FR2953331A1 - Solid photovoltaic cell for use on roof of building, has interface layers including discontinuous portions formed from oxidation products that are different from n-type and p-type semiconductor compounds and absorbing compound - Google Patents

Abstract

The cell (1) has a metal thiocyanate compound (6), and a filling layer (3) containing transparent p-type semiconductor compound i.e. copper thiocyanate, that partially fills pores (2a) of a porous substrate (2) containing transparent n-type semiconductor compound Oxidation products (5) are different from the compounds and an inorganic absorbing compound i.e. thermally annealed stibnite. The products form discontinuous portions of interface layers situated between the filling layer and the substrate and/or between absorbing compound aggregates (4) and the p-type semiconductor compound. The interface layers comprise thiocyanate polymer and/or dithiocyanate compound. An independent claim is also included for a method for preparing a solid inorganic photovoltaic cell.

Description

Inorganic photovoltaic cell

The present invention relates to a solid photovoltaic cell of the type comprising 3 inorganic and solid materials, comprising respectively: - a porous layer of an n-type semiconductor compound and transparent, - a layer of a p-type semiconductor compound and transparent, at least partially filling the pores of said porous layer, and - an inorganic absorber compound disposed between the two layers of said n-type and p-type semiconductor compounds, respectively. Such photovoltaic devices are well known and have been described, inter alia, in FR 2 281 880 (FR 05/01114), FR 2 881 881 (FR 05/01113) and FR 2 899 381 (FR 06/02791) incorporated herein by reference. by reference. Their operating principle is as follows: the radiation (photons) is only absorbed by the absorber material; then an electron is transferred to the n-type "transparent" (or non-absorber) semiconductor, while a positive charge is transferred to the p-type semiconductor. According to this principle, the transport of opposite charge carriers is carried out in two differentiated phases, which theoretically considerably reduces the drop in performance by recombination of charges. The use of the nanocrystalline or microcrystalline porous layers of the semiconductor substrate is necessary to provide a sufficient amount of absorber present in the layer per unit area projected. A photovoltaic conversion efficiency of 2.3% to 0.36 sun, with a ZnO / CdSe / CuSCN cell, has been reported (Lévy-Clément, C., Tena-Zaera, R., Ryan, MA, Katty, A. Hodes, G. Adv.Mat., 2005, 17, 1512). Photovoltaic conversion efficiency of 3.4% at 1 sun, with cell areas of 0.03 cm 2, with ZnO / In 2 S 3 / CuSCN cells has also been reported (Belaidi, A., Dittrich, T. Kieven, D, Tornow, J, Schwarzburg, K., Lux-Steiner, M.Ch. Phys Status Solidi, Rapid Res.Led., 2008, 2, 172). A photovoltaic conversion efficiency of 1.3% has been reported for 1 sun illumination (1000 W / m2), with a 0.54 cm 2 TiO 2 / CdS / CuSCN cell, using nanocrystalline TiO 2 with a large internal surface area. and a CdS coating about 5-10 nm thick (Larramona, G .; Choné, C., Jacob, A., Sakakura, D., Delatouche, B. Pere, D. Cieren, X. Nagino, M. Bayon, R. Chem Mater 2006, 18, 1688). Then, TiO2 / SbzS3 / CuSCN cells that can provide an efficiency of 3.4% with a band of about 1.65 eV (at about 750 nm), have been described in FR 2 899 381. The best external quantum efficiency ( eqe) reached a maximum of 80%, which is approximately the maximum value that can be reached because of the approximately 15% absorption / reflection loss by the glassy TCO substrate. Recently, photovoltaic conversion efficiencies of 3.37% have also been reported for similar nanoporous Sb2S3 solar cells in the TiO2 / In-OH-S / Sb2S3 / (KSCN) CuSCN configuration, with a cell area of 0, 15 cm2. In their report, the authors confirmed the beneficial effect of a pretreatment of thiocyanate, prior to the impregnation of CuSCN, previously reported in Larramona, G et al. Chem. Mater. 2006, 18, 1688. The stability and reproducibility of the photovoltaic performance of these cells are unsatisfactory for effective use. When cells are sealed to prevent possible oxidation, caused by contact with ambient air, cell performance decreases significantly.

The above problems of lack of stability and reproducibility persist, even if the gaseous atmosphere inside the box in which the cell is sealed is changed, and, if reagents are added, such as the alkali metal thiocyanates MSCN, having a beneficial effect on the photovoltaic performance of the initial unsealed cells. The reasons for this decrease in photovoltaic performance could not be understood in the light of the teaching of the prior art. The object of the present invention is to provide novel photovoltaic devices which have improved properties and, more particularly, improved stability and reproducibility of photovoltaic performance of the cell after sealing, for effective use. The object of the present invention is to obtain satisfactory photovoltaic performances, preferably improved, in particular a short-circuit photocurrent greater than 2 mA / cm 2 under irradiation of 1000 W / m2, preferably greater than 5 mA. / cm2, and a higher photovoltaic conversion efficiency, especially greater than 1%, preferably greater than 2%, after the cell is sealed and using materials that are inexpensive, stable and without serious toxicity problems or negative impact on the environment. Several experiments were conducted to identify the origin of the above problems as described below. The lack of reproducibility of the photovoltaic performances appears to be related to uncontrolled factors, such as the oxygen and water concentrations in the cell atmosphere and the water and oxygen contents adsorbed inside the cell. It has been discovered that, in order to obtain superior photovoltaic performance, the cells need to be in contact with oxygen during the intermediate stages of their preparation process, so as to create a limited oxidation of certain chemical species at the same time. inside the cell structure.

More particularly, it has been discovered that the photovoltaic performances are progressively improved from the beginning of the irradiation of visible light in the presence of oxygen-containing gas, hereinafter called illumination treatment. Some photo-catalytic oxidation reactions take place inside the cells, involving oxygen and water (in the case of ambient air) and other residual impurities reacting with the the cell, such as CuSCN and Sb2S3, to improve charge transfer kinetics at their interface after illumination has been performed for a period of time. The series resistance of the cell remains at a low level and the photovoltaic performance at a high level, even after the gaseous atmosphere has been changed to dry nitrogen. However, it has been discovered that this improvement in photovoltaic properties requires that limited and only partial oxidation of the absorber occur. Indeed, if the illumination treatment lasts too long, there is degradation of the photovoltaic performance of the cell after the initial improvement. This is probably due to the fact that, when the illumination in the presence of oxygen is continued, additional photocatalytic reactions, such as the oxidation of the absorber compound, lead to the degradation of the cell insofar as the absorber compound is gradually completely photooxidized in the presence of oxygen. More specifically, to solve the above problems, the present invention provides a solid photovoltaic cell of the type comprising 3 inorganic and solid materials, comprising respectively: a porous layer of an n-type semiconductor compound and transparent, layer of a p-type semiconductor compound and transparent, filling at least in part the pores of said porous layer, and - an inorganic absorber compound, forming aggregates, disposed between the two layers of said semiconductor compounds of type n and p-type, respectively, which are not at least partly not in contact, characterized in that it further comprises oxidation products different from said semiconductor compounds and said absorber compound, said oxidation forming discontinuous portions of interface layers located between the two layers of the two so-called n-type and p-type semiconductor compounds, and / or between said absorber compound aggregates and the p-type semiconductor compound layer. Such discontinuous portions of said interface layers reflect that the oxidation of the absorber compound is limited and therefore only partial. The presence of said oxidized species can be detected by infrared spectroscopy. More particularly, said oxidation products comprise chemical species resulting from the partial oxidation of said absorber compound and / or said p-type semiconductor compound. In a preferred embodiment, said p-type semiconductor compound is CuSCN and said absorber compound is a thermally annealed antimony sulfide antimony compound, such as Sb2S3. Preferably, a cell according to the invention further contains a thiocyanate compound MSCN (6), wherein M is an alkali metal, preferably M is Li, Na or K, and said interface layer comprises a compound (SCN) 2 and / or a polymer (SCN) n. Said interface layer is formed at the interface between Sb2S3 and CuSCN. It is composed of oxidation products, such as thiocyanogens (SCN) 2 or (SCN) n, resulting from the oxidation of SON-derivatives present in the cell, including the p-type semiconductor compound CuSCN and / or added MSCN alkali thiocyanates. When the MSCN alkali metal thiocyanates are not added to the cell, said interface layer is also formed from the photo-catalytic oxidation of CuSCN. However, the addition of MSCN is preferred to obtain higher cell photovoltaic performance. Even if MSCN is not implemented, improved photovoltaic performances are observed but the presence of MSCN favors the improvement of the photovoltaic performances by illumination treatment.

