Illumination-intensity-controlled bipolar photoresponse in α -Ga2O3 nanoarray photoelectrode for edge-enhanced solar-blind imaging

Underwater imaging often suffers from reduced edge contrast due to light attenuation, scattering, and fluctuations in illumination intensity, leading to difficulties in target recognition. Existing solutions primarily rely on post-processing algorithms or additional optical and electrical modulation techniques. To address this challenge, we propose a hardware-embedded target recognition strategy utilizing α-Ga2O3 nanorod arrays grown on fluorine-doped tin oxide substrates, which achieve a negative photocurrent response under low-light conditions and thereby enable automatic delineation of target contours. Unlike conventional unipolar photoelectrochemical (PEC) electrodes, this device achieves deterministic control over the polarity of the photocurrent through the synergistic modulation of incident light intensity and applied bias. Linear sweep voltammetry measurements reveal that as the irradiance increases from 200 to 4000 μW/cm2, the polarity transition potential systematically shifts negatively from +0.0287 V (vs saturated calomel electrode) to −0.1044 V. This intensity-dependent bipolar response is attributed to a transition in the device operating mechanism from surface-state-pinning-dominated to space-charge-layer-dominated behavior, reflecting the evolution of the photoelectrode interface barrier height with varying light intensity. To evaluate its imaging potential, a proof-of-concept underwater PEC imaging model was constructed, in which the bipolar device generates an intrinsic positive–negative–zero photocurrent profile across intensity boundaries and delivers consistently higher edge contrast than that of a conventional unipolar detector under different scattering conditions. These findings provide a viable pathway for hardware-level edge contrast enhancement in solar-blind PEC imaging.