Organo-lead halide perovskites have emerged as promising materials for high-performance photodetectors. However, the toxicity of lead cations in these materials limits their further applications. Here, a flexible photoconductor is developed based on lead-free two-dimensional (2D) perovskite (PEA)₂SnI₄via a one-step solution processing method. The flexible transparent electrodes are patterned from rGO/(PEDOT:PSS) hybrid films. The stability and reproducibility of the devices are significantly improved on adding 30 mol% SnF₂ to the perovskite. The flexible photoconductors show a photoresponsivity of 16 A W⁻¹ and a detectivity of 1.92 × 10¹¹ Jones under 470 nm illumination, which are higher than those of most of the similar devices. Besides, the devices possess much better mechanical flexibility and durability than the flexible devices with an Au electrode. Finally, this flexible photoconductor is applied as a light-stimulated synaptic device and can mimic the short-term plasticity of biological synapses. This is the first study to report that lead-free 2D perovskite can be used in flexible photoconductors and synaptic devices.

Two-dimensional (2D) layered semiconductors have shown great application potential in next generation nanoelectronic devices. The ferroelectric and piezoelectric properties of 2D semiconductors are also highly desirable in many applications, such as ferroelectric nonvolatile memory and switch. In the present work, we experimentally demonstrate the simultaneous out-of-plane and in-plane ferroelectricity of β-indium selenide (β-InSe) nanoflakes at room temperature. The polarization switching in the as-prepared β-InSe with the P63/mmc symmetry is studied by piezoresponse force microscopy. Out-of-plane polarization hysteresis loops are observed in a 7-nm-thick sample, and the in-plane and out-of-plane ferroelectric switching under the forward and reverse direct current bias are obtained in a 10-nm-thick sample at room temperature. These results indicate that β-InSe is a promising intrinsic 2D van der Waals ferroelectric material. Our work has connected the 2D materials with ferroelectric materials and inspired their applications in electronic devices.