Combined analysis of spatially resolved electronic structure and composition on a cross-section of a thin film Cu(In1–xGax)S2 solar cell



In this work we present a combination of two spatially resolved experimental methods to analyse correlations between distributions of element concentrations and electronic structure of cross sections of thin film semiconductor devices. We applied these methods to a cross section of a thin film Cu(In1–xGax)S2/CdS/ZnO solar cell. The electronic structure was analysed by measuring the work function of the cross section by Kelvin probe force microscopy. To determine the gallium concentration of the cross section of the Cu(In1–xGax)S2 layer we performed energy dispersive X-ray analysis (EDX). We were able to match the spatial coordinates of these measurements. By this we could observe a correlation between the gallium concentration of the Cu(In1–xGax)S2 layer and its work function. The EDX measurements show that the Cu(In1–xGax)S2 layer features a two-layer structure – one layer with a low gallium concentration (x ≈ 0) and one (at the back of the solar cell) with a high gallium concentration (x ≈ 1). Furthermore we discuss the influence of the two-layer structure of the Cu(In1–xGax)S2 absorber layer on the photovoltaic properties of the solar cell. The spectral quantum efficiency was measured on the same sample before the depth resolved data were taken. We observe an improvement of short circuit current and overall efficiency of the Cu(In1–xGax)S2/CdS/ZnO solar cell compared to a gallium-free CuInS2/CdS/ZnO solar cell. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)