Singlet and triplet exciton formation rates in conjugated polymer light-emitting diodes

By applying a molecular orbital perturbation approach, we calculate the for mation rates for singlet and triplet molecular excitons associated with int ermolecular charge-transfer processes. It is found that the interchain bond -charge correlation has a strong influence on the relative probabilities fo r generating singlet and triplet excitons. Most importantly, application of our approach to a model system for poly(paraphenylenevinylene) shows that the ratio between the electroluminescence and photoluminescence quantum yie lds generally exceeds the 25% spin-degeneracy statistical limit.