Interface redox engineering of Cu(In,Ga)Se-2 - based solar cells: oxygen, sodium, and chemical bath effects

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 rem oval. 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' o xygenation effect from the 'bad' ones. Na is shown to promote oxygenation a lready before the deposition of the buffer and window layers, which allows a maximization of the benefits of Se deficiency passivation and a minimizat ion of Cu removal. Next, the CBD of the CdS buffer layer restores the inter face charge, due to creation of Cd-Cu interface donors and possibly a remov al of O-Se interface accepters. This highlights the crucial role that inter face redox engineering plays in optimizing the performance of CIGS-based so lar cells. (C) 2000 Elsevier Science S.A. All rights reserved.