Influence of electrode materials (Ag, Au) on NiO/TiO2 heterojunction UV photodetectors

Ag and Au are typical electrode materials for NiO/TiO2 heterojunction ultraviolet photodetectors (UV PDs), but the influence of work functions of Ag and Au on performance of devices has not been investigated. We synthesized TiO2 NRs on FTO by hydrothermal method and then constructed heterojunction by preparing NiO nanoflakes on TiO2 NRs using chemical bath deposition (CBD) method. The devices with Ag and Au as top electrode show self-power UV response. The energy band information of NiO is determined by X-ray photoelectron spectroscopy (XPS) valence band spectra, absorption spectrum, and work functions obtained by Kelvin probe. Due to the different arrangement between Fermi energy level of NiO and work functions of Ag and Au, the downward and upward band bending is formed in interfaces of Ag/NiO and Au/NiO. The suitable bending of energy band in Au/NiO leads to more favorable hole collection than that of Ag/NiO, which results in higher responsivity of Au/NiO/TiO2/FTO UV PDs.