NANOWIRE ENHANCED TRANSPARENT CONDUCTIVE OXIDE FOR THIN FILM PHOTOVOLTAIC DEVICES
A thin-film photovoltaic devices includes transparent conductive oxide which has embedded within it nanowires at less than 2% nominal shadowing area. The nanowires enhance the electrical conductivity of the conductive oxide.
1 . A thin-film photovoltaic device comprising:
an absorber material characterized by a copper-based thin-film photovoltaic compound overlying a conductive material formed on a substrate;
a buffer material overlying the absorber material;
a window layer comprising a transparent conductive oxide material overlying the buffer material; and
conductive nanowires embedded in the window layer in a substantially random configuration with less than 2% nominal shadowing area to visible light, the nanowires having an electrical conductivity substantially higher than the transparent conductive oxide material.
2 . The structure of claim 1 wherein the absorber material comprises a CIS/CIGS/CIGSS compound including copper species, indium species, gallium species, selenium species, sulfur species, sodium species.
3 . The structure of claim 1 wherein the buffer material comprises a cadmium sulfide (CdS) layer, cadmium-free zinc oxide (ZnO) layer, zinc sulfide (ZnS) and ZnO mixed layer.
4 . The structure of claim 1 wherein the transparent conductive oxide material is characterized by a metal oxide film doped to have a sheet resistivity ranging from 10 2 to 10 4 mΩ·cm.
5 . The structure of claim 1 wherein the nanowires comprise nanostructures formed using chemical synthesis of at least one metal species selected from aluminum, copper, silver, gold, molybdenum, and tungsten.
6 . The structure of claim 1 wherein the nanowires generally have a lateral dimension between 10 nm and 100 nm and have an aspect ratio between 1:1 and 1000:1.
7 . A method for manufacturing thin-film photovoltaic devices comprising:
providing a substrate structure;
forming a barrier layer over the substrate structure;
forming a first electrode of conductive material over the barrier layer;
depositing a combination of copper, sodium, indium, and gallium on the first electrode;
forming an absorber material by heating the structure;
forming a buffer material over the absorber material;
forming a first conductive oxide over the buffer material;
disposing conductive nanowires on the first conductive oxide material; and
forming a second conductive oxide material over the nanowires.
8 . The method of claim 7 wherein the step of forming the barrier layer comprises depositing a dielectric material selected from silicon oxide, aluminum oxide, titanium nitride, silicon nitride, tantalum oxide, and zirconium oxide.
9 . The method of claim 7 wherein the step of forming the conductive material comprises depositing at least one layer of a metal and/or a metal oxide over the barrier layer, the metal being selected from molybdenum, tungsten, and zinc.
10 . The method of claim 7 wherein the absorber material comprises a CIGS/CIGSS compound material which includes copper, indium, gallium, selenium, and sulfur.
11 . The method of claim 7 wherein the step of forming a buffer material comprises performing a deposition process to apply a layer of at least one of ZnO and ZnS over the absorber material.
12 . The method of claim 7 wherein the first conductive oxide material comprises a zinc oxide film doped with boron to have sheet resistivity about 3 Ω per square and greater than 90% optical transparency for visible light.
13 . The method of claim 7 wherein the step of disposing nanowires comprises spraying conductive nanowires to form a randomly aligned matrix covering about 1% of the surface area of the first conductive oxide material.
14 . The method of claim 13 wherein the step of forming a second conductive oxide material comprises covering the nanowires to embed them within the combined layers of first and second conductive oxide material.
15 . The method of claim 13 wherein the second conductive oxide material comprises zinc oxide having substantially the same doping level of boron as the first conductive oxide material.
16 . A method for fabricating a solar cell structure comprising:
providing a substrate structure;
forming an absorber material overlying the substrate structure to form an upper surface region;
applying nanowires to the upper surface region with a coverage of at least 1%;
forming transparent conductor material over the nanowires to embed them within the transparent conductor material; and
the nanowires facilitating scattering of incident electromagnetic radiation and allowing the electromagnetic radiation to traverse the thickness of the transparent conductor material.
17 . The method of claim 16 wherein the nanowires comprise one of silver, gold, aluminum, molybdenum, or tungsten.
18 . The method of claim 16 wherein the transparent conductor is from about 1 to 3 microns thick.
19 . The method of claim 16 wherein the absorber material comprises copper, indium and gallium.
20 . The method of claim 16 wherein the step of applying comprises nanowires.
21 . The method of claim 16 wherein the step of applying nanowires and the step of forming of the transparent conductor material occur substantially simultaneously.
22 . The method of claim 16 wherein the transparent conductor material has a sheet resistivity of less than about 3 ohms/square.
23 . The method of claim 16 wherein transparent conductor material with the nanowires has a transparency of at least 90% of incident electromagnetic radiation between 350 nm and 1400 nm.
24 . The method of claim 16 wherein the nanowires comprise an aligned array, a random mesh, a cross-linked matrix, or scattered individual wires.
25 . The method of claim 16 wherein the nanowires comprise a material selected from metal, carbon, and organic material, and have a diameter of less than about 100 nm.
26 . The method of claim 16 further comprising scribing the thickness of the transparent conductor material including the nanowires to form an electrode.