Cadmium-free thin films for use in solar cells
A process for forming a cadmium-free thin film includes the steps of forming a first liquid precursor, forming a second liquid precursor, mixing the first and second liquid precursors in a vessel to form a coating material having no cadmium present, and dispensing the coating material from the vessel to a substrate to form the cadmium-free thin film.
1 . A process for forming a cadmium-free thin film, comprising the steps of:
a) forming a first liquid precursor;
b) forming a second liquid precursor;
c) mixing the first and second liquid precursors in a vessel to form a coating material having no cadmium present; and
d) dispensing the coating material from the vessel to a substrate to form said cadmium-free thin film.
2 . The process of claim 1 wherein the first liquid precursor comprises at least one salt selected from zinc salts and indium salts.
3 . The process of claim 1 wherein the second liquid precursor comprises at least one source selected from a sulfur source and a selenium source.
4 . The process of claims 1 further comprising conducting the dispensing step at a reaction temperature for a sufficient time to enable the first and second liquid precursors to react with each other.
5 . The process of claim 4 wherein the reaction temperature is from about 60° C. to 90° C.
6 . The process of claim 5 wherein the reaction temperature is from about 65° C. to 85° C.
7 . The process of claim 6 wherein the reaction temperature is about 75° C.
8 . The process of claim 1 wherein the cadmium-free thin film comprises a buffer material.
9 . The process of claim 8 wherein the buffer material is an n-type material.
10 . The process of claim 9 wherein the n-type material is selected from the group consisting of ZnO, Zn(O,S,OH) x , ZnS, Zn(Se,OH), ZnSe, In x Se y , ZnIn x Se y , In x (OH,S) y , In 2 S 3 ZnS, InS, In x S y , and In x S y ZnS, wherein x and y are integers.
11 . The process of claim 1 further comprising maintaining a temperature uniformity within a range of no more than about 2° C. between the coating solution and the substrate during the dispensing step.
12 . The process of claim 1 wherein the buffer material is ZnS.
13 . The process of claim 12 wherein the first liquid precursor comprises a solution of zinc sulfate and ammonium hydroxide.
14 . The process of claim 12 wherein the second liquid precursor comprises a solution of thiourea and ammonium hydroxide.
15 . The process of claim 1 wherein the substrate comprises a thin film of a p-type material.
16 . The process of claim 15 wherein the p-type material is selected from the group consisting of copper indium gallium selenide and copper indium selenide.
17 . The process of claim 15 wherein the substrate further comprises a thin film of an electrode material.
18 . The process of claim 17 wherein the electrode material is comprised of molybdenum.
19 . A solar cell comprising a p-type material, a cadmium-free n-type material and an electrode.