Method of reducing semiconductor window layer loss during thin film photovoltaic device fabrication, and resulting device structure
View Patent ↗A completed photovoltaic device and method forming it are described in which fluxing of a window layer into an absorber layer is mitigated by the presence of a sacrificial fluxing layer.
1. A method of manufacturing a photovoltaic device, the method comprising:
forming a first electrode;
forming a window layer containing sulfur in electrical association with the first electrode;
forming a first absorber layer adjacent the window layer;
forming a sacrificial layer containing sulfur adjacent the first absorber layer;
forming a second absorber layer adjacent the sacrificial layer;
wherein the sacrificial layer is formed in contact with the first absorber layer and the second absorber layer;
heating the device layers such that at least a portion of the sulfur from the sacrificial layer fluxes into the first and second absorber layers; and,
forming a second electrode in electrical association with the second absorber layer.
2. The method of claim 1 wherein the fluxing of the sacrificial layer into the absorber layers decreases a fluxing of the sulfur from the window layer into the first absorber layer during the heating.
3. The method of claim 1 , wherein the window layer and the sacrificial layer are formed of the same material.
4. The method of claim 1 , wherein the window layer comprises a material selected from the group consisting of cadmium sulfide and cadmium zinc sulfide.
5. The method of claim 4 , wherein the sacrificial layer comprises a material selected from the group consisting of cadmium sulfide and cadmium zinc sulfide.
6. The method of claim 1 , wherein the first and second absorber layers each comprise cadmium telluride.
7. The method of claim 1 , further comprising treating at least the second absorber layer with a compound comprising chlorine in association with the heating.
8. The method of claim 7 , wherein the sacrificial layer and the first and second absorber layers are formed to thicknesses such that after the treating and heating steps at least a portion of the first and second absorber layers are in contact with each other.
9. The method of claim 7 , wherein the sacrificial layer and first and second absorber layers are formed to thicknesses such that after the treating and heating steps a portion of each of the first and second absorber layers are separated by a portion of the sacrificial layer.
10. The method of claim 7 wherein the compound comprising chlorine comprises a material selected from the group consisting of CdCl 2 , NH 2 Cl, ZnCl 2 , and TeCl 4 .
11. The method of claim 10 wherein, wherein heating the device layers comprises a first heating at a first temperature and a second heating at a second temperature.
12. The method of claim 11 , wherein the first and second temperatures are different.
13. The method of claim 10 , wherein the treating step comprises more than one treatment step with the compound comprising chlorine.
14. The method of claim 13 , wherein the heating steps comprise a first heating to between about 400° C. and about 600° C. for between about 10 seconds and about 2 hours after a first compound comprising chlorine treatment and a second heating to between about 400° C. and about 600° C. for between about 10 seconds and about 2 hours after a second compound comprising chlorine treatment step.
15. The method of claim 14 , wherein the first and second heating steps are each to between about 420° C. and about 450° C. for between about 15 minutes and about 30 minutes.
16. The method of claim 7 , wherein the compound comprising chlorine comprises an aqueous CdCl 2 solution having a concentration between about 100 g/L and about 600 g/L.
17. The method of claim 1 , wherein the sacrificial layer is formed to a thickness of between about 50 Å and about 1000 Å.
18. The method of claim 17 , wherein the first absorber layer is formed to a thickness of between about 10 Å and about 50,000 Å.
19. The method of claim 17 , wherein the second absorber layer is formed to a thickness of between about 500 Å and about 50,000 Å.
20. The method of claim 17 , wherein the window layer is formed to a thickness of between about 50 Å and about 2,000 Å.
21. The method of claim 17 , wherein the sacrificial layer is formed to a thickness of between about 100 Å and about 800 Å.
22. The method of claim 21 , wherein the first absorber layer is formed to a thickness of between about 10,000 Å and about 30,000 Å.
23. The method of claim 21 , wherein the second absorber layer is formed to a thickness of between about 10,000 Å and about 40,000 Å.
24. The method of claim 21 , wherein the window layer is formed to a thickness of between about 75 Å and about 1000 Å.
25. The method of claim 1 , wherein heating the device layers comprises heating the device to between about 300° C. and about 600° C.
26. The method of claim 25 , wherein heating the device layers comprises heating the device to between about 400° C. and about 450° C.