HfO<inf>2</inf> nanodots incorporated in TiO<inf>2</inf> and its hydrogenation for high performance dye sensitized solar cells

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).