Solution-Based Fabrication of Photovoltaic Cell

Abstract

An ink for forming CIGS photovoltaic cell active layers is disclosed along with methods for making the ink, methods for making the active layers and a solar cell made with the active layer. The ink contains a mixture of nanoparticles of elements of groups IB, IIIA and (optionally) VIA. The particles are in a desired particle size range of between about 1 nm and about 500 nm in diameter, where a majority of the mass of the particles comprises particles ranging in size from no more than about 40% above or below an average particle size or, if the average particle size is less than about 5 nanometers, from no more than about 2 nanometers above or below the average particle size. The use of such ink avoids the need to expose the material to an H 2 Se gas during the construction of a photovoltaic cell and allows more uniform melting during film annealing, more uniform intermixing of nanoparticles, and allows higher quality absorber films to be formed.

1 . A method comprising:
 forming a liquid ink comprising a) particles containing one or more elements from group IB and b) one or more liquid metals containing one or more elements from group IIIA;   depositing the liquid ink on a substrate; and   heating the liquid ink in one or more steps to form a photovoltaic absorber layer.   
     
     
         2 . The method of  claim 1  further comprising adding a Group VIA material during the heating step. 
     
     
         3 . The method of  claim 1  wherein the heating step comprises of heating the liquid ink in an H 2  or N 2  atmosphere and then heating in a Group VIA atmosphere. 
     
     
         4 . The method of  claim 1  wherein the heating step comprises of heating the liquid ink to anneal the particles together in a non-Group VIA atmosphere and then heating in a Group VIA atmosphere. 
     
     
         5 . The method of  claim 1  wherein a Group VIA element is introduced by heating the ink in a Group VIA vapor. 
     
     
         6 . The method of  claim 1  wherein a Group VIA element is introduced by heating the ink in a sulfur vapor. 
     
     
         7 . The method of  claim 1  wherein a Group VIA element is introduced by heating the ink in a selenium vapor. 
     
     
         8 . The method of  claim 1  wherein a Group VIA element is introduced into the liquid ink by adding particles containing one or more Group VIA element. 
     
     
         9 . The method of  claim 1  wherein the particles are combined with an organic solvent to form the liquid ink and wherein the one or more liquid metals is selected from the group consisting of: gallium and indium. 
     
     
         10 . The method of  claim 1  wherein the particles are combined with an inorganic solvent to form the liquid ink and wherein the one or more liquid metals is selected from the group consisting of: gallium and indium. 
     
     
         11 . The method of  claim 1  wherein the particles are combined with water to form the liquid ink and wherein the one or more liquid metals is selected from the group consisting of: gallium and indium. 
     
     
         12 . The method of  claim 1  further comprising adding a dispersant to the liquid ink and wherein the one or more liquid metals is selected from the group consisting of: gallium and indium. 
     
     
         13 . The method of  claim 1  further comprising adding one or more surfactants, polymers, dispersants, binders, modifiers, detergents or additives to the liquid ink, and wherein the one or more liquid metals is selected from the group consisting of: gallium and indium. 
     
     
         14 . The method of  claim 1  wherein the particles are nanoparticles, and wherein the nanoparticles are added to a solvent to form a suspension. 
     
     
         15 . The method of  claim 1  wherein the particles are nanoparticles, and wherein the nanoparticles are added to a solvent to form a colloidal suspension. 
     
     
         16 . The method of  claim 1  wherein the substrate comprises a metal foil. 
     
     
         17 . The method of  claim 1  wherein the substrate comprises a metal foil up to 2 meters wide. 
     
     
         18 . The method of  claim 1  wherein the substrate comprises of at least one material from the group consisting of: stainless steel, molybdenum, and aluminum. 
     
     
         19 . The method of  claim 1  wherein the substrate comprises a metallized film. 
     
     
         20 . The method of  claim 1  wherein depositing the liquid ink comprises spreading a thin film of the liquid ink over the substrate using solution-based coating techniques selected from the group consisting of: web coating, spray coating, spin coating, doctor blade coating, printing techniques including contact printing, gravure printing, microgravure printing, ink-jet printing, jet deposition, and combinations thereof. 
     
     
         21 . The method of  claim 1  wherein depositing the liquid ink comprises spreading a thin film of the liquid ink over the substrate in a roll-to-roll manner using a web coating system. 
     
     
         22 . The method of  claim 1  wherein the particles containing the one or more elements from group IB are alloy particles. 
     
     
         23 . The method of  claim 1  further comprising removing solvents from the ink by heating the ink and substrate, and wherein the one or more liquid metals is selected from the group consisting of: gallium and indium. 
     
     
         24 . The method of  claim 1  wherein the heating occurs in a non-vacuum environment. 
     
     
         25 . A photovoltaic device precursor material comprising:
 a liquid ink comprising:
 a) particles containing one or more elements from group IB and b) one or more liquid metals containing one or more elements from group IIIA, wherein the one or more liquid metals is selected from the group consisting of: gallium and indium; 
 a dispersant; and 
 a solvent.