Method of fabricating high efficiency CIGS solar cells
A method is disclosed for fabricating high efficiency CIGS solar cells including the deposition of a multi-component metal precursor film on a substrate. The substrate is then inserted into a system suitable for exposing the precursor to a chalcogen to form a chalcogenide TFPV absorber. One or more Na precursors are used to deposit a Na-containing layer on the precursor film in the system. This method eliminates the use of dedicated equipment and processes for introducing Na to the TFPV absorber.
1. A method for forming a chalcogenide on a substrate, the method comprising:
forming a metal film on the substrate;
forming a layer comprising one of Na, K, or Ca directly on the metal film;
heating the substrate with the metal film and the layer to a first temperature while maintaining a pressure in a processing chamber at a first level of between about 760 Torr and 1520 Torr,
while maintaining the substrate with the metal film and the layer at the first temperature, reducing the pressure in the processing chamber to a second level to between about 600 Torr and 700 Torr; and
while maintaining the substrate with the metal film and the layer at the first temperature in the processing chamber having the pressure at the second level, flowing a chalcogen precursor into the processing chamber.
2. The method of claim 1 , wherein the layer comprises NaF and is formed using Chemical Vapor Deposition (CVD).
3. The method of claim 2 , wherein forming the layer comprising flowing a CVD precursor into the processing chamber, the CVD precursor comprising one of sodium hexafluoro-iso-propoxide, sodium perfluoro-t-butoxide, sodium hexafluoroacetylacetonate, or sodium heptafluoro-octadionate.
4. The method of claim 1 , wherein a thickness of the layer is between 5 nm and 100 nm.
5. The method of claim 1 , further comprising chalcogenating the metal film and the layer followed by annealing.
6. The method of claim 1 , wherein the metal film comprises Cu, In, and Ga.
7. The method of claim 6 , wherein the metal film further comprises Ag.
8. The method of claim 1 , wherein the first temperature is between 350 C and about 450C.
9. The method of claim 1 , wherein the first temperature is between 400 C and about 450 C.
10. The method of claim 1 , wherein a concentration of the chalcogen precursor is about 1 molar % when the chalcogen precursor is flown into the processing chamber.
11. The method of claim 1 , further comprising, after flowing the chalcogen precursor into the processing chamber, flowing an inert gas into the processing chamber, and heating the substrate to a second temperature of between about 450 C and about 550 C.
12. The method of claim 11 , wherein the substrate is heated to the second temperature while maintaining a pressure in a processing chamber at the first level of between about 760 Torr and 1520 Torr.
13. The method of claim 12 , further comprising, while maintaining the substrate at the second temperature, reducing the pressure in the processing chamber to the second level to between about 600 Torr and 700 Torr; and
wherein while maintaining the substrate at the second temperature in the processing chamber having the pressure at the second level, flowing an additional chalcogen precursor into the processing chamber.
14. The method of claim 13 , wherein the additional chalcogen precursor and the chalcogen precursor are same.
15. The method of claim 13 , further comprising, after flowing the additional chalcogen precursor into the processing chamber, flowing an inert gas into the processing chamber, and heating the substrate to a third temperature of between about 550 C and about 650 C.
16. The method of claim 15 , wherein the substrate is heated to the third temperature while maintaining a pressure in a processing chamber at the first level of between about 760 Torr and 1520 Torr.
17. The method of claim 16 , further comprising, while maintaining the substrate at the third temperature, reducing the pressure in the processing chamber to about 600 Torr; and
wherein while maintaining the substrate at the third temperature in the processing chamber having the pressure of about 600 Torr, flowing a sulfur containing precursor into the processing chamber.
18. The method of claim 1 , wherein the metal film is partially chalcogenized prior to forming the layer comprising one of Na, K, or Ca.
19. The method of claim 1 , wherein the layer formed directly on the metal film comprises potassium (K).
20. The method of claim 1 , wherein the layer formed directly on the metal film comprises calcium (Ca).