van der Waals Integrated Single-Crystal Tin Perovskite Transistors Toward Ultrasensitive Photodetection

Two-dimensional (2D) tin halide perovskites have emerged as promising lead-free semiconductors with strong optical absorption and high carrier mobility. While polycrystalline films have achieved impressive device performance, their intrinsic charge transport and exciton dynamics remain obscured by grain-boundary-associated defects, limiting the fundamental understanding of material properties and optimization of device performance. Herein, by using bulky π-conjugated 4Tm⁺ cations, we synthesized 2D (4Tm)₂SnI₄ single crystals and assembled their van der Waals field effect transistors, exhibiting high hole mobility up to 5.1 cm² V^-1 s^-1 at room temperature, more than two times higher than that of polycrystalline counterparts. The efficient charge transport in single crystals allows the phonon-scattering-dominated process to persist at lower temperatures, leading to an increase in mobility to 10.3 cm² V^-1 s^-1 at 120 K. Also, the single-crystal nature ensures high responsivity/specific detectivity of 1.6 × 10⁶ A W^-1/4.2 × 10¹⁶ Jones under 550 nm illumination, ranking among the best Pb and Sn perovskite photodetectors. Crucially, the transistor modulation allows the gate-voltage tunable contrast in imaging for usage as pixel-active image sensors. This work uses single-crystal 2D tin perovskites as a platform for probing intrinsic electronic/optoelectronic properties while showcasing their potential in current modulation, highly sensitive photodetection, and scalable imaging systems.