Exciton Dissociation at Thiophene/Fullerene Interfaces: The Electronic Structures and Quantum Dynamics

Exciton dissociation at donor-acceptor heterojunctions is one of the key processes that determine the energy conversion efficiency of organic solar cells. Here, we theoretically investigate the exciton dissociations at oligothiophene/C-60 donor-acceptor heterojunctions by using the long-range corrected time-dependent density functional theory and quantum dynamics calculations. We analyze the absorption spectra, electronic structures in adiabatic and diabatic representations, vibronic coupling, and dynamics of the exciton dissociations. The coupling strength and relative energy between the exciton and charge transfer (CT) states depend sensitively on the donor-acceptor distance and the stacking structure, which in turn affects the absorption spectra and the dynamics of exciton dissociations. Our quantum dynamics calculations exhibit ultrafast exciton dissociations owing to the strong coupling between the exciton and CT states, as observed in the time-resolved spectroscopies of the donor-acceptor interfaces of conjugated polymers and fullerenes.