More particularly, the weight ratio of MSCN to CuSCN is 0.001 to 2. The optimum ratio varies depending on the type of alkali metal in MSCN and the absorber. According to the inventors, the improvement in photovoltaic performance could be explained as follows. Originally, the contact between Sb2S3 and CuSCN is not optimal with regard to the transfer of charges because of interstices existing at the interface of these compounds. Thus the photo-induced holes inside Sb2S3 can not be transferred to CuSCN, resulting in low photovoltaic performance. However, M + (Li +, Na + or K +) and SCN- are dissolved in small amounts of water from the hygroscopic nature of MSCN in these same interstices. Sb2S3 is known as a photo-catalyst, so that when it is irradiated by light, it forms holes and electrons. The electrons are transferred to TiO2 where they reduce the chemical species on the surface of Sb2S3, giving it electrons. If oxygen and H + are present, H2O or H2O2 can be formed with these electrons. The photo holes generated in Sb2S3 oxidize the chemical species on its surface. It is likely that Sb2S3, itself, is also oxidized by the holes to form S and Sb3 +. SCN- can be oxidized to (SCN) 2 or polymer (SCN) n, which is a known electrical conductive polymer. This fills the space at the interface between CuSCN and Sb2S3, facilitating a charge transfer to the cell. Even without added MSCN, a small amount of SCN- is available from dipropyl sulfide, the solvent used in depositing the CuSCN layer. It is the kinetics of each oxidation that determine which species will be oxidized. While the holes generated in Sb2S3 oxidize MSCN to form thiocyanogen (SCN) 2 or thiocyanogenic polymers (SCN) n, the electrons generated reduce oxygen, and as a result, if oxygen is not present, the electrons will recombine with the holes, from which it will result that MSCN will not be oxidized. Preferably, a cell according to the invention is sealed inside walls, said walls being at least partly transparent and preferably containing a dry gas atmosphere. By "sealed" is meant here a confinement of the cell between said walls. Sealing the cell, just after its preparation, prevents or minimizes cell degradation by further oxidation, by decreasing the intrusion of oxygen and moisture into the cell. More particularly, said transparent n-type semiconductor compound is a metal oxide such as TiO2, ZnO or SnO2 and, preferably, TiO2.

Illumination treatments on flat layers stacked with different constituents were tested. However, it has not been possible to observe any effect of improvement of the photovoltaic performances as significant as those observed in an interpenetrated configuration. This is why, preferably, a cell according to the invention has an interpenetrated configuration, in which said n-type semiconductor compound is in the form of a porous substrate comprising pores with a size of 10 to 100 nm, the inner surface of said pores being at least partially coated with said aggregates of absorber compounds, said pores being filled in a volume proportion of at least 10%, preferably more than 15%, with a filling layer consisting of said semi compound p-type driver, and said portions of oxidation product interface layers having a thickness of 0.1 to 5 nm and preferably 0.1 to 1 nm. According to other advantageous characteristics of a cell according to the present invention: the roughness factor of said porous substrate, before deposition of said absorber, is greater than 50, preferably greater than 100, the porous substrate is made of particles or crystals, the size of said particles or crystals being between 30 and 50 nm and the average pore size being between 20 and 50 nm, the n-type semiconductor compound is present as a porous substrate of a metal oxide and said filler layer is composed of solid p-type semiconductor compounds, - the n-type semiconductor metal oxide of said porous substrate is TiO2, with an average particle size between 30 and 50 nm and an average pore size between 20 and 50 nm, and said filler layer also constitutes an overlayer of at least 10 nm in thickness and is situated over one of the faces of the porous substrate.

Other inorganic absorbers, such as CdS, have been tested, showing that the method of the present invention works and can be advantageously applied to other absorbers, in combination with TiO2 and CuSCN. The term "antimony sulphide-based" means that said compound is constituted at least predominantly, preferably substantially antimony sulphide, Sb 2 S 3, the antimony sulphide compound may however contain a certain percentage in excess of one percent. Sb or S elements and / or oxide and / or hydroxide ions as partial substitution of the sulfide ions.

"Transparency" is understood to mean that said compound does not absorb significantly, that is to say with an absorption percentage of less than 35%, radiation at wavelengths between 400 and 1200 nm and preferably less than 10% between 450 and 1200 nm.

The term "absorber" means that said compound absorbs with an absorption percentage of at least 50%, the radiation in a wavelength range from 400 nm to an absorption threshold of between 600 and 1200. nm. Preferably, the thermal annealing treatment consists of heating at approximately 300 ° C., preferably in a nitrogen atmosphere, said absorber compound layer after application to a layer of said n-type or p-type semiconductor compound. The photovoltaic devices according to the invention based on three solid components (two transparent semiconductors, n and p, and an absorber) have the advantage of being of a low manufacturing cost, while having a satisfactory photovoltaic efficiency, see higher in some embodiments. The term "pore size" here means the pore opening size, that is to say the average dimension of their cross section and not their length or depth in the thickness of the layer. The term "roughness factor" is used here to mean the ratio between the inner surface of the porous layer (which follows the inner surface of the pores of which it is composed) and the projected area of the layer on its substrate. This porosity may be due to the fact that the layer consists of particles or crystals whose aggregation has created pores in the interstitial space between the particles or crystals during its manufacture and / or the creation of pores directly in a material monolithic with no grain boundary. The roughness thus defined can be estimated approximately (for pores greater than 2 nm and pores approaching the spherical shape) by measuring the porosity (and the pore size distribution) using the adsorption technique. nitrogen desorption followed by calculation of BET active surface area. The porous substrate consists of particles or crystals. It is understood that the inner surface of the pores is constituted by the surface of said particles or crystals. Preferably, said n-type semiconductor metal oxide is TiO 2 having an average particle size of 30 to 50 nm and the pore size is 20 to 50 nm. For TiO 2, these particle sizes correspond to a BET surface of said porous substrate before absorber deposition, greater than 25 m 2 / g, more preferably 25 to 50 m 2 / g. Advantageously, a cell according to the invention comprises a transparent non-porous layer of a semiconductor component which is interposed between said porous layer of this semiconductor and the transparent conductive substrate layer known as "front contact". This thin layer (called barrier layer) made of the same material or another of the same type (n or p respectively) as the material of the porous layer makes it possible to avoid any short circuit between the semiconductor filling the pores and the transparent conductive substrate known as "front contact". This conductive substrate or "front contact" may consist of a transparent conductive commercial glass. Advantageously, again, a cell according to the present invention comprises a layer of thickness greater than 10 nm of a said semiconductor component which is interposed between the said porous semiconductor layer and a said layer of the conductive substrate called "rear contact ". This thin overcoat of this semiconductor or of another of the same type as the semiconductor filling the pores avoids any short circuit between the semiconductor of the porous layer and the conductive substrate called "back contact" . This conductive substrate or "back contact" may be made of coal or other conductive material such as metal.

