Doping effects on catechol functionalized anatase TiO₂(101) surface for dye-sensitized solar cells

Doping effects of Al, Mg and Cr on the structural and photoelectric properties of catechol functionalized anatase TiO₂(101) surface (CFAS) have been studied using density-functional theory. The results indicate that the adsorption processes of CFAS and catechol functionalized doped anatase TiO₂(101) surfaces (CFDAS) are all exothermic and these adsorption systems are quite stable. The relative lower formation energy of Al-doped TiO₂ means that it is energetically favorable structure under Ti-rich conditions. For band structure of catechol-Cr-doped-TiO₂, the electron transition energy will be reduced, and visible light absorption will be extended on account of the decreased band gap and widespread impurity states. The positive Fermi energy shift of Cr-doped TiO₂ suggests that it is beneficial to increase the open circuit voltage compared with pure TiO₂ under the same conditions. When catechol as a model organic sensitizer functionalizing the pure and Al, Mg and Cr doped TiO₂ (101) surfaces, a positive shift of the Fermi energies is observed in comparison with those materials without catechol functionalization. Compared with the optical properties of CFDAS, Cr doping has a greater effect on the optical properties of anatase TiO₂ (101) surface than that of Al or Mg doping. The results show that Cr doped anatase TiO₂ (101) surface is a better photoanode material and can be applied in Dye-Sensitized Solar Cells.