Interface redox engineering of Cu(In,Ga)Se2 – based solar cells: oxygen, sodium, and chemical bath effects

Abstract The chemical effects of oxygenation of Cu(In,Ga)Se 2 (CIGS) interfaces are analyzed and are shown to involve passivation of Se deficiencies and Cu removal. The former effect is beneficial at grain boundaries, but detrimental at the CdS/CIGS interface. The latter effect is purely detrimental. Na and chemical bath deposition (CBD) treatments are shown to isolate the ‘good’ oxygenation effect from the ‘bad’ ones. Na is shown to promote oxygenation already before the deposition of the buffer and window layers, which allows a maximization of the benefits of Se deficiency passivation and a minimization of Cu removal. Next, the CBD of the CdS buffer layer restores the interface charge, due to creation of Cd Cu interface donors and possibly a removal of O Se interface acceptors. This highlights the crucial role that interface redox engineering plays in optimizing the performance of CIGS-based solar cells.