Contact fabrication of emitter wrap-through back contact silicon solar cells

Abstract

Back contact solar cells including rear surface structures and methods for making same. The rear surface has small contact areas through at least one dielectric layer, including but not limited to a passivation layer, a nitride layer, a diffusion barrier, and/or a metallization barrier. The dielectric layer is preferably screen printed. Large grid areas overlay the dielectric layer. The methods provide for increasing efficiency by minimizing p-type contact areas and maximizing n-type doped regions on the rear surface of a p-type substrate.

1 . A method of forming a solar cell, comprising:
 depositing a patterned diffusion barrier on a rear surface of a substrate, the substrate having a first conductivity type;   forming a diffusion zone on a front surface of the substrate and on regions of the rear surface not covered by the diffusion barrier, wherein the diffusion zone has a second conductivity type opposite to that of the first conductivity type;   disposing a first conductive grid on the diffusion barrier in electrical contact with the substrate in a subset of the regions of the rear surface not covered by the diffusion barrier; and   disposing a second conductive grid on the rear surface in electrical contact with the diffusion zone.   
     
     
         2 . The method of  claim 1 , further comprising alloying a plurality of contacts comprising the first conductivity type with the substrate, wherein the alloying step is performed through the dielectric layer. 
     
     
         3 . The method of  claim 1 , further comprising alloying a plurality of contacts comprising the first conductivity type with the substrate, wherein the alloying step is performed after removing regions of the dielectric layer to expose regions of the rear surface. 
     
     
         4 . The method of  claim 1 , wherein the diffusion zone is lightly doped. 
     
     
         5 . The method of  claim 1 , wherein the contacts occupy less than 30% of the area of the rear surface. 
     
     
         6 . The method of  claim 1 , wherein the first conductive grid is interdigitated with the second conductive grid. 
     
     
         7 . The method of  claim 1 , wherein at least one of the first conductive grid or the second conductive grid comprise grid lines having a tapered width. 
     
     
         8 . A method of forming a solar cell, comprising:
 depositing a patterned diffusion barrier on a rear surface of a substrate, the substrate having a first conductivity type;   forming a diffusion zone comprising an opposite conductivity type on regions of the rear surface not covered by the diffusion barrier and a front surface of the substrate, wherein the diffusion zone has a second conductivity type opposite to that of the first conductivity type;   depositing a metallization barrier on the rear surface, the metallization barrier comprising:
 first openings smaller than the first regions; and 
 second openings aligned with and smaller than second regions of the rear surface that had been covered by the diffusion barrier; 
   disposing a first conductive grid partially on the metallization barrier and in electrical contact with the diffusion through the first openings; and   disposing a second conductive grid partially on the metallization barrier and in electrical contact with the substrate through the second openings.   
     
     
         9 . The method of  claim 8 , further comprising:
 forming a plurality of holes extending from a front surface of a substrate to a rear surface of the substrate, wherein the first openings are aligned with the holes the substrate.   
     
     
         10 . The method of  claim 9 , wherein material comprising the first conductive grid at least partially fills the holes. 
     
     
         11 . The method of  claim 8 , wherein the metallization barrier comprises a transition metal oxide. 
     
     
         12 . The method of  claim 8 , wherein the depositing steps comprise using screen printing. 
     
     
         13 . The method of  claim 8 , wherein the second conductive grid comprises aluminum. 
     
     
         14 . The method of  claim 8 , wherein the metallization barrier provides passivation to the rear surface. 
     
     
         15 . The method of  claim 8 , wherein a width of a grid line of the first conductive grid is wider than a width of a first opening. 
     
     
         16 . The method of  claim 8 , wherein a width of a grid line of the second conductive grid is wider than a width of a second opening. 
     
     
         17 . The method of  claim 8 , wherein the second openings occupy less than 30% of the area of the rear surface. 
     
     
         18 . The method of  claim 8 , wherein a majority of the rear surface not occupied by the second openings comprises the diffusion. 
     
     
         19 . The method of  claim 8 , wherein the first conductive grid is interdigitated with the second conductive grid. 
     
     
         20 . The method of  claim 8 , wherein at least one of the first conductive grid or the second conductive grid comprise grid lines having a tapered width.