Intermediate Band Material of Titanium-Doped Tin Disulfide for Wide Spectrum Solar Absorption

Intermediate band (IB) materials are of great significance due to their superior solar absorption properties. Here, two IBs peaking at 0.88 and 1.33 eV are reported to be present in the forbidden gap of semiconducting SnS2 (E-g = 2.21 eV) by doping titanium up to 6 atom % into the Sn site via a solid-state reaction at 923 K. The solid solution of Sn1-xTixS2 is able to be formed, which is attributed to the isostructural structure of SnS2 and TiS2. These two IBs were detected in the UV-vis-NIR absorption spectra with the appearance of two additional absorption responses at the respective regions, which in good agreement with the condusion of first-principles calculations. The valence band maximum (VBM) consists mostly of the S 3p state, and the conduction band minimum (CBM) is the hybrid state composing of Ti 3d (e(g)), S 3p, and Sn 5s, and the IBs are mainly the nondegenerate t(2g) states of Ti 3d orbitals. The electronic states of Ti 3d reveal a good ability to transfer electrons between metal and S atoms. These wide-spectrum absorption lBs bring about more solar energy utilization to enhance solar thermal collection and photocatalytic degradation of methyl orange.