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

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/TiO(2) interface, and it is strongly mediated by the vibrations of interface Ti-O bonds, which anchor the dye onto the TiO(2) surface. The obtained absorption spectrum and electron injection timescale agree with experimental measurements.