New insights into the determination of maximum chemical potentials to account for alkali doping in [formula omitted] by ab initio calculations

Abstract

We propose herein a methodology to find the upper limit of the chemical potential of an impurity/dopant in ab initio extrinsic point defect studies which takes into account the possible formation of binary and ternary phases containing the extrinsic chemical species. As a test-case, we investigate comprehensively alkali (A) doping in β-In2S3, a buffer material for CIGS solar cells. Our calculations prove that the migration of alkali from the soda-lime glass substrate to the buffer via the absorber and additionally the chemical bath post-deposition treatment may trigger the decomposition of β-In2S3 into AInS2 and InS at the grain boundaries.