Efficient black silicon photovoltaic devices with enhanced blue response

Abstract

A photovoltaic (PV) device with improved blue response. The PV device includes a silicon substrate with an emitter layer on a light receiving side. The emitter layer has a low dopant level such that it has sheet resistance of 90 to 170 ohm/sq. Anti-reflection in the PV device is provided solely by a nano-structured or black silicon surface on the light-receiving surface, through which the emitter is fanned by diffusion. The nanostructures of the black silicon are formed in a manner that does not result in gold or another high-recombina-tion metal being left in the black silicon such as with metal-assisted etching using silver. The black silicon is further processed to widen these pores so as to provide larger nanostruc-tures with lateral dimensions in the range of 65 to 150 nanometers so as to reduce surface area and also to etch away a highly doped portion of the emitter.

What is claimed is: 
     
         1 . A method of fabricating photovoltaic devices, comprising: forming black silicon on a surface of a silicon substrate; forming an emitter in the silicon substrate by diffusing a dopant into the black silicon surface; processing the silicon substrate to remove an outer layer of the black silicon surface to remove a volume of highly doped silicon; forming a surface passivation coating on the black silicon surface; and attaching front and back electrical contacts to the silicon substrate. 
     
     
         2 . The method  claim 1 , wherein after the processing of the silicon substrate to remove the outer layer, the emitter has a dopant level providing a sheet resistance of at least about 90 ohm/sq. 
     
     
         3 . The method of  claim 1 , wherein the processing of the silicon substrate to remove the outer layer includes increasing lateral structure dimensions of nanostructures in the black silicon surface to a range of 65 to 200 nanometers. 
     
     
         4 . The method of  claim 1 , wherein the processing of the silicon substrate to remove the outer layer includes etching the black silicon surface with at least one of TMAH, KOH, NaOH, HF, and HNO 3  for a period of time. 
     
     
         5 . The method of  claim 4 , wherein the etching period of time is at least about 10 seconds. 
     
     
         6 . The method of  claim 1 , wherein the forming of the black silicon on the surface of the silicon substrate comprises metal-assisted etching. The method of  claim 5 , wherein the metal-assisted etching is performed using nanoparticles formed from a non-high-recombination metal. 
     
     
         8 . The method of  claim 6 , wherein the metal-assisted etching is performed using silver or copper nanoparticles. 
     
     
         9 . A method of making a photovoltaic device, comprising: forming a black silicon layer comprising nanostructures on a surface of a silicon substrate; processing the surface of the silicon substrate to remove an outer portion of the black silicon layer to increase the lateral structure dimensions of the nanostructures forming an emitter in the silicon substrate by diffusing a dopant into the black silicon layer; and forming a surface passivation coating on the black silicon layer. 
     
     
         10 . The method of  claim 9 , wherein the processing of the surface of the silicon substrate to remove the outer poltion includes etching with a solution including at least one of TMAH, KOH, NaOH, HF, and HNO 3 . 
     
     
         11 . The method of  claim 9 , wherein the processing of the surface of the silicon substrate to remove the outer portion includes increasing average lateral structure dimensions of the nanostructures in the black silicon layer to a range of 65 to 200 nanometers. 
     
     
         12 . The method of  claim 9 , wherein the forming of the black silicon layer comprises metal-assisting etching with silver or copper nanoparticles. 
     
     
         13 . The method of  claim 9 , wherein the emitter has a dopant level providing a sheet resistance of at least about 90 ohm/sq. 
     
     
         14 . A method of fabricating a photovoltaic device, comprising: forming black silicon on a surface of a silicon wafer; and forming an emitter in the surface of the silicon wafer including diffusing a dopant into the black silicon, wherein the forming of the black silicon includes increasing average lateral structure dimensions of nanostructures in the black silicon to a range of 65 to 200 nanometers, and wherein the emitter has a dopant level providing a sheet resistance of at least about 90 ohm/sq.