Dresden 2006 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 23: POSTER Functional Organic Thin Films

CPP 23.34: Poster

Thursday, March 30, 2006, 17:00–19:00, P2

Investigation of triplet exciton quenching in red phosphorescent OLEDs — •Sebastian Reineke, Martin Pfeiffer, Karsten Walzer, and Karl Leo — Institut für Angewandte Photophysik, Technische Universität Dresden, George-Bähr-Str. 1, D-01062 Dresden, Germany

We studied the quenching processes which contribute to the roll-off in quantum efficiency of phosphorescent OLEDs at high brightness. Possible processes are triplet-triplet annihilation (TTA), energy transfer to charged molecules (polarons) and the dissociation of excitons into free charges. The investigated OLED comprises a host-guest system as emission layer (EML) within a five layer structure including blocking and p- and n-doped transport layers. Here, N,N’-di(naphthalen-2-yl)-N,N’-diphenyl-benzidine is used as matrix and tris(1-phenylisoquinoline) iridium as phosphorescent emitter material. We found that the decrease of efficiency can be appointed to both TTA and energy transfer to charged molecules. Field-induced dissociation of excitons was not observed. Time-resolved measurements for the investigation of TTA as well as cw measurements for triplet-polaron quenching were performed. They are analyzed and combined to understand the efficiency drop in OLEDs. This work shows that both processes occur in the range of current density which is typical for OLED operation. An analytical discussion of both processes will be used to point out the magnitude of the different mechanisms.