Solar cell with borderless interdigitated contacts and method of making

Abstract

A solar cell having n-type and p-type interdigitated back contacts (IBCs), which cover the entire back surface of the absorber layer. The spatial separation of the IBCs is in a direction perpendicular to the back surface, thus providing borderless contacts having a zero-footprint separation. As the contacts are on the back, photons incident on the cell's front surface can be absorbed without any shadowing.

What is claimed is: 
     
         1 . A borderless interdigitated back contact solar cell comprising:
 a lightly-doped absorber having a front surface and a back surface;   at least one of a first dopant type region and a first work function region on said back surface;   one or more trenches in said back surface;   sidewall spacers on trench sidewalls, said sidewall spacers extending from the trench floors to said back surface;   at least one of a second dopant type region and a second work function region on the trench floors between said sidewall spacers, the second regions being horizontally self-aligned to the first region by respective sidewalls spacers; and   a dopant-segregated interface of said first dopant type on said back surface between said trenches and a dopant-segregated interface of said second dopant type on the trench floors, each said dopant-segregated interface tuning work function at the interface, wherein the at least one of the first dopant type region and the first work function region and the at least one of the second dopant type region and the second work function region are at opposite ends of one of said sidewall spacers, and separated vertically from each other, and self-aligned with respect to each other, by said respective sidewalls spacers.   
     
     
         2 . The borderless interdigitated back contact solar cell according to  claim 1 , further comprising a front surface layer having a higher concentration of a dopant having the same doping type as the lightly doped absorber. 
     
     
         3 . The borderless interdigitated back solar cell according to  claim 1 , further comprising a first conductive contact region at the at least one of the p-doped region and the high work function region and a second conductive contact region at the at least one of the n-doped region and the low work function region. 
     
     
         4 . The borderless interdigitated back contact solar cell according to  claim 1 , wherein the lightly doped absorber is monocrystalline or polycrystalline. 
     
     
         5 . The borderless interdigitated back contact solar cell according to  claim 1 , wherein the lightly doped absorber is a material selected from the group consisting of Si, Ge, and SiGe alloys. 
     
     
         6 . The borderless interdigitated back contact solar cell according to  claim 1 , wherein the lightly-doped absorber is n-doped. 
     
     
         7 . The borderless interdigitated back contact solar cell according to  claim 1 , wherein the lightly-doped absorber is p-doped. 
     
     
         8 . The borderless interdigitated back contact solar cell according to  claim 1 , wherein the at least one of the p-doped region and the high work function region and the at least one of the n-doped region and the low work function region are spaced-apart by a distance of from about 1 micrometer to about 200 micrometers. 
     
     
         9 . The borderless interdigitated back contact solar cell according to  claim 1 , wherein the at least one of the p-doped region and the high work function region and the at least one of the n-doped region and the low work function region are spaced-apart by a distance of from about 5 micrometers to about 50 micrometers. 
     
     
         10 . The borderless interdigitated back contact solar cell according to  claim 1 , wherein the at least one of the p-doped region and the high work function region comprises the high work function region. 
     
     
         11 . The borderless interdigitated back contact solar cell according to  claim 10 , wherein the high work function region provides a potential difference having a magnitude of at least 0.2 volts at an interface with the lightly-doped absorber. 
     
     
         12 . The borderless interdigitated back contact solar cell according to  claim 10 , wherein the high work function region is a metal-containing material selected from the group consisting of metal, metal silicide, and metal germanides, or mixtures or multilayers thereof. 
     
     
         13 . The borderless interdigitated back contact solar cell according to  claim 12 , wherein the metal is selected from the group consisting of nickel, platinum, nickel platinum, cobalt, titanium, and tungsten. 
     
     
         14 . The borderless interdigitated back contact solar cell according to  claim 1 , wherein the at least one of a n-doped region and a low work function region comprises the low work function. 
     
     
         15 . The borderless interdigitated back contact solar cell according to  claim 14 , wherein the low work function region provides a potential difference having a magnitude of at least 0.2 volts at an interface with the lightly-doped absorber. 
     
     
         16 . The borderless interdigitated back contact solar cell according to  claim 14 , wherein the low work function region is a metal-containing material selected from the group consisting of metal, metal silicide, and metal germanides, or mixtures or multilayers thereof. 
     
     
         17 . The borderless interdigitated back contact solar cell according to  claim 16 , wherein the metal is selected from the group consisting of nickel, platinum, nickel platinum, cobalt, titanium, and tungsten. 
     
     
         18 . The borderless interdigitated back contact solar cell according to  claim 1 , wherein a dopant of the lightly-doped absorber is selected from the group consisting of Al, As, B, Ga, In, P, and Sb. 
     
     
         19 . The borderless interdigitated back contact solar cell according to  claim 1 , wherein an insulating sidewall spacer is disposed on the sidewall. 
     
     
         20 . The borderless interdigitated back contact solar cell according to  claim 19 , wherein the insulating sidewall spacer is selected from the group consisting of insulating oxides, insulating nitrides, ceramics, and polymers, or mixtures or multilayers of thereof. 
     
     
         21 . The borderless interdigitated back contact solar cell according to  claim 20 , wherein the insulating oxide is silicon oxide. 
     
     
         22 . The borderless interdigitated back contact solar cell according to  claim 20 , wherein the insulating nitride is silicon nitride. 
     
     
         23 . The borderless interdigitated back contact solar cell according to  claim 1 , further comprising at least one of a conductive contact, a transparent conductive oxide layer, an antireflective coatings, a surface texturing, and a surface passivation layer.