Sujin Jeong

Blue organic light-emitting diodes based on spiro[fluorene-indeno]pyridine derivatives

ABSTRACT We designed and synthesized two blue fluorescent materials based on spiro[9H-fluorene-9, 5′-[5H] indeno[1, 2-b] pyridine via Buchwald-Hartwig amination and Suzuki coupling reaction. To characterize their electroluminescent properties, multilayered organic light emitting diodes (OLEDs) were fabricated with the following device structures: ITO(180 nm)/2-TNATA(60 nm)/NPB(20 nm)/α,β-ADN: 3, 5, or 10 wt% blue dopants (30 nm)/Bphen(30 nm)/Liq(2 nm)/Al(100 nm). All the devices showed blue emissions with high electroluminescent efficiencies. Particularly, a device using 7′-((4-(N,N-diphenyl)-styryl)-4-phenyl)-spiro[9H-fluorene-9, 5′-[5H] indeno[1, 2-b] pyridine] as a dopant material with 10 wt% doping concentration exhibited highly efficient blue emission with an external quantum efficiency of 4.46% at 20 mA/cm2 and the CIE coordinates of (0.18, 0.30) at 1000 cd/m2. In this device, the twisted structural feature of emitter originated from spiro-type core prevented self-quenching and lead to the improved efficiencies even at high doping concentration in the device.

Blue emitting materials based on diphenylamine-substituted diphenylvinylarenes for OLEDs

ABSTRACT To develop the efficient blue emitters for Organic light-emitting diodes (OLEDs), this paper reports the synthesis and electroluminescent properties of diphenylvinylarenes end-capped with diphenylamine groups. Two OLEDs were fabricated in the following sequence: indium-tin-oxide (ITO) / N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diam-ine (NPB) (50 nm) / Blue emitters (30 nm) / bathophenanthroline (Bphen) (30 nm) / lithium quinolate (Liq) (2 nm) /Al (100 nm). Two devices exhi-bited blue electroluminescence. In particular, a device using 9,9-diethyl-N,N-diphenyl-7-(2,2-diphenylvinyl)-9H-fluoren-2-amine exhibited blue emission with a luminance efficiency, a power efficiency, an external quantum efficiency and Commission Internationale d’Énclairage (CIE) coordinates of 5.48 cd/A, 2.45 lm/W, 2.85% at 20 mA/cm² and (x = 0.17, y = 0.25) at 8.0 V, respectively.