Solution-Processed Sb₂Se₃ on TiO₂ Thin Films Toward Oxidation- and Moisture-Resistant, Self-Powered Photodetectors

Semiconductor-sensitized TiO₂ thin films with long-term air stability are attractive for optoelectronic devices and applications. Herein, we demonstrate the potential of the TiO₂ thin film (∼800 nm in thickness) sensitized with a Sb₂Se₃ layer (∼350 nm) grown from solution spin coating and processed by annealing recrystallization at 300 °C for high-performance optical detection. The type-II band alignment, p-Sb₂Se₃/n-TiO₂ heterojunction, and narrow band gap of Sb₂Se₃ (∼1.25 eV) endow the film photodetector with a large photocurrent, high switching stability and on/off ratio (>10³), and fast response speeds (<20 ms) under the broadband visible-near-infrared irradiation in a zero-bias self-powered photovoltaic mode. In particular, the photodetector shows notable resistance to oxidation and moisture for long-term operation, which is linked to the modest surface oxidation (Sb-O) of Sb₂Se₃, as verified by X-ray photoelectron spectroscopy. The first-principles calculations show that a low and medium concentration of oxygen substitution for Se (O_Se) and oxygen interstitial (O_i) with negative formation energies can lead to such a moderate surface oxidation but do not generate impurity states or just introduce a shallow-level acceptor state in the electronic structures of Sb₂Se₃ without degrading its optoelectronic performance. Our theoretical results offer a rational explanation for the air-stable and oxidation/moisture-resistant characteristics in moderately oxidized Sb₂Se₃ and may shed light on the surface oxidation-property relationship studies of other nonoxide semiconductor-sensitized devices.