Abstract
We studied the driving voltage stability of typical phosphorescent organic light emitting devices (PHOLEDs) based on 4,4′-bis(carbazol-9-yl)biphenyl and Tris(2-phenylpyridine)iridium(III) host:guest system. The results show that the gradual increase in voltage often observed with prolonged electrical driving is mainly governed by the accumulation of holes at the emission layer/hole blocking layer interface. Reducing the build-up of hole space charges in this region, for example, by means of eliminating guest molecules from the vicinity of the interface, leads to a significant improvement in the stability of PHOLED driving voltage.
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