Dissociation of hot excitons in ladder-type polymer light-emitting diodes

We present photocurrent excitation cross-correlation experiments which prov ide time-resolved information on the dissociation of photoexcited states in a prototypical pi -conjugated polymer. A first pump pulse generates single t exciton states (S-I) which are re-excited to a higher lying state by a se cond time delayed pulse resonant with a singlet exciton transition (S-I --> S-n). Dissociation is monitored via the change of photocurrent response in single layer devices. Our experiment probes diffusion driven, ultrafast di ssociation of inter-chain-hot excitons during inter-chain-migration to site s lower in energy. Once this process has concluded intrinsic dissociation o ccurs from a higher lying state reached after the second excitation. (C) 20 01 Elsevier Science B.V. All rights reserved.