Incorporation of Extrinsic Alkali Cations Modulates Ion Migration and Hysteresis in Lateral MAPbBr 3 Devices

ABSTRACT Lead halide perovskites exhibit outstanding optoelectronic properties, yet ion migration can influence device performance—detrimental in photovoltaics but beneficial in resistive‐switching devices. Intrinsic ion migration has been extensively studied, whereas the effects of extrinsic alkali cations on field‐driven ionic behavior remain less understood, particularly in lateral device architectures. Here, the effects of Li + , Na + , and K + incorporation on the ionic behavior of MAPbBr 3 thin films are investigated. Nanoscale and macroscopic measurements reveal cation‐dependent ionic responses, which are particularly pronounced at grain boundaries and surfaces. Among the three cations, 1% Li + incorporation shows the strongest effect, yielding higher current and more pronounced hysteresis in lateral ITO/MAPbBr 3 /ITO devices. The hysteresis index (H index ) increases from ∼0.61 in the first cycle (–0.15 for the control) to ∼0.85 after 20 cycles (∼0.30 for the control), accompanied by ∼40× higher current under identical conditions. Density functional theory (DFT) calculations further show cation‐dependent differences in the calculated diffusion barriers at the (100) surface and across the N–N interfacial model, with Li + exhibiting the lowest barriers. These results indicate that extrinsic alkali‐cation incorporation provides an effective approach to modulate ionic transport and hysteresis in lateral perovskite devices, offering insights for perovskite electronics where ionic effects play a key role.