Femtosecond photovoltage excitation cross-correlation on a ladder-type polymer

Femtosecond excitation cross-correlation (EXC) photovoltage experiments are carried out in methyl-substituted poly-para-phenylene ladder-type polymer light-emitting devices (LEDs). The first excitation pulse at 390 nn generat es singlet excited states in the polymer film. The second pulse at 780 nm i s in resonance with the excited state absorption. We found that the probabi lity of charge generation is enhanced in doubly excited chains only within a short period of time after excitation. The result is interpreted on the b ase of diffusion-driven exciton dissociation model in which the active site s are defects or impurities localized close to the Al electrode. (C) 2000 E lsevier Science S.A. All rights reserved.