Dimensionality-driven decoupling of electronic-ionic transport in a Cs₄PbBr₆/CsPbBr₃ heterojunction

Harnessing the interplay between electronic and ionic transport in lead halide perovskites is pivotal for advancing next-generation iontronics. Here, we demonstrate a pronounced disparity in charge transport dynamics enabled by the post-synthetic chemical transformation of a 0D Cs₄PbBr₆ single crystal surface into a 3D CsPbBr₃-rich surface layer via controlled Prussian blue treatment. Temporal response measurements reveal a fundamental divergence in transport behavior: while the pristine 0D crystal exhibits high activation barriers and restricted ionic activity due to its isolated octahedral framework, the chemically transformed CsPbBr₃-rich surface layer facilitates facile ion migration through continuous Pb-Br-Pb percolative pathways. Leveraging this structural mismatch, we construct a monolithic Cs₄PbBr₆/CsPbBr₃ heterojunction that exhibits strongly polarity-dependent transient responses, reminiscent of a memristive-diode-like behavior. We elucidate that this polarity-dependent ionic gating arises from asymmetric carrier injection at the heterointerface, where local electron accumulation under reverse bias is proposed to transiently neutralize mobile bromide vacancies (V_Br⁺ + e^- ⇄ V0Br), thereby suppressing field-driven ionic migration. These findings provide mechanistic insight into chemically engineered all-inorganic perovskite heterostructures and suggest a materials-level design principle for electronically regulating ionic defect motion in mixed conductors.