Reconfigurable diffusive to drift switching in lead-free Cs2CuBiBr6 memristors with electro-optical synaptic plasticity.

Lead-free halide perovskites, with their optoelectronic properties and environmental compatibility, offer a promising material platform for vision-inspired neuromorphic hardware combining sensing, memory, and computation. We report a multifunctional, lead-free Cs2CuBiBr6 memristive device that combines optical responsivity, electrical synaptic behavior, self-selective resistive switching, and voltage-controlled transitions between different switching modes in a single device. Unlike conventional ionotronic devices, which are typically either non-volatile (drift based) or abruptly volatile, these devices retain data for a finite time and then self-erase without external reset, acting as a leaky-integrator component. By tuning the applied voltage, the retention time can be varied on demand, effectively controlling whether the device behaves diffusively or more drift-like in a single architecture. A distinctive switching mechanism is observed, where halide ions migrate reversibly in both directions under an electric field, forming and dissolving transient conductive filaments, analogous to the motion of a simple pendulum. This symmetric, field-driven behavior enables three resistive switching modes, arising from time-dependent post-switching conductance decay due to ionic back-diffusion. In addition, the rectifying behaviour indicates the prospect of selector-free crossbar arrays, while optical stimulation induces synaptic-like conductance modulation. These combined features establish Cs2CuBiBr6 as both a functional and a conceptual advance toward reconfigurable, sustainable neuromorphic computing systems.