Field-enhanced recombination at low temperatures in an organic photovoltaic blend

We report on the non-trivial field dependence of charge carrier recombination in an organic blend at low temperatures. A new microwave resonance technique for monitoring charge recombination in organic semiconductors at low temperatures is applied in bulk heterojunction P3HT:PCBM blends with results showing that an external electric field can in fact increase recombination. Monte Carlo simulations suggest that this contradiction to conventional wisdom relates to electron-hole pairs that are separated at donor-acceptor interfaces where the electric field acts in synergy with their Coulomb attraction. For this behaviour to occur a critical initial separation of 5nm between the carriers is required.