  We develop a quantum model for the dynamics of carrier injection in a band
that presents a strong carrier-vibration coupling. This coupling modifies the
spectral density of the band and can even create pseudo-gaps that sign the
onset of polaronic states. The injection of a carrier that interacts with many
vibration modes is a complex many-body process that is treated by combining the
quantum scattering theory and the Dynamical Mean-Field Theory (DMFT). For the
model analysed here, which is adapted to compact phases, the number Z of
neighbors of a given site is large and in this limit the DMFT becomes exact.
The model is applied to the excitonic dissociation at the donor-acceptor
interface for organic solar cells. The main ingredients are the electron-hole
Coulomb interaction, the recombination process and the existence of polaronic
states in the acceptor band. Using parameters extracted from ab-initio
calculations we analyze the spectral density on the charge transfer state
(CTS), the average energy transfered to phonons on the CTS and the quantum
yield of the injection process. We find in particular that, even with a strong
electron-vibration coupling, one can get a vibrationally cold charge transfer
state with a high injection yield as often observed experimentally.
