Self-powered in-sensor computing photodetector based on BiOI/TiO₂ for motion trajectory recognition and dynamic image encryption

Traditional optoelectronic detection systems suffer from the functional separation of sensing and computing, low data transmission efficiency, and insufficient real-time performance for dynamic scene detection. To address these limitations, BiOI/TiO₂ heterojunction film was synthesized via a two-step hydrothermal route, and Pt/BiOI/TiO₂/FTO self-powered photodetector (PD) was accordingly fabricated in this work. The morphological features, crystal structure, band structure, and optoelectronic response characteristics were characterized. The results show that the PD exhibits excellent photoresponse characteristics to ultraviolet (UV)-blue light in the 300-475 nm wavelength range under zero bias. Under 385 nm illumination, the PD achieves a responsivity (R) of 0.68 A/W, a detectivity (D*) of 7.0 × 10¹¹ Jones, an external quantum efficiency (EQE) of 225%, and a linear dynamic range (LDR) of 99 dB. Owing to the synergistic effects of the Z-scheme band configuration, built-in electric field, and the interface potential well, the device exhibits a distinctive nonlinear time-domain photocurrent response under UV light illumination, consisting of an instantaneous sharp peak, exponential decay, and slow steady-state saturation. Leveraging this unique photoelectric characteristic, software simulations were performed to validate the practical applications of PD arrays in moving target trajectory recognition and dynamic ultraviolet image encryption. Real-time tracking of directional motion trajectories was realized, and gradual concealment of encrypted text “TJUT” within 5.5 s was achieved through dynamic imaging. This study demonstrates that the fabricated BiOI/TiO₂ self-powered PD integrates in-situ sensing and computing capabilities, rendering it promising for advanced applications including intelligent perception, secure communication, and dynamic image.