic semiconductors by the crosslinking agent during step (E2),

 (E3) is deposited on all or part of the surface of a support the mixture M thus produced and is removed by evaporation of the solvent S present in the deposit thus produced, and is carried, simultaneously or subsequently, the medium at a sufficient temperature to ensure crosslinking.

Given the specificities of the fractions F1 and F2 employed, during the drying step (E3) of the solvent S, a very particular process takes place, which induces the formation of a specific morphology in the coating obtained in fine. .

More precisely, during step (E3), fraction F1, more volatile than fraction F2, evaporates first, which leads to an enrichment in phase F2 in the solvent medium of the deposit produced, which makes the solvent medium less and less capable of solvating the compound that the fraction F 2 is not capable of solvating. It follows a desolvation of at least a part of one of the compounds C _P or C _N proper to lead to a demixing phenomenon of this compound, the other compound (respectively C _N or C _P ) remaining instead, first, in a solvated form, taking into account the presence of a sufficient amount of S1 fraction in the medium, not yet evaporated. It is only in a second phase of step (E3) that all of the solvents are evaporated, to leave as a coating a mixture of compounds C _N and C _P substantially free of solvent. Given this two-stage desolvation of the compounds C _N and C _P and the immiscibility of the compounds C _N and C _P , the solid coating obtained on the support has a specific morphology at the nanoscale, having a high contact interface. between the compounds C _N and C _P.

 For more details on this subject, reference can be made to the application WO201 1/036421.

Whatever the exact embodiment of the steps (E1), (E2) and (E3), these are specifically conducted under conditions such that crosslinking by the crosslinking agent is inhibited in step (E2), to operate only in step (E3). This specificity of the process makes it possible to obtain a particularly interesting crosslinking which, schematically, freezes the structure which is formed by phase segregation in the step (E3). For this purpose, step (E2) is conducted at a temperature below the temperature leading to the crosslinking (typically at a temperature below 50 ° C, more preferably below 40 °, or even 30 ° C). Typically, the temperature is then increased, only after the step (E2), beyond the temperature at which the crosslinking operates. Alternatively, step (E3) can be carried out by exposing the mixture to UV radiation, typically radiation at 254 nm, with or without (and preferably without) temperature rise. It should be noted that step (E1) generally requires hot dissolution (above 60 ° C in general) to form the mixture M1. Following this hot mix, it is essential to cool the medium before implementing the mixture of step (E2).

In this context, it should be noted that the step (E2) has the advantage of being able to be conducted at room temperature, which is of significant economic interest when the process is used on an industrial scale.

According to a particular embodiment of the invention, the crosslinking agent is 4,4'-bis (azidomethyl) -1,1'-biphenyl of formula N ₃ -CH ₂ -Ph-Ph-CI- ₁₂ -N3, where Ph is a phenyl group, hereinafter referred to as BPN. This compound can in particular be synthesized according to the method described in J. Am. Chem. Soc., 127 (36), pp. 12434-12435 (2005). In the case of the use of the BPN:

the concentration of BPN in the mixture formed in step (E2) is typically less than 0.1 mg / ml and / or with a molar ratio BPN / C _{N of} less than 2.

the semiconductor compound C _N is preferably a fullerene derivative, for example PCBM, with a BPN / C _N ratio preferably less than 2, more preferably less than 1, in particular less than 0.5, for example lower or equal to 0.25.

the temperature in step (E2) is preferably less than βΟ 'Ό, for example between 15 and 25 ° (ambient temperature, for example).

More generally, it is possible to use according to the invention other compounds bearing exactly two azide groups, for example the compounds chosen from the following list:

Alternatively, it is possible according to the invention to use compounds bearing more than two azide groups, for example bearing exactly three or four azide groups, or even more, for example:

According to another embodiment of the invention, the crosslinking agent employed in step (E2) is an agent which also provides a role of texturing agent during the formation of the layer in the step ( E3). According to this embodiment, the crosslinking agent is a compound which, in addition to carrying azide groups, has a selective solvent character of one of the compounds C _P or C _N and not of the other.

