Trap‐Assisted Transport and Neuromorphic Plasticity in Lead‐Free 2D Perovskites PEA2SnI4

Tin-based perovskites offer one of the most viable sustainable alternatives totheir lead counterparts, combining comparable band structures with strongvisible-light absorption and favorable charge transport. Most studies havefocused on thin films, where grain boundaries dominate charge transport, andthe large surface area accelerates the oxidation of tin, obscuring the intrinsicproperties of the material. Here, single crystals of phenethylammonium tiniodide (PEA2 SnI 4 ) are investigated, isolating their fundamental optoelectronicresponse from film-related artefacts. It is found that air and light exposureprimarily affect surface layers, with partial recovery achievable throughexfoliation. Photodetectors fabricated from single crystals exhibit aphotoresponsivity of ≈60 A W−1 under low-intensity 650 nm illumination,with photocurrent scaling quadratically with bias in a space charge-limitedcurrent regime, and transport displaying a transition from thermal excitationto phonon scattering at 225 K. Time-resolved photocurrent measurementsfurther reveal prolonged decay dynamics and cumulative pulse responses,characteristic of short-term synaptic plasticity such as temporal integrationand voltage-modulated persistence. These findings establish PEA 2 SnI 4 singlecrystals as a benchmark for understanding degradation and transport inlead-free perovskites, while positioning them as a viable materials platform forneuromorphic vision and adaptive optoelectronics.