More particularly, a cell according to the present invention is characterized in that: - a first face of said porous substrate is deposited on a first conductive and transparent front contact substrate such as conductive glass, which is also covered with a compact barrier layer (nonsporous) preferably transparent from said n-type semiconductor metal oxide, and - said porous substrate constitutes a layer with a thickness greater than 1 μm, preferably from 2 to 10 μm, - said absorber compounds form aggregates of size 10-200 nm, and said filler layer fills at least 10% of the pore volume, preferably more than 15%, and the second face of the porous substrate is covered by a second rear contact conductive substrate, and preferably, said filling layer also constitutes an overlap layer at least 10 nm thick between said porous substrate and the conductive layer of said second rear contact conductive substrate, and - said porous substrate and its absorption and filling layers are confined between said two conductive substrates of front contact and rear contact. Said second rear contact conductive substrate may be transparent or not, in particular consisting of metal or coal.

Deposition of the porous nanocrystalline layer of metal oxide semiconductor such as TiO2 can be achieved using low cost manufacturing techniques such as that known from "doctor blading" (or "tape casting"), using colloidal dispersions of said metal oxide such as TiO2, or such as screen printing with a paste based on said TiO2 metal oxide.

Deposition of the absorber layer can be achieved using a low cost manufacturing technique such as chemical bath deposition or electro-deposition. The filling of the free pore volume with the second "transparent" semiconductor can be done using a low cost manufacturing technique such as impregnation with a solution of the dissolved material followed by evaporation of the solvent, or by a technique for impregnating a precursor solution followed by the spin coating method, or by electro-deposition.

A cell according to the present invention can be prepared by various controlled oxidation processes, such as processes including heat treatment. However, according to a preferred embodiment, the present invention provides a method for preparing cells, wherein said oxidation products of said interface layer are obtained by an oxidation treatment by illumination by visible light, in the presence an oxygen-containing gas atmosphere, a device comprising the following components of said cell, a said porous layer of a transparent n-type semiconductor compound and a said semiconductor compound layer of the type transparent p filling at least in part said pores of said porous layer, and an inorganic absorber compound, present in aggregate form, disposed between said layers of said n-type and p-type semiconductor compounds, which are not , at least in part, not in contact. Several gaseous atmospheres have been tested including, in particular, dry oxygen, dry synthetic air without moisture, ambient air, pure nitrogen and humidified nitrogen. It has been concluded that irradiation with visible light in gaseous atmosphere containing oxygen, preferably ambient air, leads to an improvement of the photovoltaic performances. In fact, limited amounts of moisture in the ambient air lead to better results, but excessive humidity levels, on the contrary, have a negative effect on the photovoltaic performance of the cell. Lower photovoltaic performances were also observed under a nitrogen atmosphere. In this case, however, it is believed that oxygen initially adsorbed inside the cell reacts under illumination in visible light. Consistent with this conclusion, it has been observed that when the cell is treated by heating to remove water and adsorbed oxygen before irradiation, the effect of improving photovoltaic performance under N2 atmosphere decreases. In the present application, the term "visible light", light at a wavelength of 400 to 1200 nm. Preferably, during the illumination treatment, said oxygen-containing gas atmosphere is ambient air, preferably containing a moisture content lower than the supersaturation rate of air at room temperature. Indeed, the photovoltaic performance of the cell is related to the degree of humidity of the ambient air, indicating that the water is involved in the transfer of charges. It is very likely that water is formed by reduction of oxygen in the presence of H +. However, according to the present invention, it has been observed that small amounts of water, such as the residual water present in the ambient air, below the supersaturation of the air, below the moisture content to supersaturation of the air, are beneficial, but that higher amounts of water degrade the photovoltaic performance of the cell. According to another particular advantageous feature of the present invention, said illumination treatment comprises illumination of the cell with a visible light of 0.1 to 5 kW / m2, for a period of 5 minutes to 20 hours.

Advantageously, said illumination treatment comprises illumination of the cell under open circuit conditions. By "open circuit" is meant that the + and - poles are not connected and that the electrons can not leave the cell. On the other hand, in the opposite state of short-circuit, the + and - poles are directly connected and the electrons can leave the cell. According to another advantageous characteristic of the method of the present invention, the series resistance and the parameters on which the photovoltaic conversion efficiency of the cell depends, such as the photocurrent short circuit density (Jsc), and the voltage open circuit (Voc), are monitored during said illumination process and said cell is subjected to said illumination process as the photovoltaic conversion efficiency increases, said irradiation being stopped when said photovoltaic conversion efficiency is highest, and / or as long as the series resistance of said cell decreases, said irradiation being stopped when said resistance is the lowest. The photovoltaic conversion efficiency depends on the short-circuit current (Jsc), the open circuit voltage (Voc) and the fill factor (ff). Conventionally, all the parameters Jsc, Voc and ff are improved when the interfacial layer portions appear, when the illumination treatment according to the invention is carried out. The relationship between the series resistor and the above parameters will be explained in more detail in the detailed description below.

In a first embodiment of the method of the invention, said illumination treatment is performed on an unsealed cell, said cell being sealed just after said illumination treatment, preferably under a dry gas atmosphere, preferably in an atmosphere of dry nitrogen or dry synthetic air.

The term "sealed cell" means that the cell is confined inside said walls. In a preferred embodiment, a said cell comprising an alkali metal thiocyanate compound MSCN (6), in which M is an alkali metal, preferably Li, Na or K, is prepared by carrying out the steps in which: depositing said absorber compound on said porous layer of n-type semiconductor compound, and introducing said alkali metal thiocyanate salt MSCN, which is poured onto said porous substrate coated with said absorber compound, and depositing a said p-type semiconductor compound filler layer, comprising CuSCN, on said porous substrate comprising said absorber compound and said MSCN alkali metal thiocyanate, by pouring over a solution of CuSCN, preferably a solution of CuSCN in dipropyl sulphide, and - said illumination treatment is carried out on the device thus obtained. The advantage of the new photovoltaic device of the present invention is that it can maintain high photovoltaic efficiency when stored in a sealed state while maintaining a low manufacturing cost since it uses materials that do not require not high purity and since it can be manufactured with low cost techniques (in particular, it does not use a high vacuum technique such as that used for silicon-based devices).

