Surface photovoltage analysis of thin CdS layers on polycrystalline chalcopyrite absorberlayers by Kelvin probe force microscopy

Abstract

An extensive Kelvin probe force microscopy study in an ultrahigh vacuum has been undertakento examine the influence of growth modifications of a few nm thick CdS buffer layers in thinfilm chalcopyrite solar cells. In regions around the grain boundaries of the polycrystallineCu(In,Ga)Se2 substrate a lowering of the work function extending to about 200 nm away from this verticalinterface was observed. This electrical inhomogeneity depends strongly on theCu(In,Ga)Se2 surface condition and is interpreted by a diffusion process along the substrate grainboundaries. Our results contribute to the understanding of the crucial role of the severalnm thick CdS layer for improving the photovoltaic performance of chalcopyrite thin filmsolar cells.