Determination of charge carrier mobility in tris(8-hydroxy-quinolinato) aluminum by means of impedance spectroscopy measurements

The hole mobility of tris(8-hydroxy-quinolinato) aluminum (Alq(3)) thin films and double layer films of a 4,4'-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (NPB) and Alq(3), have been determined using impedance spectroscopy (IS) measurements. The theoretical basis of mobility measurement with IS rests on a theory for single-injection space-charge limited current. The NPB thin film operates as an injection layer to reduce the hole injection barrier between an injection electrode and the Alq(3) thin film. The hole mobilities of Alq(3) thin films measured with IS are identical to those measured by a time-of-flight (TOF) transient photocurrent technique. The hole drift mobility determined using IS measurements in NPB/Alq(3) double layer hole-only devices where the thickness of NPB is comparable to that of Alq3 are also identical to the hole drift mobility of Alq(3) layer. The origin of the observation is discussed using a device simulation and the results are useful for the determination of charge carrier mobility in multilayer devices. (C) 2011 Elsevier B.V. All rights reserved.