Cu(In,Ga)Se-2 solar cells with a ZnSe buffer layer: Interface characterization by quantum efficiency measurements

We investigate Cu(In,Ga)Se-2-based solar cells with a new ZnSe buffer layer deposited by metal-organic vapour deposition and compare their electronic properties to reference cells using a standard CdS buffer layer. The best s olar cell with a ZnSe buffer layer achieves an efficiency of 11.6%. We furt her investigate a large series of solar cells with varied thickness of both types of buffer layers by means of quantum efficiency measurements in equi librium and under light and voltage bias, The characterization of the devic es concentrates on the analysis of the collection of photogenerated holes f rom the buffer layer. We introduce a nero method to determine the recombina tion probability of holes at the buffer/absorber ber interface, We find a s imilar interface recombination probability of about 40% for both devices, t hose with a ZnSe buffer layer and those with a CdS buffer layer. An anomalo us enhancement of the quantum efficiency measured under current bias is asc ribed to a barrier modulation effect which is caused by light absorbed in t he buffer layer. Copyright (C) 1999 John Wiley & Sons, Ltd.