Nano wire array based solar energy harvesting device

Abstract

A photovoltaic device operable to convert light to electricity, comprising a substrate, a plurality of structures essentially perpendicular to the substrate, one or more recesses between the structures, each recess having a planar mirror on a bottom wall thereof and each recess filled with a transparent material. The structures have p-n or p-i-n junctions for converting light into electricity. The planar mirrors function as an electrode and can reflect light incident thereon back to the structures to be converted into electricity.

What is claimed: 
     
         1 . A photovoltaic device operable to convert light to electricity, comprising a substrate, a plurality of structures essentially perpendicular to the substrate, one or more recesses between the structures, each recess having a sidewall and a bottom wall, and a planar reflective layer disposed on the bottom wall of each recess, wherein the structures comprise a semiconductor material; the sidewall of each recess is free of the planar reflective layer; and each recess is filled with a material, wherein the structures have an overhanging portion along an entire contour of a top surface of the structures. 
     
     
         2 . The photovoltaic device of  claim 1 , wherein the semiconductor material is selected from a group consisting of silicon, germanium, group III-V compound materials, group II-VI compound materials, and quaternary materials. 
     
     
         3 . The photovoltaic device of  claim 1 , wherein the structures are cylinders or prisms with a cross-section selected from a group consisting of elliptical, circular, rectangular, and polygonal cross-sections, strips, or a mesh. 
     
     
         4 . The photovoltaic device of  claim 1 , wherein the structures are pillars with diameters from 50 nm to 5000 nm, heights from 1000 nm to 20000 nm, a center-to-center distance between two closest pillars of 300 nm to 15000 nm. 
     
     
         5 . The photovoltaic device of  claim 1 , wherein the planar reflective layer has a thickness of at least 5 nm. 
     
     
         6 . The photovoltaic device of  claim 1 , wherein each recess has a rounded or beveled inner edge between the sidewall and the bottom wall thereof. 
     
     
         7 . The photovoltaic device of  claim 1 , wherein the planar reflective layer comprises ZnO, Al, Au, Ag, Pd, Cr, Cu, Ti, Ni, or a combination thereof. 
     
     
         8 . The photovoltaic device of  claim 1 , wherein the planar reflective layer is an electrically conductive material. 
     
     
         9 . The photovoltaic device of  claim 1 , wherein the planar reflective layer is a metal. 
     
     
         10 . The photovoltaic device of  claim 1 , wherein the planar reflective layer has a reflectance of at least 50% for visible light of any wavelength. 
     
     
         11 . A method of making a photovoltaic device comprising a substrate, a plurality of structures essentially perpendicular to the substrate, one or more recesses between the structures, each recess having a sidewall and a bottom wall, a planar reflective layer disposed on the bottom wall of each recess and each recess filled with a material, the method comprising:
 forming the structures and recesses by etching the substrate;   depositing the planar reflective layer to the bottom wall, such that the sidewall of each recess is free of the planar reflective layer;   depositing the material such that each recess is completely filled by the material;   wherein the structures comprise a semiconductor material, wherein the structures have an overhanging portion along an entire contour of a top surface of the structures.   
     
     
         12 . The method of  claim 11 , further comprising:
 planarizing the material; coating the substrate with the resist layer;   developing the pattern in the resist layer;   depositing a mask layer; and   lifting off the resist layer.   
     
     
         12 . The method of  claim 11 , further comprising ion implantation or depositing a dopant layer. 
     
     
         13 . The method of  claim 11 , wherein the structures and recesses are formed by deep etch followed by isotropic etch. 
     
     
         14 . The method of  claim 11 , further comprising applying a resist layer by a print coating method, the print coating method comprising:
 coating a roller of a flexible material with a resist layer; transferring the resist layer to a surface of a substrate by rolling the roller on the surface, wherein the surface is flat or textured.   
     
     
         15 . The method of  claim 11 , further comprising applying a resist layer by a print coating method, the print coating method comprising:
 coating a stamp of a flexible material with a resist layer; transferring the resist layer to a surface of a substrate by pressing the stamp on the surface, wherein the surface is flat or textured.   
     
     
         16 . A method of converting light to electricity comprising:
 exposing a photovoltaic device to light, wherein the photovoltaic device comprises a substrate, a plurality of structures essentially perpendicular to the substrate, one or more recesses between the structures, each recess having a sidewall and a bottom wall, a planar reflective layer disposed on the bottom wall of each recess, the sidewall of each recess being free of the planar reflective layer, and each recess filled with a material;   reflecting light to the structures using the planar reflective layer;   absorbing the light and converting the light to electricity using the structures;   drawing an electrical current from the photovoltaic device;   wherein the structures comprise a semiconductor material, wherein the structures have an overhanging portion along an entire contour of a top surface of the structures.   
     
     
         16 . The method of  claim 15 , wherein the electrical current is drawn from the planar reflective layer. 
     
     
         17 . The method of  claim 16 , wherein the electrical signal is an electrical current, an electrical voltage, an electrical conductance and/or an electrical resistance. 
     
     
         18 . The method of  claim 16 , wherein a bias voltage is applied to the structures in the photovoltaic device. 
     
     
         19 . A photo detector comprising the photovoltaic device of  claim 1 , wherein the photo detector is functional to output an electrical signal when exposed to light. 
     
     
         20 . A method of detecting light comprises: exposing the photovoltaic device of  claim 1  to light; measuring an electrical signal from the photovoltaic device.