Method of making a transparent conductive oxide layer and a photovoltaic device
View Patent ↗In one aspect of the present invention, a method is provided. The method includes disposing a substantially amorphous cadmium tin oxide layer on a support; and thermally processing the substantially amorphous cadmium tin oxide layer in an atmosphere substantially free of cadmium from an external source to form a transparent layer, wherein the transparent layer has an electrical resistivity less than about 2×10 −4 Ohm-cm. Method of making a photovoltaic device is also provided.
1. A method, comprising:
disposing a substantially amorphous cadmium tin oxide layer in an atmosphere comprising oxygen at a concentration greater than about 60% by volume on a support; and
thermally processing the substantially amorphous cadmium tin oxide layer at a temperature in a range from about 550° C. to about 650° C., in an atmosphere substantially free of cadmium from an external source, and at pressure conditions less than atmospheric pressure, to form a transparent layer,
wherein the transparent layer comprises cadmium tin oxide having a substantially single-phase spinel crystal structure, and has an electrical resistivity less than about 2×10 −4 Ohm-cm wherein an atomic ratio of cadmium to tin in the substantially amorphous cadmium tin oxide layer is less than about 2.5:1.
2. The method of claim 1 , wherein the transparent layer has an electrical resistivity less than about 1.8×10 −4 Ohm-cm.
3. The method of claim 1 , wherein the transparent layer has an electrical resistivity less than about 1.5×10 −4 Ohm-cm.
4. The method of claim 1 , wherein an atomic ratio of cadmium to tin in the substantially amorphous cadmium tin oxide layer is equal to or less than about 2:1.
5. The method of claim 1 , wherein an atomic ratio of cadmium to tin in the substantially amorphous cadmium tin oxide layer is equal to or less than about 1.8:1.
6. The method of claim 1 , wherein an atomic ratio of cadmium to tin in the substantially amorphous cadmium tin oxide layer is in a range from about 1.7:1 to about 2.1.
7. The method of claim 1 , wherein thermally processing comprises heating the amorphous cadmium tin oxide layer at a treatment temperature, under vacuum conditions, and for a time duration sufficient to allow formation of the transparent layer.
8. The method of claim 1 , wherein thermal processing comprises heating the substantially amorphous cadmium tin oxide layer for a time duration in a range from about 1 minute to about 60 minutes.
9. The method of claim 1 , wherein thermal processing is conducted at a pressure less than about 500 Torr.
10. The method of claim 1 , wherein thermal processing is conducted at a pressure equal to or less than about 250 Torr.
11. The method of claim 1 , wherein disposing a substantially amorphous cadmium tin oxide layer comprises sputtering, evaporation, chemical vapor deposition, spin coating, or dip coating.
12. The method of claim 1 , wherein disposing a substantially amorphous cadmium tin oxide layer comprises sputtering from one or more target having an atomic ratio of cadmium to tin in a range from about 1.5:1 to about 2.5:1.
13. The method of claim 1 , wherein disposing a substantially amorphous cadmium tin oxide layer comprises sputtering from one or more target having an atomic ratio of cadmium to tin in a range from about 1.5:1 to about 2:1.
14. The method of claim 1 , wherein disposing a substantially amorphous cadmium tin oxide layer comprises sputtering from a single target comprising cadmium tin oxide.
15. The method of claim 1 , wherein disposing a substantially amorphous cadmium tin oxide layer comprises reactive sputtering from a single target comprising cadmium and tin.
16. The method of claim 1 , wherein the transparent layer comprises:
(a) a first region comprising cadmium tin oxide; and
(b) a second region comprising cadmium, tin, and oxygen, wherein an atomic concentration of cadmium in the second region is less than an atomic concentration of cadmium in the first region.
17. The method of claim 1 , wherein the transparent layer has a thickness in a range of from about 100 nm to about 400 nm.
18. The method of claim 1 , wherein the transparent layer has a mobility greater than about 45 cm2/Vs.
19. The method claim 1 , wherein the transparent layer has an average optical transmission greater than about 95%.
20. The method of claim 1 , wherein thermal processing is conducted in the presence of nitrogen, argon, or combinations thereof.
21. A method, comprising:
disposing a substantially amorphous cadmium tin oxide layer on a support by reactive sputtering from one or more target in an atmosphere comprising oxygen at a concentration greater than about 60% by volume; and
thermally processing the substantially amorphous cadmium tin oxide layer at a temperature in a range from about 550° C. to about 650° C., in an atmosphere substantially free of cadmium from an external source, and at pressure conditions less than atmospheric pressure, to form a transparent layer,
wherein the transparent layer comprises cadmium tin oxide having a substantially single-phase spinel crystal structure, and has an electrical resistivity less than about 2×10 −4 Ohm-cm wherein an atomic ratio of cadmium to tin in the substantially amorphous cadmium tin oxide layer is less than about 2.5:1.
22. The method of claim 21 , wherein an atomic ratio of cadmium to tin in the one or more target is equal to or less than about 2:1.
23. The method of claim 21 , wherein disposing a substantially amorphous cadmium tin oxide layer comprises reactive sputtering from a target comprising cadmium and tin.
24. The method of claim 21 , wherein disposing a substantially amorphous cadmium tin oxide layer comprises reactive sputtering from a first target comprising cadmium and a second target comprising tin.
25. The method of claim 21 , wherein disposing a substantially amorphous cadmium tin oxide layer comprises reactive sputtering from one or more target in an atmosphere comprising oxygen at a concentration greater than about 60% by volume.
26. The method of claim 21 , wherein disposing a substantially amorphous cadmium tin oxide layer comprises reactive sputtering from one or more target at a pressure in a range from about 1 milliTorr to about 20 milliTorr.
27. The method of claim 21 , wherein the transparent layer has an electrical resistivity less than about 1.5×10 −4 Ohm-cm.
28. The method claim 21 , wherein the transparent layer has an average optical transmission greater than about 95%.
29. A method, comprising:
disposing a substantially amorphous cadmium tin oxide layer in an atmosphere comprising oxygen at a concentration greater than about 60% by volume on a support;
thermally processing the substantially amorphous cadmium tin oxide layer at a temperature in a range from about 550° C. to about 650° C., in an atmosphere substantially free of cadmium from an external source, and at pressure conditions less than atmospheric pressure, to form a transparent layer, wherein the transparent layer comprises cadmium tin oxide having a substantially single-phase spinel crystal structure, and has an electrical resistivity less than about 2×10 −4 Ohm-cm;
disposing a first semiconductor layer on the transparent layer;
disposing a second semiconductor layer on the first semiconductor layer; and
disposing a back contact layer on the second semiconductor layer to form a photovoltaic device.
30. The method of claim 29 , wherein the first semiconductor layer comprises cadmium sulfide.
31. The method of claim 29 , wherein the second semiconductor layer comprises cadmium telluride.
32. The method of claim 29 , further comprising disposing a buffer layer between the transparent layer and the first semiconductor layer.
33. The method of claim 29 , wherein the buffer layer comprises an oxide selected from the group consisting of tin oxide, indium oxide, zinc oxide, and combinations thereof.