NSOM Investigation of Carrier Generation, Recombination, and Drift in a Conjugated Polymer

The migration of charge carriers in response to a pulsed electric field was investigated on the 100-nm length scale and microsecond time scale by a recently introduced method employing photoluminescence detection and near field optical excitation through a sharpened optical fiber. A metal coating on the near field probe serves as a ∼100 nm diameter electrode which acts to either collect or repel majority charge carriers, depending on the sign of the applied voltage. The local carrier density is determined by carrier-induced photoluminescence quenching. The transient response is described by a model including carrier drift and diffusion. The role of oxygen in photoinduced carrier generation, exciton quenching, and charge trapping is also investigated.