Carrier transport properties of organic materials for EL device operation

We have measured drift mobilities in vacuum deposited films of tris(8-quinolinolato)aluminum (Alq3), a triphenylamine derivative (TPD) and a naphtyl-substituted benzidine derivative (α-NPD) using a time-of-flight (TOF) technique. The hole mobilities of TPD and α-NPD are about two orders of magnitude higher than the electron mobility of Alq3. This implies that the current density versus applied voltage characteristics is dominated by the electron mobility of Alq3 rather than the hole mobility of TPD or α-NPD in double-layered devices ITO/TPD or α-NPD (50 nm)/Alq3 (50 nm)/MgAg.