Controlling carrier localization in 2D lead-free halide perovskites for dual-functional photodetector and photosynapse

Low-dimensional tin halide perovskites are regarded as ideal channel materials for phototransistors owing to their high carrier mobility and light absorption coefficient. To date, phototransistors have been developed along two distinct directions: photodetectors with rapid response and recovery dynamics, and photosynapses with persistent photoconductivity and slow decay characteristics for emulating long-term memory. However, strategies to simultaneously achieve these divergent functionalities remain poorly understood. In this work, the defect density and carrier dynamics in PEA2SnI4 films are tuned through a solvent engineering approach, enabling dual operational modes for photodetector and photosynapse devices. Phototransistors based on dimethyl sulfoxide (DMSO) exhibit defect-assisted carrier localization, leading to robust synaptic behavior. In comparison, 1,3-dimethyl-2-imidazolidinone (DMI) suppresses trapping sites, enabling fast photoresponse for photodetection. This work provides insights into the defect-mediated photoresponse mechanisms and offers a rationale for tailoring tin perovskite phototransistors in multifunctional optoelectronics.