MIXED OXIDES AND SULPHIDES OF BISMUTH AND COPPER FOR PHOTOVOLTAIC USE

Abstract

The invention relates to a material comprising at least one compound having formula Bi.sub.1-xM.sub.xCu.sub.1-y-M.sub.yOS.sub.1-zM.sub.z, the methods for producing said material and the use thereof as a semiconductor, such as for photovoltaic or photochemical use and, in particular, for supplying a photocurrent. The invention further relates to photovoltaic devices using said compounds.

Claims

1. A material comprising at least one compound of formula (I):
Bi.sub.1-xM.sub.xCu.sub.1-y-M.sub.yOS.sub.1-zM.sub.z(I) wherein: M is an element or a mixture of elements chosen from group (A) consisting of Pb, Sn, Hg, Ca, Sr, Ba, Sb, In, Tl, Mg, rare earth metals, M is an element or a mixture of elements chosen from group (B) consisting of Ag, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Ga, Mg, Al, Cd, M is a halogen, x, y and z are numbers less than 1, with at least one of the numbers x, y or z being non-zero, and 0<0.2.

2. A process for preparing a material according to claim 1, the process comprising solid milling a mixture comprising at least one of the inorganic compounds of bismuth and copper, and optionally at least one oxide, sulfide, oxysulfide, halide or oxyhalide of at least one element chosen from Bi and elements from group (A), and optionally at least one oxide, sulfide, oxysulfide, halide or oxyhalide of at least one element chosen from Cu and elements from group (B).

3. A process for preparing a material according to claim 1, the process comprising: (a) preparation of at least one solution comprising metallic precursors in the form of at least one salt of the inorganic compounds of bismuth, and optionally at least one oxide, sulfide, oxysulfide, halide or oxyhalide of at least one element chosen from Bi and elements from group (A) consisting of Pb, Sn, Hg, Ca, Sr, Ba, Sb, In, Tl, Mg, rare earth metals, and (b) preparation of at least one solution comprising metallic precursors in the form of at least one salt of the inorganic compounds of copper, and optionally at least one oxide, sulfide, oxysulfide, halide or oxyhalide of at least one element chosen from Cu and elements from group (B) consisting of Ag, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Ga, Mg, Al, Cd, and (c) optionally preparation of at least one solution comprising a source of sulfur, (d) precipitation by mixing the solutions obtained on conclusion of steps (a), (b) and optionally (c), (e) filtration, and washing if necessary, of the compound of formula (I) obtained on conclusion of step (d).

4. A process for preparing a material according to claim 1, the process comprising: (a) provision of a mixture comprising at least, in dispersed form, inorganic compounds of bismuth and copper, and optionally at least one oxide, sulfide, oxysulfide, halide or oxyhalide of at least one element chosen from Bi and elements from group (A), and optionally at least one oxide, sulfide, oxysulfide, halide or oxyhalide of at least one element chosen from Cu and elements from group (B), and optionally a source of sulfur, (b) dissolving the mixture in water or an aqueous medium under hydrothermal conditions, and (c) cooling of the solution obtained, whereby particles of the compound of formula (I) Bi.sub.1-xM.sub.xCu.sub.1-y-M.sub.yOS.sub.1-zM.sub.z are obtained.

5. A semiconductor comprising the material according to claim 1.

6. The semiconductor according to claim 5, wherein the compound of formula (I) is in the form of isotropic or anisotropic objects having at least one dimension of less than 50 m.

7. The semiconductor according to claim 6, wherein the compound of formula (I) is in the form of particles with dimensions of less than 10 m.

8. The semiconductor according to claim 7, wherein the compound of formula (I) is in the form of anisotropic particles of platelet type, or of agglomerates of a few dozen to a few hundred particles of this type.

9. The semiconductor according to claim 6, wherein the compound of formula (I) is in a continuous layer based on the compound of formula (I) whose thickness is less than 50 m, said layer comprising-the compound of formula (I) in a proportion of at least 95% by mass.

10. The semiconductor according to claim 6, wherein the compound of formula (I) is in a continuous layer based on the compound of formula (I) whose thickness is less than 50 m, said layer comprising a polymer matrix and, dispersed in this matrix, particles based on the compound of formula (I) with dimensions of less than 5 m.

11. A photovoltaic device comprising, between a hole-conducting material and an electron-conducting material, a layer based on a p-type compound of formula (I) according to claim 1, and a layer based on an n-type semiconductor, wherein: the layer based on the p-type compound of formula (I) is in contact with the layer based on the n-type semiconductor; the layer based on the p-type compound of formula (I) is close to the hole-conducting material; and the layer based on the n-type semiconductor is close to the electron-conducting material.

12. The material according to claim 1, wherein x, y and z are numbers less than 0.6.

13. The material according to claim 12, wherein x, y and z are numbers less than 0.5.

14. The semiconductor according to claim 5, wherein the semiconductor is utilized in a photoelectrochemical or photochemical application.