More specifically, according to this particular embodiment, the method is conducted under the following conditions:

(E1) preparing the first mixture M1 comprising, in a solvent S1, the organic semiconductor C _P and the second organic semiconductor C _N ,

(E2) is added to this mixture M1 a composition including at least one crosslinking additive of the aforementioned type, optionally dissolved in the same solvent S1 as that of the mixture M1, where:

the solvent S1 is a solvent medium having a boiling point lower than that of the compounds C _P and C _N and which is capable of solvating these two compounds C _P or C _N ; and

the crosslinking additive is a solvent-miscible compound S1, which has a boiling point greater than that of S1 and lower than that of compounds C _P and C _N and which is capable of selectively solvating one of the compounds C _P or C _N but not the other (ie unable to solvate respectively C _N or C _P ),

 this addition being carried out under conditions of sufficiently low temperature to inhibit the crosslinking of one and / or the other of the two organic semiconductors by the crosslinking agent during step (E2),

(E3) the mixture M thus produced is deposited on all or part of the surface of a support and the solvent S1 is evaporated off, whereby the texturing of the layer is obtained, and then the textured coating thus obtained is brought to a temperature sufficient to ensure the crosslinking. As examples of crosslinking agents that may be used according to this specific embodiment, mention may notably be made of:

 the 1, 10-diazidodecane of formula

N ₃ - (CH ₂ ) ₁₀ -N ₃

 which can in particular be synthesized according to the method described in J. Am. Chem. Soc., Vol. 127, pp. 12434-12455 (2005),

compounds of formula N ₃ -Ra -O-C = O-Rb-C = O-O-Ra-N ₃ ,

 or :

 -Ra- is a linear or branched hydrocarbon chain, saturated or unsaturated, preferably linear, Ra being preferably an -alkyl- or -alkenyl- group, advantageously comprising from 2 to 18 carbon atoms; and

 -Rb- is a linear or branched hydrocarbon chain, saturated or unsaturated, preferably linear, Ra being preferably an -alkyl- or -alkenyl- group, advantageously comprising from 1 to 18 carbon atoms,

 such as, for example, bis (8-azidooctyl) 2-methylpentanedioate of formula:

N ₃ - (CH ₂ ) ₈ -O-C = OCHCH ₃ CH ₂ CH ₂ C = 0-0 (CH ₂ ) ₈ N ₃

The compounds of formula N ₃ -Ra -O-C = O-Rb-C = O-O-Ra-N ₃ may typically be prepared by reaction of a diacid of formula HOOC-Rb-COOH where Rb has the above-mentioned meaning (Methyl-2-glutaric acid, for example) with a compound of formula HO-Ra-N ₃ wherein Ra has the abovementioned meaning, preferably in the presence of para toluene sulfonic acid, as illustrated in Example 3 given below.

These compounds useful in the context of the implementation of step (E2) are compounds which, to the knowledge of the inventors, have never been described. They constitute, in another aspect, a specific object of the present invention.

These "texturizing effect" crosslinking agents may in particular be used for the production of coating based on a mixture of PCBM / P3HT type semiconductors, where they may be used with a solvent S1 of the type recommended for carrying out the depositing this mixture of polymers of this type, well known in itself. In particular, the solvent S1 used according to this embodiment may comprise one or more solvents chosen from chlorobenzene, dichlorobenzene (o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene), trichlorobenzene, benzene, toluene, chloroform, dichloromethane, dichloroethane, xylenes (especially ortho-xylene), Γα, α, α-trichlorotoluene, methylnaphthalene (1-methylnaphthalene and / or 2-methylnaphthalene), chloronaphthalene (1-chloronaphthalene and / or 2-chloronaphthalene). According to one embodiment, the solvent S1 comprises at least one xylene, preferably at least one ortho-xylene. Preferably, the fraction S1 is entirely composed of one or more xylene (s), for example by ortho-xylene.

According to another more specific aspect, the subject of the present invention is the supports provided with a photovoltaic coating of the type obtained (that is to say obtained or obtainable) according to the method described above in the present description.

In particular, the subject of the invention is the use of the method of the invention for producing photovoltaic cells. In this context, the photovoltaic coating is generally deposited on an anode (generally an anode transparent to visible radiation, for example ITO, advantageously a layer of ITO deposited on a plastic sheet). The anode may be pre-coated with a layer of conductive material. Then, a thin layer of photovoltaic nature according to the invention is deposited (by implementing steps (E1), (E2), and (E3)), then a cathode is deposited on the photovoltaic coating (for example in the form a metal overlay, for example an aluminum overlay). The method of the invention can be implemented to perform both devices using the extraction of holes or the extraction of electrons by the lower and upper electrodes (direct or inverse devices).

