Bifacial solar cells with overlaid back grid surface

Abstract

A simplified manufacturing process and the resultant bifacial solar cell (BSC) are provided, the simplified manufacturing process reducing manufacturing costs. The BSC includes an active region located on the front surface of the substrate, formed for example by a phosphorous diffusion step. After removing the PSG, assuming phosphorous diffusion, and isolating the front junction, dielectric layers are deposited on the front and back surfaces. Contact grids are formed, for example by screen printing. Prior to depositing the back surface dielectric, a metal grid may be applied to the back surface, the back surface contact grid registered to, and alloyed to, the metal grid during contact firing.

1 . A bifacial solar cell, comprising:
 a silicon substrate with a front surface and a back surface;   an active region of a first conductivity type located on at least a portion of said front surface of said silicon substrate;   a first dielectric layer deposited on said active region;   a second dielectric layer deposited on said back surface of said silicon substrate;   a first contact grid applied to said first dielectric layer, said first contact grid comprised of a first metal, wherein after a firing step said first contact grid is alloyed through said first dielectric layer to said active region; and   a second contact grid applied to said second dielectric layer, said second contact grid comprised of a second metal, wherein after said firing step said second contact grid is alloyed through said second dielectric layer to said back surface of said silicon substrate.   
     
     
         2 . The bifacial solar cell of  claim 1 , further comprising a floating junction of said first conductivity type located on at least a portion of said back surface of said silicon substrate. 
     
     
         3 . The bifacial solar cell of  claim 1 , wherein said silicon substrate is comprised of a p-type silicon, said active region is comprised of n +  material resulting from a phosphorous diffusion step, and said first and second dielectric layers are selected from the group consisting of silicon nitride, silicon oxide and silicon oxynitride. 
     
     
         4 . The bifacial solar cell of  claim 1 , further comprising a grid pattern of a third metal deposited directly on said back surface of said silicon substrate and interposed between said back surface of said silicon substrate and said second dielectric layer, wherein said second screen printed contact grid is registered to said grid pattern, and wherein after said firing step said second screen printed contact grid is alloyed through said second dielectric layer to said grid pattern of said third metal. 
     
     
         5 . The bifacial solar cell of  claim 1 , further comprising a groove on said front surface of said silicon substrate, said groove isolating a front junction formed by said active region and said silicon substrate. 
     
     
         6 . A bifacial solar cell, comprising:
 a silicon substrate with a front surface and a back surface;   an active region of a first conductivity type located on at least a portion of said front surface of said silicon substrate;   a first dielectric layer deposited on said active region;   a second dielectric layer deposited on said back surface of said silicon substrate;   a first metal contact grid on the first dielectric layer;   a second metal contact grid on the second dielectric layer; and   a back surface contact grid aligned with the second metal contact grid.   
     
     
         7 . The bifacial solar cell of  claim 6 , wherein the active region of the first conductivity type includes an n-type active region. 
     
     
         8 . The bifacial solar cell of  claim 6 , wherein the active region has a depth between approximately 0.3 and 0.6 microns. 
     
     
         9 . The bifacial solar cell of  claim 6 , wherein the first dielectric layer includes silicon oxynitride. 
     
     
         10 . The bifacial solar cell of  claim 6 , wherein the second dielectric layer includes silicon oxynitride. 
     
     
         11 . The bifacial solar cell of  claim 6 , wherein the first dielectric layer includes a laminate of more than one dielectric material. 
     
     
         12 . The bifacial solar cell of  claim 6 , wherein the laminate includes approximately 10 nanometers of silicon dioxide and approximately 70 nanometers of silicon nitride. 
     
     
         13 . The bifacial solar cell of  claim 6 , wherein the first metal contact grid includes silver. 
     
     
         14 . The bifacial solar cell of  claim 6 , wherein the second metal contact grid includes aluminum. 
     
     
         15 . A bifacial solar cell, comprising:
 a silicon substrate with a front surface and a back surface;   an active region of a first conductivity type located on at least a portion of said front surface of said silicon substrate;   a first dielectric layer deposited on said active region;   a second dielectric layer deposited on said back surface of said silicon substrate;   a first metal contact grid on the first dielectric layer; and   a second metal contact grid on the second dielectric layer, wherein the first metal contact grid is aligned to the second metal contact grid, and the second metal contact grid uses a finer spacing than the first metal contact grid.   
     
     
         16 . The bifacial solar cell of  claim 15 , wherein the second metal contact grid includes aluminum. 
     
     
         17 . The bifacial solar cell of  claim 16 , wherein the second metal contact grid includes a silver-aluminum alloy. 
     
     
         18 . The bifacial solar cell of  claim 15 , further including a back surface contact grid aligned with the second metal contact grid. 
     
     
         19 . The bifacial solar cell of  claim 18 , wherein the back surface contact grid is alloyed to the second metal contact grid.