Photovoltaic devices and method of manufacturing
A photovoltaic device includes a substrate structure and at least one Se-containing layer, such as a CdSeTe layer. A process for manufacturing the photovoltaic device includes forming the CdSeTe layer over a substrate by at least one of sputtering, evaporation deposition, CVD, chemical bath deposition process, and vapor transport deposition process. The process can also include controlling a thickness range of the Se-containing layer.
1. A method of forming a photovoltaic device comprising the steps of:
depositing a material comprising CdSe over a TCO layer;
depositing a material comprising CdTe over the material comprising CdSe to form a precursor;
annealing the precursor to form an absorber layer, whereby the material comprising CdSe and at least a portion of the material comprising CdTe interdiffuse to form a CdSeTe alloy;
depositing a material comprising tellurium and zinc, over the absorber layer, to form a back contact over the absorber layer; wherein:
the absorber layer is p-type;
a ratio of Te atoms to a sum of Se atoms and the Te atoms throughout the absorber layer is between about 99 to 100 and about 60 to 100; and
a Se concentration declines across a thickness of the absorber layer toward the back contact.
2. The method of claim 1 , wherein:
a ratio of Se atoms to a sum of Se atoms and Te atoms in the absorber layer is between about 5 to 100 and about 10 to 100.
3. The method of claim 1 , further comprising:
forming a buffer layer between the TCO layer and the absorber layer, wherein the buffer layer comprises Mg, and wherein a peak concentration of Se is located at an interface between the buffer layer and the absorber layer.
4. The method of claim 1 , further comprising:
activating the absorber layer by contacting a surface of the absorber layer with a material containing chlorine and heating the absorber layer to a temperature in a range of 350° C. to 475° C. for a duration of 90 minutes or less, wherein the material containing chlorine includes at least one of CdCl 2 , MnCl 2 , MgCl 2 , NH 4 Cl, ZnCl 2 , or TeCl 4 .
5. The method of claim 1 , wherein the material comprising CdSe is a CdSeTe alloy.
6. The method of claim 1 , wherein the step of depositing the material comprising CdTe, comprises forming a CdTe layer by vapor transport deposition of the material comprising CdTe, wherein the material comprising CdTe consists essentially of CdTe.
7. The method of claim 1 , further comprising:
depositing a second layer of CdTe between the material comprising CdTe and the back contact prior to the annealing step.
8. The method of claim 1 , wherein, prior to annealing, a CdSeTe layer is disposed between a layer of CdSe disposed adjacent the TCO layer, and a CdTe layer disposed over the CdSeTe layer; and whereby the CdTe layer is substantially consumed during the annealing to form the CdSeTe alloy.
9. The method of claim 1 , wherein, prior to annealing, a first layer of CdSe is deposited over the TCO layer, a first layer of CdTe is deposited over the first layer of CdSe, and a second layer of CdTe is deposited over the first layer of CdTe, wherein annealing forms a CdSeTe alloy and the annealing consumes substantially all of the first layer of CdSe.
10. The method of claim 1 , wherein the back contact comprises one or more layers of ZnTe, CdZnTe, or ZnTe:Cu.
11. The method of claim 1 , further comprising depositing an interfacial layer comprising copper between the absorber layer and the back contact.
12. The method of claim 1 , further comprising:
depositing a back metal electrode over the back contact, the back metal electrode comprising a MoN x layer adjacent the back contact, an aluminum layer over the MoN x layer, and a chromium layer over the aluminum layer.
13. The method of claim 1 , further comprising:
forming a window layer over the TCO layer; wherein:
the window layer comprises a n-type semiconductor,
the absorber layer is formed over the window layer,
the absorber layer is p-type, and forms a p-n junction with the window layer.
14. The method of claim 1 , wherein the photovoltaic device comprises a layer comprising at least one of: zinc sulfide, cadmium sulfide, cadmium selenide, zinc magnesium oxide, cadmium magnesium sulfide, cadmium tin oxide, indium tin oxide, indium-doped cadmium oxide, aluminum-doped zinc oxide, indium zinc oxide, zinc tin oxide, cadmium oxide, zinc aluminum oxide, zinc silicon oxide, zinc zirconium oxide, tin aluminum oxide, tin silicon oxide, or tin zirconium oxide.
15. The method of claim 1 , wherein the material comprising CdTe includes a dopant.
16. A method of forming a photovoltaic device comprising the steps of:
depositing a TCO layer;
depositing a material comprising CdSe over the TCO layer;
depositing a material comprising CdTe to form at least one precursor layer;
annealing the at least one precursor layer to form an absorber layer, whereby the material comprising CdSe and at least a portion of the material comprising CdTe interdiffuse to form a CdSeTe alloy; and
forming a back contact over the absorber layer; wherein forming the back contact comprises:
depositing a layer of ZnTe over the absorber layer;
depositing a layer of CdTe over the layer of ZnTe;
depositing a layer of Cu; and
annealing to form a copper-doped CdZnTe layer, wherein a copper dopant concentration in the back contact is a range of 0.01-1.0% Cu by atomic weight.
17. The method of claim 16 , further comprising cleaning the absorber layer with an acid prior to forming the back contact.
18. The method of claim 17 , wherein the acid is a mixture of hydrochloric acid and copper and the absorber layer is doped with copper during the cleaning step.
19. The method of claim 17 , further comprising doping the absorber layer with copper after the cleaning step.