Various aspects and preferred features of the invention are illustrated in the following implementation examples, in which photovoltaic coatings according to the invention based on

 (i) an organic P-type semiconductor (electron donor):

 P3HT available from Plextronics or Sigma-Aldrich

 (ii) an organic N-type semiconductor (electron acceptor):

PCBM ([6,6] -phenyl-C ₆ methylbutyrate) marketed by Solaris Chem.

Inc.

(iii) a crosslinking agent which is, according to the example: BPN, synthesized according to the method described in J. Am. Chem. Soc., 127 (36), pp. 12434-12435 (2005),

1, 10-diazidodecane of formula N ₃ - (CH ₂ ) 10 -N ₃ , synthesized according to the method described in J. Am. Chem. Soc., Vol. 127, pp.12434- 12435 (2005), or

bis (8-azidooctyl) 2-methylpentanedioate of formula

N ₃ - (CH ₂ ) ₈ -O-C = OCHCH ₃ CH ₂ CH ₂ C = 0-0 (CH ₂ ) ₈ N ₃

EXAMPLES

Example 1: Production of a crosslinked photovoltaic coating (BPN)

Preparation of a first solution S containing the semiconductors N and P

20 mg of P3HT and 20 mg of PCBM were dissolved in 1 ml of ODCB (orthodichlorobenzene), stirring the mixture at 0 ° C. (hotplate), to obtain a mother solution.

S solution thus obtained was allowed to cool to room temperature (20 ^<€).

Preparation of a Second Solution S 'Containing the Crosslinking Agent

 A solution S 'of BPN was made in ODCB at a concentration of 20 mg / mL in BPN.

Mixing of the two solutions

Once the first solution S cooled to 20 ° C, are introduced 50 μ \ - of the solution S ', also at temperature 20 ^q C, whereby there was obtained a said composition hereinafter "ink 1" Photovoltaic .

Immediate realization of the photovoltaic coating from the mixture

 Once this mixture has been produced, the ink 1 is deposited in the form of a thin film on a glass plate. The deposit was made by spin coating at 2000 rpm, with 5 seconds of acceleration and 60 seconds at 2000 rpm. In this example, as in the following, we also obtain interesting results with speeds of only 1000 revolutions per minute and 1 second of acceleration.

The deposit was made using a freshly prepared mixture. In this regard, it should be noted that the deposition must be carried out in the minutes following the mixing of the solutions S and S '.

An annealing at δΟ'Ό was then carried out to ensure the crosslinking. Example 2: Production of a crosslinked photovoltaic coating (N ₃ - (CH ₂ ) 10 -N ₃ )

Preparation of a first solution S containing the semiconductors N and P

20 mg of P3HT and 20 mg of PCBM were dissolved in 1 ml of ODCB, bringing the mixture to 60 ° with stirring (hot plate), so as to obtain a mother solution.

S solution thus obtained was allowed to cool to room temperature (20 ^<€).

Preparation of a Second Solution S 'Containing the Crosslinking Agent

A solution S 'of N ₃ - (CH ₂ ) 10 -N 3 in ODCB at a concentration of 20 mg / ml of N ₃ - (CH ₂ ) 10 -N _{3 was made} .

Mixing of the two solutions

Once the first solution S cooled to 20 ° C, are introduced 25 μ \ - of the solution S ', also at temperature 20 ^q C, whereby there was obtained a said composition hereinafter "ink 2".

Immediate realization of the photovoltaic coating from the mixture

Once this mixture has been produced, the ink 2 is deposited in the form of a thin film on a glass plate. The deposit was made by spin coating at 2000 rpm, with 5 seconds of acceleration and 60 seconds at 2000 rpm.

The deposit was made using a freshly prepared mixture. In this regard, it should be noted that the deposition must be carried out in the minutes following the mixing of the solutions S and S '.

An annealing at δΟ'Ό was then carried out to ensure the crosslinking. Example 3: Making a crosslinked photovoltaic coating

 (bis (8-azidooctyl) 2-methylpentanedioate)

Preparation of (bis (8-azidooctyl) -2-methylpentanedioate)

Synthesis of bis (8-azidooctyl) 2-methylpentanedioate was carried out in one step from 8-azido-1-octanol (N ₃ (CH ₂ ) ₈ OH) according to Scheme 1 below.

