Metal-doped cu(In,Ga) (S,Se)2 nanoparticles

Abstract

Various methods are used to provide a desired doping metal concentration in a CIGS-containing ink when the CIGS layer is deposited on a photovoltaic device. When the doping metal is sodium, it may be incorporated by: adding a sodium salt, for example sodium acetate, together with the copper-, indium- and/or gallium-containing reagents at the beginning of the synthesis reaction of Cu(In,Ga)(S,Se).sub.2 nanoparticles; synthesizing Cu(In,Ga)(S,Se).sub.2 nanoparticles and adding a sodium salt to the reaction solution followed by mild heating before isolating the nanoparticles to aid sodium diffusion; and/or, using a ligand that is capable of capping the Cu(In,Ga)(S,Se).sub.2 nanoparticles with one end of its molecular chain and binding to sodium atoms with the other end of its chain.

Claims

1. A process for preparing sodium-doped nanocrystals comprising: adding a sodium dialkyldithiocarbamate to a mixture of copper-, indium-, and gallium-containing reagents at the beginning of a synthesis reaction to form sodium-doped Cu(In,Ga)(S,Se).sub.2 nanoparticles.

2. The process of claim 1 wherein the sodium dialkyldithiocarbamate is sodium diethyldithiocarbamate.

3. The process of claim 1 wherein the sodium dialkyldithiocarbamate is sodium dimethyldithiocarbamate.

4. The process of claim 1 wherein the sodium dialkyldithiocarbamate is sodium methylhexyldithiocarbamate.

5. The process of claim 1 wherein the sodium dialkyldithiocarbamate is sodium ethylhexyldithiocarbamate.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

(1) FIG. 1 is a flowchart depicting a method for formulating a CIGS nanoparticle-based ink that can be processed to form a thin film and then fabricate a photovoltaic device incorporating such a film.

(2) FIG. 2 is a schematic depiction of a process for incorporating metals into CIGS nanoparticles.

(3) FIG. 3 is a schematic depiction of a ligand-capped nanoparticle according to the invention.

DETAILED DESCRIPTION

(4) The present disclosure involves a method to controllably incorporate metals, such as sodium and/or antimony, into CIGS nanoparticles. The metal-doped CIGS nanoparticles may be deposited with different printing methods to form films of suitable thickness.

(5) The following are different methods that incorporate sodium (by way of example) into CIGS nanoparticles:

(6) In a first embodiment, a sodium salt, for example sodium acetate, is added together with the copper-, indium- and/or gallium-containing reagents at the beginning of the synthesis reaction of Cu(In,Ga)(S,Se).sub.2 nanoparticles (e.g., that disclosed in U.S. Pub. No. 2009/0139574). Suitable sodium salts other than sodium acetate include, but are not limited to, inorganic salts such as sodium chloride, sodium fluoride, sodium bromide and other organic salts such as sodium oleate and sodium alkyldithiocarbamate salts such as sodium diethyldithiocarbamate, sodium dimethyldithiocarbamate, sodium methylhexyldithiocarbamate and sodium ethylhexyldithiocarbamate.

(7) In a second embodiment, the Cu(In,Ga)(S,Se).sub.2 nanoparticles are synthesized and a sodium salt is subsequently added to the reaction solution, followed by mild heating, before isolating the nanoparticles to aid sodium diffusion. This method permits the incorporation of sodium without the need for having sodium salts present throughout the synthesis of the CIGS nanoparticles. This method is particularly useful when the sodium salt may interfere at some stage during the synthesis. This method may also be performed as a separate step after the isolation of the nanoparticles, as illustrated in FIG. 2 wherein TOP is trioctylphosphine and NC is nanocrystal. In some embodiments, the sodium salt is incorporated at room temperature. In alternative embodiments, the sodium salt is added to a dispersion of the CIGS nanoparticles, followed by heating, for example at 200 C.

(8) In a third embodiment, a sodium-containing ligand is used that is capable of capping the Cu(In,Ga)(S,Se).sub.2 nanoparticles with one end of its molecular chain and binding to sodium atoms with the other end of the chain. An example of this type of ligand is a thiol ligand with a carboxylate group at the other end capable of binding sodium as illustrated in FIG. 3.

(9) This method may be extended to the doping of CIGS nanoparticles with other metals, for example antimony (Sb). Suitable antimony salts include, but are not restricted to, antimony acetate, triphenylantimony and tris(dimethylamino)antimony, antimony halides such as antimony chloride, antimony fluoride, antimony bromide and antimony iodide, and antimony dialkyldithiocarbamates such as antimony diethyldithiocarbamate, antimony dimethyldithiocarbamate, antimony methylhexyldithiocarbamate and antimony ethylhexyldithiocarbamate.

