Optically Tunable Threshold Switching and Thermally Activated Transport in Planar Ag/MAPbI ₃ Thin Single‐Crystal Devices

ABSTRACT

Halide perovskites have enabled major advances in optoelectronics, extending well beyond photovoltaics. Their mixed ionic‐electronic conduction, once regarded as detrimental to device stability, is increasingly viewed as a functional degree of freedom for memory and neuromorphic‐inspired devices, especially when coupled to external stimuli such as light. Specifically, single crystals are attractive models because they suppress grain‐boundary effects and microstructural disorder that can mask intrinsic transport and interfacial mechanisms in polycrystalline films. Here, we report the growth of thin methylammonium lead iodide (MAPbI ₃ ) single crystals by a space‐confined method and their integration into planar two‐terminal devices with directly deposited Ag contacts. At room temperature, the devices exhibit ultra‐low dark currents (10 ⁻¹³ ‐10 ⁻¹² A) and negligible hysteresis in the dark. Under illumination, the current increases due to photogeneration and the I‐V characteristics develop a pronounced polarity‐dependent hysteresis and a threshold‐like transition between two conductance states. Temperature‐dependent dark measurements (300–400 K) show thermionically activated, contact‐influenced transport and a weakly varying normalized hysteresis metric. Together with the back‐to‐back Schottky‐diode analysis and control devices using more inert contact materials, these results support a transport model in which Ag/perovskite interfaces play a central role and the hysteretic response is influenced by coupled interfacial and ionic processes.