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Enhanced Optical Absorption Due to Symmetry Breaking in TiO2(1–x)S2x Alloys

Titania (TiO2) is frequently used in photovoltaic and photocatalytic applications, despite the fact that its main optical absorption occurs only at ∼4 eV. Absorption across the band gap of 3 eV is dipole-forbidden in rutile TiO2. By means of first-principles theoretical spectroscopy calculations, we demonstrate that alloying with TiS2 introduces an absorption band into the fundamental gap of TiO2. In addition, band-edge transitions contribute to optical absorption because the S incorporation breaks the symmetry of the TiO2 lattice. Both effects lead to pronounced absorption of visible light for S concentrations as low as 1.5%.