Trap‐Assisted Transport and Neuromorphic Plasticity in Lead‐Free 2D Perovskites PEA ₂ SnI ₄

Abstract Tin‐based perovskites offer one of the most viable sustainable alternatives to their lead counterparts, combining comparable band structures with strong visible‐light absorption and favorable charge transport. Most studies have focused on thin films, where grain boundaries dominate charge transport, and the large surface area accelerates the oxidation of tin, obscuring the intrinsic properties of the material. Here, single crystals of phenethylammonium tin iodide (PEA ₂ SnI ₄ ) are investigated, isolating their fundamental optoelectronic response from film‐related artefacts. It is found that air and light exposure primarily affect surface layers, with partial recovery achievable through exfoliation. Photodetectors fabricated from single crystals exhibit a photoresponsivity of ≈60 A W ⁻¹ under low‐intensity 650 nm illumination, with photocurrent scaling quadratically with bias in a space charge‐limited current regime, and transport displaying a transition from thermal excitation to phonon scattering at 225 K. Time‐resolved photocurrent measurements further reveal prolonged decay dynamics and cumulative pulse responses, characteristic of short‐term synaptic plasticity such as temporal integration and voltage‐modulated persistence. These findings establish PEA ₂ SnI ₄ single crystals as a benchmark for understanding degradation and transport in lead‐free perovskites, while positioning them as a viable materials platform for neuromorphic vision and adaptive optoelectronics.