Evidence for exciton fusion as the origin of charge production in molecularly doped polymers

Picosecond-pulse- (ultraviolet-) excited photoconductivity measurements in a molecularly doped polymer have provided direct evidence that the dominant mode of charge production in this random molecular system is (triplet-) exciton fusion. The effective rate constant ${\gamma }_{\mathrm{eff}}$ of the fusion process is shown to be strongly dependent on the electric field, thus establishing a contribution to the field dependence of the photogeneration yield that cannot be associated with the familiar Onsager process. Time-resolved luminescence measurements in both the picosecond and microsecond range in this system confirm that the time dependence of mobile charge production is controlled by the dynamics of the interacting triplet-exciton population.