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 forming a doped semiconductor absorber layer, comprising:
disposing an absorber layer of a photovoltaic stack to form an absorber film comprising cadmium, tellurium, and selenium, wherein disposing the absorber layer comprises depositing in one or more layers:
a first material and a second material onto a window stack in a first deposition environment, wherein:
the first material comprises a II-VI semiconductor or precursor, and
the second material comprises a group V dopant or dopant precursor;
contacting at least a portion of the absorber film with a third material, wherein the third material comprises a passivating agent;
heating the photovoltaic stack with a reducing agent in a reducing environment, wherein:
the reducing agent comprises hydrogen gas (H 2 );
the reducing environment comprises at least a trace amount of oxygen (O 2 );
the reducing environment comprises H 2 in a range from 0.06% to 3.0%; and
a ratio of the partial pressure of H 2 to the partial pressure of O 2 is equal to or greater than 0.24.
2 . The method of claim 1 , wherein a concentration of the group V dopant in the absorber layer is between 1×10 16 cm −3 and 5×10 20 cm −3 , and wherein heating the absorber layer in the reducing environment activates between 1 at. % to 10 at. % of the group V dopant; whereby after the heating step, the absorber layer has a p-type charge carrier concentration of at least 1×10 15 cm −3 .
3 . The method of claim 1 , wherein the photovoltaic stack comprises a plurality of layers on a substrate, and wherein heating the absorber layer in the reducing environment is subsequent to the substrate being moved through multiple and various deposition stations with their own vapor distributor and supply.
4 . The method of claim 1 , wherein disposing the absorber layer comprises one or more of: sputtering, spray, evaporation, molecular beam deposition, pyrolysis, closed space sublimation, pulse laser deposition, electrochemical deposition, atomic layer deposition, or vapor transport deposition.
5 . The method of claim 1 , wherein the reducing environment has a total pressure in a range of 200 Torr to 800 Torr, and a partial pressure of oxygen in the reducing environment is less than 1 Torr.
6 . The method of claim 1 , wherein the reducing environment has a total pressure in a range of 200 Torr to 800 Torr, and H 2 is provided at a partial pressure in a range of 0.24 Torr to 50 Torr.
7 . The method of claim 1 , wherein the ratio of the partial pressure of H 2 to the partial pressure of O 2 is equal to or greater than 3.
8 . The method of claim 1 , further comprising depositing a buffering semiconductor layer on the window stack prior to depositing the first and second materials, wherein the buffering semiconductor layer comprises CdSe.
9 . The method of claim 1 , wherein:
the passivating agent is a halogen compound selected from one or more of: CdCl 2 , MnCl 2 , MgCl 2 , NH 4 Cl, ZnCl 2 , or TeCl 4 ; and
the group V dopant is selected from: Bismuth, Antimony, Arsenic, Phosphorus, Nitrogen, or combinations thereof.
10 . The method of claim 1 , 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 , AsCl 3 , or combinations thereof.
11 . The method of claim 1 , wherein the second material is deposited simultaneously with the first material.
12 . A method for forming a doped semiconductor absorber layer, comprising:
disposing an absorber layer of a photovoltaic stack to form an absorber film, wherein disposing the absorber layer comprises depositing in one or more layers:
a first material and a second material onto a window stack in a first deposition environment, wherein:
the first material comprises a II-VI semiconductor or a II-VI semiconductor material precursor, and
the second material comprises a group V dopant or a group V dopant precursor;
applying a first heat treatment to the absorber film in a first heat-treating environment;
contacting at least a portion of the absorber film with a passivating agent;
applying a second heat treatment to the absorber film in a second heat-treating environment; and
supplying a reducing gas to the second heat-treating environment to produce a reducing environment; wherein:
the reducing gas comprises hydrogen gas (H 2 );
the reducing environment comprises at least a trace amount of oxygen (O 2 );
the reducing environment comprises H 2 in a range from 0.06% to 3.0%; and
a ratio of the partial pressure of H 2 to the partial pressure of O 2 is equal to or greater than 0.24.
13 . The method of claim 12 , wherein the group V dopant precursor comprises Cd 3 As 2 .
14 . The method of claim 12 , wherein a concentration of the group V dopant in the absorber layer is between 1×10 16 cm −3 and 5×10 20 cm −3 , and wherein heating the absorber layer in the reducing environment activates between 1 at. % to 10 at. % of the group V dopant; whereby after the heating step, the absorber layer has a p-type charge carrier concentration of at least 1×10 15 cm −3 .
15 . The method of claim 12 , wherein disposing the absorber layer comprises one or more of: sputtering, spray, evaporation, molecular beam deposition, pyrolysis, closed space sublimation, pulse laser deposition, electrochemical deposition, atomic layer deposition, or vapor transport deposition.
16 . The method of claim 12 , wherein:
the reducing environment has a total pressure in a range of 200 Torr to 800 Torr;
a partial pressure of oxygen in the reducing environment is less than 1 Torr; and
a partial pressure of hydrogen in the reducing environment is in a range of 0.24 Torr to 50 Torr.
17 . The method of claim 12 , wherein the ratio of the partial pressure of H 2 to the partial pressure of O 2 is equal to or greater than 3.
18 . The method of claim 12 , further comprising depositing a buffering semiconductor layer on the window stack prior to depositing the first material and the second material, wherein the buffering semiconductor layer comprises CdSe.
19 . The method of claim 12 , wherein:
the passivating agent is a halogen compound selected from one or more of: CdCl 2 , MnCl 2 , MgCl 2 , NH 4 Cl, ZnCl 2 , and TeCl 4 ; and
the group V dopant is selected from: Bismuth, Antimony, Arsenic, Phosphorus, Nitrogen, or combinations thereof.
20 . The method of claim 12 , 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 , AsCl 3 , or combinations thereof.