8-Azido-1-octanol (N ₃ (CH ₂ ) ₈ OH) was synthesized from the commercial product 8-chloro-1-octanol (Cl (CH ₂ ) ₈ OH) according to a procedure described by Pukin, Aliaksei V .;

Van Lagen, Barend; Screw, Gerben M .; Wennekes, Tom; Zuilhof, Han; Florack, Dion

E. A .; Brochu, Denis; Gilbert, Michel in Organic and Biomolecular Chemistry, vol. 9

5809-5815 (201-1).

 Para toluene sulphonic acid

 Diagram 1

To a solution of methyl-2-glutaric acid (2.3 g, 16 mmol) and 2.5 equivalents of 8-azido-1-octanol (6.9 g, 40 mmol) in 300 mL of anhydrous toluene are added 5 mol% of para-toluenesulfonic acid (150 mg, 0.78 mmol) in a 500 ml flask. The set is surmounted by a Dean-Stark assembly and refluxed for 48 hours. The water (0.57 mL) generated during the formation of the diester is removed by mounting Dean-Stark. After returning to ambient temperature, the mixture is washed twice with an aqueous solution of sodium hydroxide (4 g of NaOH in 250 ml of water) and then twice with water (2 × 250 ml). The organic phase is dried over Na ₂ SO ₄ and then concentrated under reduced pressure. The product was finally purified by chromatographic column (silica, pentane / dichloromethane) to give 4.5 g of bis (8-azidooctyl) 2-methylpentanedioate as a colorless oil (4.5 g, 62%).

1 H NMR (CDCl3) δ ppm: 4.061 (t, J = 6.8 Hz, 2H); 4.054 (t, J = 6.8 Hz, 2H); 3.25 (t, J = 6.8 Hz, 4H); 2.47 (tq, J = 7.2 and 1 Hz, 1H); 2.32 (m, 2H); 1.97 (m, 1H); 1.76 (m, 1H); 1.59 (m, 8H); 1.33 (m, 16H); 1, 17 (d, J = 7.2 Hz, 3H). 13 C NMR (CDCl3) δ ppm: 176.03; 173.16; 64.52; 64.46; 51.44; 38.86; 31.95; 29.08; 29.02; 28.81; 28.59; 26.63; 25.79; 17.08. IR max / cm-1: 2931; 2857; 2091; 1730; 1462; 1456; 1252; 1,160. Preparation of a first solution S containing the semiconductors N and P

20 mg of P3HT and 20 mg of PCBM were dissolved in 1 ml of ODCB (orthodichlorobenzene), while stirring the mixture at ΘΟ'Ό (hotplate), to obtain a mother solution.

S solution thus obtained was allowed to cool to room temperature (20 ^<€).

Preparation of a Second Solution S 'Containing the Crosslinking Agent

A solution S 'of bis (8-azidooctyl) 2-methylpentanedioate in ODCB at a concentration of 20 mg / mL of bis (8-azidooctyl) 2-methylpentanedioate was made.

Mixing of the two solutions

Once the first solution S cooled to 20 ° C, there was introduced 100 μΙ_ of solution S ', also ^q temperature 20 C, whereby there was obtained a composition called hereinafter "Ink 3".

Immediate realization of the photovoltaic coating from the mixture

Once this mixture has been produced, the ink 3 is deposited in the form of a thin film on a glass plate. The deposit was made by spin coating at 2000 rpm, with 5 seconds of acceleration and 60 seconds at 2000 rpm.

The deposit was made using a freshly prepared mixture. In this regard, it should be noted that the deposition must be carried out in the minutes following the mixing of the solutions S and S '.

An annealing at δΟ'Ό was then carried out to ensure the crosslinking. Example 4: stability tests

The coatings made in Examples 1 to 3 were subjected to a heat treatment at 150 ° C. and the evolution of their structure was studied over time by optical microscopy. By way of comparison, the same experiment was carried out with a coating produced under the conditions of Example 1 but without adding solution S 'to solution S.

The tests show the substantial absence of formation of crystals with the thin layers according to the invention whereas such crystals appear after 20 minutes with the control.

