Laser Annealing for Thin Film Solar Cells

Abstract

A method for forming copper indium gallium (sulfide) selenide (CIGS) solar cells, cadmium telluride (CdTe) solar cells, and copper zinc tin (sulfide) selenide (CZTS) solar cells using laser annealing techniques to anneal the absorber and/or the buffer layers. Laser annealing may result in better crystallinity, lower surface roughness, larger grain size, better compositional homogeneity, a decrease in recombination centers, and increased densification. Additionally, laser annealing may result in the formation of non-equilibrium phases with beneficial results.

What is claimed: 
     
         1 . A thin film solar cell comprising:
 a back contact disposed on a substrate;   an absorber layer disposed on the back contact;
 the absorber layer comprising non-equilibrium solid phases formed by solidifying multiple different liquid phases that are not stable under equilibrium conditions; 
   a buffer layer disposed on the absorber layer; and   a conductive layer disposed on the buffer layer.   
     
     
         2 . The thin film solar cell of  claim 1 , wherein the absorber layer comprises one of CdTe, CIGS, or CZTS. 
     
     
         3 . The thin film of solar cell  claim 1 , wherein the absorber layer comprises CIGS and Na. 
     
     
         4 . The thin film solar cell of  claim 1 , further comprising an interface layer comprising MoSe 2 , the interface layer disposed between the back contact and the absorber layer. 
     
     
         5 . The thin film solar cell of  claim 1 , further comprising an intermediate layer comprising one of ZnO or SnO 2 , the intermediate layer disposed between the buffer layer and the conductive layer. 
     
     
         6 . The thin film solar cell of  claim 1 , further comprising an antireflection layer disposed over the conductive layer. 
     
     
         7 . The thin film solar cell of  claim 6 , wherein the antireflection layer comprises MgF 2 . 
     
     
         8 . The thin film solar cell of  claim 1 , wherein the absorber layer comprises CIGS, and wherein a concentration of Ga in the absorber layer is non-uniform. 
     
     
         9 . The thin film solar cell of  claim 8 , wherein the concentration of Ga in the absorber layer is higher at a side of the absorber layer facing the back contact than at an opposite side of the absorber layer. 
     
     
         10 . The thin film solar cell of  claim 8 , wherein the concentration of Ga in the absorber layer is higher at a side of the absorber layer facing the back contact and at a side of the absorber layer facing the buffer layer than in a middle of the absorber layer between these sides. 
     
     
         11 . The thin film solar cell of  claim 1 , further comprising a layer of Na 2 Se disposed between the absorber layer and the buffer layer. 
     
     
         12 . The thin film solar cell of  claim 1 , wherein the absorber layer comprises CIGS and a dopant, the dopant comprises one of Cl, Br, or I. 
     
     
         13 . The thin film solar cell of  claim 1 , wherein the absorber layer comprises an inverted n-type sub-layer. 
     
     
         14 . The thin film solar cell of  claim 1 , wherein the absorber layer has a thickness of between about 0.5 micrometers and 3.0 micrometers. 
     
     
         15 . The thin film solar cell of  claim 1 , wherein the buffer layer has a thickness of between about 30 nanometers and 80 nanometers. 
     
     
         16 . The thin film solar cell of  claim 1 , wherein the buffer layer comprises CdS. 
     
     
         17 . The thin film solar cell of  claim 1 , wherein the conductive layer has a thickness of between about 0.3 micrometers and 2.0 micrometers. 
     
     
         18 . The thin film solar cell of  claim 1 , wherein the conductive layer comprises one of Al:ZnO, InSnO, InZnO, B:ZnO, Ga:ZnO, F:ZnO, or F:SnO 2 . 
     
     
         19 . The thin film solar cell of  claim 1 , wherein the back contact comprises one of Cu:graphite, HgTe, ZnTe:Cu, Te, Cu 2 Te, As 2 Te 3 /Cu, or Sb 2 Te 3 . 
     
     
         20 . The thin film solar cell of  claim 1 , wherein the back contact has a thickness of between about 0.3 micrometers and 2.0 micrometers.