Heterojunction solar cell based on epitaxial crystalline-silicon thin film on metallurgical silicon substrate design

Abstract

One embodiment of the present invention provides a heterojunction solar cell. The solar cell includes a metallurgical-grade Si (MG-Si) substrate, a layer of heavily doped crystalline-Si situated above the MG-Si substrate, a layer of lightly doped crystalline-Si situated above the heavily doped crystalline-Si layer, a backside ohmic-contact layer situated on the backside of the MG-Si substrate, a passivation layer situated above the heavily doped crystalline-Si layer, a layer of heavily doped amorphous Si (a-Si) situated above the passivation layer, a layer of transparent-conducting-oxide (TCO) situated above the heavily doped a-Si layer, and a front ohmic-contact electrode situated above the TCO layer.

What is claimed is: 
     
         1 . A solar cell, comprising:
 a lightly doped crystalline silicon base layer adapted to generate carriers in response to absorbing light;   a heavily doped silicon surface field and barrier layer on a first side of the lightly doped crystalline silicon base layer and adapted to reduce electron-hole recombination at an interface between the lightly doped crystalline silicon base layer and the heavily doped silicon surface field and barrier layer;   a passivation layer on a second side of the lightly doped crystalline silicon base layer, wherein the passivation layer comprises intrinsic amorphous silicon, silicon-oxide, or both;   a heavily doped amorphous silicon emitter layer adjacent to the passivation layer, wherein a doping type of the heavily doped amorphous silicon emitter layer is opposite to that of the lightly doped crystalline silicon base layer, thereby creating a built-in electrical field which separates the carriers generated in the base layer from light absorption;   a transparent-conducting-oxide layer adjacent to the heavily doped amorphous silicon emitter layer as an anti-reflective layer; and   an ohmic-contact electrode coupled to the transparent-conducting-oxide layer.   
     
     
         2 . The solar cell of  claim 1 , wherein the heavily doped silicon surface field and barrier layer has a doping concentration greater than 1×10 17 /cm 3 . 
     
     
         3 . The solar cell of  claim 1 , wherein a surface of the lightly doped crystalline silicon base layer is texturized. 
     
     
         4 . The solar cell of  claim 1 , wherein the passivation layer has a thickness between 1 nm and 15 nm. 
     
     
         5 . The solar cell of  claim 1 , wherein the heavily doped amorphous silicon emitter layer has a doping concentration greater than 1×10 17 /cm 3 . 
     
     
         6 . The solar cell of  claim 1 , wherein the heavily doped amorphous silicon emitter layer has a doping concentration less than 1×10 20 /cm 3 . 
     
     
         7 . The solar cell of  claim 1 , wherein the heavily doped silicon surface field and barrier layer and the lightly doped crystalline silicon base layer are n-type doped, and wherein the heavily doped amorphous silicon emitter layer is p-type doped. 
     
     
         8 . The solar cell of  claim 1 , wherein the heavily doped silicon surface field and barrier layer and the lightly doped crystalline silicon base layer are p-type doped, and wherein the heavily doped amorphous silicon emitter layer is n-type doped. 
     
     
         9 . A method for fabricating a solar cell, comprising:
 forming a heavily doped silicon surface field and barrier layer on a first side of a lightly doped crystalline silicon base layer, wherein the lightly doped crystalline silicon base layer is adapted to generate carriers in response to absorbing light, and wherein the heavily doped silicon surface field and barrier layer is adapted to reduce electron-hole recombination at an interface between the lightly doped crystalline silicon base layer and the heavily doped silicon surface field and barrier layer;   forming a passivation layer on a second side of the lightly doped crystalline silicon base layer, wherein the passivation layer comprises intrinsic amorphous silicon, silicon-oxide, or both;   forming a heavily doped amorphous silicon emitter layer adjacent to the passivation layer, wherein a doping type of the heavily doped amorphous silicon emitter layer is opposite to that of the lightly doped crystalline silicon base layer, thereby creating a built-in electrical field which separates the carriers generated in the base layer from light absorption;   forming a transparent-conducting-oxide layer adjacent to the heavily doped amorphous silicon emitter layer as an anti-reflective layer; and   forming an ohmic-contact electrode coupled to the transparent-conducting-oxide layer.   
     
     
         10 . The method of  claim 9 , wherein the heavily doped silicon surface field and barrier layer has a doping concentration greater than 1×10 17 /cm 3 . 
     
     
         11 . The method of  claim 9 , further comprising texturizing a surface of the lightly doped crystalline silicon base layer. 
     
     
         12 . The method of  claim 9 , wherein the passivation layer has a thickness between 1 nm and 15 nm. 
     
     
         13 . The method of  claim 9 , wherein the heavily doped amorphous silicon emitter layer has a doping concentration greater than 1×10 17 /cm 3 . 
     
     
         14 . The method of  claim 9 , wherein the heavily doped amorphous silicon emitter layer has a doping concentration less than 1×10 20 /cm 3 . 
     
     
         15 . The method of  claim 9 , wherein the heavily doped silicon surface field and barrier layer and the lightly doped crystalline silicon base layer are n-type doped, and wherein the heavily doped amorphous silicon emitter layer is p-type doped. 
     
     
         16 . The method of  claim 9 , wherein the heavily doped silicon surface field and barrier layer and the lightly doped crystalline silicon base layer are p-type doped, and wherein the heavily doped amorphous silicon emitter layer is n-type doped.