Light-Written Nonvolatile Polarization via Defect-Engineered Charge Trapping

Defect engineering offers a practical route to control interfacial charge states in polymer-inorganic composites, yet translating this control into optically writable and non-volatile polarization in soft dielectrics remains difficult. Here, we introduce a Polydimethylsiloxane (PDMS)-based composite that can be written by light to form an interfacial polarization state. The design relies on FeTiO₃ (FTO) nanoparticles with oxygen-vacancy associated trap states, whose density is tuned by spark plasma sintering to create a trap-rich polymer-oxide interface. Under illumination, photocarriers promote interfacial charge transfer by reducing the effective barrier at the metal-composite contact, producing a rapid rise in interfacial charge accumulation. After the light is removed, a large fraction of the photoexcited electrons becomes immobilized, leaving a residual polarization that relaxes only slowly. We quantify the write-relax behavior using a triboelectric nanogenerator configuration as a sensitive probe of interfacial charge transfer, and we directly visualize the photo-written electrostatic state and its retention by Kelvin probe force microscopy. These results present defect-mediated charge trapping as a materials-level mechanism for light-programmable, long-retention polarization in soft composites, enabling remotely addressable electrostatic interfaces for soft electronic systems.