Defect Auger exciton dissociation and impact ionization in conjugated polymers - art. no. 125202

We study theoretically the exciton dissociation and carrier generation in c onjugated polymers via defect Auger process, in which the electron (hole) o f the exciton drops into the deep defect level while the energy is released to the hole (electron) through Coulomb scattering. Contrary to the usual A uger process among free carriers at high densities, defect Auger process fo r excitons takes place independent of the exciton density, and is identifie d as the dominant mechanism of photocarrier generation for excitation below the band gap. The dissociation probability for each passage through the de fect is found to be close to one for excitons with thermal velocity, consis tent with the picture that exciton decay in oxidized polymers is controlled by diffusion on a chain with quenching centers. We also study the reverse process, i.e., defect impact ionization, in which excitons or free electron hole pairs are created via the impact of hot holes (electrons) on electron s (holes) in the defect level. Excitons are found to be produced predominan tly for driving electric field in a window around 10(5) V/cm along the chai n. Light emission under unipolar carrier injection is predicted.