(10) The method allows the incorporation of a metal directly in the nanoparticle precursor without the use of vacuum techniques.

(11) The methods described above allow the incorporation of a metal while the nanoparticle precursor is being synthesized thereby removing the need for an additional step to include the metal. Because the synthetic method enables control of the amount of metal introduced, levels of incorporated metal may be accurately tuned. The metal distribution is likely preserved during the sintering process to produce metal-doped CIGS films.

(12) A process for producing nanoparticles incorporating ions selected from groups 13 [Al, Ga, In], 16 [S, Se, Te], and 11 [Ce, Ag, Au] or 12 [Zn, Cd] of the periodic table is disclosed in U.S. Publication No. 2009/0139574 by Nigel Pickett and James Harris the disclosure of which is hereby incorporated by reference in its entirety. In one embodiment, the disclosed process includes effecting conversion of a nanoparticle precursor composition comprising group 13, 16, and 11 or 12 ions to the material of the nanoparticles in the presence of a selenol compound. Other embodiments include a process for fabricating a thin film including nanoparticles incorporating ions selected from groups 13, 16, and 11 or 12 of the periodic table as well as a process for producing a printable ink formulation including the nanoparticles.

(13) Although particular embodiments have been shown and described, they are not intended to limit what this patent covers. One skilled in the art will understand that various changes and modifications may be made.

(14) Various embodiments are illustrated by the following examples.

Example 1: Preparation of Sodium-Doped CuInS2 Nanoparticles Using Sodium Diethyldithiocarbamate

(15) An oven-dried 250 mL round-bottom flask was charged with copper(I) acetate (2.928 g, 23.88 mmol), indium(III) acetate (9.706 g, 33.25 mmol) and benzyl ether (50 mL). The flask was fitted with a Liebig condenser and collector, and the mixture was degassed at 100 C. for 1 hour. The flask was then back-filled with nitrogen. Degassed 1-octanethiol (40 mL, 230 mmol) was added to the mixture, which was subsequently heated to 200 C. for 2 hours. A suspension of sodium diethyldithiocarbamate trihydrate (1.390 g, 6.169 mmol) in benzyl ether (18 mL)/oleylamine (2 mL) was added and the residue was rinsed with a small amount of methanol. The temperature was maintained at 200 C. for a further 30 minutes, before being allowed to cool to 160 C. and stirring for 18 hours. The mixture was then cooled to room temperature.

(16) The nanoparticles were isolated in aerobic conditions, via centrifugation, using isopropanol, toluene, methanol and dichloromethane, then dried under vacuum.

(17) Characterization by inductively coupled plasma organic emission spectroscopy (ICP-OES) gave the following elemental composition by mass: 13.04% Cu; 30.70% In; 0.628% Na; 20.48% S. This equates to a stoichiometry of CuIn.sub.1.30Na.sub.0.13S.sub.3.11, i.e. 13% sodium compared to the number of moles of copper. The organo-thiol ligand contributes to the total sulfur content.

Example 2: Preparation of Sodium-Doped CuInS2 Nanoparticles Using Sodium Oleate

(18) An oven-dried 250 mL round-bottom flask was charged with copper(I) acetate (2.929 g, 23.89 mmol), indium(III) acetate (9.707 g, 33.25 mmol) and benzyl ether (50 mL). The flask was fitted with a Liebig condenser and collector, and the mixture was degassed at 100 C. for 1 hour. The flask was then back-filled with nitrogen. Degassed 1-octanethiol (40 mL, 230 mmol) was added to the mixture, which was subsequently heated to 200 C. for 2 hours. A suspension of sodium oleate (1.879 g, 6.172 mmol) in benzyl ether (20 mL) was added and the residue was rinsed with a small amount of methanol. The temperature was maintained at 200 C. for a further 30 minutes, before being allowed to cool to 160 C. and stirring for 18 hours. The mixture was then cooled to room temperature.

(19) The nanoparticles were isolated in aerobic conditions, via centrifugation, using isopropanol, toluene, methanol and dichloromethane, then dried under vacuum.

(20) Characterization by inductively coupled plasma organic emission spectroscopy (ICP-OES) gave the following elemental composition by mass: 13.04% Cu; 28.31% In; 0.784% Na; 19.86% S. This equates to a stoichiometry of CuIn.sub.1.20Na.sub.0.17S.sub.3.02, i.e. 17% sodium compared to the number of moles of copper. The organo-thiol ligand contributes to the total sulfur content.

