PHOTOVOLTAIC DEVICE WITH RESISTIVE CIGS LAYER AT THE BACK CONTACT
A photovoltaic device including a substrate, a first electrode layer over the substrate and a resistive p-type semiconductor layer over the first electrode layer. The device also includes a p-type absorber layer over the resistive p-type semiconductor layer, an n-type semiconductor layer over the p-type absorber layer and a second electrode layer over the n-type semiconductor layer. Additionally, a resistivity of the resistive p-type semiconductor layer is greater than a resistivity of the p-type absorber layer.
1 . A photovoltaic device, comprising:
a substrate;
a first electrode layer over the substrate;
a resistive p-type semiconductor layer over the first electrode layer;
a p-type absorber layer over the resistive p-type semiconductor layer;
an n-type semiconductor layer over the p-type absorber layer; and
a second electrode layer over the n-type semiconductor layer;
wherein a resistivity of the resistive p-type semiconductor layer is greater than a resistivity of the p-type absorber layer.
2 . The device of claim 1 , wherein a hole mobility of the resistive p-type semiconductor layer is lower than a hole mobility of the p-type absorber layer.
3 . The device of claim 2 , wherein a hole carrier concentration of the resistive p-type semiconductor layer is equal to or higher than a hole carrier concentration of the p-type absorber layer.
4 . The device of claim 2 , wherein the resistive p-type semiconductor layer has at least one of a smaller average grain size or a higher vacancy concentration than the p-type absorber layer.
5 . The device of claim 4 , wherein the resistive p-type semiconductor layer comprises copper indium gallium selenide, and the p-type absorber layer comprises copper indium gallium selenide.
6 . The device of claim 2 , wherein the resistive p-type semiconductor layer comprises a semiconductor material which has a lower hole mobility than p-type copper indium gallium selenide, and the p-type absorber layer comprises p-type copper indium gallium selenide.
7 . The device of claim 6 , wherein the resistive p-type semiconductor layer comprises a p-type semiconductor selected from the group consisting of Si, CuS, ZnSe, CdSe, GaAs and GaP.
8 . The device of claim 7 , wherein the p-type semiconductor layer comprises sodium doped ZnSe and wherein the sodium diffuses into the p-type absorber layer during or after deposition of the p-type absorber layer.
9 . The device of claim 2 , wherein the resistive p-type semiconductor layer comprises a phase separated p-type semiconductor material or a laminate of plural p-type semiconductor material layers.
10 . The device of claim 1 , wherein the resistive p-type semiconductor layer is capable of sodium diffusion, the first electrode comprises molybdenum which contains sodium, and the sodium diffuses from the first electrode through the resistive p-type semiconductor layer into the p-type absorber layer during or after deposition of the p-type absorber layer.
11 . The device of claim 1 , wherein the n-type semiconductor layer comprises n-CdS and the second electrode layer comprises a first transparent layer comprising Indium Tin Oxide (ITO), Zinc Oxide (ZnO) or Aluminum Zinc Oxide (AZO) over a second transparent layer comprising resistive Aluminum Zinc Oxide (RAZO).
12 . A photovoltaic device, comprising:
a substrate;
a first electrode layer over the substrate;
a p-type absorber layer over the resistive p-type semiconductor layer;
an n-type semiconductor layer over the p-type absorber layer; and
a second electrode layer over the n-type semiconductor layer,
wherein the junction of the p-type absorber layer and the n-type semiconductor layer form a diode and a thickness of the p-type absorber layer is greater than a sum of a depletion width of the diode in the p-type absorber layer and a hole diffusion length in the p-type absorber layer.
13 . The device of claim 12 , wherein the p-type absorber layer comprises copper indium gallium selenide having a thickness greater than 0.7 microns.
14 . A method of making a photovoltaic device, comprising:
depositing a first electrode layer over a substrate;
depositing a resistive p-type semiconductor layer over the first electrode layer;
depositing a p-type absorber layer over the resistive p-type semiconductor layer;
depositing an n-type semiconductor layer over the p-type absorber layer; and
depositing a second electrode layer over the n-type semiconductor layer;
wherein a resistivity of the resistive p-type semiconductor layer is greater than a resistivity of the p-type absorber layer.
15 . The method of claim 14 , wherein a hole mobility of the resistive p-type semiconductor layer is lower than a hole mobility of the p-type absorber layer.
16 . The method of claim 15 , wherein a hole carrier concentration of the resistive p-type semiconductor layer is equal to or higher than a hole carrier concentration of the p-type absorber layer.
17 . The method of claim 15 , wherein the resistive p-type semiconductor layer is deposited at a lower temperature than the p-type absorber layer to provide at least one of a smaller average grain size or a higher vacancy concentration in the resistive p-type semiconductor layer than in the p-type absorber layer.
18 . The method of claim 17 , wherein the resistive p-type semiconductor layer comprises copper indium gallium selenide, and the p-type absorber layer comprises copper indium gallium selenide.
19 . The method of claim 15 , wherein the resistive p-type semiconductor layer comprises a semiconductor material which has a lower hole mobility than p-type copper indium gallium selenide, and the p-type absorber layer comprises p-type copper indium gallium selenide.
20 . The method of claim 19 , wherein the resistive p-type semiconductor layer comprises a p-type semiconductor selected from the group consisting of Si, CuS, ZnSe, CdSe, GaAs and GaP.
21 . The method of claim 20 , wherein the p-type semiconductor layer comprises sodium doped ZnSe and wherein the sodium diffuses into the p-type absorber layer during deposition of the p-type absorber layer or during a heating step which occurs after deposition of the p-type absorber layer.
22 . The method of claim 15 , wherein the resistive p-type semiconductor layer comprises a phase separated p-type semiconductor material or a laminate of plural p-type semiconductor material layers.
23 . The method of claim 14 , wherein the resistive p-type semiconductor layer is capable of sodium diffusion, the first electrode comprises molybdenum which contains sodium, and the sodium diffuses from the first electrode through the resistive p-type semiconductor layer into the p-type absorber layer during deposition of the p-type absorber layer or during a heating step which occurs after deposition of the p-type absorber layer.
24 . The method of claim 14 , wherein the n-type semiconductor layer comprises n-CdS; and
wherein depositing the second electrode layer further comprises:
depositing a first transparent layer comprising resistive Aluminum Zinc Oxide (RAZO); and
depositing a second transparent layer comprising Indium Tin Oxide (ITO), Zinc Oxide (ZnO) or Aluminum Zinc Oxide (AZO) over the RAZO layer.
25 . A method of operating a photovoltaic device, comprising:
a substrate;
a first electrode layer over the substrate;
a p-type absorber layer over the resistive p-type semiconductor layer;
an n-type semiconductor layer over the p-type absorber layer; and
a second electrode layer over the n-type semiconductor layer,
wherein the method comprises applying a current or voltage to the first and the second electrode layers such that a junction of the p-type absorber layer and the n-type semiconductor layer form a diode with a depletion region which partially extends from the junction into the p-type absorber layer to a depth which differs from the thickness of the p-type absorber layer by at least a hole diffusion length in the p-type absorber layer.
26 . The method of claim 25 , wherein the p-type absorber layer comprises copper indium gallium selenide having a thickness greater than 0.7 microns.