Method and structure for thin film photovoltaic cell using similar material junction
View Patent ↗A method for forming a thin film photovoltaic device. The method provides a transparent substrate including a surface region. A first electrode layer overlies the surface region. A copper layer is formed overlying the first electrode layer and an indium layer is formed overlying the copper layer to form a multi-layered structure. At least the multi-layered structure is subjected to a thermal treatment process in an environment containing a sulfur bearing species to forming a bulk copper indium disulfide. The bulk copper indium disulfide material has a surface region characterized by a copper poor surface region having a copper to indium atomic ratio of less than about 0.95:1 and n-type impurity characteristics. The bulk copper indium disulfide material excluding the copper poor surface region forms an absorber region and the copper poor surface region forms at least a portion of a window region for the thin film photovoltaic device. The method optionally forms a high resistivity transparent material having an intrinsic semiconductor characteristic overlying the copper poor surface region. A second electrode layer overlies the high resistivity transparent layer.
1. A method for forming a thin film photovoltaic device comprising:
providing a transparent substrate having a surface;
forming a first electrode layer over the surface;
depositing a barrier layer over the first electrode layer to protect the first electrode layer from contamination;
forming a copper layer over the barrier layer;
forming an indium layer over the copper layer to form a multi-layered structure comprising the copper layer and the indium layer;
subjecting the multi-layered structure to a thermal treatment process in an environment containing a sulfur bearing species to thereby form bulk copper indium disulfide material, the bulk copper indium disulfide material comprising a copper poor surface region with n-type impurity characteristic, wherein the copper poor surface region comprises a copper to indium atomic ratio of less than about 0.95:1;
exposing the bulk copper indium disulfide material to an aluminum species to form a p-type copper indium aluminum disulfide material;
forming a high resistivity transparent material over the copper indium aluminum disulfide material; and
forming a second electrode layer having a p-type impurity characteristic over the high resistivity transparent layer.
2. The method of claim 1 wherein the thermal treatment process comprises heating to a temperature ranging from about 100 degrees Celsius to about 500 degrees Celsius.
3. The method of claim 1 wherein the copper indium disulfide is between about 1 and about 10 microns thick.
4. The method of claim 1 wherein the high resistivity transparent material comprises one of cadmium sulfide (CdS), zinc sulfide (ZnS), zinc selenium (ZnSe), zinc oxide (ZnO), and zinc magnesium oxide (ZnMgO).
5. The method of claim 1 wherein the copper layer is deposited using a sputtering process.
6. The method of claim 1 wherein the barrier layer comprises one of platinum, titanium, chromium and silver.
7. The method of claim 1 wherein the high resistivity transparent material is doped with an impurity to make it n + conductivity type.
8. The method of claim 7 wherein the second electrode layer comprises a transparent conductive oxide material.
9. The method of claim 1 wherein the second electrode layer comprises a material selected from aluminum doped zinc oxide, indium doped tin oxide, and fluorine doped tin oxide.
10. The method of claim 9 wherein the high resistivity transparent material comprises one of zinc oxide and tin oxide.
11. The method of claim 1 wherein the sulfur bearing species comprises hydrogen sulfide in fluid phase.