Example 5: Photovoltaic efficiency evolution over time

A photovoltaic cell was made using the coating made according to Example 1; and these cells were taken at Ι δΟ 'Ό, where the evolution of the yield over time was studied and the time t was noted at _80% at the end of which the yield drops by 80%. The results obtained are shown in the table below:

Example 6: Production of a crosslinked photovoltaic coating

 ([60] PCB-C3-N3 or [60] PCB-C6-N3)

This example describes the preparation of coating based on [60] PCB-C3-N3 or [60] PCB-C6-N3), which were obtained according to identical protocols.

Preparation of compounds [60JPCB-C3-N3 and [60JPCB-C6-N3

[60] PCBA was obtained by hydrolysis of [60] PCBM according to the procedure described by JC Hummelen, BW Knight, F. LePeq and F. Wudl in J. Org. Chem., Vol. 60, pp. 532-538 (1995). From this [60] PCBA, [60] PCB-C3-N3 and [60] PCB-C6-N3 were separately prepared according to the following esterification protocol:

To a solution (degassed by argon bubbling) of [60] PCBA (200 mg, 0.245 mmol) in CH ₂ Cl ₂ (HPLC-stabilized with amylene) (30 mL) is successively added hydroxybenzotriazole (HOBt). ) (33 mg, 0.223 mmol), N- (3-dimethylaminopropyl) -N-carbodiimide (EDC) (120 μM, 0.669 mmol), 4-dimethylaminopyridine (27 mg, 0.223 mmol), then a solution in 10 mL of CH ₂ Cl ₂ of 1.11 mmol of 3-azidopropan-1-ol (for the synthesis of [60] PCB-C3-N3) or 1.11 mmol of 6-azidohexan-1-ol (for the synthesis of [60] PCB-C6-N3).

The reaction mixture is stirred at room temperature under an argon atmosphere for 3 days. The solvent is then removed by concentration on a rotary evaporator and the residue is purified by chromatography on silica gel with CH ₂ Cl ₂ / Pentane 7/3 or 8/2 as a solvent mixture. After concentrating the solvent (without heating the bath of the rotary evaporator), the compounds [60] PCB-C3-N3 and [60] PCB-C6-N3 are obtained in the form of a black powder with a yield of 70 to 80%. These compounds are rapidly dissolved in the concentration of 20 mg / mL in the ODCB.

The 3-azidopropan-1-ol and 6-azidohexan-1-ol used are prepared by reaction of NaN ₃ with commercial 3-bromopropan-1-ol and 6-bromohexan-1-ol, according to procedures described respectively in J. Mater. Chem. flight. 22, pp. 1100-1106 (2012) and J. Med. Chem. flight. 54, pp. 7363-7374 (201 1).

The compounds obtained have the following characteristics:

[60JPCB-C3-N3:

H NMR (CDCl ₃ , 300 MHz): δ = 7.94 (d, J = 6.0 Hz, 2H, δH), δ = 7.53 (m, 3H, m, pH), δ = 4.17 (t, J = 6.3 Hz, 2H, COOCH ₂ ), δ = 3.36 (t, J = 6.6 Hz, 2H, CH ₂ N ₃ ), δ = 2.91 (m, 2H, PhCCH 2), δ = 2.53 (t, J = 7.2 Hz, 2H; ₂ COO), δ = 2.18 (m, 2H, CH ₂ CH ₂ COO), δ = 1.9 (m, 2H, CH ₂ CH ₂ N ₃ ).

3C NMR (CDCl ₃ , 75 Mhz): 172.9, 148.7, 147.7, 145.8, 145.2, 145.0, 144.8, 144.6, 144.5,

144.4, 144.0, 143.7, 143.0, 142.99, 142.91, 142.2, 142.16, 142.12, 140.9, 140.7, 138.0,

137.5, 136.7, 132.1, 128.4, 128.3, 79.8, 61.5, 51.8, 48.2, 33.9, 33.6, 28.1, 22.3.

MS (MALDI-TOF, pos mode, dithranol): m / z: 979.13, calcd for: C₁ HH₂N; found: 980.2 [M] ⁺ . [60] PCB-C6-N3:

H NMR (CDCl ₃ , 300 MHz): δ = 7.94 (d, J = 6.9 Hz, 2H, oH), δ = 7.52 (m, 3H, m, pH), δ = 4.07 (t, J = 6.6 Hz, 2H, COOCH ₂ ), δ = 3.26 (t, J = 6.6 Hz, 2H, CH ₂ Br), δ = 2.91 (m, 2H, PhCCH 2), δ = 2.53 (t, J = 7.5 Hz, 2H, CH ₂₎ COO), δ = 2.23-2.15 (m, 2H, CH ₂ CH ₂ COO), δ = 1.63 (m, 4H, CH ₂ CH ₂ N ₃ and COOCH ₂ CH ₂ ), 5 = 1 .4-1 .33 (m, 4H, COOCH ₂ CH ₂ CH ₂ CH ₂ ).

