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Lead-free 2D halide perovskites are promising materials for sustainable optoelectronics and neuromorphic photonics, but their intrinsic transport properties are often obscured in polycrystalline films by grain boundaries and Sn oxidation. Here, we investigate single crystals of PEA$_2$SnI$_4$ to clarify the interplay between surface degradation, charge transport, and photoresponse, extending previous studies on related 2D single-crystal perovskites such as PEA$_2$PbI$_4$ [1]. We find that air and light exposure mainly affect the surface, with partial recovery enabled by exfoliation. PEA$_2$SnI$_4$ devices exhibit strong visible-light photoconductivity, with responsivity up to 60 A W$^{-1}$ under low-intensity 650 nm illumination. The sublinear power dependence indicates trap-assisted photoconductivity, while temperature-dependent measurements reveal a crossover around 225 K from thermally activated transport to phonon-scattering- and ion-migration-influenced conduction. Time-resolved photocurrent measurements further show persistent and cumulative responses typical of short-term synaptic plasticity. These results establish layered single-crystal perovskites as a versatile platform for investigating transport, degradation, and adaptive photoresponse in advanced optoelectronic systems [2].
[1] Demontis, V., Durante, O., et al. Advanced Optical Materials 13.6 (2025): 2402469.
[2] Durante, O., et al. Advanced Functional Materials (2025): e26339.