Diffusion length of triplet excitons in organic semiconductors

The exciton diffusion length in organic semiconductors strongly impacts the efficiency of energy harvesting organic optoelectronics. We demonstrate an experimental technique to estimate the diffusion length of triplet excitons in a ladder-type conjugated organic semiconductor from quenching of the triplet-triplet absorption in the presence of acceptor molecules. The diffusion lengths are consistent with a phenomenological random-walk model. Experiments on two different molecular weights of the polymer sample show that the diffusion length of triplet excitons is in the few micrometers range and depends upon the size of the $\ensuremath{\pi}$-conjugated system.