Theoretical studies of heteroatom-doping in TiO2 to enhance the electron injection in dye-sensitized solar cells

Abstract

Density functional calculations have been explored to analyze the structural, electronic and charge transfer properties of a doped TiO₂ substrate and catechol–TiO₂ interfaces for dye-sensitized solar cells. The results demonstrate that the dopant W⁶⁺ moves the CB (conduction band) edge downward and introduces 5d-unoccupied orbitals located in the CB bottom of the TiO₂. On the other hand, the dopant Zn²⁺ shifts the CB edge upward with an insertion of 3d-occupied orbitals into the VB (valence band). In catechol–TiO₂ systems, W⁶⁺ enlarges the energy difference between the LUMO of catechol and LUMO of TiO₂, which enlarges the driving force for electron injection in turn and results in an increased short circuit current (J_sc). Our modeling injection dynamics and quantitative Bader analysis of the interfacial charge transfer have revealed that the catechol–TiO₂ doped with W⁶⁺ provides faster and more electron injection for dye sensitized solar cells (DSSCs). While the Zn²⁺ doped system exhibits lower electron efficiency due to the minimized energy difference between the catechol LUMO and TiO₂ CB.