Recombination of two triplet excitons in conjugated polymers

Combining the one-dimensional tight-binding Su-Schrieffer-Heeger (SSH) model including interchain interactions and the extended Hubbard model (EHM), we investigate the recombination processes between two triplet excitons in conjugated polymers using a nonadiabatic evolution method. Due to the interchain coupling, the electron and/or hole in the two triplet excitons can exchange, and new species are formed. Depending on the interchain coupling and electron-electron interactions, it is found that the main product is excited-polaron state in which two electrons and a hole (or two holes and an electron) are bound together in a lattice deformation, with a small amount of singlet exciton, biexciton and bipolaron. In these products, the excited polaron, the singlet exciton and the biexciton can contribute to the emission. The results indicate that the recombination of two triplet excitons may play an important role in polymer light-emitting diodes. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2012