Abstract
Carrier transport and recombination have been studied in single component layers and blends of the soluble PPV‐derivative poly[2,5‐dimethoxy‐1,4‐phenylenevinylene‐2‐methoxy‐5‐(2‐ethyl‐hexyloxy)‐1,4‐phenylenevinylene] (M3EH‐PPV) and the small molecule acceptor 4,7‐bis(2‐(1‐hexyl‐4,5‐dicyanoimidazole‐2‐yl)vinyl) benzo[c][1,2,5]‐thiadiazole (HV‐BT). Measurements on single carrier devices show significantly smaller electron mobility in the blend compared to the pure HV‐BT layer, which is suggestive of the formation of isolated clusters of the acceptor in a continuous polymer matrix. The significant change in fill factor (FF) with increasing illumination intensity is consistently explained by a model taking into account bimolecular recombination and space charge effects. The decay of the carrier density after photoexcitation has been studied by performing photo‐CELIV measurements on pure and blend layers. It is found that the decay at long delay times follows a power‐law dependence, which is, however, not consistent with a Langevin‐type bimolecular recombination of free charges. A good description of the data is obtained by assuming trimolecular recombination to govern the charge carrier dynamics in these systems.