Stability behaviour of Cd-free Cu(In,Ga)Se2 solar modules with In2S3 buffer layer prepared by atomic layer deposition

Regarding their I–V performance, Cu(In,Ga)Se2 (CIGS) solar modules using an In2S3 buffer layer deposited by the atomic layer deposition (ALD) technique have shown to be a competitive alternative to devices with the CdS buffer. An efficiency of 12.9% was already realised for a substrate area of 30×30 cm2. For implementation in industrial production, however, the lifetime of the solar modules is very important. In this work, the results from long-term stability testing of Cd-free devices are presented in comparison with reference devices with the CdS buffer layer. Indoor tests were performed at the ZSW laboratories, including damp heat and thermal cycling tests, and the I–V performance under light soaking and under different irradiances was investigated. The outdoor testing was performed at the Widderstall solar test field in Germany. The results show comparable stability behaviour of the CIGS modules with different buffer layers and thus reinforce the qualification of In2S3 as buffer material for high-efficiency CIGS thin-film solar modules.