15. The semiconductor according to claim 14, wherein the semiconductor is utilized for providing a photocurrent.

16. The semiconductor according to claim 6, wherein the isotropic or anisotropic objects having at least one dimension of less than 20 m.

17. The semiconductor according to claim 9, wherein the thickness is less than 20 m.

18. The semiconductor according to claim 10, wherein the thickness is less than 20 m.

Description

[0152] The invention will now be illustrated in greater detail with reference to the illustrative examples given below and to the attached figures, in which:

[0153] FIG. 1 is a schematic representation in cross section of a photoelectrochemical cell used in example 4 described below;

[0154] FIG. 2 is a schematic representation in cross section of a photodetector device;

[0155] FIG. 3 is a schematic representation in cross section of a photovoltaic device;

[0156] FIG. 4 is a schematic representation in cross section of a photovoltaic device according to the invention, not exemplified.

[0157] FIG. 1 shows a photoelectrochemical cell 10 which comprises: [0158] a photoactive electrode 11 consisting of a support 12 based on a glass covered with a conductive layer of ITO of 2 cm1 cm onto which has been deposited over the entire surface a layer 13 about 1 m thick based on particles 14 of a compound of formula (I) according to the invention, the particles 14 were previously dispersed in terpineol and then deposited by coating (doctor blade coating) onto the conductive glass plate 11; [0159] an (Ag/AgCl) reference electrode 15; and [0160] a counter-electrode (platinum wire) 16.
The three electrodes 11, 15 and 16 are immersed in an electrolyte 17 of 1M KCl. The three electrodes are linked via a potentiostat 18.

[0161] FIG. 2 shows a photodetector device 20 which comprises particles 21 of a compound of formula (I) according to the invention. This device comprises an FTO layer 22 about 500 nm thick onto which is electro-deposited a layer 23 about 1 m thick based on ZnO. Layer 24 about 1 m thick based on particles 21 of a compound of formula (I) according to the invention is deposited on the surface of layer 23 by deposition of the drops from a suspension of particles of a compound of formula (I) according to the invention at 25-30% by mass in ethanol. A gold layer 25 about 1 m thick is deposited on layer 24 by evaporation.

[0162] FIG. 3 shows the photovoltaic device 30 which comprises particles 31 of a compound of formula (I) according to the invention. This device comprises an FTO layer 32 about 500 nm thick onto which is electro-deposited a layer 33 about 1 m thick based on ZnO. Layer 34 about 1 m thick based on particles 31 of a compound of formula (I) according to the invention is deposited on the surface of layer 33 by deposition of the drops from a suspension of particles of formula (I) according to the invention at 25-30% by mass in ethanol. An electrolyte containing the I.sub.2/I.sup. couple 35 serving as redox mediator is deposited by deposition of the drops onto the surface of layer 34, and on which a gold layer 36 about 1 m thick is deposited by evaporation.

[0163] FIG. 4 shows the photovoltaic device 40 which comprises a layer 41 based on particles of a compound of formula (I) according to the invention deposited onto a layer 42 based on ZnO by coating, layer 42 based on ZnO being prepared by sol-gel deposition, layer 41 being in contact with a gold layer 43 and layer 42 based on ZnO being in contact with an FTO layer 44.

[0164] The placing in contact of a compound of formula (I) according to the invention with an n-type semiconductor ZnO forms a p-n junction. When the device is placed under a light source, the electrons generated move into the ZnO and the holes generated remain in the compound of formula (I) according to the invention. The ZnO is in contact with FTO (electron conductor) to extract the electrons therefrom and the compound of formula (I) according to the invention is in contact with gold (hole conductor) to extract the holes therefrom.

[0165] The examples that follow illustrate the invention without, however, limiting the scope.

EXAMPLES

Example 1

Process for Preparing BiCu.SUB.0.5.Ag.SUB.0.5.OS Particles by Solid Milling

[0166] A BiCu.sub.0.5Ag.sub.0.5OS powder was prepared by reactive milling at room temperature, according to the following protocol:

[0167] 1.028 g of Bi.sub.2S.sub.3, 1.864 g of Bi.sub.2O.sub.3, 0.477 g of Cu.sub.2S and 0.744 g of Ag.sub.2S are placed in an agate mortar in the presence of agate milling beads.

[0168] The mortar is then covered and placed in a Fritsch No. 6 planetary mill with a spin speed of about 500 rpm. Milling is continued for 120 minutes until a pure phase is obtained.

[0169] The compound C.sub.1 obtained characterized by x-ray diffraction has the following tetragonal lattice parameters: a=3.866 , c=8.5805 , V=128.27 .sup.3.

