Direct Measurement of Electric Field-Assisted Charge Separation in Polymer: Fullerene Photovoltaic Diodes

The electric field dependence of transient optical absorption of photogenerated charge carriers in working organic photovoltaic cells is reported. Charge lifetimes are extended under reverse bias, revealing that the mechanism of photocurrent generation is the electric field-assisted separation of Coulombically bound charge pairs in kinetic competition with geminate charge recombination.