Electron transit time and reliable mobility measurements from thick film hydroxyquinoline-based organic light-emitting diode

The time delay (tau(d)) in the transient electroluminescence (EL) signal of a bilayer organic light-emitting diode with a structure of indium-tin oxide /N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine/tris(8-hydroxyquinoline) aluminum (Alq(3))/Al has been measured and analyzed as a function of the thickness (D) of the Alq(3) layer. For a thin layer of Alq(3) (D < 180 nm), it is found that τ(d) is affected by both the charging effect and carrier transit time through the Alq(3) layer. For a thicker layer of Alq(3) (D > 200 nm), tau(d) approaches the intrinsic electron transit time through Alq(3). Electron mobility of Alq(3) can be evaluated for the thick-film devices and the results are in excellent agreement with independent time-of-flight measurements. The application of transient EL in mobility measurement for C540-doped Alq(3) is discussed. (C) 2003 American Institute of Physics.