Inorganic Salt-Nanoparticle Ink for Thin Film Photovoltaic Devices and Related Methods

Abstract

Compositions for solution-based deposition of CIGS films are described. The compositions include ternary, quaternary or quinary chalcogenide nanoparticles (i.e., CIGS nanoparticles) and one or more inorganic salts dissolved or dispersed in a solvent to form an ink. The ink can be deposited on a substrate by conventional coating techniques and then annealed to form a crystalline layer. Further processing can be employed to fabricate a PV device. The inorganic salts are included to (i) tune the stoichiometry of the CIGS precursor ink to a desirable ratio, thus tuning the semiconductor band gap, to (ii) dope the CIGS layer with additives, such as Sb and/or Na, to promote grain growth, and/or to (iii) modify and improve the coating properties of the CIGS precursor ink.

What is claimed is: 
     
         1 . A composition comprising:
 a solvent,   a population of nanoparticles having the formula Cu w In x Ga 1-x Se y S 2-y , wherein 0≤w≤2, 0≤x≤1 and 0≤y≤2, and   an inorganic salt.   
     
     
         2 . The composition of  claim 1 , wherein the nanoparticles are about 2 to about 10 nm in diameter. 
     
     
         3 . The composition of  claim 1 , wherein the nanoparticles comprise a capping agent adsorbed to the nanoparticle surface, wherein the capping agent is a thiol or a selenol. 
     
     
         4 . The composition of  claim 1 , wherein the inorganic salt comprises one or more of Cu, In, Ga, S and Se. 
     
     
         5 . The composition of  claim 1 , wherein the inorganic salt comprises Na or Sb. 
     
     
         6 . The composition of  claim 1 , wherein the inorganic salt is present at a concentration of about 0.01-10 mol. % relative to the moles of nanoparticles. 
     
     
         7 . The composition of  claim 1 , further comprising one or more of a foam inhibiter, thickening agent, dispersing agent, surface tension modifier, or viscosity modifier. 
     
     
         8 . The composition of  claim 1 , further comprising oleic acid. 
     
     
         9 . A method of forming a PV absorber layer, the method comprising:
 providing a first ink composition comprising a solvent, a population of first nanoparticles having the formula Cu w In x Ga 1-x Se y S 2-y , wherein 0.1≤w≤2, 0≤x≤1 and 0≤y≤2, and an inorganic salt;   forming a film of the first ink composition on a substrate;   annealing the film of the first ink composition;   providing a second ink composition comprising a solvent, a population of second nanoparticles having the formula Cu w In x Ga 1-x Se y S 2-y , wherein 0.1≤w≤2, 0≤x≤1 and 0≤y≤2;   forming a film of the second ink composition on a substrate; and   annealing the film of the second ink composition.   
     
     
         10 . The method of  claim 9 , wherein the first and second nanoparticles are the same. 
     
     
         11 . The method of  claim 9 , wherein the second ink composition further comprises an inorganic salt. 
     
     
         12 . The method of  claim 11 , wherein the inorganic salt comprises at least one of Ga, Sb, and Na. 
     
     
         13 . The method of  claim 9 , wherein at least one of the first and second ink composition further comprises an additive, the additive being one or more of a foam inhibitor, a thickening agent, a dispersing agent, a surface tension modifier, and a viscosity modifier. 
     
     
         14 . The method of  claim 9 , wherein annealing the film of the first ink composition and/or annealing the film of the second ink composition comprises annealing at a first temperature over a first time interval followed by annealing at a second temperature for a second time interval, the second temperature being greater than the first temperature. 
     
     
         15 . The method of  claim 14 , wherein the first temperature is from 250 to 300° C. and the first time interval is from 3 to 7 minutes. 
     
     
         16 . The method of  claim 14 , wherein the second temperature is from 400 to 430° C. and the first time interval is from 3 to 7 minutes.