Stable pure-blue emission of poly(9,9-dioctylfluorene) via suppression of the green emission

Stable pure-blue electroluminescence (EL) is obtained from polymer light-emitting devices by dispersing poly(9,9-dioctylfluorene) (PFO) into a wide band-gap mixed-matrix of poly(9-vinylcarbazole) (PVK):2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD). From the EL spectra of the PFO-doped films, we find that the additional green emission observed in the EL spectra of the pure PFO devices was significantly suppressed in the PFO-doped devices. The spectral stability was also improved through evaluating the EL spectra of the PFO-doped films annealed at different temperatures (from 80 to 150 °C). These results demonstrate that doping of PFO into a matrix to weaken the aggregate and oxidation of the PFO molecules is a simple strategy to suppress the green emission.