Method for forming solar cells

Abstract

A thin film solar cell and process for forming the same. The solar cell includes a bottom electrode layer, semiconductor light absorbing layer, top electrode layer, and a protective moisture barrier layer. In some embodiments, the barrier layer is formed of a water-insoluble material. The barrier layer helps protect the top electrode layer from exposure and damage caused by water and oxygen.

What is claimed is: 
     
         1 . A thin film solar cell comprising:
 a bottom electrode layer formed on a substrate;   a semiconductor absorber layer formed on the bottom electrode layer;   a buffer layer formed on the absorber layer;   a top electrode layer formed on the buffer layer, the top electrode layer being electrically connected to the bottom electrode layer through a P2 scribe line defining a vertical channel extending through the buffer and absorber layers;   a protective first moisture barrier layer formed on the top electrode layer for protecting the top electrode layer from environmental moisture and oxygen damage, wherein the first moisture barrier layer is formed of a material that is insoluble in water; and   an encapsulant formed on the first moisture barrier layer.   
     
     
         2 . The solar cell of  claim 1 , wherein the encapsulant contains EVA and butyl. 
     
     
         3 . The solar cell of  claim 1 , wherein the first moisture barrier layer extends into the scribe line. 
     
     
         4 . The solar cell of  claim 1 , wherein the P2 scribe line is at least partially filled with material from the top electrode layer that contacts the bottom electrode, the first moisture barrier layer covering exposed sidewall portions of the top electrode layer material within the P2 scribe line. 
     
     
         5 . The solar cell of  claim 1 , wherein the first moisture barrier layer has a thickness from about 10 nm to about 150 nm. 
     
     
         6 . The solar cell of  claim 1 , wherein a material forming the first moisture barrier layer is a stable oxide compound having a Gibbs Free Energy of at least −600 KJ/mol. 
     
     
         7 . The solar cell of  claim 1 , wherein the first barrier layer material is selected from the group consisting of MgO, In2O3, CaO, Ga2O3, Cr2O3, Ta2O5, TiO2, ZrO2, Al2O3, HfO2, La2O3, Lu2O3, SiONx, SiNx, and SiOx. 
     
     
         8 . The solar cell of  claim 1 , wherein the absorber layer is comprised of p-type chalcogenide materials or CdTe. 
     
     
         9 . The solar cell of  claim 1 , wherein the absorber layer is comprised of a material selected from the group consisting of Cu(In,Ga)Se 2 , Cu(In,Ga)(Se, S) 2 , CuInSe 2 , CuGaSe 2 , CuInS 2 , and Cu(In,Ga)S 2 . 
     
     
         10 . The solar cell of  claim 1 , wherein the top electrode is an n-type material selected from the group consisting of zinc oxide, aluminum doped zinc oxide, gallium doped zinc oxide, indium doped zinc oxide, fluorine tin oxide, indium tin oxide, indium zinc oxide, antimony tin oxide (ATO), and a carbon nanotube layer. 
     
     
         11 . The solar cell of  claim 1 , further comprising a P3 scribe line forming a vertical channel through the solar cell to the substrate, wherein the first moisture barrier layer extends into the P3 scribe line. 
     
     
         12 . The solar cell of  claim 1 , further comprising a second moisture barrier layer formed on the first moisture barrier layer, the second moisture barrier being formed of the same or different material than the first moisture barrier. 
     
     
         13 . The solar cell of  claim 12 , wherein the second moisture barrier layer extends into the P2 scribe line. 
     
     
         14 . A thin film solar cell comprising:
 a bottom electrode layer formed on a substrate;   a semiconductor absorber layer formed on the bottom electrode layer;   a buffer layer formed on the absorber layer;   a top electrode layer formed on the buffer layer and made of an electrically conductive TCO material, the top electrode layer being electrically connected to the bottom electrode layer through a P2 scribe line defining a vertical channel extending through the buffer and absorber layers; and   a protective first moisture barrier layer deposited on the top electrode layer for protecting the top electrode layer from environmental moisture and oxygen damage, wherein the first moisture barrier layer is made of a material that is insoluble in water, the first moisture barrier material covering portions of the top electrode layer material disposed in the P2 scribe line to protect the top electrode material from moisture and oxygen damage.   
     
     
         15 . The solar cell of  claim 14 , further comprising an encapsulant formed above the first moisture barrier layer. 
     
     
         16 . The solar cell of  claim 14 , further comprising a P3 scribe line forming a vertical channel through the solar cell to the substrate, wherein the first moisture barrier layer extends into the P3 scribe line and covers exposed portions of the top electrode layer therein. 
     
     
         17 . The solar cell of  claim 14 , further comprising:
 a P3 scribe line forming a vertical channel through the solar cell to the substrate; and   a discrete second moisture barrier layer formed on the first moisture barrier layer, the second moisture barrier being formed of the same or different material than the first moisture barrier, wherein the second moisture barrier layer extends into the P3 scribe line and covers exposed portions of the top electrode layer therein.   
     
     
         18 . A method for forming a thin film solar cell comprising:
 depositing a conductive bottom electrode layer on a substrate;   depositing an absorber layer on the bottom electrode layer;   depositing a buffer layer on the absorber layer;   cutting an open P2 scribe line in the absorber layer, the scribe line forming an open channel with exposed sidewalls on the absorber layer from exposed portions of the absorber and buffer layers;   depositing a top electrode layer on the buffer layer after cutting the P2 scribe line, material from the top electrode layer at least partially filling the P2 scribe line;   depositing a first moisture barrier layer made of a water-insoluble material on the top electrode layer; and   covering portions of the top electrode layer material in the P2 scribe lines with the first moisture barrier layer material for protection against water and oxygen damage to the top electrode layer material within the P2 scribe line.   
     
     
         19 . The method of  claim 18 , further comprising cutting a P3 scribe line before depositing the first moisture barrier layer, wherein the steps of depositing the first moisture barrier layer also covers exposed sidewalls of the top electrode layer within the P3 scribe line. 
     
     
         20 . The method of  claim 18 , further comprising:
 cutting a P3 scribe line after depositing the first moisture barrier layer;   depositing a second moisture barrier layer on the first moisture barrier layer after forming the P3 scribe line; and   covering exposed sidewall portions of the top electrode layer material in the P3 scribe lines with the second moisture barrier layer material for protection against moisture and oxygen damage to the top electrode layer material within the P3 scribe line.