Leave-In Etch Mask for Foil-Based Metallization of Solar Cells

Abstract

Approaches for fabricating foil-based metallization of solar cells based on a leave-in etch mask, and the resulting solar cells, are described. In an example, a solar cell includes a substrate having a back surface and an opposing light-receiving surface. A plurality of alternating N-type and P-type semiconductor regions is disposed in or above the back surface of the substrate. A conductive contact structure is disposed on the plurality of alternating N-type and P-type semiconductor regions. The conductive contact structure includes metal foil portions in alignment with corresponding ones of the alternating N-type and P-type semiconductor regions. A patterned wet etchant-resistant polymer layer is disposed on the conductive contact structure. Portions of the patterned wet etchant-resistant polymer layer are disposed on and in alignment with the metal foil portions.

1 . A method of fabricating a solar cell, the method comprising:
 forming a plurality of alternating N-type and P-type semiconductor regions in or above a back surface of a substrate, opposite a light-receiving surface of the substrate;   adhering a metal foil to the alternating N-type and P-type semiconductor regions;   coating the light-receiving surface of the substrate and the metal foil with a wet etchant-resistant polymer layer;   laser ablating through the wet etchant-resistant polymer layer and through only a portion of the metal foil at regions in alignment with locations between the alternating N-type and P-type semiconductor regions, the laser ablating forming a patterned wet etchant-resistant polymer mask; and   subsequent to the laser ablating, wet etching the metal foil with a wet etchant at the regions in alignment with locations between the alternating N-type and P-type semiconductor regions to isolate remaining portions of the metal foil in alignment with the alternating N-type and P-type semiconductor regions.   
     
     
         2 . The method of  claim 1 , wherein coating the light-receiving surface of the substrate and the metal foil with the wet etchant-resistant polymer layer comprises coating with a layer of a polyolefin material. 
     
     
         3 . The method of  claim 1 , wherein wet etching the exposed regions of the metal foil with the wet etchant comprises etching using a wet etchant selected from the group consisting of a solution of potassium hydroxide (KOH), a solution of sodium hydroxide (NaOH), a solution of hydrochloric acid, and a phosphoric acetic water nitric (PAWN) etchant. 
     
     
         4 . The method of  claim 1 , further comprising:
 completing fabrication of the solar cell, wherein a completed solar cell retains the patterned wet etchant-resistant polymer mask.   
     
     
         5 . The method of  claim 1 , further comprising:
 prior to adhering the metal foil, forming a metal seed material layer on the alternating N-type and P-type semiconductor regions, wherein adhering the metal foil to the alternating N-type and P-type semiconductor regions comprises adhering the metal foil the metal seed material layer.   
     
     
         6 . The method of  claim 5 , wherein wet etching the metal foil with the wet etchant at the regions in alignment with locations between the alternating N-type and P-type semiconductor regions further comprises wet etching the metal seed material layer with the wet etchant at regions of the metal seed material layer in alignment with locations between the alternating N-type and P-type semiconductor regions. 
     
     
         7 . The method of  claim 6 , wherein wet etching the metal seed material layer with the wet etchant comprises exposing portions of a patterned bottom anti-reflective coating (BARC) layer formed at locations between the alternating N-type and P-type semiconductor regions. 
     
     
         8 . The method of  claim 1 , wherein adhering the metal foil to the alternating N-type and P-type semiconductor regions comprises:
 locating the metal foil above the plurality of alternating N-type and P-type semiconductor regions; and   laser welding or thermal compression bonding the metal foil to the alternating N-type and P-type semiconductor regions.   
     
     
         9 . The method of  claim 1 , wherein laser ablating through only the portion of the metal foil comprises laser ablating a thickness approximately in the range of 80-99% of an entire thickness of the metal foil. 
     
     
         10 . A solar cell fabricated according to the method of  claim 1 . 
     
     
         11 . A method of fabricating a solar cell, the method comprising:
 forming a plurality of alternating N-type and P-type semiconductor regions in or above a back surface of a substrate, opposite a light-receiving surface of the substrate;   adhering a metal foil to the alternating N-type and P-type semiconductor regions;   forming a wet etchant-resistant polymer layer on the metal foil but not on the light-receiving surface of the substrate;   laser ablating through the wet etchant-resistant polymer layer and through only a portion of the metal foil at regions in alignment with locations between the alternating N-type and P-type semiconductor regions, the laser ablating forming a patterned wet etchant-resistant polymer mask from the wet etchant-resistant polymer layer; and   subsequent to the laser ablating, wet etching the metal foil with a wet etchant at the regions in alignment with locations between the alternating N-type and P-type semiconductor regions to isolate remaining portions of the metal foil in alignment with the alternating N-type and P-type semiconductor regions.   
     
     
         12 . The method of  claim 11 , wherein forming the wet etchant-resistant polymer layer comprises forming a layer of an epoxy material. 
     
     
         13 . The method of  claim 11 , wherein forming the wet etchant-resistant polymer layer comprises forming a layer of a polyolefin material. 
     
     
         14 . The method of  claim 11 , wherein wet etching the exposed regions of the metal foil with the wet etchant comprises etching using a wet etchant selected from the group consisting of a solution of potassium hydroxide (KOH), a solution of sodium hydroxide (NaOH), a solution of hydrochloric acid, and a phosphoric acetic water nitric (PAWN) etchant. 
     
     
         15 . The method of  claim 11 , further comprising:
 completing fabrication of the solar cell, wherein a completed solar cell retains the patterned wet etchant-resistant polymer mask.   
     
     
         16 . The method of  claim 11 , further comprising:
 prior to adhering the metal foil, forming a metal seed material layer on the alternating N-type and P-type semiconductor regions, wherein adhering the metal foil to the alternating N-type and P-type semiconductor regions comprises adhering the metal foil the metal seed material layer.   
     
     
         17 . The method of  claim 16 , wherein wet etching the metal foil with the wet etchant at the regions in alignment with locations between the alternating N-type and P-type semiconductor regions further comprises wet etching the metal seed material layer with the wet etchant at regions of the metal seed material layer in alignment with locations between the alternating N-type and P-type semiconductor regions. 
     
     
         18 . The method of  claim 17 , wherein wet etching the metal seed material layer with the wet etchant comprises exposing portions of a patterned bottom anti-reflective coating (BARC) layer formed at locations between the alternating N-type and P-type semiconductor regions. 
     
     
         19 . The method of  claim 11 , wherein adhering the metal foil to the alternating N-type and P-type semiconductor regions comprises:
 locating the metal foil above a plurality of alternating N-type and P-type semiconductor regions; and   laser welding or thermal compression bonding the metal foil to the alternating N-type and P-type semiconductor regions.   
     
     
         20 . The method of  claim 11 , wherein laser ablating through only the portion of the metal foil comprises laser ablating a thickness approximately in the range of 80-99% of an entire thickness of the metal foil. 
     
     
         21 .- 25 . (canceled)