Thin refractory metal layer used as contact barrier to improve the performance of thin-film solar cells

Abstract

A thin film amorphous silicon solar cell may have front contact between a hydrogenated amorphous silicon layer and a transparent conductive oxide layer. The cell may include a layer of a refractory metal, chosen among the group composed of molybdenum, tungsten, tantalum and titanium, of thickness adapted to ensure a light transmittance of at least 80%, interposed therebetween, before growing by PECVD a hydrogenated amorphous silicon p-i-n light absorption layer over it. A refractory metal layer of just about 1 nm thickness may effectively shield the oxide from the reactive plasma, thereby preventing a diffused defect when forming the p.i.n. layer that would favor recombination of light-generated charge carriers.

1 - 12 . (canceled) 
     
     
         13 . A method for making a thin film amorphous silicon solar cell comprising a hydrogenated amorphous silicon layer, and a transparent conductive oxide layer under the hydrogenated amorphous silicon layer, the method comprising:
 depositing the transparent conductive oxide layer for a cell contact;   depositing a layer of refractory metal comprising at least one of molybdenum, tungsten, tantalum, and titanium, with a thickness for a light transmittance of at least 80%, the layer of refractory metal being over a contact surface of the transparent conductive oxide layer; and   plasma enhanced chemical vapor depositing hydrogenated amorphous silicon to grow a cell p-i-n layer, the hydrogenated amorphous silicon being over the layer of refractory metal.   
     
     
         14 . The method of  claim 13  wherein the layer of refractory metal comprises molybdenum; and wherein depositing the layer of refractory metal comprises depositing the layer of refractory metal to form a continuous layer having a thickness of about 1 nm. 
     
     
         15 . The method of  claim 13  wherein depositing the layer of refractory metal comprises sputtering the layer of refractory metal. 
     
     
         16 . The method of  claim 13  wherein depositing the layer of refractory metal comprises chemical vapor depositing the layer of refractory metal. 
     
     
         17 . The method of  claim 13  further comprising texturing a surface of the transparent conductive oxide layer before depositing the layer of refractory metal. 
     
     
         18 . The method of  claim 17  wherein texturing comprises hydrochloric acid etching the transparent conductive oxide layer. 
     
     
         19 . The method of  claim 17  wherein texturing morphology is adjusted during deposition by chemical vapor deposition of the transparent conductive oxide layer by selectively setting pressure, temperature, and gas flow rate in a deposition chamber. 
     
     
         20 . The method of  claim 13  wherein depositing the layer of refractory metal comprises low pressure chemical vapor depositing. 
     
     
         21 . The method of  claim 13  wherein depositing the layer of refractory metal comprises sequential chemical vapor depositing of atom-thick layers of the refractory metal. 
     
     
         22 . A method for making a solar cell comprising an amorphous silicon layer, and a transparent conductive oxide layer under the amorphous silicon layer, the method comprising:
 forming the transparent conductive oxide layer for a cell contact;   forming a layer of refractory metal over a contact surface of the transparent conductive oxide layer; and   forming amorphous silicon over the layer of refractory metal.   
     
     
         23 . The method of  claim 22  wherein depositing comprises plasma enhanced chemical vapor depositing the hydrogenated amorphous silicon to grow a cell p-i-n layer. 
     
     
         24 . The method of  claim 22  wherein the layer of refractory metal comprises at least one of molybdenum, tungsten, tantalum, and titanium. 
     
     
         25 . The method of  claim 22  wherein the layer of refractory metal has a thickness for a light transmittance of at least 80%. 
     
     
         26 . The method of  claim 22  wherein the layer of refractory metal comprises molybdenum; and wherein forming the layer of refractory metal comprises depositing the layer of refractory metal to form a continuous layer having a thickness of about 1 nm. 
     
     
         27 . The method of  claim 22  wherein forming the layer of refractory metal comprises sputtering the layer of refractory metal. 
     
     
         28 . The method of  claim 22  wherein forming the layer of refractory metal comprises chemical vapor depositing the layer of refractory metal. 
     
     
         29 . The method of  claim 22  wherein forming the layer of refractory metal comprises low pressure chemical vapor depositing. 
     
     
         30 . The method of  claim 22  wherein forming the layer of refractory metal comprises sequential chemical vapor depositing of atom-thick layers of the refractory metal. 
     
     
         31 . A method for making a silicon solar cell comprising an amorphous silicon layer, and a transparent conductive oxide layer under the amorphous silicon layer, the method comprising:
 forming the transparent conductive oxide layer for a cell contact;   forming a layer of refractory metal over a contact surface of the transparent conductive oxide layer to have a light transmittance of at least 80%;   forming amorphous silicon over the layer of refractory metal; and   texturing a surface of the transparent conductive oxide layer before depositing the layer of refractory metal.   
     
     
         32 . The method of  claim 31  wherein depositing comprises plasma enhanced chemical vapor depositing the hydrogenated amorphous silicon to grow a cell p-i-n layer. 
     
     
         33 . The method of  claim 31  wherein the layer of refractory metal comprises at least one of molybdenum, tungsten, tantalum, and titanium.