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 nm generates singlet excited states in the polymer film. The second pulse at 780 nm is in resonance with the excited state absorption. We found that the probability of charge generation is enhanced in doubly excited chains only within a short period of time after excitation. The result is interpreted on the base of diffusion-driven exciton dissociation model in which the active sites are defects or impurities localized close to the Al electrode.