Bipolar Carrier Transport In Tris(8-Hydroxy-Quinolinato) Aluminum Observed By Impedance Spectroscopy Measurements

We studied bipolar carrier transport in tris(8-hydroxy-quinolinato) aluminum (Alq(3)) thin films using impedance spectroscopy (IS). Two transit times were observed in the impedance spectra of the Alq(3) double-injection diodes. The mobilities determined from the transit times are in good agreement with the electron and the hole mobilities in Alq(3) measured by IS using single injection diodes and by the time-of-flight transient photocurrent technique. The bipolar carrier transport observed in Alq(3) shows that the carrier recombination of Alq(3) is weak on the basis of the simulation [M. Schmeits, J. Appl. Phys. 101, 084508 (2007)]. Simultaneous measurements of electron and hole mobilities are useful in the study of charge-carrier transport in active layers in organic light-emitting diodes and organic solar cells. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3615950]