Interstitial Hydrogen Anions: A Cause of p-Type Conductivity in CsSnI3

The all-inorganic tin halide perovskite CsSnI3, currently under intensive investigation for photovoltaics and other optoelectronics, characteristically exhibits strong p-type conductivity and consequently poor power conversion efficiency regardless of growth and processing conditions. This has been traditionally attributed to the prevalence of native acceptor defects; however, such a mechanism falls short of explaining the observed high hole concentration under Sn-rich growth conditions in experiments. Here, by using first-principles calculations, we reveal that hydrogen impurities, existing as hydrogen anions, are an important cause for the high p-type character in CsSnI3. Hydrogen anions can be present with high densities and act as shallow acceptors, significantly enhancing the background hole concentrations, even under excess Sn treatment. Careful control and utilization of hydrogen anions are important for improving the performance of CsSnI3-based optoelectronic devices.