TiO₂ Nanorod Arrays Based Self-Powered UV Photodetector: Heterojunction with NiO Nanoflakes and Enhanced UV Photoresponse

The self-powered ultraviolet photodetectors (UV PDs) have attracted increasing attention due to their potential applications without consuming any external power. It is important to obtain the high-performance self-powered UV PDs by a simple method for the practical application. Herein, TiO₂ nanorod arrays (NRs) were synthesized by hydrothermal method, which were integrated with p-type NiO nanoflakes to realize a high performance pn heterojunction for the efficient UV photodetection. TiO<i>_x</i> thin film can improve the morphological and carrier transport properties of TiO₂ NRs and decrease the surface and defect states, resulting in the enhanced photocurrent of the devices. NiO/TiO₂ nanostructural heterojunctions show excellent rectifying characteristics (rectification ratio of 2.52 × 10⁴ and 1.45 × 10⁵ for NiO/TiO₂ NRs and NiO/TiO₂ NRs/TiO<i>_x</i>, respectively) with a very low reverse saturation current. The PDs based on the heterojunctions exhibit good spectral selectivity, high photoresponsivity, and fast response and recovery speeds without external applied bias under the weak light radiation. The devices demonstrate good stability and repeatability under UV light radiation. The self-powered performance could be attributed to the proper built-in electric field of the heterojunction. TiO₂ NRs and NiO nanoflakes construct the well-aligned energy-band structure. The enhanced responsivity and detectivity for the devices with TiO<i>_x</i> thin films is related to the increased interfacial charge separation efficiency, reduced carrier recombination, and relatively good electron transport of TiO₂ NRs