Photovoltaic Cell and Production Thereof

Abstract

An efficient photovoltaic cell, and its process of manufacture, is disclosed wherein the back surface p-n junction is removed from a doped substrate having an oppositely doped emitter layer. A front surface and edges and optionally the back surface periphery are masked and a back surface etch is performed. The mask is not removed and acts as an anti-reflective coating, a passivating agent, or both. The photovoltaic cell retains an untextured back surface whether or not the front is textured and the dopant layer on the back surface is removed to enhance the cell efficiency. Optionally, a back surface field is formed.

1 . A photovoltaic device comprising:
 (a) a substrate comprising silicon doped with a first dopant the substrate having a front surface, a substantially smooth back surface, and at least one edge surface;   (b) a first layer comprising a second dopant of a conductivity type opposite to the first dopant at the front surface and at the at least one edge surface; and   (c) a surface coating disposed over the front surface.   
     
     
         2 . The photovoltaic device of  claim 1  wherein the surface coating is disposed over the at least one edge surface. 
     
     
         3 . The photovoltaic device of  claim 2  wherein the surface coating is disposed over the periphery of the back surface. 
     
     
         4 . The photovoltaic device of  claim 1  wherein the front surface is textured. 
     
     
         5 . The photovoltaic device of  claim 1  wherein the back surface is free or substantially free of the second dopant. 
     
     
         6 . The photovoltaic device of  claim 5  further comprising a back surface field. 
     
     
         7 . The photovoltaic device of  claim 6  wherein the back surface field is formed by a second layer at at least a portion of the back surface, the second layer comprising aluminum alloyed with the substrate. 
     
     
         8 . The photovoltaic device of  claim 1  wherein the surface coating comprises silicon nitride. 
     
     
         9 . A photovoltaic module comprising the photovoltaic device of  claim 1 . 
     
     
         10 . A photovoltaic device comprising:
 (a) a substrate comprising doped silicon, the substrate having a back surface substantially free of a p-n junction and having a p-n junction proximal to a front surface and a p-n junction proximal to at least one edge surface; and   (b) a surface coating disposed over the front surface.   
     
     
         11 . The photovoltaic device of  claim 10  wherein the surface coating is disposed over the at least one edge surface. 
     
     
         12 . The photovoltaic device of  claim 11  wherein the surface coating is disposed over the periphery of the back surface. 
     
     
         13 . The photovoltaic device of  claim 10  wherein the front surface is textured. 
     
     
         14 . The photovoltaic device of  claim 13  wherein the back surface is substantially smooth. 
     
     
         15 . The photovoltaic device of  claim 14  further comprising a back surface field. 
     
     
         16 . The photovoltaic device of  claim 10  wherein the surface coating comprises silicon nitride. 
     
     
         17 . (canceled) 
     
     
         18 . (canceled) 
     
     
         19 . (canceled) 
     
     
         20 . (canceled) 
     
     
         21 . (canceled) 
     
     
         22 . A process for making a photovoltaic device using a substrate comprising doped silicon, the process comprising the steps of:
 (a) forming a p-n junction proximal to the entire surface of the substrate;   (b) forming a surface coating disposed over the substrate such that a back surface remains free or substantially free of the surface coating; and   (c) removing the p-n junction from the back surface such that the back surface is free or substantially free of the p-n junction.   
     
     
         23 . The process according to  claim 22  wherein the surface coating comprises silicon nitride. 
     
     
         24 . The process according to  claim 22  further comprising the step of texturing the substrate. 
     
     
         25 . The process according to  claim 24  further comprising the step of removing the texture from the back surface such that the back surface is substantially smooth. 
     
     
         26 . The process according to  claim 25  further comprising the step of forming a back surface field. 
     
     
         27 . A process for making a photovoltaic device using a substrate comprising silicon doped with a first dopant, the process comprising the steps of:
 (a) forming a first layer on at least a front surface of the substrate, the first layer comprising a second dopant of a conductivity type opposite the first dopant;   (b) forming a surface coating disposed over the substrate such that a back surface of the substrate is free or substantially free of the surface coating; and   (c) etching the back surface of the substrate.