Use of delayed electroluminescence as a tool to investigate the emission mechanism of phosphorescent organic light emitting devices

摘要

Delayed electroluminescence (Delayed EL) measurements are used to investigate the emission mechanism in typicalPhosphorescent Organic Light Emitting Devices (PHOLEDs). In this work, emission mechanism of PHOLED based onCBP (4,4'-bis(carbazol-9-yl)biphenyl : Ir(ppy)sub3/sub (Tris(2-phenylpyridine)iridium(III)) host:guest system is studied. Thetechnique is used to understand whether the EL emission arises from charge recombination directly on guest sites orfrom recombination on host material followed by host to guest energy transfer. The results show that the emissionmechanism changes with the emission layer (EML) thickness. In the case of devices with a thick EML, strong hosttriplet-triplet annihilation (TTA) is observed, suggesting the presence of significant energy transfer from host to theguest. For the case of devices with thin EML, on the other hand, host TTA is insignificant, suggesting that direct chargetrapping on the guest is the main emission mechanism. The results also show that the thickness of the hole transport layer(HTL) has negligible effect on the emission mechanism of PHOLED, showing that the emission mechanism mainlydepends on the EML.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.