Deposition of Zn(O, S) Buffer Layers by Reactive Sputtering - Impact of substrate temperature on layer composition and solar cell performance

摘要

Zn(S, O) was deposited by reactive sputtering from a ZnS cathode in an Ar/O_2 mixture on CuInS_2 thin film absorbers to replace CdS as buffer material in chalcopyrite thin film solar cells. We examined the dependence of material properties and the performance of resulting devices on the substrate temperature during deposition of the buffer layers. Furthermore we explored the benefits of a thin ZnS layer placed between the chalcopyrite absorber and the Zn(S, O) buffer. A clear dependence of the S/O-ratio and the resulting band gap on the substrate temperature was observed. The efficiency of the resulting devices increased with substrate temperature and reached a maximum value of 7.4% without, and 8% with the ZnS interlayer, when deposited at a substrate temperature of 200°C. Reference cells made from the same absorber batch with the established double-layer of wet-chemically deposited CdS and sputtered i-ZnO reached 8.6% efficiency.