3C NMR (CDCI ₃ , 75 MHz): 173.1, 148.8, 148.0, 145.9, 145.8, 145.3, 145.2, 145.2, 145.1,

145.0, 145.0, 144.8, 144.7, 144.7, 144.6, 144.5, 144.4, 144.0, 143.7, 143.1, 143.02, 142.97, 142.92, 142.90, 142.2, 142.2, 142.1, 142.0, 141.0, 140.7, 138.0, 137.5, 136.7,

132.1, 128.4, 128.2, 79.9, 64.5, 51.8, 51.3, 34.1, 33.6, 28.7, 28.5, 28.4, 26.4, 25.5, 22.4 MS (MALDI-TOF, pos mode, dithranol): m / z: 1021 .18, calcd for: C 7 H ₇ 0 _{2 2} 3 N _3; found: 1022.19 [M] ⁺ .

Preparation of a first solution S1 containing the semiconductor N

40 mg of P3HT were dissolved in 1 ml of ODCB (ortho-dichlorobenzene), bringing the mixture to 60 ° C with stirring (heating plate), so as to obtain a first mother solution S1.

S1 solution thus obtained was allowed to cool to room temperature (20 ^<€).

Preparation of a second solution S2 containing the semiconductor P

40 mg of PCBM were dissolved in 1 ml of ODCB (ortho-dichlorobenzene), bringing the mixture to 60 ° C with stirring (hot plate), so as to obtain a second mother solution S2.

S2 solution thus obtained was allowed to cool to room temperature (20 ^<€).

Preparation of a third solution S 'containing the crosslinking agent ([60JPCB-C3-N3 or ([60JPCB-C6-N3)

A solution S 'of [60] PCB-C3-N3 (or respectively [60] PCB-C6-N3) was made in ODCB at a concentration of 40 mg / ml in [60] C3-PCB. -N3 (or in [60] PCB-C6-N3 respectively). The solution S 'thus obtained was allowed to cool to room temperature (20 ^<€). Mix of three solutions

Once the three solutions cooled to 20 ^q C was mixed 1 mL of solution S1 with 850 μΙ_ solution S2, and was added to this mixture 150 microliter of solution S ', whereby there was obtained a so-called following composition -after "ink 6".

Immediate realization of the photovoltaic coating from the mixture

Once this mixture has been produced, the ink 6 is deposited in the form of a thin film on a glass plate. The deposit was carried out by spin coating at 1000 rpm, with 1 second of acceleration and 60 seconds at 1000 rpm.

The deposit was made using a freshly prepared mixture. In this regard, it should be noted that the deposit must be made within minutes of mixing the solutions.

An annealing at δΟ'Ό was then carried out to ensure the crosslinking. Example 7 Properties of the Layers Obtained

The coatings made in Example 6 were subjected to a heat treatment at 150 ° C. and the evolution of their structure was studied over time by optical microscopy.

By way of comparison, the same experiment was carried out with a coating carried out under the conditions of Example 6 but without the addition of ([60] PCB-C3-N3) or ([60] PCB-C6-N3). The tests show the substantial absence of formation of crystals with the thin layers according to the invention whereas such crystals covered the entire surface of the layer after 24 hours with the control. A photovoltaic cell was made using the coating made according to Example 6, and these cells were brought to 100 ° C., where the evolution of the yield over time was studied.

For comparison, the same experiment was performed with a photovoltaic cell using the coating made according to Example 6 but without the addition of a crosslinking agent and the evolution of the ECP over time was noted. The results obtained are shown in the table below:

These tests show the thermal stability of the ECP of the cell with a thin layer made according to Example 6 according to the invention, whereas the ECP of the control cell drops significantly after 24 hours.

