Construction of a MoO_x/MoS₂ Heterojunction via the Surface Sulfurization of the Oxide and Its Photocurrent-Switching Characteristics in the Range of the Broadband Light Spectrum

In order to utilize the longer wavelength light, the surface sulfurization of MoO₃ was carried out. The photocurrent responses to typical 650, 808, 980, and 1064 nm light sources with Au gap electrodes were investigated. The results showed that the surface S–O exchange of MoO₃ improved the interfacial charge transfer in the range of the broadband light spectrum. The S and O can be exchanged on the surface of MoO₃ nanosheets under the hydrothermal condition, leading to the formation of a surface MoO_x/MoS₂ heterojunction. The interfacial interaction between the MoO₃ nanosheets and MoS₂ easily generated free electrons and holes, and it effectively avoided the recombination of photogenerated carriers. Meanwhile, the surface S-doping of MoO₃ also resulted in the generation of an oxygen vacancy and sulfur vacancy on MoO_3−xS_2−y. The plasmonic characteristics of MoO_3−x contributed to the enhancement of the interfacial charge transfer by photoexcitation. Otherwise, even with zero bias applied, a good photoelectric signal was still obtained with polyimide film substrates and carbon electrodes. This indicates that the formation of the heterojunction generates a strong built-in electric field that drives the photogenerated carrier transport, which can be self-powered. This study provides a simple and low-cost method for the surface functionalization of some metal oxides with a wide bandgap.