Electron-paramagnetic resonance (EPR) and light-induced EPR investigationsof CuGaSe2

The chalcopyrite compound CuGaSe2 is considered as potential absorber mater ial for thin film solar cells due to its suitable optoelectronic properties . We investigated intentionally undoped bulk material that is used as sourc e material in a thin film deposition process by electron-paramagnetic reson ance (EPR) and light-induced EPR (LEPR). Both methods are well suited to de termine the concentration and electronic activity of transition metal ions in the chalcopyrite host lattice. The recently identified N+ centre was fou nd by LEPR to act as recombination centre for photogenerated charge carrier s. Moreover, the typical signature of Cu2+ could be detected in EPR spectra of aged CuGaSe2 powders indicating an oxidation process to which the mater ial is subjected at ambient conditions. The ageing process is significantly accelerated in water-saturated air of 100% humidity compared to dry air of 50% humidity. The connection of this microscopic process with the electron ic degradation of the material during solar cell processing will be discuss ed. (C) 2000 Elsevier Science S.A. All rights reserved.