Example 2

Process for Preparing BiCuOS.SUB.0.95.I.SUB.0.05 .Particles by Solid Milling

[0170] A BiCuOS.sub.0.5I.sub.0.5 powder was prepared by reactive milling at room temperature, according to the following protocol:

[0171] 1.028 g of Bi.sub.2S.sub.3, 1.864 g of Bi.sub.2O.sub.3, 0.906 g of Cu.sub.2S and 0.114 g of CuI are placed in an agate mortar in the presence of agate milling beads.

[0172] The mortar is then covered and placed in a Fritsch No. 6 planetary mill with a spin speed of about 500 rpm. Milling is continued for 120 minutes until a pure phase is obtained.

[0173] The compound C.sub.2 obtained characterized by x-ray diffraction has the following tetragonal lattice parameters: a=3.88 , c=9.595 , V=129.47 .sup.3.

Example 3

Process for Preparing BiCu.SUB.0.7.Zn.SUB.0.3.OS Particles by Solid Milling

[0174] A BiCu.sub.0.7Zn.sub.0.3OS powder was prepared by reactive milling at room temperature, according to the following protocol:

[0175] 0.720 g of Bi.sub.2S.sub.3, 1.584 g of Bi.sub.2O.sub.3, 0.668 g of Cu.sub.2S and 0.349 g of ZnS are placed in an agate mortar in the presence of agate milling beads.

[0176] The mortar is then covered and placed in a Fritsch No. 6 planetary mill with a spin speed of about 500 rpm. Milling is continued for 120 minutes until a pure phase is obtained.

[0177] The compound C.sub.3 obtained characterized by x-ray diffraction has the following tetragonal lattice parameters: a=3.870 , c=8.571 , V=128.36 .sup.3.

Example 4

Process for Preparing BiCu.SUB.0.2.Zn.SUB.0.2.OS Particles from Soluble Precursors

1) Bismuth Precursor Solution (50 mL at 0.1 M):

[0178] 4 mL of concentrated HNO.sub.3 (commercial 52.5%) are added to 2.425 g of BiNO.sub.3.5H.sub.2O in a container, and the mixture is then diluted with 10 mL of water. In another beaker, 3 g of sodium hydroxide are mixed with 3 g of dibasic sodium tartrate (C.sub.4H.sub.4Na.sub.2O.sub.6.2H.sub.2O).

[0179] The two solutions obtained are mixed rapidly. A white precipitate forms and disappears immediately. The solution obtained is of transparent color. It is then diluted to a volume of 50 mL with water.

2) Solution of the Precursor of Copper I and of Zinc (II) (50 mL at a Cation Concentration of 0.1 M (Cu+Zn))

[0180] 0.992 g of copper sulfate pentahydrate (CuSO.sub.4.5H.sub.2O) and 0.285 g of zinc sulfate heptahydrate are dissolved in 30 mL of distilled water. 1.5 mL of concentrated ammonia (28%) are added and a dark blue solution is obtained. 15 g of sodium thiosulfate pentahydrate are then added.

[0181] The mixture is heated moderately (50 C.) for four hours. A colorless solution is obtained. It is preferable to use closed containers to avoid oxidation of the copper(I).

3) Solution of Na.SUB.2.S

[0182] 12.25 g of Na.sub.2S.9 H.sub.2O are dissolved in 100 mL of distilled water.

4) Formation of the Compound

[0183] The solutions prepared previously containing Bi and (Cu(+Zn) are mixed rapidly. A white precipitate forms and disappears immediately. The mixture is heated to a temperature of 90 C. The Na.sub.2S solution is heated to 90 C.

[0184] When the two solutions are at the desired temperature, the solution of the cations (Bi,Cu,Zn) is added to the Na.sub.2S solution. A black precipitate forms immediately. The solution is stirred at 90 C. for four hours. It is then filtered, washed with distilled water and dried at 80 C. in an oven.

[0185] The product obtained has a single phase when it is observed by x-ray diffraction.

Example 5

Use of Compounds C.SUB.1 .to C.SUB.3 .in a Photoelectrochemical Device

[0186] The device described in FIG. 1 was used, by polarizing the working electrode at a potential of 0.8 V vs Ag/AgCl. The system is irradiated under an incandescent lamp (whose color temperature is 2700 K) alternating periods of darkness and periods of light. The current intensity increased when the system was placed in light. This is a photocurrent, which confirms the capacity of each of the compounds C.sub.1 to C.sub.3 to generate a photocurrent. This photocurrent is cathodic (i.e. negative), which is in agreement with the fact that each of these compounds C.sub.1 to C.sub.3 is a p-type semiconductor.

[0187] For each of the compounds C.sub.1 to C.sub.5, the measurements of the photocurrent obtained are as follows:

TABLE-US-00001 Compound Photocurrent (A .Math. cm.sup.2) Compound C.sub.1 75 Compound C.sub.2 150 Compound C.sub.3 100