Photovoltaic effect of TiO₂ films with large photoelectric responsivity

Ferroelectric photovoltaic effects usually exhibit low photocurrent, which limits their wide application. Here, we report the discovery of a photovoltaic effect with high photocurrent in TiO₂ films prepared by sol-gel method. It is found that an open circuit voltage of 0.58 V and a short circuit current density of 0.64 mA/cm² (26 mA/W) are achieved in the TiO₂ film annealed at 850 °C. Based on the experiment and calculation results, a possible mechanism is put forward to explain the photovoltaic effect in the TiO₂ films. The self-polarization is caused by the electric field generated by the gradient distribution of Ti³⁺ ions in the TiO₂ film. Ferroelectricity in microscopic regions in the TiO₂ film was confirmed by both piezoelectric force microscope analysis and density function theory calculation. In addition, the TiO₂ film annealed at 750 °C exhibits high photoresponse stability over a long time (>6800 s) and excellent self-powered photodetection performances with a rising time of 1.5 ms, a falling time of 5.9 ms, an optical responsivity of 15.8 mA/W, and a specific detection rate of 1.06 × 10¹² Jones under 365 nm light (25 mW/cm²) at 0 V bias. This work not only provides an economically effective approach for designing high performance FePV films devices, but also further guides the application of ferroelectric films in self-powered photodetection and other optoelectronic fields.