Doped photovoltaic semiconductor layers and methods of making
Provided are structures and methods for doping polycrystalline thin film semiconductor materials in photovoltaic devices. Embodiments include methods for forming and treating a photovoltaic semiconductor absorber layer.
1. A method for treating a photovoltaic semiconductor absorber layer comprising:
supplying a reducing agent to produce a reducing environment;
contacting at least a portion of an absorber layer with a passivating agent while the absorber layer is in the reducing environment, wherein the absorber layer is doped with a group V dopant, and wherein the absorber layer comprises a II-VI semiconductor; and
annealing the absorber layer with the passivating agent while in the reducing environment at a selected temperature and a selected pressure for a selected treatment duration, wherein the reducing environment comprises at least a trace amount of oxygen and a ratio of the partial pressure of the reducing agent to a partial pressure of the oxygen is at least 3.
2. The method of claim 1 , wherein the partial pressure of the oxygen in the reducing environment is less than 1 Torr.
3. The method of claim 1 , wherein a majority of the reducing environment is formed with an inert gas.
4. The method of claim 3 , wherein the reducing environment consists essentially of a mixture of hydrogen and nitrogen gas.
5. The method of claim 1 , wherein the absorber layer comprises cadmium, selenium, and tellurium.
6. The method of claim 1 , wherein the group V dopant comprises arsenic.
7. The method of claim 1 , wherein the passivating agent comprises CdCl 2 .
8. The method of claim 1 , wherein the selected temperature is in a range of 350° C. to 500° C., the selected pressure is in a range of 200 Torr to 800 Torr, and the selected treatment duration is in a range of 5 minutes to 45 minutes.
9. The method of claim 1 , wherein the absorber layer comprises a concentration of the group V dopant between 1×10 16 cm −3 and 5×10 20 cm −3 throughout a thickness of the absorber layer, and wherein annealing the absorber layer in the reducing environment activates between 1 at. % to 10 at. % of the group V dopant.
10. The method of claim 1 , wherein the passivating agent comprises one or more of: MnCl 2 , MgCl 2 , NH 4 Cl, ZnCl 2 , and TeCl 4 .
11. The method of claim 1 , wherein the group V dopant is selected from: bismuth, antimony, arsenic, phosphorus, nitrogen, and combinations thereof.
12. The method of claim 1 , wherein the reducing environment comprises 99.4% nitrogen.
13. The method of claim 1 , wherein the reducing agent comprises H 2 , hydrogen sulfide, methane, carbon monoxide, an ammonia compound, or a combination thereof.
14. The method of claim 13 , wherein the reducing agent comprises H 2 .
15. The method of claim 1 , wherein the absorber layer is formed by co-depositing a II-VI semiconductor material and a group V dopant precursor, wherein the group V dopant precursor is selected from: Cd 3 As 2 , AsH 3 , Bi 2 Te 3 , Sb 2 Te 3 , Cd 3 P 2 , Zn 3 P 2 , Bi(NO 3 ) 3 , Bi 2 S 3 , PCl 3 , PH 3 , SbH 3 and AsCl 3 , and combinations thereof.
16. The method of claim 1 , wherein the absorber layer is formed by co-depositing a II-VI semiconductor material and a group V dopant precursor, wherein the group V dopant precursor comprises Cd 3 As 2 .