Carrier transport behaviour of molecular doped poly (N-vinylcarbozole) in polymer light-emitting diodes

Single-layer polymer light-emitting diodes are prepared from blends of poly(N-vinylcarbozole) (PVK) doped with tris(8-hydroxy-quinoline) aluminium (Alq(3)) of 2wt% (sample a) and 0.2wt% (sample b). The onset of PVK transient electroluminescence (EL) is delayed with respect to that of Alq(3) in sample a under pulsed excitation, while the EL onsets of Alq(3) and PVK in sample b are simultaneous. The total carrier mobility of the Alq(3)-rich regions in sample a is larger than that of the PVK-rich regions. However, the total carrier mobility is homogeneous in sample b. The phase image of atomic force microscopy and photoluminescence spectra of samples a and b indicate that the separated phase of samples a and b exists in the PVK-rich and Alq(3)-rich regions. The variance of the doping concentration and separated phase in blends results in the different carrier transport mobility of Alq(3)-rich and PVK-rich regions.