Host-Guest Triplet- Triplet Annihilation Directly Observed

摘要

During the last years the research field of organic semiconductors, in particular light emitting diodes (OLEDs), has rapidly developed. Many of the targeted applications, such as flat and highly efficient white light sources, demand OLEDs to be operated at high brightness levels. This is accompanied by bimolecular, non-linear quenching effects reducing the device efficiency. Especially phosphorescent dyes are facing very high excitation densities owing to their naturally longer excited state lifetime in the range of microseconds. In a recent Rapid Research Letter Sebastian Reineke et al. address host-guest triplet-triplet annihilation (TTA) which is an additional, unwanted quenching pathway for highly excited triplet states. The authors observe this host-guest TTA directly in time-resolved photolumi-nescence (PL) experiments on typical test devices made of/ac-tris(2-phenyl-pyridine) iridium. They are able to deduce the TTA contribution to the overall bimolecular annihilation at high brightness from the change in PL transients as a function of excitation power.