The phase separation of polymer blends doped with low concentration probed by transient electroluminescence

Three mixtures of poly(N-vinylcarbozole) (PVK) doped with 3, 1.5 and 0.1 wt% poly [2-methoxy 5-(2-ethylhexyloxy)-p-phenylene vinylene] (MEHPPV) are prepared. The phase-separation in these mixtures has been observed with atomic force microscopy (AFM) and demonstrated by photoluminescence (PL). The transient electroluminescence (EL) of PVK and MEHPPV in mixed PVK polymer light-emitting diodes (PLEDs) has been measured. The onset of PVK EL driven by electric pulse lagged behind that of MEHPPV in the mixture with 1.5, and 3 wt% dopant. But the EL onsets of MEHPPV and that of PVK in the mixture with 0.1 wt% dopant are the same. Moreover, the lag of EL onset of PVK behind that of MEHPPV increases with increasing doping concentration. The results demonstrate that the resultant carrier mobility of different phases of mixed polymers with low concentration dopant might be differentiated by means of transient EL.