Photo-transport in poly(p-phenylene)-type polymers

Based on the photocurrent (PC) action spectrum, the dark current characteristics, and the transient response of the PC the charge carrier generation in substituted laddertype poly-(p-phenylene) (LPPP) is interpreted. We find that the transport of charge carriers in LPPP is determined by shallow traps located 0.1 and 0.4 eV above the conduction band edge. The ionized traps act as dissociation centers for photoexcited excitons. After pulsed photoexcitation the PC decays with 140 ps, the charge carriers having a mean free path within a single polymer chain. The intensity of the onset in the PC action spectrum gives evidence of mobile charged excitations above the valence band edge.