Proceedings Article | 27 August 2009
KEYWORDS: Organic light emitting diodes, Printing, Electroluminescence, Polymers, Energy transfer, Luminescence, Electron transport, Thin films, Molecules, Polymer thin films
The emission properties of polymer light-emitting diode (PLEDs), using blue emissive poly(9,9-dioctylfluorene) (PFO)
and yellow-green emissive poly[9,9-dioctylfluorenyl-2,7-diyl)-co-1,
4-benzo-{2,1'-3}- thiadiazole)] (F8BT) fabricated by
the spin-coating method, the toluene vapor method and the thermal printing method, were investigated.
poly(2,7-(9,9-din-octylfluorene)-alt-(1,4-phenylene-(
(4-sec-butylphenyl)imino)-1,4-phenylene)) (TFB) is useful for buffer layer and a
dopant when we use the spin-coating method. When we use TFB as interlayer of PLED, TFB acts as exciton-blocking
layer, thus prevents luminescence quenching. When we use TFB with
2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD)
as dopants of PFO, better current efficiency was achieved, compared to PFO only device. This result derives from these
materials working as hole and electron transporting molecules. The blue and yellow-green PLEDs fabricated by the spincoating
method showed maximum efficiencies of approximately 1.1 and 1cd/A, respectively. The device with
bis[1-(9,9-dimethyl-9H-fluoren-2-yl)-isoquinoline](acetylacetonate)iridium(III) (Ir(fliq)2acac) doped in PFO showed red-emission
and a maximum efficiency of approximately 1cd/A. Current efficiencies of PLEDs with the β phase of PFO fabricated
by the thermal printing method and the toluene vapor method were found to have better emission efficiency than that
with the amorphous phase of PFO by the spin-coating method. The EL spectra of PLEDs using PFO and PFO:F8BT
fabricated by the thermal printing method were polarized. The transient characteristics of PLEDs using β phase of PFO
were better than amorphous phase of that. It is expected to improve the characteristics of PLEDs by the optimization of
the thermal printing method. We demonstrated improved light emission of PLEDs with the high-quality β phase by the
thermal printing method.
