Measuring carrier mobility in conventional multilayer organic light emitting devices by delayed exciton generation

The authors present an alternative method for the determination of the charge carrier mobility of organic thin films. In contrast to known methods like space charge limited current, field effect transistor and time of flight approaches, we determine the charge carrier mobility of a mixed film, serving as emission layer, within the conventional multilayer device architecture. We make use of a strong delayed generation feature in the electroluminescent decay, following a short voltage pump pulse in a time-resolved set-up. Taking into account the preferentially electron transporting properties of the film, the mobility of a N,N-di(naphthalen-2-yl)-N,N'-diphenyl-benzidine (NPB):tris(1 phenylisoquinoline) iridium [Ir(piq)(3)] mixed film is found to be on the order of 10(-5) cm(2) (Vs)(-1). (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.