The photovoltaic cells of the present invention exhibit better photovoltaic performance compared to older devices using the same design; they have in particular a photocurrent higher short circuit and higher photovoltaic conversion efficiencies. The present invention more specifically provides a device which has a short-circuit photocurrent greater than or equal to 10 mA / cm 2, an open-circuit voltage Voc (at I = 0) greater than 0.50 V and a conversion efficiency higher than 3% under an irradiation of 1000 W / m2 and the photovoltaic performances remain stable for at least 300 days. In addition to this interpenetrating configuration, the three constituents must satisfy certain conditions, especially as regards the adaptation of the respective energy bands. Taking into account the band model for semiconductors as a first approximation, the conduction band of the absorber compound must be less negative than the conduction band of the n-type semiconductor compound (in the convention most frequently used, the energy levels have negative values, which start at zero which is the vacuum level), and the valence band of the absorber compound must be more negative than the valence band of the p-type semiconductor compound, and all this to allow the injection of electrons and holes respectively. The fact that the three constituents are inorganic and solid materials provides the potential advantage of a much longer durability for outdoor applications and more particularly for application on home roofs. Other advantages and features of the present invention will appear more clearly in light of the following detailed description of various examples and embodiments and the results obtained in association with the following figures. FIG. 1 represents the curve of the photocurrent density (mA / cm 2) as a function of the voltage (V) (curves IV) of a TiO 2 / Sb 2 S 3 / (LiSCN) CuSCN cell illuminated at 1 sun (1,006 W / m 2) ) measured at different times t after the start of illumination in open-circuit ambient air (the active area of the cell being 0.54 cm -1): (a) t = 0; (b) t = 10 minutes; (c) t = 20 minutes; (d) t = 100 minutes. FIGS. 2A to 2E show the evolution curves over time (t = 0 to 3000 minutes) of the short-circuit current density Jsc (FIG. 2A), of the open-circuit voltage Voc (FIG. 2B). , the filling factor ff (FIG. 2C), the efficiency ri (%) (FIG. 2D) and the series resistance Rs (4) (FIG. 2E) during the open-circuit illumination and at about 1 sun, of TiO2 / SbzS3 / (LiSCN) CuSCN cells under an initial dry N2 (A) atmosphere, then dry air (B) and finally dry N2 (C) for three different cell types: (o) without heat treatment before illumination (stored in a glove box under N2 at room temperature for 15 hours); (•) heated in a N2 glove box at 80 ° C for 15 hours; (a) heated in a glove box in synthetic dry air at 80 ° C for 15 hours. FIGS. 3A to 3D show the evolution curves over time (t = 0 to 400 days) of four normalized performance parameters at 1 sun: short-circuit current density Jsc (mA / cm 2) (FIG. 3A) , open-circuit voltage Voc (V) (FIG. 3B), efficiency ri (%) (FIG. 3C) and fill factor ff (FIG. 3D) under continuous irradiation of about 1 sun of three TiO2 / SbzS3 / type cells. (LiSCN) CuSCN under controlled flow atmosphere under different conditions: (.) N2 flow, open circuit (CO); (A) N2 flow, short circuit (C.C.); (o) Synthetic air flow, open circuit (OO).

FIGS. 4A to 4D show the evolution curves of t = 0 at t = 3000 minutes of the efficiency r ~ (FIG. 4A), the short-circuit current density Jsc (FIG. 4B), the filling ff (FIG. 4C), open-circuit voltage Voc (FIG. 4D) during open-circuit illumination and at about 1 sun for TiO2 / SbzS3 / (alkali metal thiocyanate) cells CuSCN under an initial N2 atmosphere dry (A), then dry air (B) and finally dry N2 (C) having undergone four different thiocyanate treatments and three different heat treatments. For each thiocyanate treatment: (o) untreated with salt, (A) treated with LiSCN, (^) treated with KSCN, (0) treated with NaSCN for thermally treated cells under N2; the symbols corresponding to the black color represent the untreated cells; the symbols corresponding to the gray color represent heat-treated cells in dry air. FIG. 5 represents the evolution curve of t = 0 at t = 3000 minutes of the series resistance of the cell during open-circuit illumination at about 1 sun for TiO 2 / Sb 2 S 3 / (alkali metal thiocyanate) cells. ) CuSCN under an initial atmosphere of dry N2 (A), then dry air (B) and finally dry N2 (C) having undergone four different thiocyanate treatments and three different heat treatments. For each thiocyanate treatment: (o) untreated with salt (D), (A) treated with LiSCN, (^) treated with KSCN, (0) treated with NaSCN for cells treated thermally under N2; the symbols corresponding to the black color represent non-heat treated cells; the symbols corresponding to the gray color represent heat-treated cells in dry air. FIG. 6 shows the photocurrent density (mA / cm 2) versus voltage (V) curves (curves IV) of 1 TiO 2 / Sb 2 S 3 / (KSCN) CuSCN cells at sun with different concentrations of KSCN, ie with the following concentrations for the following symbols: (^) =: 0.001M; (o) = 0.O1M; (•) _, (•) 0.1M; (?), (?) 0.5M; (x) _, (x) 1M; (A), (A) 2M 2M and (A) = 5M. FIG. 7 is a schematic representation of the internal structure of a cell with portions of an oxidized interface layer according to the invention as observed by Transmission Electron Microscopy (TEM) analysis. . Experimental section 1.1. Preparation of compact and porous TiO2 layers. Transparent conductive oxide (TCO) glasses of commercially available F-doped SnO2 from Asahi Glass were used as the front contact. Spin pyrolysis was deposited on a TiO 2 compact hole barrier layer about 20 nm thick (confirmed by MEB and MET). Porous nanocrystalline TiO 2 layers having a thickness of about 3 μm, average particle size of about 40-50 nm and 150-300 roughness factors were manufactured as described in a previous publication.

1.2. Preparation of TiO2 / Sb2S3 / (alkali metal thiocyanate) CuSCN cells. Antimony sulphide was deposited on the porous nanocrystalline TiO 2 by Chemical Bath Deposition (DBC) 3-9 as described below.

The DBC bath was obtained by preparing an initial solution of about 1M SbCl3 in acetone and diluting it with cold aqueous solution of about 1M Na25203 and cold water to obtain final concentrations of Sb3 +. and S2O32- about 0.025 M and about 0.25 M, respectively. The samples were immersed vertically in the bath and placed in a refrigerator at 5-10 ° C. The DBC reaction was allowed to proceed for a typical duration of 2 hours. The samples were then rinsed twice in two beakers containing distilled water, immersing the sample successively in each beaker and shaking for 5 seconds and dried by blowing N2 gas on the surface of the sample. horizontally for several seconds. After this, the samples were annealed in a glove box under nitrogen at 300-320 ° C for about 15-30 minutes. The samples were then immersed in 0.5M aqueous solution of either of LiSCN, KSCN or NaSCN for 19 seconds. Salt untreated samples were also prepared for comparison. Other concentrations for the KSCN salt were also used for comparison purposes. The samples were then dried by blowing N2 gas on the surface for several seconds. Just after this process, a filling with CuSCN was carried out by impregnation and evaporation of a solution of CuSCN in dipropyl sulphide and, just after the filling of CuSCN, a gold layer back contact was deposited. approximately 40 nm thickness by thermal evaporation using an Edwards 306 evaporator.

1.3. Drying of the cell by heat treatment. Until their characterization, some of the cells completed under the following three different conditions were stored in a glove box under nitrogen at room temperature for 15 hours (hereinafter referred to as non-heat treated cells). a hot plate at 80 ° C placed in a glove box under nitrogen for 15 hours (cited as thermally treated cells under N2), 3. on a hot plate at 80 ° C disposed in a glove box in synthetic dry air for 15 hours. hours (cited as heat-treated cells in dry air). These post-treatments after the deposition of the rear contact electrode constitute the final process of the preparation of the cell: a test was carried out in order to verify the effect of the drying on the cell (such as the elimination of possible traces of dipropyl sulfide solvent used in CuSCN filling and the effect of residual moisture inside the cell).

The measurements of current-voltage curves I-V and quantum efficiency (QE also known as IPCE) were recorded with the assemblies mentioned. 1.4. Illumination treatment.

