Niobium-doped TiO2 films as window layer for chalcopyrite solar cells

Smooth and semitransparent NbxTi1-xOy (x = 0.03, y = 1.84 -1.91) films have been prepared by reactive magnetron sputtering at temperatures below 420 K. Structural investigations by RAMAN-spectroscopy together with resistivity and temperature-dependent Hall-measurements were used in order to analyze the film structure and the nature of the charge transport in this material. These films can be used as a window layer (TCO) for thin film solar cells. Cu(In, Ga)Se-2 solar cells equipped with the new window layer keep their functionality which excludes first, the presence of strong energetic barriers and second, a strong interfacial recombination. The development of TiO2-based window layers is expected to make thin film solar cells less sensitive against corosion after contact with humidity. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.