Molecular-weight-engineered phase separation enables broadband neuromorphic phototransistors based on P3HT/Sn-Pb perovskite heterojunctions

Broadband optoelectronic synaptic devices capable of integrating light sensing and information processing are highly desirable for neuromorphic vision systems. Herein, we report a broadband neuromorphic phototransistor based on a P 3 HT/FAPb 0.5 Sn 0.5 I 3 heterojunction, in which the interfacial properties of the polymer channel are regulated through molecular-weight-dependent phase separation of polystyrene (PS). Low-molecular-weight PS (13 K) preferentially enriches the surface region of P 3 HT, whereas high-molecular-weight PS (650 K) remains buried beneath the P 3 HT-rich surface layer, leading to distinct interfacial configurations. Ultraviolet photoelectron spectroscopy reveals that PS 13 K optimizes the energy-level alignment at the heterojunction, while photoluminescence studies demonstrate enhanced interfacial charge separation. Moreover, the PS 13 K -modified surface promotes uniform crystallization of the narrow-bandgap Sn-Pb perovskite, resulting in improved carrier transport and reduced interfacial trapping. Consequently, the optimized P 3 HT/FAPb 0.5 Sn 0.5 I 3 heterojunction exhibits enhanced field-effect mobility and broadband photoresponse spanning the ultraviolet, visible, and near-infrared regions, with responsivities of 4.4, 3.3, and 1.5 A W −1 at 375, 600, and 940 nm, respectively. Benefiting from the improved heterointerface, the device further demonstrates diverse synaptic functions, including excitatory postsynaptic current responses, short- and long-term plasticity, and reversible memory-forgetting behaviors. Furthermore, a time-delayed reservoir computing framework based on the broadband phototransistors achieves a satellite remote-sensing image recognition accuracy of 99.42 ± 0.18%, substantially outperforming narrowband sensing.