Claims

1. A process for preparing a thin film photovoltaic character heterojunction by depositing on a support a composition comprising a first organic semiconductor _P C, type electron donor and a second organic semiconductor C _N, type electron acceptor, then phase segregation, comprising the following steps: - one achieves, in one or more stages; a mixture M comprising the semiconductors C _P and C _N and crosslinking agents bearing azide groups in a solvent adapted to phase segregation under conditions of sufficiently low temperature to inhibit the precipitation by crosslinking of the one and / or the other of the two organic semiconductors by reaction of the crosslinking agents; then the mixture M thus produced is deposited on all or part of the surface of a support and the phase segregation is carried out, by raising the temperature during or after this phase segregation and / or by subjecting the reaction medium to UV radiation of wavelength adapted to be placed under conditions where the crosslinking additive reacts to form covalent bonds with at least a portion of the organic semiconductors, whereby a crosslinking within the photovoltaic thin film is achieved . The method of claim 1, comprising the steps of: (E1) preparing a first mixture M1 comprising organic semiconductors C _N and C _P in a solvent medium; then (E2) is added to this mixture M1 a crosslinking additive bearing at least two azide functional groups and optionally a solvent, under conditions of sufficiently low temperature to inhibit the precipitation by crosslinking of one and / or the other of the two organic semiconductors with the crosslinking additive during step (E2), so as to form a mixture M comprising the semiconductors C _P and C _N and the additive in a solvent adapted to phase segregation, then (E3) the mixture M thus produced is deposited on all or part of the surface of a support and the phase segregation is carried out, by raising the temperature during or after this phase segregation and / or by subjecting the reaction medium to a wavelength UV radiation adapted to be placed under conditions where the crosslinking additive reacts to form covalent bonds with at least a portion of the organic semiconductors whereby crosslinking within the thin film is achieved realized photovoltaic. The method of claim 1, comprising the steps of: (E1) a first mixture M1 is prepared comprising only part of organic semiconductors C _N and C _P in a solvent medium; then (E2) the remainder of the organic semiconductors, previously modified by grafting azide functional groups and optionally a solvent, under conditions of a sufficiently low temperature to inhibit the precipitation by crosslinking of the one and / or the other of the two organic semiconductors with the crosslinking additive during step (E2), so as to form a mixture M comprising the semiconductors C _P and C _N and the additive in a suitable solvent phase segregation; then (E3) the mixture M thus produced is deposited on all or part of the surface of a support and the phase segregation is carried out; and, during or after this phase segregation, and typically only after the phase segregation, the temperature is raised and / or the reaction medium is subjected to UV radiation of wavelength adapted so as to be placed in conditions where the crosslinking additive reacts to form covalent bonds with at least a part of the organic semiconductors, whereby a crosslinking is obtained within the photovoltaic thin film produced. 4. Method according to claim 3, wherein the semiconductors modified by grafting azide functional groups which are used in step (E2) are organic semiconductors C _N functionalized by at least one group carrying at least one function. azide, for example the compounds [60] PCB-C3-N3 or [60] PCB-C6-N3 obtained by hydrolysis of PCBA to PCBA and then esterification of the PCBA obtained respectively with HO- (CH ₂ ) ₃ -N ₃ and with HO - (CH ₂ ) ₆ -N ₃ . 5. Process according to any one of claims 1 to 4, wherein the organic semiconductor compound C _N is chosen from the following compounds: fullerenes and fullerene derivatives, such as C60, C70, methyl [6,6] -phenyl-cerbutyrate) or PCBM, and methyl [6,6] -phenyl-C ₇ -butyrate or PC ₇₁ BM;  polymers of the polyfluorene type;  PCNEPV (poly [oxa-1,4-phenylene- (1-cyano-1,2-vinylene) - (2-methoxy-5- (3,7-dimethyloctyloxy) -1,4-phenylene) -1,2 - (2-cyanovinylene) -1,4-phenylene); and poly (styrene sulfonate) (PSS). 6. Process according to any one of claims 1 to 5, wherein the organic semiconductor compound C _P is chosen from the following compounds:  polythiophene derivatives, such as poly [3-hexylthiophene-2,5-diyl] P3HT;  - Tetracene;  anthracene;  polythiophenes;  derivatives of PPV (polyphenylenevinylene) such as MDMO-PPV (poly [2-methoxy-5- (3,7-dimethyloctyloxy) -1,4-phenylenevinylene]) and MEH-PPV (poly [ 2-methoxy-5- (2-ethylhexyloxy) -1,4-phenylenevinylene]); and  polymers with low bandgap, such as PCDTBT. 