The cells were subjected to illumination under different gaseous atmospheres in order to observe the effect of gas and heat treatments. This illumination treatment consists of an irradiation of about 1 sun (about 1000 W / m2) in open circuit from 20 minutes to 1200 minutes in a controlled atmosphere of gas. The cells were left in a solar simulator under continuous illumination with irradiation close to 1 sun. The temperature of the cell was not controlled but was in the range of about 30-35 ° C. Illumination was achieved under the following three conditions: (a) ambient air (surrounding air) or (b) controlled atmosphere of synthetic dry air or (c) flow of N2 gas. The I-V curves were periodically measured during illumination. The cells were sealed prior to illumination as follows. They are deposited in a cell container consisting of a canister with a glass window for illumination and a gas inlet and outlet to allow a controlled gas environment, under a controlled flow of gas either: (a ) dry N2, or (b) synthetic dry air. Sealed cell measurements were then made in such controlled atmospheres. They were initially illuminated in synthetic dry air for a few hours. The N 2 gas atmosphere was either modified or stored in dry air and a low flow of this gas was continuously maintained. The cells were left open or short-circuited and performance was measured from moment to moment. In these controlled stability tests, the evolution of performance parameters for three cells in different states over almost a year is examined.

1.5. Measures. The I-V curves and the evolution of Jsc (mA / cm2), Voc (V), ff, the Rs series resistance (4) and the efficiency ri (%) were periodically measured.

The solar cell series resistance was estimated from a single I-V plot under illumination. This consists in obtaining the derivative of curve IV (under a single irradiation) by scanning up to a sufficiently high forward bias voltage in order to make a plateau on the (-dV / dI) = f (V) plot. , which directly provides the value of Rs. SEM images were obtained with a Hitachi S-4700 field-effect scanning electron microscope coupled with Noran's SIX EDX (Energy-Dispersive X-Ray Microanalysis) system. MET analysis was then performed with a JEOL 2100F FEG-200 kV microscope, equipped with a STEM accessory, and an integrated JEOL JED-2300T EDX analysis device.

2. Examples The following Examples 1-4 were carried out with the material and according to the methods described in paragraph 1 above and the results are discussed in paragraph 3.

Comparative Example (1) An untreated TCO / (Nanocrystalline TiO2) / Sb2S3 / CuSCN / Au sealed cell was prepared for use and its photovoltaic performance was characterized under N2 atmosphere. The energy conversion efficiency was less than 0.1%.

Example (2) The same cell as in Example (1) was treated with an illumination treatment of the invention and was characterized under ambient air (surrounding air). Efficiency increased to 1.2% in 15 hours after illumination started because of the formation of said oxidized species interface layer. However, when the atmosphere was changed by N2, the performance dropped to 0.4% due to insufficient formation of the interface layer with this cell composition.

Comparative Example (3) A TCO / (Nanocrystalline TiO2) / Sb2S3 / LiSCN, CuSCN / Au cell was prepared and characterized for its voltaic performance under an N2 atmosphere with illumination treatment. LiSCN was introduced into the cell by immersing the sample in 0.05 M aqueous LiSCN solution prior to CuSCN deposition. The initial efficiency at start of illumination was about 0.2%, then increased to 1.5% in 5 days leaving the cell in open circuit under illumination. The slow evolution of the performance is attributed to the lack of oxygen for the formation of the interface layer. Only adsorbed oxygen initially existing inside the cell seems to be functional. The formation of the interface layer does not appear due to the limited amount of oxygen.

Example (4) of the present invention The same cell as in Example (3) was illuminated and measured in dry air. Initial efficiency was about 0.2%, then increased to 3.8% in 2 hours leaving the cell in open circuit under illumination. The faster evolution of the performance is due to the formation of the interface layer in the presence of oxygen and illumination. It has been possible to maintain for more than 300 days an efficiency higher than 1.7% during the modification in N2 atmosphere after the illumination treatment.

3. Results and discussion 3.1. Performance of the cell with illumination in the ambient air. The cells were strongly influenced by illumination in that cell performance typically evolved from a low initial efficiency to a higher efficiency when placed in contact with ambient air for a period of time. illumination and storage. It has been shown that oxygen is involved in this effect. The best cell efficiency was 3.7% at about 1 sun for LiSCN treated cells. The cells have been shown to function for more than 300 days maintaining an efficiency greater than 1.5% at about 1 sun.

The cells were stored overnight in a glove box under N2 prior to measurement. Higher cell efficiencies were obtained after holding the cells under a sunlight in ambient air and in an open circuit for about 20-200 minutes. The cells presented before illumination an efficiency typically <1% in their first I-V measurements. Figure 1 shows the evolution of the I-V curves of one of the best cells during illumination. As shown in the figure, the performance improved over time, the highest cell efficiency r ~ at about 1 sun (1006 W / m2) and at t = 100 minutes after the start of illumination being 3.7% with a 1-sun normalized short circuit current density of 11.6 mA / cm 2, an open-circuit voltage Voc of 0.56 V and a fill factor ff of 0.58 then that the initial efficiency before the start of illumination (t = 0) was only 0.8%. The time required to achieve maximum efficacy varied from cell to cell. In a systematic experiment performed on approximately 36 cells made and measured under similar conditions with LiSCN treatment, the cell efficiency was in the range of 1.5-3.7% (mean 2.9%). %), Jsc in the range of 6.1-13.2 mA / cm 2 (average 10.5 mA / cm 2), Voc in the range of 0.43-0.58 V (average 0.53 V) and ff in the range of 0.44-0.60 (mean 0.52). Although LiSCN treatment was used for cells with a TiO2 / Sb2S3 / CuSCN configuration for their superior performance, it was found that non-salt-treated cells also benefit from the illumination effect from an initial efficiency at 1 sun of <0.5% to a final efficiency of 1-1.5% (Jsc about 6-9 mA / cm 2, Voc about 0.4, ff about 0.4). Their performance evolution during illumination is slower than for LiSCN-treated cells, the time required to reach peak performance typically being about 10-20 hours. Higher series resistance and lower Voc are characteristic of untreated salt cells. Different salt treated cells using different thiocyanates, such as KSCN and NaSCN, were also studied. Although slightly different in behavior, the overall pattern was similar to that of LiSCN-treated cells.

The difference in behavior may be related to the difference in their hygroscopic nature or the type of cation and the volume of the latter. The detailed results will be quoted below. The effect of illumination also appeared without the UV portion of the radiation (using a separating UV filter with 100% transmission coefficient <500 nm), so that the effect of the illumination It is not exclusive to UV, unlike the UV effects cited by using other nanocrystalline TiO 2 cells. Following the above results, the stability of the sealed cells prepared under N2. It then appeared that they did not have the same illumination effect as that of cells exposed to ambient air. This suggests that oxygen and / or moisture are related to the observed illumination effect. In order to clarify these influences, experiments were carried out under a controlled atmosphere as described below.

3.2. Effect of gas and heat in the illumination. Three different types of thermally treated or non-heat treated cells, as described in section 1.3, were subjected to illumination in different gaseous atmospheres in order to observe the effect of gas and heat treatments, illumination at about 1 sunshine (maintaining the temperature of the cell at 40 ° C) starting under N2 dry for 500 minutes (about 8 hours), continuing under dry air for 1000 minutes (about 16.5 hours), then finally under N2 dry again for 1200 minutes (about 20 hours). The I-V curves were periodically measured during open-circuit illumination. Figure 2 shows the evolution of Jsc (mA / cm2), Voc (V), ff, Rs series resistance (4) and efficiency ri (%) during illumination. The clear difference in all performance parameters can be seen between the first dry N2 illumination and the subsequent dry air illumination for all three different cell types. It is clear that oxygen plays an important role in improving the performance of the cell.

