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 MA0.2Cs0.8SnI3 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.