7. Method according to one of claims 1 to 6, wherein the organic semiconductor compound C _N is a fullerene derivative such as PCBM, and the organic semiconductor compound C _P is a polythiophene derivative such as P3HT. 8. Method according to one of claims 1 to 7, wherein the organic semiconductor compound C _N is a fullerene derivative such as PCBM and wherein the molar ratio C _N crosslinking agent / semiconductor is less than 2, and more preferentially less than 1. 9. Method according to one of claims 1 to 8, wherein: (E1) preparing the first mixture M1 comprising, in the solvent medium S1, the organic semiconductor C _P and the second organic semiconductor C _N , (E2) is added to this mixture M1 the crosslinking additive in the form of a mixture M2 comprising the additive in a second solvent medium S2, whereby a mixture M is obtained comprising a solvent S including the solvent S1 and the optional solvent S2, where the solvent S of the mixture M is constituted by a mixture of: a first fraction F1 consisting of a solvent or mixture of solvents having a boiling point lower than that of compounds C _P and C _N and which is capable of solvating the two compounds C _P or C _N ; a second fraction F2, miscible with the first fraction, consisting of a solvent or mixture of solvents which has a boiling point greater than that of fraction F1 and less than that of compounds C _P and C _N and which is capable of to selectively solvate one of the compounds C _P or C _N but not the other (ie incapable of solvating respectively C _N or C _P ), this addition being operated under conditions of sufficiently low temperature to inhibit the crosslinking of the one and / or of the other of the two organic semiconductors by the crosslinking agent during step (E2),  (E3) is deposited on all or part of the surface of a support the mixture M thus produced and is removed by evaporation of the solvent S present in the deposit thus produced, and is carried, simultaneously or subsequently, the medium at a sufficient temperature to ensure crosslinking. 10. Method according to one of claims 1 to 9, wherein the step (E2) is conducted at a temperature below 50 ° C, preferably below 40 ° C. 1 1. Process according to one of Claims 1 to 10, in which the crosslinking agent is 4,4'-bis (azidomethyl) -1, 1'-biphenyl (BPN). 12. Method according to one of claims 1 to 1 1 wherein the process is conducted under the following conditions: (E1) preparing the first mixture M1 comprising, in a solvent S1, the organic semiconductor C _P and the second organic semiconductor C _N , (E2) is added to this mixture M1 a composition including at least one crosslinking additive of the aforementioned type, optionally dissolved in the same solvent S1 as that of the mixture M1, where: the solvent S1 is a solvent medium having a boiling point lower than that of the compounds C _P and C _N and which is capable of solvating these two compounds C _P or C _N ; and the crosslinking additive is a solvent-miscible compound S1, which has a boiling point greater than that of S1 and lower than that of compounds C _P and C _N and which is capable of selectively solvating one of the compounds C _P or C _N but not the other (ie unable to solvate respectively C _N or C _P ,  this addition being carried out under conditions of sufficiently low temperature to inhibit the crosslinking of one and / or the other of the two organic semiconductors by the crosslinking agent during step (E2),  (E3) the mixture M thus produced is deposited on all or part of the surface of a support and the solvent S1 is evaporated off, whereby the texturing of the layer is obtained, and then the textured coating thus obtained is brought to a temperature sufficient to ensure the crosslinking. 13. Thin layer photovoltaic nature obtainable according to the method of one of claims 1 to 9. 14. Compound of formula N ₃ -Ra -O-C = O-Rb-C = O-O-Ra-N ₃  or  -Ra- is a linear or branched hydrocarbon chain, saturated or unsaturated, preferably linear, Ra being preferably an -alkyl- or -alkenyl- group, advantageously comprising from 2 to 18 carbon atoms; and -Rb- is a linear or branched hydrocarbon chain, saturated or unsaturated, preferably linear, Ra being preferably an -alkyl- or -alkenyl- group, advantageously comprising from 1 to 18 carbon atoms. 15. Compounds [60] PCB-C3-N3 and [60] PCB-C6-N3, as obtained by hydrolysis of PCBA to PCBA and then esterification of PCBA obtained respectively with HO- (CH ₂ ) ₃ -N ₃ and with HO- (CH ₂ ) ₆ -N ₃ .