Hybrid Vapor Phase-Solution Phase Growth Techniques for Improved CZT(S,Se) Photovoltaic Device Performance

Abstract

A hybrid vapor phase-solution phase CZT(S,Se) growth technique is provided. In one aspect, a method of forming a kesterite absorber material on a substrate includes the steps of: depositing a layer of a first kesterite material on the substrate using a vapor phase deposition process, wherein the first kesterite material includes Cu, Zn, Sn, and at least one of S and Se; annealing the first kesterite material to crystallize the first kesterite material; and depositing a layer of a second kesterite material on a side of the first kesterite material opposite the substrate using a solution phase deposition process, wherein the second kesterite material includes Cu, Zn, Sn, and at least one of S and Se, wherein the first kesterite material and the second kesterite material form a multi-layer stack of the absorber material on the substrate. A photovoltaic device and method of formation thereof are also provided.

What is claimed is: 
     
         1 . A photovoltaic device, comprising:
 a substrate;   a layer of a first kesterite material on the substrate, wherein the first kesterite material comprises copper (Cu), zinc (Zn), tin (Sn), and at least one of sulfur (S) and selenium (Se);   a layer of a second kesterite material on a side of the first kesterite material opposite the substrate, wherein the second kesterite material comprises Cu, Zn, Sn, and at least one of S and Se, and wherein the first kesterite material and the second kesterite material form a multi-layer stack of an absorber material on the substrate;   a buffer layer on a side of the multi-layer stack of the absorber material opposite the substrate; and   a transparent front contact on a side of the buffer layer opposite the multi-layer stack of the absorber material.   
     
     
         2 . The photovoltaic device of  claim 1 , further comprising:
 at least one layer of a third kesterite material on the multi-layer stack of the absorber material.   
     
     
         3 . The photovoltaic device of  claim 2 , wherein the third kesterite material comprises Cu, Zn, Sn, and at least one of S and Se. 
     
     
         4 . The photovoltaic device of  claim 2 , wherein the first kesterite material and the third kesterite material both comprise S and are both Se-free, and wherein the second kesterite material comprises both S and Se, such that an oscillatory concentration profile is present throughout the multi-layer stack of the absorber material. 
     
     
         5 . The photovoltaic device of  claim 2 , wherein the first kesterite material and the third kesterite material both comprise Se and are both S-free, and wherein the second kesterite material comprises both S and Se, such that an oscillatory concentration profile is present throughout the multi-layer stack of the absorber material. 
     
     
         6 . The photovoltaic device of  claim 5 , wherein an oscillatory concentration profile of S and Se is present throughout the multi-layer stack of the absorber material. 
     
     
         7 . The photovoltaic device of  claim 1 , wherein the layer of the first kesterite material has a thickness of from about 50 nm to about 300 nm, and ranges therebetween. 
     
     
         8 . The photovoltaic device of  claim 1 , wherein the layer of the first kesterite material has a thickness of from about 100 nm to about 300 nm, and ranges therebetween. 
     
     
         9 . The photovoltaic device of  claim 1 , wherein the layer of the first kesterite material is pinhole-free. 
     
     
         10 . The photovoltaic device of  claim 1 , wherein the first kesterite material has an average grain size of from about 1 μm to about 2 μm, and ranges therebetween. 
     
     
         11 . The photovoltaic device of  claim 1 , wherein the first kesterite material is doped with sodium (Na). 
     
     
         12 . The photovoltaic device of  claim 1 , wherein the layer of the second kesterite material has a thickness of from about 50 nm to about 500 nm, and ranges therebetween. 
     
     
         13 . The photovoltaic device of  claim 1 , wherein the layer of the second kesterite material has a thickness of from about 100 nm to about 500 nm, and ranges therebetween. 
     
     
         14 . The photovoltaic device of  claim 1 , wherein the substrate comprises a transparent conductive oxide (TCO) on which an oxide material is disposed. 
     
     
         15 . The photovoltaic device of  claim 14 , wherein the transparent conductive oxide (TCO) is selected from the group consisting of: indium tin oxide (ITO) and fluorinated tin oxide (FTO). 
     
     
         16 . The photovoltaic device of  claim 1 , further comprising:
 metal contacts on a side of the transparent front contact opposite the buffer layer.   
     
     
         17 . The photovoltaic device of  claim 16 , wherein the metal contacts comprise a material selected from the group consisting of: aluminum (Al), nickel (Ni), and combinations thereof. 
     
     
         18 . The photovoltaic device of  claim 16 , further comprising:
 an antireflective coating on the transparent front contact covering the metal contacts.   
     
     
         19 . The photovoltaic device of  claim 18 , wherein the antireflective coating comprises a material selected from the group consisting of: magnesium oxide (MgO) and magnesium fluoride (MgF 2 ). 
     
     
         20 . The photovoltaic device of  claim 1 , wherein the buffer layer comprises a material selected from the group consisting of: cadmium sulfide (CdS), a cadmium-zinc-sulfur material of the formula Cd 1-x Zn x S (wherein 0<x≤1), indium sulfide (In 2 S 3 ), zinc oxide, zinc oxysulfide, aluminum oxide (Al 2 O 3 ), and combinations thereof.