New insights into the ZnO/a-SiC:H(B) interface using XPS analysis

Abstract

A poor electric contact between the ZnO and the p-type a-SiC:H(B) layer limits the fill factor of amorphous silicon solar cells using ZnO as front electrode. To gain a deeper understanding of the chemical and electronic properties of the ZnO/p interface, in-situ XPS measurements were applied to thin a-SiC:H(B) films deposited on ZnO. The effects of H2 plasma pretreatments on clean ZnO surfaces and the influence of deposition conditions on the ZnO/a-SiC:H interface were investigated. Upon H2 plasma treatment, a shift of all core levels towards higher binding energies indicates the formation of an accumulation layer. Depth profiling across the ZnO/a-SiC:H interface shows SiO2 formation on ZnO. The depth profile of the ZnO related core levels exhibits two features: a reduction of the ZnO at the interface and a hydrogen induced accumulation layer in the n-type ZnO. The latter causes a depletion of the p-layer resulting in an enhanced series resistance and diminished fill factor.