Heterojunction III-V photovoltaic cell fabrication
A method for forming a heterojunction III-V photovoltaic (PV) cell includes performing layer transfer of a base layer from a wafer of a III-V substrate, the base layer being less than about 20 microns thick; forming an intrinsic layer on the base layer; forming an amorphous silicon layer on the intrinsic layer; and forming a transparent conducting oxide layer on the amorphous silicon layer. A heterojunction III-V photovoltaic (PV) cell includes a base layer comprising a III-V substrate, the base layer being less than about 20 microns thick; an intrinsic layer located on the base layer; an amorphous silicon layer located on the intrinsic layer; and a transparent conducting oxide layer located on the amorphous silicon layer.
1. A method for forming a heterojunction III-V photovoltaic (PV) cell, the method comprising:
forming a first intrinsic layer on a substrate;
forming a first back surface field layer on the first intrinsic layer;
forming a first amorphous silicon layer on the first back surface field layer;
performing a layer transfer of a base layer from the substrate, the base layer having a thickness of less than about 20 microns, wherein the layer transfer comprises spalling, and wherein spalling comprises:
forming a metal layer having a tensile stress on the first amorphous silicon layer;
adhering a flexible substrate to the metal layer;
using the tensile stress in the metal layer to cause a fracture in the wafer below the base layer, wherein a location of the fracture and the thickness of the base layer are determined by the tensile stress and a thickness of the metal layer; and
removing the flexible substrate from the metal layer;
forming a second-intrinsic layer on the base layer;
forming a second-amorphous silicon layer on the second intrinsic layer; and
forming a transparent conducting oxide layer on the second amorphous silicon layer.
2. The method of claim 1 , wherein the layer transfer comprises smart cut, and wherein smart cut comprises:
performing hydrogen implantation in the wafer below the base layer; and
annealing the wafer to initiate a fracture below the base layer.
3. The method of claim 1 , wherein the layer transfer comprises epitaxial layer transfer, and wherein epitaxial layer transfer comprises:
forming a sacrificial layer in the wafer below the base layer; and
using a wet chemical etch of the sacrificial layer to remove the base layer from the wafer.
4. The method of claim 1 , wherein the metal layer comprises nickel.
5. The method of claim 1 , wherein the flexible substrate comprises a material having a radius of curvature of less than 5 meters.
6. The method of claim 1 , further comprising forming a second back surface field on the substrate before performing layer transfer, wherein the second back surface field comprises at least one of zinc, indium, and wherein the second back surface field is layer transferred from the substrate with the base layer.
7. The method of claim 1 , wherein the first amorphous silicon layer comprises a doping type that is opposite a doping type of the substrate, and the first amorphous silicon layer is configured to act as an emitter.
8. The method of claim 1 , wherein the second amorphous silicon layer comprises a doping type that is the opposite to a doping type of the substrate, and the second amorphous silicon layer is configured to act as an emitter.
9. The method of claim 1 , wherein the substrate comprises one of germanium or gallium arsenide.