Dopant‐Enhanced Inhibitory Negative Photoconductance and Hetero‐interfacial Switchable Synaptic Response in CsPbI 3 Perovskite

All‐inorganic halide perovskites, particularly CsPbI 3 , are excellent candidates for neuromorphic devices owing to their unique defect‐tolerant electronic structure and mixed ionic‐electronic transport. Here, we demonstrate that the inherent synaptic plasticity of CsPbI 3 can be modulated by cationic doping and heterojunction engineering. By introducing transition metal dopants (Cu, Mn and Zn) into the perovskite lattice, we modify the trap‐state density and charge‐carrier dynamics. CsPbI 3 naturally exhibits negative photoconductance (NPC) due to its defect‐mediated charge dynamics and Mn‐doping increases this effect manifold. First‐principles calculations reveal that Mn‐substitution creates highly localized states within the bandgap, significantly amplifying light‐activated charge trapping kinetics. This manifests as a robust negative photoconductance, enhancing biomimetic inhibitory responses with a high paired‐pulse depression index of 188%. Also, we show that the polarity of the optical synaptic response is not merely a bulk property but can be inverted via interfacial charge‐transfer at the CsPbI 3 /ZnO heterostructure. This transition from inhibitory to excitatory behavior underscores the role of material interfaces in controlling synaptic polarity. These findings establish a materials‐based strategy for developing CMOS‐compatible, dual‐mode neuromorphic architectures on monolithic substrates.