Inter- and intrachain electron-hole recombination in polythiophene

The initial state of electron-hole recombination leading to electroluminescence in polythiophene-based light emitting diodes is studied theoretically. Interacting electron and hole polarons as well as polaron excitons are considered and the energies and life times of these excited states are calculated for transitions to the ground state of the system. We find that the life time for the pair of charge separated polarons is large enough to allow for the system to reach its equilibrium geometry before recombination. This initial state of the recombination process is best described as a neutral polaron exciton, i.e., no charge separation exists in this state. This exciton is quasi one-dimensional, i.e., it is mainly localized to one chain but spreads out slightly over the neighboring chains.