Transparent Conductive Oxide in Silicon Heterojunction Solar Cells

Abstract

Devices and methods for reducing optical losses in transparent conductive oxides (TCOs) used in silicon heterojunction (SHJ) solar cells while enhancing series resistance are disclosed herein. In particular, the methods include reducing the thickness of TCO layers by about 200% to 300% and depositing hydrogenated dielectric layers on top to form double layers of antireflection coating. It has been discovered that the conductivity of a thin TCO layer can be increased through a hydrogen treatment supplied from the capping dielectric during the post deposition annealing. The optimized cells with ITO/SiOx:H stacks achieved more than 41 mA/cm2 generation current on 120-micron-thick wafers while having approximately 100 Ohm/square sheet resistance. Further, solar cells and methods may include integration of ITO/SiOx:H stacks with Cu plating and use ITO/SiNx/SiOx triple layer antireflection coatings. The experimental data details the improved optics and resistance in cell stacks with varying materials and thicknesses.

What is claimed is: 
     
         1 . A solar cell, comprising:
 a silicon base layer;   an emitter layer disposed on a first side of the silicon base layer, wherein the emitter layer comprises amorphous silicon;   a first antireflective coating layer disposed on the emitter layer, wherein the first antireflective coating layer comprises a transparent conducting oxide; and   a second antireflective coating layer disposed on the first antireflective coating layer, wherein the second antireflective coating layer comprises a hydrogenated silicon oxide.   
     
     
         2 . The solar cell of  claim 1 , wherein the first antireflective coating layer is hydrogenated by the second antireflective coating layer after annealing such that conductivity of the first antireflective coating layer is increased. 
     
     
         3 . The solar cell of  claim 2 , wherein conductivity of the first antireflective coating layer is increased by about 20% to about 40%. 
     
     
         4 . The solar cell of  claim 1 , wherein the second antireflective coating layer has an atomic percentage of hydrogen between about 10% and about 40%. 
     
     
         5 . The solar cell of  claim 4 , wherein the atomic percentage of hydrogen is about 25%. 
     
     
         6 . The solar cell of  claim 1 , further comprising:
 a conducting grid disposed on the second antireflective coating layer.   
     
     
         7 . The solar cell of  claim 6 , wherein the conducting grid comprises at least one of silver, copper, and nickel. 
     
     
         8 . The solar cell of  claim 1 , wherein the silicon base layer includes a crystalline-Si substrate. 
     
     
         9 . The solar cell of  claim 1 , wherein the silicon base layer includes an epitaxially formed crystalline-Si thin film. 
     
     
         10 . A solar cell, comprising:
 a silicon base layer;   an emitter layer disposed on a first side of the silicon base layer, wherein the emitter layer comprises amorphous silicon;   a first antireflective coating layer disposed on the emitter layer, wherein the first antireflective coating layer comprises a transparent conducting oxide; and   a second antireflective coating layer disposed on the first antireflective coating layer, wherein the second antireflective coating layer comprises a hydrogenated silicon oxide,   wherein the first antireflective coating layer is hydrogenated by the second antireflective coating layer after annealing such that conductivity of the first antireflective coating layer is increased.   
     
     
         11 . The solar cell of  claim 10 , wherein conductivity of the first antireflective coating layer is increased by about 20% to about 40%. 
     
     
         12 . The solar cell of  claim 10 , wherein the second antireflective coating layer has an atomic percentage of hydrogen between about 10% and about 40%. 
     
     
         13 . The solar cell of  claim 12 , wherein the atomic percentage of hydrogen is about 25%. 
     
     
         14 . The solar cell of  claim 10 , further comprising:
 a conducting grid disposed on the second antireflective coating layer.   
     
     
         15 . The solar cell of  claim 14 , wherein the conducting grid comprises at least one of silver, copper, and nickel. 
     
     
         16 . The solar cell of  claim 10 , wherein the silicon base layer includes a crystalline-Si substrate. 
     
     
         17 . The solar cell of  claim 10 , wherein the silicon base layer includes an epitaxially formed crystalline-Si thin film. 
     
     
         18 . A solar cell, comprising:
 a silicon base layer;   an emitter layer disposed on a first side of the silicon base layer, wherein the emitter layer comprises amorphous silicon;   a first antireflective coating layer disposed on the emitter layer, wherein the first antireflective coating layer comprises a transparent conducting oxide comprising an indium oxide; and   a second antireflective coating layer disposed on the first antireflective coating layer, wherein the second antireflective coating layer comprises a hydrogenated silicon oxide.   
     
     
         19 . The sensor of  claim 18 , wherein the transparent conducting oxide comprises indium tin oxide, GaInO, GaInSnO, ZnInO, and/or ZnInSnO. 
     
     
         20 . The solar cell of  claim 18 , wherein the first antireflective coating layer is hydrogenated by the second antireflective coating layer after annealing such that conductivity of the first antireflective coating layer is increased.