Indium sputtering method and materials for chalcopyrite-based material usable as solar cell absorber layers
A solar cell includes an absorber layer formed of a CIGAS, copper, indium, gallium, aluminum, and selenium. A method for forming the absorber layer provides for using an indium-aluminum target and depositing an aluminum-indium film as a metal precursor layer using sputter deposition. Additional metal precursor layers such as a CuGa layer are also provided and a thermal processing operation causes the selenization of the metal precursor layers. The thermal processing operation/selenization operation converts the metal precursor layers to an absorber layer. In some embodiments, the absorber layer includes a double graded chalcopyrite-based bandgap.
1. A method for forming a solar cell, said method comprising:
providing an InAl target of indium and aluminum;
providing a solar cell substrate with a back contact layer thereon;
forming metallic precursor layers over said back contact layer including sputtering materials of said InAl target onto said solar cell substrate over said back contact layer; and
thermally processing thereby converting said metal precursor layers to an absorber layer.
2. The method as in claim 1 , wherein said InAl target comprises about 0.05 to 30 atomic percentage of aluminum.
3. The method as in claim 1 , wherein said InAl target comprises about 1 atomic percent of aluminum and said thermally processing includes a temperature within the range of about 400° C. to 600° C.
4. The method as in claim 1 , wherein said forming metallic precursor layers further includes sputtering CuGa material from a CuGa target onto said solar cell substrate over said back contact layer, prior to said sputtering material of said InAl target.
5. The method as in claim 4 , wherein said absorber layer comprises a CIGAS (copper-indium-gallium-aluminum-selenium) absorber layer.
6. The method as in claim 5 , wherein said thermally processing includes a selenization process followed by a sulfurization process and produces said absorber layer being a chalcopyrite crystalline layer.
7. The method as in claim 6 , wherein said sputtering materials of said InAl target produces an InAl film having a thickness of about 100 nm on said back contact layer and said CIGAS absorber layer includes a thickness of about 2-3 micrometers.
8. The method as in claim 1 , wherein said back contact layer comprises molybdenum and further comprising forming a buffer layer between said back contact layer and said metallic precursor layers and forming a window layer over said absorber layer.
9. The method as in claim 1 , wherein said thermally processing includes a selenization process that incorporates selenium into said absorber layer.
10. The method as in claim 9 , wherein said thermally processing comprises said selenization process using H 2 Se gas as a selenium source and followed by a sulfurization process, said thermally processing causing said absorber layer to be a chalcopyrite crystalline material.