Photovoltaic devices and semiconductor layers with group V dopants and methods for forming the same
A photovoltaic device ( 100 ) can include an absorber layer ( 160 ). The absorber layer ( 160 ) can be doped p-type with a Group V dopant and can have a carrier concentration of the Group V dopant greater than 4×10 15 cm −3 . The absorber layer ( 160 ) can include oxygen in a central region of the absorber layer ( 160 ). The absorber layer ( 160 ) can include an alkali metal in the central region of the absorber layer ( 160 ). Methods for carrier activation can include exposing an absorber layer ( 160 ) to an annealing compound in a reducing environment ( 220 ). The annealing compound ( 224 ) can include cadmium chloride and an alkali metal chloride.
1. A method for carrier activation, comprising:
exposing an absorber layer to a reducing environment, wherein the absorber layer comprises cadmium, tellurium, selenium, and a Group V dopant;
contacting the absorber layer with an annealing compound, wherein:
the annealing compound comprises cadmium chloride and an alkali metal chloride;
the alkali metal chloride comprises an alkali metal;
an atomic ratio of alkali metal to cadmium in the annealing compound is less than 10,000 parts per million; and
annealing the absorber layer, whereby at least a portion of the Group V dopant is activated, and wherein, after the absorber layer is annealed, the absorber layer has a carrier concentration greater than 4×10 15 cm −3 .
2. The method of claim 1 , wherein the reducing environment comprises a forming gas configured to mitigate formation of group V oxides, the forming gas comprising hydrogen, nitrogen, or combinations thereof.
3. The method of claim 1 , wherein the reducing environment is at a vacuum pressure between 200 Torr and 800 Torr.
4. The method of claim 1 , wherein the absorber layer is annealed at a temperature between 350° C. and 500° C. for between 5 minutes and 60 minutes.
5. The method of claim 1 , wherein the alkali metal chloride comprises LiCl, KCl, RbCl, or combinations thereof.
6. The method of claim 1 , wherein the atomic ratio of the alkali metal to cadmium in the annealing compound is between 500 parts per million and 6,000 parts per million.
7. The method of claim 6 , wherein the alkali metal is potassium.
8. The method of claim 6 , wherein the alkali metal is rubidium.
9. The method of claim 1 , wherein, after the absorber layer is annealed, the absorber layer has a carrier concentration between 8×10 15 cm −3 and 6×10 16 cm −3 .
10. The method of claim 9 , wherein an atomic concentration of the Group V dopant in the absorber layer is greater than 1×10 17 cm −3 .
11. The method of claim 1 , wherein the Group V dopant is arsenic.
12. The method of claim 1 , wherein after the absorber layer is annealed:
an atomic concentration of the Group V dopant in a central region of the absorber layer is between about 3×10 17 cm −3 and about 1×10 19 cm −3 ;
the absorber layer has a carrier concentration between 8×10 15 cm −3 and 6×10 16 cm −3 ;
the absorber layer comprises oxygen in the central region of the absorber layer;
the absorber layer comprises the alkali metal in the central region of the absorber layer; and
a ratio of an atomic concentration of the alkali metal to an atomic concentration of the oxygen in the central region of the absorber layer is in a range between 0.1 and 100.
13. A method for carrier activation, comprising:
contacting an absorber layer with an annealing composition, wherein:
the absorber layer comprises cadmium, tellurium, selenium, and a first dopant including at least one of phosphorous, arsenic, antimony, or bismuth;
the annealing composition comprises cadmium chloride and an alkali metal chloride;
the alkali metal chloride comprises an alkali metal, including at least one of potassium or rubidium;
an atomic ratio of alkali metal to cadmium in the annealing composition is between 500 parts per million to 6,000 parts per million;
exposing an absorber layer to a reducing environment, wherein:
the reducing environment is at a vacuum pressure between 200 Torr and 800 Torr;
the reducing environment comprises hydrogen gas, nitrogen gas, methane, carbon monoxide, or combinations thereof; and
annealing the absorber layer, by heating the absorber layer at a temperature between 350° C. and 500° C. for a duration of 5 minutes to 60 minutes, in the reducing environment, wherein, after the absorber layer is annealed:
an atomic concentration of the first dopant in a central region of the absorber layer is between about 3×10 17 cm −3 and about 1×10 19 cm −3 ;
the absorber layer has a carrier concentration between 8×10 15 cm −3 and 6×10 16 cm −3 ;
the absorber layer comprises oxygen in the central region of the absorber layer;
the absorber layer comprises the alkali metal in the central region of the absorber layer; and
a ratio of an atomic concentration of the alkali metal to an atomic concentration of the oxygen in the central region of the absorber layer is in a range between 0.1 and 100.