It should be noted in the first illumination under N2 sec of FIG. 2 that the heat treated cell under N2 had the lowest ri with the weakest Jsc and Voc among the three cell types. Although there was a slight change in the performance parameters, such as Voc, ff, and Rs for the heat treated cell under N2, the rI was nearly constant at lower values. It should also be noted that the initial series resistance of the thermally treated cell under N2 was significantly higher than that of the other cells. It appeared, for the untreated heat cell, a clear evolution of ri unlike the thermally treated cell under N2, as shown in FIG. Its initial series resistance was the lowest of the three cell types. For the heat-treated cell under dry air, the highest Jsc, Voc and ri can be observed among the cells and the Rs much lower than for the heat-treated cell under N2 at the start. Then the Jsc, Voc and ri of the cell heat treated in dry air are then lower than those of the untreated heat cell 30 minutes after the start of the illumination. Such behaviors can be interpreted during the first illumination under N2 sec as follows. The untreated heat cell contains the most residual water among the cells, providing the lowest Rs before illumination. It also contains adsorbed oxygen during cell manufacture, providing the influence of oxygen on illumination. The residual water comes from the hygroscopicity of LiSCN associated with the wet chemical process for the preparation of the cell. The relationship between the series resistance and the water content is based on results obtained in separate experiments, in which the series resistance is significantly lowered by the humidity of the ambient gas. The heat-treated cell under N2 contains the least water and oxygen adsorbed inside the cell, resulting in the highest Rs series resistance and almost no effect of oxygen during illumination in the direction performance improvement. Note, however, a remarkable decrease in Rs for this cell during illumination in the figure. This is interpreted as a consequence of the fact that the cell still contains a small amount of oxygen to cause this change with illumination. The following possible reactions involving oxygen and illumination may be considered: photocatalytic oxidation of organic impurities, such as the dipropyl sulfide solvent, and / or doping of CuSCN with (SCN) 2 formed by photocatalytic oxidation of SCN- or with active oxygen species, such as OH radicals. It is believed that the heat-treated cell in dry air contains less water than the untreated heat cell and more adsorbed oxygen than the heat-treated cell under N2. This higher oxygen content thus leads to a lower initial Rs even just after the start of illumination despite its lower water content before illumination. Another possible interpretation is that the illumination can be done in N2 even in the absence of adsorbed oxygen but an increase in the photocurrent would appear over a much longer period (several days). This process could in this case be due to the removal or photodegradation of organic impurities under a gas flow, possibly assisted by photoactive antimony sulphide. The beneficial effect of oxygen on the Voc and the series resistance would not be reached under N2, as explained below, and the final efficiency in an N2 atmosphere after continuous illumination for several days would be less than that in an atmosphere of dry air. We can see in Figures 2 the rapid evolution of Jsc, Voc and r ~ in the subsequent illumination under dry air. It should be noted in the figure an initial decrease of ff for the three types of cells just after the modification in the illumination under dry air. Such a decrease corresponds to the increase of Jsc as shown in the figure. The decrease in ff suggests that the evolution of cell performance is not necessarily related solely to series resistance. We interpret such a behavior as follows: the photocurrent increases by a certain mechanism at the start of the illumination under dry air; the series resistance, however, is not low enough to maintain a higher ff with a higher photocurrent in the initial step of dry air illumination, resulting in a decrease in ff. The decrease in Rs, however, accompanies the process, making it possible to recover ff slowly after having reached its minimum. Increasing Voc under dry air also helps to recover ff. This can be clearly noticed, particularly for the heat-treated cell under dry N 2. It can be concluded from the previous discussion that oxygen has two independent roles: the first is to lower Rs and the second to increase Jsc and Voc independently of Rs. The role of residual water present within the cell is not clear today although it is found that water accelerates the degradation of the cell especially with oxygen.

In the last illumination under dry N2 following dry air illumination, the Jsc of the three cell types increased for several hours and then slowly decreased, the Voc starting to decrease just after the change to dry N2, as shown in FIG. FIG. 2 can be seen in FIG. 2 a decrease in ff and an increase in Rs for the thermally treated cell under N2 but such a modification can not be observed in FIG. 2 for the other cells. As shown in the following paragraph concerning cell stability tests, such an initial decrease in cell performance after modification in N2 atmosphere tends to stabilize over time, with efficiency being maintained at more than 1 , 5% after illumination for more than 300 days in open circuit. This is one of the most important features of LiSCN-treated cells. In the case of untreated salt cells, which achieved an efficiency of about 1.2% by dry air illumination, the efficiency dropped to less than 0.5% typically in about 15 hours after the modification. in an atmosphere of N2 (lines not shown in FIG. 2).

3.3. Cell stability tests.

Cells were made according to the standard procedure given above with LiSCN treatment. They were initially illuminated in synthetic dry air for a few hours. The gaseous atmosphere was either changed to N2 or kept in dry air; the gas flow being introduced continuously at a low flow rate. The cells were left open or short-circuited and performance was measured from moment to moment. Figure 3 shows the evolution of performance parameters for three cells under different conditions over almost a year in these stability tests. The cell under N2 shorted seems to be stable while the other two cells in open circuit (N2 or air) show a decrease in performance in the first 100-150 days and after that tend to stabilize. Efficiency after one year is greater than 1.5% for all three cells and 1-sun Jsc is maintained in the 7.5-10 mA / cm2 range. The fluctuations observed in the plots are due to the fluctuations of the irradiation of the old lamp used in these stability tests (even if it is well calibrated) and can also be explained by the changes in cell temperatures between the points measurement. As compared to ambient air stability tests, it appears that ambient humidity is the cause of cell degradation and should be avoided. For initial activation of MSCN or CuSCN oxidation, the water is beneficial, but after reaching maximum efficiency, the water would cause or facilitate further oxidation of the absorber compound, resulting in degradation of the cell.

3.4. TiO2 / Sb2S3 / (alkali metal thiocyanate) CuSCN cells. Although it has already been found above that a LiSCN treatment in the cell preparation and the ambient gas strongly influence the performance of the cell, several different cells treated with other thiocyanates, such as KSCN, NaSCN and untreated by IV curve measurement to obtain an insight into the origin of the effect of thiocyanates and ambient gas. For each cell treated with thiocyanate and untreated with salt, three different conditions were adopted for storing samples after completion of cell manufacture to prepare the following three cell types (with reference to the experimental section): thermally treated cells under N2, heat-treated cells in dry air and non-heat treated cells. These three different types of cells were then subjected to illumination under different gaseous atmospheres in order to observe the effect of gas and heat treatment, illumination at about 1 sun (maintaining the temperature of the cell at 40 ° C. ) starting under N2 dry for 500 minutes, continuing under dry air for 1000 minutes, then finally under N2 dry again for 1200 minutes. Illumination refers to an illumination in visible light at about 1 sun in open circuit. The I-V curves were periodically measured during illumination. FIGS. 3A to 3D show the evolution curves of the energy conversion efficiency ri (%), the short-circuit current density Jsc (mA / cm 2), the open-circuit voltage Voc (V) and ff filling factor during illumination for twelve different cells consisting of non-salt treated cells, treated with LiSCN, NaSCN and KSCN with the three different sample storage conditions for each type of thiocyanate treatment.

