HfO2 nanodots incorporated in TiO2 and its hydrogenation for high performance dye sensitized solar cells

Abstract

Black titania (H-TiO₂) as a photoanode material has attracted huge attention due to its extremely high optical absorption in the visible region. Herein, black TiO₂ doped with HfO₂ shows ∼45.7% higher photo-conversion efficiency than H-TiO₂ under identically similar conditions. The incorporation of HfO₂ nanodots increased the optical scattering in H-TiO₂ only when it underwent hydrogenation along with TiO₂. Hafnia-doped TiO₂ (HfO₂/TiO₂) is synthesized by a combination of simple sol–gel and hydrothermal method followed by thermal annealing under controlled hydrogen atmosphere. The hydrogenated H-(TiO₂/HfO₂) exhibited very high optical absorption but slightly lower than H-TiO₂ due to light scattering by HfO₂ nanodots. We observed a sharp decrease in optical band gap of TiO₂/HfO₂ from 3.2 to 2.4 eV up on hydrogen annealing, which is important in solar applications as demonstrated by the fabrication of high efficiency dye sensitized solar cells (DSSC).