Example 3: Preparation of Sodium-Doped CuInS2 Nanoparticles Using Sodium Oleate

(21) An oven-dried 250 mL round-bottom flask was charged with copper(I) acetate (2.928 g, 23.88 mmol), indium(III) acetate (9.705 g, 33.24 mmol), sodium oleate (0.743 g, 2.44 mmol) and benzyl ether (50 mL). The flask was fitted with a Liebig condenser and collector, and the mixture was degassed at 100 C. for 1 hour. The flask was then back-filled with nitrogen. Degassed 1-octanethiol (40 mL, 230 mmol) was added to the mixture, which was subsequently heated to 200 C. for 2 hours, before being allowed to cool to 160 C. and annealing for 18 hours. The mixture was then cooled to room temperature.

(22) The nanoparticles were isolated in aerobic conditions, via centrifugation, using isopropanol, toluene, methanol, dichloromethane and acetone, then dried under vacuum.

(23) Characterization by inductively coupled plasma organic emission spectroscopy (ICP-OES) gave the following elemental composition by mass: 13.43% Cu; 28.56% In; 0.96% Na; 20.19% S. This equates to a stoichiometry of CuIn.sub.1.18Na.sub.0.20S.sub.2.98, i.e. 20% sodium compared to the number of moles of copper. The organo-thiol ligand contributes to the total sulfur content.

Example 4: Preparation of Antimony-Doped Cu(In,Ga)S2 Nanoparticles Using Triphenylantimony

(24) A 100 mL round-bottom flask was charged with copper(I) acetate (0.369 g, 3.01 mmol), indium(III) acetate (0.7711 g, 2.641 mmol), gallium(III) acetylacetonate (0.4356 g, 1.187 mmol), triphenylantimony (0.055 g, 160 mol), benzyl ether (6 mL) and a 1 M solution of sulfur in oleylamine (9 mL, 9 mmol). The mixture was degassed at 100 C. for 1 hour, then the flask was back-filled with nitrogen. 1-Octanethiol (4.8 mL, 28 mmol) was injected into the flask, which was subsequently heated to 200 C. and held for 2 hours. The temperature was decreased to 160 C. and held overnight. The mixture was then cooled to room temperature.

(25) The nanoparticles were isolated in aerobic conditions, via centrifugation, using toluene and methanol.

(26) Characterization by inductively coupled plasma organic emission spectroscopy (ICP-OES) gave the following elemental composition by mass: 15.47% Cu; 26.09% In; 6.41% Ga; 0.25% Sb; 20.67% S. This equates to a stoichiometry of CuIn.sub.0.93Ga.sub.0.38Sb.sub.0.01S.sub.2.65, i.e. 1% antimony compared to the number of moles of copper. The organo-thiol ligand contributes to the total sulfur content.

Example 5: Preparation of Antimony-Doped Cu(In,Ga)S2 Nanoparticles Using Antimony Acetate

(27) A 100 mL round-bottom flask was charged with copper(I) acetate (0.369 g, 3.01 mmol), indium(III) acetate (0.7711 g, 2.641 mmol), gallium(III) acetylacetonate (0.4356 g, 1.187 mmol), antimony(III) acetate (0.047 g, 160 mol), benzyl ether (6 mL) and a 1 M solution of sulfur in oleylamine (9 mL, 9 mmol). The mixture was degassed at 100 C. for 1 hour, then the flask was back-filled with nitrogen. 1-Octanethiol (4.8 mL, 28 mmol) was injected into the flask, which was subsequently heated to 200 C. and held for 2 hours. The temperature was decreased to 160 C. and held overnight. The mixture was then cooled to room temperature.

(28) The nanoparticles were isolated in aerobic conditions, via centrifugation, using toluene and methanol.

(29) Characterization by inductively coupled plasma organic emission spectroscopy (ICP-OES) gave the following elemental composition by mass: 15.39% Cu; 26.02% In; 6.17% Ga; 0.92% Sb; 21.20% S. This equates to a stoichiometry of CuIn.sub.0.94Ga.sub.0.37Sb.sub.0.03S.sub.2.73, i.e. 3% antimony compared to the number of moles of copper. The organo-thiol ligand contributes to the total sulfur content.

(30) Although particular embodiments of the present invention have been shown and described, they are not intended to limit what this patent covers. One skilled in the art will understand that various changes and modifications may be made without departing from the scope of the present invention as literally and equivalently covered by the following claims.