Transient electroluminescence of organic quantum-well light-emitting diodes

Time-resolved electroluminescence (EL) is used for to investigate the dynamic distribution of charge carriers in organic quantum-well light-emitting diodes (QWLEDs). In organic QWLEDs, N,N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine and 2,9-dimethyl-4,7-diphenyl-1,10phenanthroline (BCP) act as a hole-transporting layer and a potential barrier layer, respectively. Tris(8-quinolinolato) aluminum is used as a potential well, a light-emitting layer, and an electron-transporting layer. Both traditional bilayer LED and QWLEDs with one, two, and four wells are investigated. For the QWLED with one well, the transient EL spectra are similar to those of traditional LEDs. In the transient EL spectra of QWLEDs with two and four wells, two distinct peaks are observed. This is due to the fact that holes first distribute in two different wells next to the NPB layer and recombine with electrons that subsequently move in when a voltage pulse is applied. This accounts for the time-resolved light emission in different recombination zones. The interval between the cutoffs of the two EL peaks is considered to be the transit time for electrons to cross the BCP layer, corresponding to electron mobility of 6×10−7 cm2 V−1 S−1 at 7×105 V/cm.