Method and Device Utilizing Strained AZO Layer and Interfacial Fermi Level Pinning in Bifacial Thin Film PV Cells
A method for forming a bifacial thin film photovoltaic cell includes providing a glass substrate having a surface region covered by an intermediate layer and forming a thin film photovoltaic cell on the surface region. Additionally, the thin film photovoltaic cell includes an anode overlying the intermediate layer, an absorber over the anode, and a window layer and cathode over the absorber mediated by a buffer layer. The anode comprises an aluminum doped zinc oxide (AZO) layer forming a first interface with the intermediate layer and a second interface with the absorber. The AZO layer is configured to induce Fermi level pinning at the first interface and a strain field from the first interface to the second interface.
1 . A method for forming a bifacial thin film photovoltaic cell, the method comprising:
providing a glass substrate having a surface region covered by an intermediate layer;
forming a thin film photovoltaic cell on the surface region, the thin film photovoltaic cell comprising an anode overlying the intermediate layer, an absorber over the anode, and a window layer and cathode over the absorber mediated by a buffer layer;
wherein the anode comprises an aluminum doped zinc oxide (AZO) layer forming a first interface with the intermediate layer and a second interface with the absorber, the AZO layer is configured to induce Fermi level pinning at the first interface and a strain field from the first interface to the second interface.
2 . The method of claim 1 wherein the intermediate layer comprises a film made by material selected from fluorine doped tin oxide (TFO), indium tin oxide (ITO), Si 3 N 4 , SiO 2 , molybdenum, and combinations thereof.
3 . The method of claim 1 wherein the absorber comprises a p-type semiconductor layer made by CdTe material or copper indium gallium diselenide CIGS material.
4 . The method of claim 1 wherein the AZO layer comprises a heavily doped Al species ranging from 5×10 19 cm −3 to 1×10 21 cm −3 .
5 . The method of claim 1 wherein both the Fermi level pinning at the first interface and the strain field from the first interface to the second interface cause a reduction in internal electric field strength at the second interface.
6 . The method of claim 5 wherein the reduction in internal electric field strength at the second interface reduce a barrier for hole tunneling across the second interface from the absorber to the anode.
7 . The method of claim 1 wherein both the Fermi level pinning at the first interface and the strain field from the first interface to the second interface cause a flipping in internal electric field direction at the second interface.
8 . The method of claim 7 wherein the flipping in electric internal field direction at the second interface directly aids a collection of holes at the second interface from the absorber to the anode.
9 . The method of claim 1 wherein the substrate comprises soda lime glass.
10 . The method of claim 1 wherein the substrate comprises an optically transparent material.
11 . A thin film solar device utilizing a strained AZO layer for anode-absorber interface, the device comprising:
an optically transparent substrate;
an intermediate layer overlying the transparent substrate;
an anode layer comprising an aluminum doped zinc oxide (AZO) layer forming a first interface with the intermediate layer;
an absorber comprising copper indium gallium diselenide with p-type dopant forming a second interface with the AZO layer;
a buffer layer followed by a window layer overlying the absorber; and
a cathode layer overlying the window layer;
wherein the AZO layer induces a strain field in the anode layer and Fermi level pinning at the first interface for changing internal electric field at the second interface.
12 . The device of claim 11 wherein the optically transparent substrate comprises soda lime glass.
13 . The device of claim 11 wherein the intermediate layer comprises a film made by material selected from fluorine doped tin oxide (TFO), indium tin oxide (ITO), Si 3 N 4 , SiO 2 , molybdenum, and combination thereof.
14 . The device of claim 11 wherein the AZO layer comprises a heavily doped Al species ranging from 5×10 19 cm −3 to 1×10 21 cm −3 .
15 . The device of claim 11 wherein the strain field in the anode layer and Fermi level pinning at the first interface causes a reduction of the internal electric field strength at the second interface for facilitating hole collection by the anode layer from the absorber.
16 . The device of claim 11 wherein the strain field in the anode layer and Fermi level pinning at the first interface causes a flipping of internal electric field direction at the second interface for facilitating hole collection by the anode layer from the absorber.
17 . The device of claim 11 wherein the buffer layer comprises cadmium sulfide with n-type dopant.
18 . The device of claim 11 wherein the window layer comprises a transparent conductive oxide including aluminum doped zinc oxide.
19 . The device of claim 11 wherein the cathode layer comprises heavily aluminum doped zinc oxide.
20 . The device of claim 11 wherein the absorber comprises cadmium telluride with p-type dopant