Wavelength-controlled bipolar photoresponse in BiOI/TiO₂ heterojunctions for reconfigurable optoelectronic logic gates and biomimetic in-sensor processing

Optoelectronic logic gate devices (OELGD) utilizing photons as input signals hold great potential for high-speed, high-capacity data transmission and processing, offering a promising solution to the “electronic bottleneck” problem. Wavelength-controlled bipolar photoresponse photodetectors (PDs) are critical for advancing such as OELGDs. In this study, BiOI/TiO₂ heterojunctions were constructed by depositing two-dimensional layered BiOI nanoflakes onto TiO₂ thin film via a solvothermal method. Leveraging the large conduction-band and valence-band offsets of the heterojunction, wavelength-tunable dual-polarity photocurrent was achieved by modulating barrier tunneling and recombination processes of photo-generated carriers at the interface under ultraviolet (UV) and visible light illumination. The stoichiometric ratio of BiOI was adjusted by introducing glycerol during synthesis, which regulated the BiOI conduction-band position and consequently modulating the conduction-band offset of BiOI/TiO₂ heterojunction. The optimized heterojunction with 1 mL glycerol addition exhibited wavelength-controlled bipolar photoresponse across the UV–visible dual bands over a broad voltage range (‒0.5 to +0.5 V). Using UV and visible light as input signals, five basic logic gates (“AND”, “OR”, “NAND”, “NOR”, and “NOT”) were implemented in a single BiOI/TiO₂ heterojunction PDs. Furthermore, by harnessing this UV–visible logic functionality, in-sensor processing of Chrysanthemum carinatum images was realized, simulating the biological phenomenon where bees perceive UV nectar guides on flower petals that are invisible to humans. These results demonstrate the potential of BiOI/TiO₂ devices as innovative components for reconfigurable OELGDs.