In this experimental study, poly(n-vinyl carbazole) (PVK)-based single-layer polymer light
emitting diodes (PLED) were fabricated. We used PVK with 1 100 000 (PVK(h)) and 50 000
(PVK(l)) molecular weights as host polymers and 2-(4-biphenyl)-5-phenyl-1,3,4-oxadiazole
(PBD) as an electron-transporting small molecule and also terabutylammonium
hexafluorophosphate (TBAPF6) as an organic salt. The weight ratios of PBD and TBAPF6
were constant in all devices and the effects of PVK molecular weight on the performances of
ITO/PVK(l):PBD:TBAPF6/AL (device A), ITO/PVK(h):PBD:TBAPF6/AL (device B) and
ITO/PVK(l):PVK(h):PBD:TBAPF6/AL (device C) structures were investigated. We found
that the molecular weight of polymer (PVK) has considerable effects on the performances of
these diodes, and consequently, their electrical and optical properties are completely
dissimilar. We also observed a tendency for the formation of aggregates (in the EL) and
excimers (in the PL) in the case of device (C).
