Synergistic Effect of Dielectric Property and Energy Transfer on Charge Separation in Non-Fullerene-Based Solar Cells

In non-fullerene-based photovoltaic devices, it is unclear how excitons efficiently dissociate into charge carriers under small driving force. Here, we developed a modified method to estimate dielectric constants of PM6 donor and non-fullerene acceptors. Surprisingly, most non-fullerene acceptors and blend films showed higher dielectric constants. Moreover, they exhibited larger dielectric constants differences at the optical frequency. These results are likely bound to reduced exciton binding energy and bimolecular recombination. Besides, the overlap between the emission spectrum of donor and absorption spectra of non-fullerene acceptors allowed the energy transfer from donor to acceptors. Hence, based on the synergistic effect of dielectric property and energy transfer resulting in efficient charge separation, our finding paves an alternative path to elucidate the physical working mechanism in non-fullerene-based photovoltaic devices.