Photovoltaic device including a p-n junction and method of manufacturing

Abstract

A photovoltaic device includes a substrate structure and a p-type semiconductor absorber layer. A photovoltaic device may include a CdSeTe layer. A process for manufacturing a photovoltaic device includes forming a CdSeTe layer over a substrate. The process includes forming a p-type cadmium selenide telluride absorber layer.

What is claimed is: 
     
         1 . A photovoltaic structure, comprising:
 a substrate structure comprising a transparent conductive oxide (TCO) layer; and   an absorber layer formed over the substrate structure, wherein:
 a p-n junction is formed between the absorber layer and the substrate structure, 
 the absorber layer comprises a p-type cadmium selenide telluride layer, 
 the p-type cadmium selenide telluride layer comprises a CdSe x Te 1−x  compound, wherein a value of x is between 0 and 1, 
 the absorber layer has a gradient of selenium, whereby a concentration of selenium varies through a thickness of the absorber layer, and 
 the absorber layer has higher selenium concentration adjacent to the substrate structure and decreasing through the thickness of the absorber layer. 
   
     
     
         2 . The photovoltaic structure of  claim 1 , wherein the gradient of selenium in the CdSe x Te 1−x  compound has a selenium to tellurium ratio such that x varies in value through a thickness of the absorber layer, and wherein x has a value within a range of 0.01 to 0.25. 
     
     
         3 . The photovoltaic structure of  claim 1 , wherein the substrate structure further comprises a buffer layer and a barrier layer. 
     
     
         4 . The photovoltaic structure of  claim 1 , further comprising a back contact formed over the absorber layer. 
     
     
         5 . The photovoltaic structure of  claim 1 , wherein the concentration of selenium varies through a thickness of the absorber layer in a continuous gradient. 
     
     
         6 . The photovoltaic structure of  claim 1 , wherein the concentration of selenium varies through a thickness of the absorber layer in a stepwise gradient. 
     
     
         7 . The photovoltaic structure of  claim 1 , wherein the absorber layer further comprises a dopant. 
     
     
         8 . The photovoltaic structure of  claim 1 , wherein the absorber layer further comprises a dopant, and wherein the dopant includes copper in a concentration of 0.5 ppm to 1.0 ppm in the absorber layer. 
     
     
         9 . The photovoltaic structure of  claim 1 , wherein the back contact comprises zinc. 
     
     
         10 . The photovoltaic structure of  claim 1 , wherein the back contact comprises an alloy of cadmium, tellurium, and zinc. 
     
     
         11 . The photovoltaic structure of  claim 1 , wherein the absorber layer consists of p-type material. 
     
     
         12 . A method for forming a photovoltaic structure, comprising:
 providing a substrate structure comprising a transparent conductive oxide (TCO) layer;   depositing a CdSeTe layer over the substrate structure;   alloying the CdSeTe layer whereby an absorber layer is formed over the substrate structure, wherein:
 the absorber layer comprises a p-type cadmium selenide telluride layer, 
 the p-type cadmium selenide telluride layer is composed of a CdSe x Te 1−x  compound, wherein a value of x is between 0 and 1; and 
   depositing a back contact over the CdSeTe layer; wherein:
 the absorber layer comprises a p-type cadmium selenide telluride layer, 
 the p-type cadmium selenide telluride layer is composed of a CdSe x Te 1−x  compound, wherein a value of x is between 0 and 1; and 
 the absorber layer has a compositional profile having a gradient of selenium, wherein a concentration of Se is greater adjacent the TCO layer than adjacent the back contact. 
   
     
     
         13 . The method of  claim 12 , wherein the step of depositing the CdSeTe layer includes:
 co-evaporating cadmium telluride powder and cadmium selenide powder.   
     
     
         14 . The method of  claim 12 , wherein the step of depositing the CdSeTe layer includes:
 evaporating a pre-alloyed cadmium telluride selenide powder.   
     
     
         15 . The method of  claim 12 , wherein the step of depositing the CdSeTe layer includes:
 evaporating a powder alloy comprising cadmium, and at least one of tellurium or selenium, wherein a composition of the powder is tailored to deposit the CdSe x Te 1−x  layer, with a compositional gradient wherein x varies across a thickness of the CdSe x Te 1−x  layer.   
     
     
         16 . The method of  claim 12 , wherein the CdSe x Te 1−x  compound has a compositional profile such that x varies in value through a thickness of the cadmium selenide telluride layer, and the value of x is in a range of 0.01 to 0.40. 
     
     
         17 . The method of  claim 12 , further comprising depositing a dopant. 
     
     
         18 . The method of  claim 12 , wherein the alloying step occurs concurrently with the step of depositing the CdSeTe layer over the substrate structure. 
     
     
         19 . The method of  claim 12 , wherein the alloying step occurs after the step of depositing the CdSeTe layer over the substrate structure. 
     
     
         20 . The method of  claim 12 , wherein the alloying step further comprises:
 annealing with a CdCl 2  flux at a temperature in a range from 420° C. to 460° C. for a duration in a range from five minutes to sixty minutes.