Fabrication Processes for Effectively Transparent Contacts

Abstract

In conventional solar cells with metal contacts, a non-negligible fraction of the incoming solar power is immediately lost either through absorption or reflection upon interaction with the contacts. Effectively transparent contacts (“ETCs”) for solar cells can be referred to as three-dimensional contacts designed to redirect incoming light onto a photoabsorbing surface of a solar cell. In many embodiments, the ETCs have triangular cross-sections. Such ETCs can be placed on a photoabsorbing surface such that at least one of their sides forms an angle with the photoabsorbing surface. In this configuration, the ETCs can redirect incident light onto the photoabsorbing surface, mitigating or eliminating reflection loss compared to conventional solar cells. When constructed in accordance with a number of embodiments of the invention, ETCs can be effectively transparent and highly conductive.

What is claimed is: 
     
         1 . A method for fabricating solar cells incorporating effectively transparent contacts, the method comprising:
 providing a photoabsorbing surface;   providing a mold stamp, wherein one of the surfaces of the mold stamp defines a plurality of grooves; and   forming effectively transparent contacts on the photoabsorbing surface using the mold stamp.   
     
     
         2 . The method of  claim 1 , wherein:
 the photo-absorbing surface comprises metal contacts;   the plurality of grooves comprises parallel grooves having a periodicity matching the periodicity of the metal contacts; and   the effectively transparent contacts are formed on top of the metal contacts.   
     
     
         3 . The method of  claim 2 , wherein the effectively transparent contacts are formed by:
 depositing conductive ink onto the metal contacts;   placing the mold stamp in contact with the photosbsorbing surface such that the conductive ink fills the hollow channels formed by the plurality of grooves and the photoabsorbing surface;   curing the conductive ink; and   removing the mold stamp such that the cured conductive ink remains on the metal contacts.   
     
     
         4 . The method of  claim 1 , wherein:
 the photo-absorbing surface comprises metal contacts in a branching pattern, wherein the width of the metal contact reduces after each branching fork;   the plurality of grooves comprises grooves matching the pattern of the metal contacts; and   the effectively transparent contacts are formed on top of the metal contacts.   
     
     
         5 . The method of  claim 1 , wherein the effective transparent contacts are formed by:
 filling the plurality of grooves with conductive ink;   placing the mold stamp in contact with the photosbsorbing surface such that the side of the mold stamp with the filled plurality of grooves is adjacent with the photoabsorbing surface;   curing the conductive ink; and   removing the mold stamp such that the cured conductive ink remains on the photoabsorbing surface.   
     
     
         6 . The method of  claim 1 , wherein the effective transparent contacts are formed by:
 placing the mold stamp in contact with the photosbsorbing surface such that the side of the mold stamp with the plurality of grooves is adjacent with the photoabsorbing surface;   filling the volume created by the plurality of grooves and the photoabsorbing surface with conductive ink;   curing the conductive ink; and   removing the mold stamp such that the cured conductive ink remains on the photoabsorbing surface.   
     
     
         7 . The method of  claim 6 , wherein forming the effectively transparent metal contacts further comprises annealing the cured conductive ink after the removal of the mold stamp from the photoabsorbing surface. 
     
     
         8 . The method of  claim 6 , wherein the plurality of grooves is filled with conductive ink using capillary action. 
     
     
         9 . The method of  claim 6 , wherein forming the effectively transparent contacts further comprises performing a selective surface treatment on the mold stamp to render the inside of the plurality of grooves hydrophilic. 
     
     
         10 . The method of  claim 6 , wherein the plurality of grooves is filled with conductive ink using a combination of capillary action and a pressure system. 
     
     
         11 . The method of  claim 10 , wherein the pressure system applies positive pressure to fill the plurality of grooves with the conductive ink. 
     
     
         12 . The method of  claim 6 , wherein the conductive ink comprises a silver nanoparticle ink. 
     
     
         13 . The method of  claim 12 , wherein the conductive ink further comprises glass particles. 
     
     
         14 . The method of  claim 12 , wherein curing the silver nanoparticle ink comprises a process selected from the group consisting of: thermal curing, ultraviolet radiation, electromagnetic radiation tuned to the nanoparticles in the silver nanoparticle ink, and applying a current. 
     
     
         15 . The method of  claim 1 , wherein the mold stamp comprises a material selected from the group consisting of polydimethylsiloxane, polymethyl methacrylate, and ethylene-vinyl acetate. 
     
     
         16 . The method of  claim 1 , wherein the plurality of grooves comprises parallel triangular grooves. 
     
     
         17 . The method of  claim 16 , wherein at least one of the plurality of grooves has a depth-to-width ratio of at least 2-to-1. 
     
     
         18 . The method of  claim 1 , wherein:
 the photoabsorbing surface comprises a textured surface;   the mold stamp is made of polydimethylsiloxane, wherein the polydimethylsiloxane is formulated such that the elasticity of the polydimethylsiloxane compensates for the textured surface of the absorbing surface to promote adhesion between the mold stamp and the photoabsorbing surface.   
     
     
         19 . The method of  claim 1 , wherein the effectively transparent contacts are formed in an environment having a temperature of less than 21° C. 
     
     
         20 . The method of  claim 1 , wherein the mold stamp comprises a gravure printing roll.