  Hybrid interfaces formed by inorganic semiconductors and organic molecules
are intriguing materials for opto-electronics. Interfacial charge transfer is
primarily responsible for their peculiar electronic structure and optical
response. Hence, it is essential to gain insight into this fundamental process
also beyond the static picture. Ab initio methods based on real-time
time-dependent density-functional theory coupled to the Ehrenfest molecular
dynamics scheme are ideally suited for this problem. We investigate a
laser-excited hybrid inorganic/organic interface formed by the electron
acceptor molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane
(F4TCNQ) physisorbed on a hydrogenated silicon cluster, and we discuss the
fundamental mechanisms of charge transfer in the ultrashort time window
following the impulsive excitation. The considered interface is $p$-doped and
exhibits charge transfer in the ground state. When it is excited by a resonant
laser pulse, the charge transfer across the interface is additionally
increased, but contrary to previous observations in all-organic donor/acceptor
complexes, it is not further promoted by vibronic coupling. In the considered
time window of 100~fs, the molecular vibrations are coupled to the electron
dynamics and enhance intramolecular charge transfer. Our results highlight the
complexity of the physics involved and demonstrate the ability of the adopted
formalism to achieve a comprehensive understanding of ultrafast charge transfer
in hybrid materials.
