Methods of forming a conductive transparent oxide film layer for use in a cadmium telluride based thin film photovoltaic device
View Patent ↗Methods for forming a conductive oxide layer on a substrate are provided. The method can include sputtering a transparent conductive oxide layer (“TCO layer”) on a substrate from a target (e.g., including cadmium stannate) at a sputtering temperature of about 10° C. to about 100° C. The TCO layer can then be annealed in an anneal temperature comprising cadmium at an annealing temperature of about 500° C. to about 700° C. The method of forming the TCO layer can be used in a method for manufacturing a cadmium telluride based thin film photovoltaic device, further including forming a cadmium sulfide layer over the transparent conductive oxide layer and forming a cadmium telluride layer over the cadmium sulfide layer.
1. A method for forming a conductive oxide layer on a substrate, the method comprising:
sputtering a transparent conductive oxide layer on a substrate from a target, wherein the target comprises cadmium stannate, and wherein the transparent conductive oxide layer is sputtered at a sputtering temperature of about 10° C. to about 100° C.;
annealing the transparent conductive oxide layer at an anneal temperature of about 500° C. to about 700° C. in an annealing atmosphere comprising cadmium; and,
etching the transparent conductive oxide layer to remove any excess cadmium deposited during annealing.
2. The method as in claim 1 , wherein the annealing atmosphere comprises an organo-cadmium gas.
3. The method as in claim 2 , wherein the organo-cadmium gas comprises dimethyl cadmium.
4. The method as in claim 1 , further comprising:
heating a metallic cadmium source to provide cadmium gas to the annealing atmosphere.
5. The method as in claim 4 , wherein the metallic cadmium source is heated to a source temperature that is lower than the anneal temperature.
6. The method as in claim 5 , wherein the source temperature is about 50° C. to about 100° C. lower than the anneal temperature.
7. The method as in claim 1 , wherein the annealing atmosphere has a pressure of about 50 mTorr to about 1000 Torr.
8. The method as in claim 1 , wherein cadmium constitutes about 1% to about 50% by volume of the annealing atmosphere.
9. The method as in claim 1 , wherein the annealing atmosphere further comprises a reducing gas.
10. The method as in claim 9 , wherein the reducing gas comprises hydrogen sulfide, hydrogen, or a mixture thereof.
11. The method as in claim 1 , wherein the anneal temperature is about 550° C. to about 650° C.
12. The method as in claim 1 , wherein the transparent conductive oxide layer is annealed for about 30 seconds to about 20 minutes.
13. The method as in claim 1 , further comprising:
forming a cadmium sulfide layer over the resistive transparent conductive oxide layer; and,
forming a cadmium telluride layer over the cadmium sulfide layer.
14. The method as in claim 13 , further comprising:
forming a resistive transparent buffer layer on the transparent conductive oxide layer prior to forming the cadmium sulfide layer.
15. The method as in claim 1 , further comprising:
prior to etching, cooling the transparent conductive oxide layer after annealing.
16. The method as in claim 1 , wherein the transparent conductive oxide layer is chemically etched via applying an etchant onto the transparent conductive oxide layer.
17. The method as in claim 16 , wherein the etchant provides selective removal of cadmium without substantially affecting the transparent conductive oxide layer.
18. The method as in claim 16 , wherein the etchant comprises hydrochloric acid, nitric acid, or mixtures thereof.