Transient electroluminescence of molecularly doped poly(N-vinylcarbozole) light-emitting diodes

Abstract

The poly(N-vinylcarbozole) (PVK)/tris(8-hydroxy-quinoline) aluminium (Alq3) blend thin films that exhibit asynchronism or simultaneity of transient electroluminescence (EL) onset of PVK and Alq3 under pulsed voltage, depending on the relative composition concentration or the extent of phase separation of blends, have been investigated. The resultant mobility of Alq3 rich regions of blends (doped with Alq3 concentration of several per cent, such as 2 wt% Alq3 and 1.0 wt% Alq3 with heat treatment) is larger than that of PVK rich regions of the same blends due to the percolation path formed by Alq3 when the doping concentration or the phase separation of blends is high enough. When the hopping rate of carriers from PVK to PVK sites is equivalent to or larger than that of Alq3 molecules, such as doping concentration of 0.2 and 1 wt% of Alq3 without heat treatment, the resultant mobility of blends is determined by PVK and their luminescence is synchronous. Transient EL is an effective method for the detection of spatial distribution variation of the product of mobility and electric field of blends in a range of doping concentrations depending on the different orders of luminescence of dopants and host.