Intrinsic Defect Physics in Indium-based Lead-free Halide Double Perovskites.

Lead-free halide double perovskites (HDPs) are expected to be promising photovoltaic (PV) materials beyond organic-inorganic halide perovskite, which is hindered by its structural instability and toxicity. The defect- and stability-related properties of HDPs are critical for the use of HDPs as important PV absorbers, yet their reliability is still unclear. Taking CsAgInBr as a representative, we have systemically investigated the defect properties of HDPs by theoretical calculations. First, we have determined the stable chemical potential regions to grow stoichiometric CsAgInBr without structural decomposition. Second, we reveal that Ag-rich and Br-poor are the ideal chemical potential conditions to grow n-type CsAgInBr with shallow defect levels. Third, we find the conductivity of CsAgInBr can change from good n-type, to poorer n-type, to intrinsic semiconducting depending on the growth conditions. Our studies provided important guidance for experiments to fabricate Pb-free perovskite-based solar cell devices with superior PV performances.