The correlation between local defect absorbance and quasi-Fermi level splitting in CuInS2 from photoluminescence

Abstract

Analogously with Cu(In,Ga)Se2, CuInS2 shows a high degree of spatial inhomogeneities in structural, optical and electronic properties on the length scale of grain sizes and above which is caused by the grainy structure and the inhomogeneous growth of absorber layers. To analyse these locally fluctuating magnitudes, spectrally resolved photoluminescence measurements with high lateral resolution (⩽1μm) have been performed in a confocal microscope setup. Based on these data sets and on Planck's generalized law determination of the spatial variation in the splitting of the quasi-Fermi levels and access to the local absorbance is possible. A detailed analysis of these properties, crucial for the solar light conversion efficiency of a final cell, is made for a CuInS2 absorber layer for data obtained from statistically representative scan areas. A cross-correlation between the splitting of the local quasi-Fermi levels and the local absorbance of an absorber leads to the conclusion that the splitting of quasi-Fermi levels is strongly governed by the excess-carrier recombination via deep defects.