Impact of Argon, Nitrogen, and Oxygen Exposure on the Structural and Optoelectrical Properties of Mixed Tin–Lead Halide Perovskites

Mixed tin-lead halide perovskites are considered promising materials for narrow-bandgap photovoltaic applications, particularly in tandem solar cells. However, their practical implementation is hindered by stability issues, especially due to tin oxidation and trap-state formation. In this study, we investigate the impact of argon, nitrogen, and oxygen storage environments on the structural, optical, and electronic properties of mixed tin-lead halide CsFAPb_0.5Sn_0.5I₃ perovskites. Optical absorption, transient photoluminescence (PL), transient photocurrent, and time-delayed collection field (TDCF) measurements reveal the significant role of environmental conditions on carrier dynamics. Carrier trapping over tens of nanoseconds is observed in samples prepared and stored in argon, with a trapping rate increasing several times after exposure to nitrogen (with less than 0.1 ppm of oxygen) and further increasing upon exposure to O₂. Photocurrent transients also show a fast photocurrent decay component occurring within tens of nanoseconds, independent of the oxygen-created traps. Based on the TDCF measurements, we attribute this fast photocurrent decay component to the spatial traps created by the perovskite boundaries, which reduce the carrier mobility to values below 0.05 cm²/V·s, as estimated from transient photocurrent measurements. Our findings highlight the importance of carefully controlling fabrication and storage conditions, often overlooked due to their initially minor impact on device performance, as these conditions critically affect material stability and charge carrier dynamics.