Atomistic mechanism of charge separation upon photoexcitation at the dye–semiconductor interface for photovoltaic applications

Abstract

Charge separation in excited states upon visible light absorption is a central process in photovoltaic solar cell applications. Employing state-of-the-art first principles calculations based on time-dependent density functional theory (TDDFT), we simulate electron–hole dynamics in real time and illustrate the microscopic mechanism of charge separation at the interface between organic dye molecules and oxide semiconductor surfaces in dye-sensitized solar cells. We found that electron–hole separation proceeds non-adiabatically on an ultrafast timescale <100 fs at an anthocyanin/TiO₂ interface, and it is strongly mediated by the vibrations of interface Ti–O bonds, which anchor the dye onto the TiO₂ surface. The obtained absorption spectrum and electron injection timescale agree with experimental measurements.