Optimization of buffer-window layer system for CIGS thin film devices with indium sulphide buffer by in-line evaporation

Compound In2S3 powder was evaporated on Cu(In,Ga)Se2 substrates from the ZSW inline multi-stage co-evaporation process. Laboratory devices with the complete layer structure Mo/CIGS/In2Sx/i-ZnO/ZnO:Al/Ni–Al grid on 0.5cm2 total cell area were prepared and analysed for their J–V characteristics. A post-annealing step in air after completing the device is essential to enhance the cell performance. In this work the influence of window process conditions like process temperature, layer thickness and sputtering gas composition on the cell characteristics was investigated. Electrical characterisation by temperature-dependent current voltage and admittance spectroscopy were performed to better understand the impact of buffer parameters on electrical transport. By optimization of the buffer layer thickness in combination with window layer variations, cell efficiencies >16% could be achieved. A record cell efficiency of 18.2% with anti-reflective coating was obtained.