Precise Control of Broadband Light Absorption and Density of Ti3+ States in Sputtered Black TiO2 Thin Films

Defect-rich black titanium dioxide (B-TiO2) has been extensively studied over the past decade due to its enhanced photoelectrochemical efficiency compared to titanium dioxide (TiO2), which is known for its outstanding photocatalytic stability. So far, most of the B-TiO2 material is obtained by hydrogenation of crystalline TiO2, resulting in a disordered outer layer of a few nanometers thickness. Recently, a new sputtering process has been introduced to produce B-TiO2 thin films without the usage of hydrogen. Herein, the influence of the sputtering process on the creation of Ti3+ defect states within the films is discussed. Comprehensive optical, structural, and electronic studies of the thin film suggest that increasing the density of Ti3+ states enhances the conductivity of the films and results in increased and broadband light absorption. In addition, the new sputtering method can also be used to alter the density of the defect states in the film in a controlled manner, allowing the optical and electronical properties of the thin film to be changed in a precise and controllable way.