We first focused on the untreated thiocyanate cell. The highest efficiency was about 1.2% for this cell type under dry N2 illumination at t = about 1450 minutes. Regardless of this experiment, the highest efficiency recorded so far is 1.5%, all cells exhibiting similar characteristics of evolution of the performance parameter during illumination. It should be noted in FIG. 4 that the initial efficiency, Voc and Jsc for the heat-treated cell under dry air are the highest among the three different heat treatments at the start of the initial illumination in N2 sec, the factor ff being the weakest of these. Ri, Voc and Jsc then decreased over time in N2 sec, with the factor ff increasing. In a subsequent atmosphere of dry air, all three cells responded rapidly to the introduction of air, with the ri, Voc, Jsc increasing, and the ff factor decreasing. At the end of dry air illumination, the untreated heat cell had the highest ri. It should be noted that the factor ff is recovered in the middle of the illumination under dry air, as shown in the figure. During the second N2 atmosphere introduction at t = about 1500 minutes, the rI, Voc and Jsc began to gradually decrease although the initial temporary increase of Jsc was observed for the untreated heat cell. The results for untreated salt cells clearly indicate that oxygen is involved in photovoltaic processes. It can be postulated that the heat treatment influences the adsorption of oxygen and water, producing the evolution difference during illumination. Thereafter, the cells treated with thiocyanate were concentrated. The efficiencies shown in FIG. 3A for the nine thiocyanate-treated cells are between 1.8 and 3%, the heat-treated cell under dry air in a KSCN treatment having the highest efficiency. It is possible, however, that the observed difference in cell characteristics may be due to the difference in thiocyanates or experimental variation due to other unknown factors since a similar degree of variation between 1.5 and 3.5 was observed. % (mean 2.9%) for 36 identical cells treated with LiSCN in separate experiments. It has also been found that the humidity in the measuring atmosphere influences the evolution of the performance of the cell during illumination. These facts are really the reason why the measurements were made in this study in a state of dry gas with a heat treatment. The following general laws have been deduced by repeating similar experiments several times. Thiocyanate-treated cells always provide higher performance than non-salt-treated cells after dry air illumination. KSCN-treated cells show the highest Jsc and Voc in dry N2 illumination among four different thiocyanate treatments. The heat-treated cell under dry air provides, for KSCN-treated cells, the highest cell performance among the three different heat treatments. For LiSCN-treated cells, the untreated cells still provide the highest cell performance. The ff factor of the KSCN-treated cells is the highest and that of the weakest LiSCN-treated cells. During the second introduction of dry N2 atmosphere following dry air illumination, after the initial temporary increase of Jsc, a subsequent progressive decrease thereof and a simultaneous decrease of Voc are observed.

Although the data are not shown, illumination has always been performed in ambient air (surrounding air) with untreated heat-treated cells containing thiocyanates, especially before recognizing the influence of oxygen and moisture. The following general aspects have been found under such conditions. For cells treated with KSCN and NaSCN, the initial evolution of the illumination is not reproducible as a function of the water content. They are very sensitive to water coming from the ambient air and existing initially inside the cells. Higher water content results in much lower performance. In the case of LiSCN-treated cells, the evolution is observed with a higher initial Jsc, a poor ff and S-shaped deformed I-V curves even with a higher water content. Cell characteristics typically vary from cell to cell or moment to moment. In a state of ambient air (ambient air), even the performance progresses during illumination with an appropriate humidity, the performance begins to fall gradually after reaching the maximum performance with the initial illumination. Efficiency typically drops to less than 1% in several days depending on the degree of humidity. Once the performance of these cells has dropped into a wet state, it is not recovered by drying. This suggests that some irreversible change occurs with water. The untreated salt cell also does not suffer from such an influence of moisture over a period of several tens of hours. Its efficiency typically begins to increase with an improvement in ff and a decrease in the series resistance of the cell during the introduction of moist air. Figure 5 shows the series resistance of the twelve different cells above, which was measured at different times during illumination. At t = 0 (actually several tens of seconds to several minutes after start of illumination due to the sequential acquisition of the data), the four thermally treated cells under N2 with KSCN, LiSCN, NaSCN and untreated salt exhibited higher series resistance compared to other cells as shown in the figure. It should be noted in the figure a clear difference between thiocyanate-treated and non-salt-treated cells, the former having a lower resistance. By estimating that the heat treatment makes the difference from the series resistance, it can be postulated that the initial series resistance at t = 0 is related to the initial amount of adsorbed oxygen and water inside the cells. The results shown in Figure 5 can then be interpreted as the consequence of a photocatalytic reaction occurring during illumination involving oxygen, thiocyanate, water and other residual impurities. It should be remembered, however, that the series resistance measured in the dry N2 atmosphere is not high enough to significantly lower Jsc. In other words, the series resistance itself is not the main reason for r ~ and lower Jsc during illumination under dry N2 in Figure 1. The improvement in the performance of the cell, observed during the introduction of oxygen can therefore be interpreted as a consequence of the injection of photogenerated charge carriers improved for some reasons. 3.5. Effect of the concentration of the solution used for KSCN treatment. Figure 6 shows the I-V curves of KSCN-treated cells with different concentrations of 1 KSCN dipping solutions. The I-V curves, for which the highest performance was obtained during ambient air illumination (surrounding air), are shown for each concentration of KSCN immersion solution in the figure. It is quite surprising that even the cell treated with a 5M immersion solution provides an important performance. Thiocyanates were thought to be adsorbed on the TiO2 layers embedded in the adsorber compound and found only at the boundary between them and the CuSCN layers since the influence of the thiocyanates was initially determined. for TiO2 / CdS / CuSCN cells. To support this first assumption, a MET analysis with a STEM-HAADF imaging device in the middle of the cross-section of the KSCN 5M-treated cell and an EDX spectrum for the surface corresponding to the insertion into the image.

The estimated atomic ratio of K / Cu was about 1.7 for this sample. Values, however, were scattered between 0.3 and 2 depending on the layout. For the various TEM and STEM image formations with different modes, it was found that the CuSCN and KSCN layer consisted of nanocrystalline points of about 5 nm in size. We could not distinguish each material in the MET image. The data, however, indicate that KSCN is distributed through porous TiO2 with CuSCN. The same analysis was performed for the 0.5 M KSCN treated cell. The estimated atomic ratio of K / Cu was 0.03 to 0.07. KSCN was distributed similarly with CuSCN.

3.6. Structure analysis. An analysis presenting the MET, STEM / HAADF image formation and the STEM / EDX mapping shows that the morphology of a cell structure according to the invention can be schematically represented in FIG. 7, in which the cell (1) comprises a porous substrate (2) consisting of 10 to 100 nm TiO 2 nanocrystals which constitutes a layer with a thickness greater than 1 μm, preferably from 2 to 10 μm, a first face of said porous substrate located on a first a front contact substrate (7) which is conductive and transparent, similar to a conductive glass, and which is also coated with a barrier layer which is compact (non-porous) and transparent (7a), preferably made of said semiconducting metal oxide; n-type conductor, and - said absorber forming aggregates (4) with a size of 10-200 nm, said absorber aggregates being embedded in TiO2 nanocrystals with smaller aggregates of CuSCN and said absorber not reco not uniformly and completely TiO2 with the Sb2S3 deposition process, and - a CuSCN (3) filler layer consisting of well-crystallized nano-domains (3-1) of size about 3-5 nm, which fills less than 10% of the pore volume (2a) of the porous TiO 2 substrate, preferably more than 15%, and - MSCN molecules (6) taken in the CuSCN (3) filler layer as well as in the TiO 2 structure porous (2) in which absorber aggregates (Sb2S3) are embedded, the aggregates of MSCN (6) and CuSCN (3-1) being mixed they are uniformly distributed in the porous structure as well as in the overlay (3) of CuSCN, and - interface layer portions (5) of oxidized species formed between some of said absorber aggregates and said TiO2 (2b) particles or CuSCN particles (3), said interface layer portions (5). having a thickness of 0.1 to 5 nm, the second face of the porous substrate (2) covered with a uxth rear contact conductive substrate (8), and - said filler layer also constitutes an overlayer having a thickness of at least 10 nm located between said porous substrate (2) and the conductive layer of said rear contact of the conductive substrate (8a ), and - said porous substrate and its absorber and its filler layers (2, 4, 3) are confined between said two conductive substrates of front contact (7) and rear contact (8). A metal box with a glass window was used in the above experiment to seal the above cell for practical purposes. The actual cell will however be covered with a layer of glass or transparent plastic to seal the cell walls (9).

