Lattice Disorder in CuI Enables Filament-Free Transparent Memristors

The realization of invisible neuromorphic electronics hinges on transparent memories that reconcile high optical transparency with stable analog tunability, which is a challenge unmet by conventional filamentary devices. Here, we introduce an alloyed Cu_{1- x}Ag_xI halide transparent semiconductor with dual ionic-electronic character, which enables a filament-free switching platform. Ag⁺ incorporation induces lattice distortions within the γ-phase CuI matrix, expanding interstitial channels and lowering the migration barrier without phase transition. This activates room-temperature ion migration to dynamically modulate the p-type hole conductance. Asymmetric electrodes induce spatially distributed ion migration and interfacial modulation, avoiding localized metallic percolation. In situ TEM and EDS mapping confirm reversible Cu⁺/Ag⁺ redistribution without continuous conductive pathways. Pt/Cu_{1- x}Ag_xI/Ag devices exhibit > 80% transparency, low-voltage readout, and > 2-year retention. They emulate synaptic plasticity and achieve high-accuracy handwritten digit recognition. Our findings establish a design strategy for transparent memristors, enabling reliable neuromorphic hardware via ionically mediated electronic transport.