High-Performance (PEA) ₂ PbI ₄ /SnS ₂ van der Waals Heterostructure Phototransistor with Gate-Tunable Breaking of the Responsivity–Speed Trade-Off

Tin disulfide (SnS₂) exhibits strong photoresponse and strong gate controllability, making it a promising material for optoelectronic integrated circuits. However, its intrinsically high on-state dark current severely constrains further improvement of photosensitivity and limits its potential for low-power applications. In this work, we develop a low-dark-current, high-responsivity, and highly stable phototransistor based on a (PEA)₂PbI₄/SnS₂ van der Waals heterostructure via an all-dry transfer technique. Importantly, we demonstrate that gate-voltage tuning enables the device to overcome the long-standing responsivity-speed trade-off typically observed in photodetectors. With interfacial modification provided by (PEA)₂PbI₄, the on-state dark current of the SnS₂-channel phototransistor is reduced by approximately 2 orders of magnitude. The device exhibits high photodetection performance, achieving a maximum responsivity of 218 A W^-1, a specific detectivity of 3.97 × 10¹² Jones, and an external quantum efficiency of 47,447%. Moreover, the phototransistor remains operational after 4000 h of storage under ambient conditions, with the dark current increasing by less than 3 nA, demonstrating long-term environmental stability. Notably, the photoresponse time decreases monotonically with increasing gate voltage, while the responsivity simultaneously increases, representing an unconventional behavior opposite to that of conventional photodetectors and effectively breaking the traditional responsivity-speed trade-off. The strategy presented here can be widely applied to two-dimensional perovskite/two-dimensional metal-sulfide heterostructures for constructing high-performance optoelectronic devices.