Carrier Transport Behaviour of Molecularly Doped Poly (N-Vinylcarbozole) in Polymer Light-Emitting Diodes

Single-layer polymer light-emitting diodes (PLEDs) are prepared from blends of poly (N-vinylcarbozole) (PVK) doped with tris (8-hydroxy-quinoline) aluminum (Alq₃) of 2 wt% (sample a) and 0.2 wt% (sample b). The onset of PVK transient electroluminescence (EL) is delayed with respect to that of Alq₃ in sample a under pulsed excitation, While the EL onset of Alq₃ and PVK in sample b are simultaneous. The total carrier mobility of Alq₃-rich regions in sample a is larger than that of PVK-rich regions. However, the total carrier mobility is homogenous in sample b. The phase image of atomic force microscopy and photoluminescence spectra of sample a and sample b indicate that the separated phase of samples a and b exists in PVK-rich regions and Alq₃-rich regions. The variance of the doping concentration and separated phase in blends results in the different carrier transport mobility of Alq₃-rich regions and PVK-rich regions.