The electrodes 9a through the walls (9) allow contact with the front contact (7) and the rear contact (8).

References: (1) Kavan, L .; Gratzel, M. Electrochim. Acta 1995, 40, 643. (2) Larramona, G .; Choné, C .; Jacob, A .; Sakakura, D .; Delatouche, B .; Pere, D .; Cieren, X .; Nagino, M .; Bayon, R. Chem. Mater. 2006, 18, 1688. (3) Mandate, K.C .; Mondai, A. J. Phys. Chem. Solids 1990, 51, 1339. (4) Deshmukh, L.P .; Holikatti, S.G .; Rane, B.P .; More, B.M .; Hankare, P.P.J. Electrochem. Soc. 1994, 141, 1779. (5) Lokhande, C.D .; Sankapal, B.R .; Mana, R.S .; Pathan, H.M .; Muller, M .; Giersig, M .; Ganesan, V. Appt. Surface Sci. 2002, 193, 1. (6) Grozdanov, I.T. Semicond. Sci. Technol. 1994, 9, 1234. (7) Nair, M.T.S .; Paria, Y .; Campos, J .; Garcia, V.M .; Nair, P.K. 3. Electrochem. Soc. 1998, 145, 2113. (8) Salem, A.M .; Selim, M.S. J. Phys. D: Appt. Phys. 2001, 34, 12. (9) Yesugade, N.S .; Lokhande, C.D .; Bhosale, C. H. Thin Solid Films 1995, 263, 145. (10) O'Regan, B .; Schwartz, D.T., Chem. Mater. 1998, 10, 1501.

Claims (15)

REVENDICATIONS1. Solid photovoltaic cell (1) of the type comprising 3 inorganic and solid materials, comprising respectively: - a porous layer of an n-type and transparent semiconductor compound (2), - a layer of a semiconductor compound of the type p and transparent (3), filling at least in part the pores (2a) of said porous layer (2), and - an inorganic absorber compound, forming aggregates (4), disposed between the two layers of said semiconductor compounds n-type and, respectively, p-type, which are not at least partly in contact, characterized in that it further comprises oxidation products (5) different from said semiconductor compounds and said compound absorber, said oxidation products forming discontinuous portions of interface layers located between the two layers (2, 3) of said two n-type and p-type semiconductor compounds and / or between said aggregates of absorber compound (4) and a layer of p-type semiconductor compound (3). 2. Cell according to claim 1, characterized in that said oxidation products comprise chemical species resulting from the partial oxidation of said absorber compound and / or said p-type semiconductor compound. 3. Cell according to one of claims 1 or 2, characterized in that said p-type semiconductor compound is CuSCN and said absorber compound is an antimony antimony sulfide compound thermally annealed, such as Sb2S3 . 4. Cell according to claim 3, characterized in that it further contains a thiocyanate compound MSCN (6), wherein M is an alkali metal, preferably M is Li, Na or K, and said interface layer comprises a compound (SCN) 2 and / or a polymer (SCN) n. 5. Cell according to claims 3 and 4, characterized in that the weight ratio of MSN to CuSCN is 0.001 to 2. 6. Cell according to one of claims 1 to 5, characterized in that it is sealed inside walls (9), said walls being at least partly transparent and preferably containing a dry gas atmosphere. 7. Cell according to one of claims 1 to 6, characterized in that said transparent n-type semiconductor compound is a metal oxide such as TiO2, ZnO or SnO2 and, preferably, TiO2. 8. Cell according to one of claims 1 to 7, characterized in that it has an interpenetrated configuration, wherein said n-type semiconductor compound is in the form of a porous substrate (2) comprising pores ( 2a) of size from 10 to 100 nm, the inner surface of said pores being at least partially coated by said aggregates of absorber compounds (4), and said pores being filled in a volume proportion of at least 10%, preferably of more than 15%, with a filling layer (3) consisting of said p-type semiconductor compound, and said portions of oxidation product interface layers (5) having a thickness of 0.1 to 5 nm and, preferably, from 0.1 to 1 nm. 9. A method for preparing a cell according to one of claims 1 to 8, wherein said oxidation products of said interface layer (5) are obtained by an oxidation treatment by illumination with visible light, in the presence of an oxygen-containing gas atmosphere, a device comprising the following components of said cell, a said porous layer of a transparent n-type semiconductor compound (2) and a said layer of compounds transparent p-type conductor (3) at least partially filling said pores (2a) of said porous layer (2), and an inorganic absorber compound, present in the form of aggregates (4), disposed between said layers of said semi compounds and n-type and p-type drivers, which are not, at least in part, not in contact. 10. The method of claim 9, characterized in that said oxygen-containing gas atmosphere is ambient air, preferably containing a moisture content lower than the supersaturation rate of air at room temperature. 11. Method according to one of claims 9 to 10, wherein said illumination treatment comprises illumination of the cell with a visible light of 0.1 to 5 kW / m2, for a period of 5 minutes to 20 hours. . 12. Method according to one of claims 9 to 11, characterized in that said illumination treatment comprises illumination of the cell under open circuit conditions. 13. Method according to one of claims 9 to 12, characterized in that the series resistance and the parameters on which the photovoltaic conversion efficiency of the cell depends, such as the short-circuit photocurrent density (Jsc ), and the open circuit voltage (Voc), are monitored during said illumination process and said cell is subjected to said illumination process as the photovoltaic conversion efficiency increases, said irradiation being stopped when said photovoltaic conversion efficiency is the highest, and / or as the series resistance of said cell decreases, said irradiation being stopped when said resistance is the lowest. 14. Method according to one of claims 9 to 13, characterized in that said illumination treatment is performed on a nonscelled cell, said cell being sealed just after said illumination treatment, preferably in a dry gas atmosphere. 15. Method according to one of claims 9 to 14, characterized in that one prepares a said cell comprising an alkali metal thiocyanate compound MSCN (6), wherein M is an alkali metal, preferably Li, Na or K, by performing the steps in which: - depositing said absorber compound on said porous layer of n-type semiconductor compound, and - introducing said alkali metal thiocyanate salt MSCN, which is poured on said porous substrate coated with said absorber compound, and - depositing a said p-type semiconductor compound filler layer, comprising CuSCN, on said porous substrate comprising said absorber compound and said alkali metal thiocyanate MSCN, by pouring therefrom above a solution of CuSCN, preferably a CuSCN solution in dipropyl sulphide, and said illumination treatment is carried out on the device thus obtained.