Strain-modulated electrical and optical bandgaps of tetragonal WO3: An HSE06 hybrid functional calculation

The Heyd–Scuseria–Ernzerhof screened hybrid functional is used to investigate the strain-modulated band structure and optical properties of tetragonal WO3. An electronic bandgap of 1.53 eV for the ground state of unstrained WO3 is obtained, which is consistent with the experimental value. Upon in-plane strains of 1.36%, 3.18%, 3.37%, and 4.36% along the directions of lattice vectors a→ and b→, i.e., biaxial strains, as realized by growing WO3 on the (001) surface of LaAlO3, NdGaO3, La0.3Sr0.7Al0.65Ta0.35O3, and SrTiO3, the bandgap decreases down to 1.47 eV, 1.37 eV, 1.36 eV, and 1.30 eV, respectively. The largest change in band structure can induce the downshift of the optical absorption edge, with the optical bandgap decreasing from 2.65 eV to 2.28 eV. Further applying a strain along the direction of lattice vector c→, the bandgap can be additionally tuned very finely. Our research provides a promising tuning method for designing high efficient inorganic photovoltaic materials.