Surface-layer band gap widening in Cu(In,Ga)Se2 thin films

Transmission electron microscopy observations, cathodoluminescence spectroscopy and spectrum imaging are combined to investigate the emission spectrum in Cu(In,Ga)Se-2 (CIGS) thin films with improved spatial resolution. We report direct evidence for a surface layer of wider band gap, which forms spontaneously in CIGS films. The existence of such a surface layer is critical for attaining high efficiency in solar cells based on these chalcopyrite semiconductor compounds. (C) 2003 American Institute of Physics.