Processing of Cu(In,Ga)Se2 solar cells from electrodeposited precursors

Multi-step processing of Cu(In,Ga)Se₂, incorporating electrodeposition (ED) of single-phase precursors coupled with physical vapor deposition (PVD) to tune film composition, is described. ED conditions for a range of precursors, including CuSe, Cu/In alloys and bi-layers, In₂Se₃, and Cu metal, were optimized. Precursors were processed by PVD at ~500°C for 45-60 minutes. Resultant Cu(In,Ga)Se₂ devices obtained from CuSe precursors showed promising performance, ~13% efficiency, but only with KCN etching of the absorber layer following PVD. This suggests Cu_2-xSe secondary phases remain in the grain boundaries. The other precursors produced poorly adhered Cu(In,Ga)Se₂ films. E-beam evaporated Cu precursors gave similar results to CuSe precursors. A low toxicity electrochemical-based etch was preliminarily explored, but was less effective than KCN etching.