Preparation of Copper-Rich Copper Indium (Gallium) Diselenide/Disulphide Nanoparticles

Abstract

A method for the preparation of copper indium gallium diselenide/disulfide (CIGS) nanoparticles utilizes a copper-rich stoichiometry. The copper-rich CIGS nanoparticles are capped with organo-chalcogen ligands, rendering the nanoparticles processable in organic solvents. The nanoparticles may be deposited on a substrate and thermally processed in a chalcogen-rich atmosphere to facilitate conversion of the excess copper to copper selenide or copper sulfide that may act as a sintering flux to promote liquid phase sintering and thus the growth of large grains. The nanoparticles so produced may be used to fabricate CIGS-based photovoltaic devices.

What is claimed is: 
     
         1 . CIGS nanoparticles prepared by a process, the process comprising:
 heating a copper salt together with at least one salt selected from the group consisting of indium salts and gallium salts in a solvent at a first temperature to produce a reaction solution;   adding an organo-chalcogen precursor to the reaction solution;   heating the reaction solution to a second temperature while stirring for a first time interval;   cooling the reaction solution to room temperature; and   isolating nanoparticles from the reaction solution.   
     
     
         2 . CIGS nanoparticles as recited in  claim 1 , wherein the molar ratio of Cu salts to the combined total of In and Ga salts is between about 1:0.65 and about 1:0.85. 
     
     
         3 . CIGS nanoparticles as recited in  claim 1 , wherein the preparation process further comprises:
 cooling the reaction solution to a third temperature and stirring for a second time interval after heating the reaction solution to a second temperature.   
     
     
         4 . A method for preparing CIGS nanoparticles, the method comprising:
 mixing salts selected from the group consisting of copper salts, indium salts and gallium salts in a solvent at a first temperature to produce a reaction solution;   adding an organo-chalcogen precursor to the reaction solution;   heating the reaction solution to a first temperature while stirring for a first time interval;   heating the reaction solution to a second temperature and adding a second chalcogen precursor over a second time interval;   stirring the reaction solution at the second temperature for a third time interval;   cooling the reaction solution to a third temperature and stirring for a fourth time interval;   cooling the reaction solution to room temperature; and   isolating the nanoparticles.   
     
     
         5 . The method recited in  claim 4 , wherein the molar ratio of Cu salts to the combined total of In and Ga salts is between about 1:0.65 and about 1:0.85. 
     
     
         6 . The method recited in  claim 4 , wherein the group consisting of copper salts, indium salts and gallium salts comprises salts selected from the group consisting of acetates, acetylacetonates, chlorides, bromides, and iodides. 
     
     
         7 . The method recited in  claim 4 , wherein the solvent is a non-coordinating solvent. 
     
     
         8 . The method recited in  claim 7 , wherein the non-coordinating solvent is selected from the group consisting of 1-octadecene, benzylether, diphenylether and heat transfer fluids comprising hydrogenated terphenyls. 
     
     
         9 . The method recited in  claim 4 , wherein the organo-chalcogen precursor is of the form R—X—H, where R is an alkyl or aryl group and X is sulfur or selenium. 
     
     
         10 . The method recited in  claim 9 , wherein the organo-chalcogen precursor is selected from the group consisting of 1-octanethiol, 1-octane selenol, and 1-dodecane selenol. 
     
     
         11 . The method recited in  claim 4 , wherein the organo-chalcogen precursor has a boiling point below about 250° C. 
     
     
         12 . The method recited in  claim 4 , wherein the first time interval is sufficient to effect distillation of substantially all volatile by-products. 
     
     
         13 . The method recited in  claim 4 , wherein the second temperature is between about 120° C. and about 160° C. 
     
     
         14 . The method recited in  claim 4 , wherein the second chalcogen precursor comprises an elemental chalcogen dissolved in a coordinating solvent. 
     
     
         15 . The method recited in  claim 14 , wherein the coordinating solvent is selected from the group consisting of trioctylphosphine sulfide and trioctylphosphine selenide. 
     
     
         16 . The method recited in  claim 4 , wherein second temperature is between about 120° C. and about 160° C. 
     
     
         17 . The method recited in  claim 4 , wherein the third time interval is between about 30 minutes about 2 hours. 
     
     
         18 . The method recited in  claim 4 , wherein third temperature is between about 80° C. and about 120° C. 
     
     
         19 . The method recited in  claim 4 , wherein the fourth time interval is between about 3 hours and about 6 hours. 
     
     
         20 . The method recited in  claim 4 , wherein isolating the nanoparticles comprises precipitating the nanoparticles from solution by the addition of at least one other solvent. 
     
     
         21 . CIGS nanoparticles prepared a process, the process comprising:
 mixing salts selected from the group consisting of copper salts, indium salts and gallium salts in a solvent at a first temperature to produce a reaction solution;   adding an organo-chalcogen precursor to the reaction solution;   heating the reaction solution to a first temperature while stirring for a first time interval;   heating the reaction solution to a second temperature and adding a second chalcogen precursor over a second time interval;   stirring the reaction solution at the second temperature for a third time interval;   cooling the reaction solution to a third temperature and stirring for a fourth time interval;   cooling the reaction solution to room temperature; and   isolating the nanoparticles.   
     
     
         22 . CIGS nanoparticles as recited in  claim 21 , wherein the molar ratio of Cu salts to the combined total of In and Ga salts is between about 1:0.65 and about 1:0.85. 
     
     
         23 . A photovoltaic device comprising the CIGS nanoparticles of  claim 1 . 
     
     
         24 . A photovoltaic device comprising the CIGS nanoparticles of  claim 21 .