Dual-Polarity Photocurrent in Photoelectrochemical Cell Based on
P-type Copper Iodide Thin Films

Semiconductor p–n heterojunctions are widely used in modern electronic and optoelectronic devices, typically generating unipolar photocurrents. By integrating a photoelectrochemical cell (PEC), it becomes possible to achieve more versatile behavior, including bidirectional photocurrents with polarity switching under different applied biases. In this study, we fabricated and optimized PEC photodetectors based on solution-processed p-type CuI thin films combined with n-type 1D TiO₂ nanorods. The optimization was performed by adjusting the number of CuI layers via spin-coating and the applied voltage to enhance the photoresponse. Interestingly, dual-polarity photocurrent was observed in the p-CuI/n-TiO₂ PEC device under visible light illumination (420 nm). Although the 1D n-TiO₂ nanorods are transparent to this blue light and the p-CuI itself typically produces a negative photocurrent, a positive photocurrent was generated under a specific biased voltage. This unique behavior is attributed to the built-in electric field at the p–n junction, which enables bidirectional photocurrent under varying bias conditions. The findings suggest that the device's photocurrent polarity can be effectively tuned by adjusting the applied bias and material configuration. This behavior presents a promising strategy for improving the performance and efficiency of PEC-based photodetectors, offering potential applications in advanced optoelectronic devices for energy conversion, light sensing, and future nanotechnology-based applications in renewable energy systems.