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 for making a back-contact solar cell, the method comprising the steps of: 
 forming a plurality of holes extending from a front surface of a semiconductor substrate to a rear surface of the substrate, the substrate comprising a first conductivity type;    providing a diffusion comprising an opposite conductivity type on the front surface, the rear surface, and on surfaces enclosing the holes;    depositing a patterned dielectric layer on the rear surface;    alloying a plurality of contacts comprising the first conductivity type with the substrate;    disposing a first conductive grid on the dielectric layer in electrical contact with the contacts; and    disposing a second conductive grid on the rear surface in electrical contact with the diffusion.    
     
     
         2 . The method of  claim 1  wherein the alloying step is performed through existing regions of the dielectric layer.  
     
     
         3 . The method of  claim 1  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 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 5  wherein the contacts occupy less than 20% of the area of the rear surface.  
     
     
         7 . The method of  claim 6  wherein the contacts occupy less than 10% of the area of the rear surface.  
     
     
         8 . The method of  claim 1  wherein substantially all portions of the rear surface not occupied by the contacts comprise the diffusion.  
     
     
         9 . The method of  claim 1  wherein the contacts comprise aluminum.  
     
     
         10 . The method of  claim 1  wherein material comprising the second conductive grid at least partially fills the holes.  
     
     
         11 . The method of  claim 1  wherein a width of a grid line of the first conductive grid is wider than a width of the contact.  
     
     
         12 . The method of  claim 1  wherein the first conductive grid is interdigitated with the second conductive grid.  
     
     
         13 . 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.  
     
     
         14 . A back-contact solar cell made according to the method of  claim 1 .  
     
     
         15 . A method of making a back-contact solar cell, the method comprising the steps of: 
 forming a plurality of holes extending from a front surface of a semiconductor substrate to a rear surface of the substrate, the substrate comprising a first conductivity type;    depositing a patterned diffusion barrier on the rear surface;    providing a diffusion comprising an opposite conductivity type on the front surface, regions of the rear surface not covered by the diffusion barrier, and on surfaces enclosing the holes;    disposing a first conductive grid on the diffusion barrier in electrical contact with the substrate in a subset of the regions; and    disposing a second conductive grid on the rear surface in electrical contact with the diffusion.    
     
     
         16 . The method of  claim 15  further comprising the step of changing the conductivity type of the subset of the regions substantially to the first conductivity type.  
     
     
         17 . The method of  claim 15  wherein the depositing step comprises using screen printing.  
     
     
         18 . The method of  claim 15  wherein the first conductive grid comprises aluminum.  
     
     
         19 . The method of  claim 15  wherein material comprising the second conductive grid at least partially fills the holes.  
     
     
         20 . The method of  claim 15  wherein a width of a grid line of the first conductive grid is wider than a width of one of the regions.  
     
     
         21 . The method of  claim 15  wherein the second conductive grid partially overlaps the diffusion barrier.  
     
     
         22 . The method of  claim 15  wherein the first conductive grid is interdigitated with the second conductive grid.  
     
     
         23 . The method of  claim 15  wherein at least one of the first conductive grid or the second conductive grid comprise grid lines having a tapered width.  
     
     
         24 . A back-contact solar cell made according to the method of  claim 15 .  
     
     
         25 . A method of making a back-contact solar cell, the method comprising the steps of: 
 forming a plurality of holes extending from a front surface of a semiconductor substrate to a rear surface of the substrate, the substrate comprising a first conductivity type;    depositing a patterned diffusion barrier on the rear surface;    providing a diffusion comprising an opposite conductivity type on the front surface, first regions of the rear surface not covered by the diffusion barrier, and on surfaces enclosing the holes;    removing the diffusion barrier;    depositing a metallization barrier on the rear surface, the metallization barrier comprising:    first openings smaller than the first regions and aligned with the holes; 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.    
     
     
         26 . The method of  claim 25  wherein the metallization barrier provides passivation to the rear surface.  
     
     
         27 . The method of  claim 25  wherein the metallization barrier comprises a transition metal oxide.  
     
     
         28 . The method of  claim 25  wherein the depositing steps comprise using screen printing.  
     
     
         29 . The method of  claim 25  wherein the second conductive grid comprises aluminum.  
     
     
         30 . The method of  claim 25  wherein material comprising the first conductive grid at least partially fills the holes.  
     
     
         31 . The method of  claim 25  wherein a width of a grid line of the first conductive grid is wider than a width of a first opening.  
     
     
         32 . The method of  claim 25  wherein a width of a grid line of the second conductive grid is wider than a width of a second opening.  
     
     
         33 . The method of  claim 25  wherein the second openings occupy less than 30% of the area of the rear surface.  
     
     
         34 . The method of  claim 33  wherein the second openings occupy less than 20% of the area of the rear surface.  
     
     
         35 . The method of  claim 34  wherein the second openings occupy less than 10% of the area of the rear surface.  
     
     
         36 . The method of  claim 25  wherein a majority of the rear surface not occupied by the second openings comprises the diffusion.  
     
     
         37 . The method of  claim 25  wherein the first conductive grid is interdigitated with the second conductive grid.  
     
     
         38 . The method of  claim 25  wherein at least one of the first conductive grid or the second conductive grid comprise grid lines having a tapered width.  
     
     
         39 . A back-contact solar cell made according to the method of  claim 25 .  
     
     
         40 . A back-contact solar cell comprising: 
 a substrate comprising a first conductivity type;    a diffusion comprising an opposite conductivity type on portions of a rear surface of said substrate;    a screen printed dielectric layer on said rear surface;    a plurality of openings in said dielectric layer, wherein regions of the rear surface exposed through said openings comprise said first conductivity type;    a plurality of conductive contacts disposed in said openings; and    a plurality of gridlines electrically connected to said contacts, said gridlines comprising a width greater than a width of said openings.    
     
     
         41 . The solar cell of  claim 40  wherein said dielectric layer is selected from the group consisting of passivation layer, nitride layer, diffusion barrier, and metallization barrier.  
     
     
         42 . The solar cell of  claim 40  wherein said contacts comprise aluminum.  
     
     
         43 . The solar cell of  claim 40  wherein said openings comprise less than 30% of the surface area of said rear surface.  
     
     
         44 . The solar cell of  claim 43  wherein said openings comprise less than 20% of the surface area.  
     
     
         45 . The solar cell of  claim 44  wherein said openings comprise less than 10% of the surface area.  
     
     
         44 . The solar cell of  claim 40  wherein a majority of the rear surface not exposed through said openings comprises the diffusion.  
     
     
         45 . The solar cell of  claim 40  wherein said substrate comprises holes extending from a front surface of said substrate to said rear surface.  
     
     
         46 . The solar cell of  claim 45  wherein material comprising a metallization in contact with said diffusion at least partially fills the holes.