Tuning of CsSNi₃ Crystal Structure for Thin-film Energy Conversion Devices

Solution-processed CsSnI₃-based perovskite thin films with partial MA (methyl amine) substitution were fabricated and assessed for structural, morphological, and transport properties both as-prepared and after 48 h of air exposure. X-ray diffraction revealed that MA_0.2Cs_0.8SnI₃ retained the black-γ perovskite phase despite morphological changes, whereas CsSnI₃ showed notable decomposition. Device analyses in p–n diode architectures indicated significantly lower dark current and enhanced shunt resistance for MA-modified films. In unipolar p–n–p devices, a slight threshold voltage reduction and stable trap concentrations (10¹⁴ cm^–3) suggest improved Fermi level pinning and mild doping compensation. Transient photocurrent measurements confirmed negligible capacitive or inductive impacts, underscoring improved inter-grain connectivity and moderated donor-acceptor defects. Overall, partial MA substitution mitigates oxidation-driven phase transitions in CsSnI₃, offering stable microcrystalline perovskites with reduced leakage currents and superior charge transport–key for advancing tin-based perovskite device performance.