Synthesis and characterization of high Tg carbazole-based amorphous hole-transporting materials for organic light-emitting devices (original) (raw)
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Thin Solid Films, 2008
Amorphous hole-transporting carbazole dendrimers, 1,4-bis[3,6-di(carbazol-9-yl)carbazol-9-yl]-2,6-di(2-ethylhexyloxy)benzene (G2CB) and 1,4-bis[3,6-di(carbazol-9-yl)carbazol-9-yl]-9-(2-ethylhexyl)carbazole (G2CC), were synthesized by a divergent approach involving bromination and Ullmann coupling reactions. Compounds G2CB and G2CC showed high thermal stability (T g = 206 to 245°C) and excellent electrochemical reversibility. Double-layer organic light-emitting diodes were fabricated by using G2CB and G2CC as hole-transporting layers (HTLs) and tris (8-quinolinato)aluminum (Alq 3 ) as light-emissive layer with the device configuration of indium tin oxide/HTL/Alq 3 /LiF:Al. Both devices exhibited bright green emission from Alq 3 . The device using G2CC as HTL has the best performance with a maximum brightness of 8900 cd/m 2 at 14 V and a low turn-on voltage of 3.5 V.
High hole mobility hole transport material for organic light-emitting devices
Synthetic Metals, 2013
A new hole-transporting material, 5,10,15-triphenyl-5H-diindolo[3,2-a:3 ,2-c]carbazole (TPDI) is reported for organic light-emitting device (OLED) applications. It shows excellent hole mobility (6.14 × 10 −3 cm 2 /V s), one order higher than that of NPB (4,4-bis(N-phenyl-1-naphthylamino)biphenyl), and a good HOMO level of 5.3 eV. Fabricated fluorescent blue OLEDs exhibit about 1.0 V voltage reduction and 18% external quantum efficiency (EQE) improvement by replacing TPDI instead of NPB as a hole transport layer. In the green phosphorescent OLEDs, the driving voltage improves about 1.8 V and EQE increases about 65%. This TPDI will be applicable to not only in fluorescent OLEDs but also in phosphorescent OLEDs.
Tetrahedron Letters, 2006
New triphenylamine-carbazole end-capped molecules were synthesized by a divergent approach using bromination and Suzuki cross-coupling reactions. All compounds showed an excellent electrochemical reversibility and a good thermal stability. They were fabricated as hole-transporting layers (HTLs) with the device configuration of ITO/HTL/Alq 3 /LiF:Al. A bright green emission from the Alq 3 layer with a maximum luminance of 7500 cd/m 2 was observed at 9.8 V and a low turn-on voltage of 3.4 V.
Thin Solid Films, 2012
Two hole transport materials with high glass transition temperatures (T g~2 00°C) have been synthesized by replacing the phenyl groups of 4,4′-bis[N-(1-naphthyl-1)-N′-phenyl-amino]-biphenyl (α-NPD) with the bulkier phenanthrene (N,N′-di(naphthalene-1-yl)-N,N′-di(phenanthrene-9-yl)biphenyl-4,4′-diamine, NPhenD) or anthracene (N, N′-di(anthracene-9-yl)-N,N′-di(naphthalene-1-yl)biphenyl-4,4′-diamine, NAD). The organic light-emitting diodes (OLEDs) using these hole transport materials exhibited stable operation at high temperatures up to 420 K, improved device lifetimes, and reduced operating voltage changes compared to the conventional hole transport materials owing to their high T g. Although NAD has quite small bandgap as a hole transport material, superior thermal properties of NPhenD and NAD suggest that they can be promising materials for highly stable and high temperature-durable OLEDs and other organic optoelectronic devices.
Novel hole transporting materials based on 4-(9H-carbazol-9-yl)triphenylamine derivatives for OLEDs
Molecules (Basel, Switzerland), 2014
During the past few years, organic light emitting diodes (OLEDs) have been increasingly studied due to their emerging applicability. However, some of the properties of existing OLEDs could be improved, such as their overall efficiency and durability; these aspects have been addressed in the current study. A series of novel hole-transporting materials (HTMs) 3a-c based on 4-(9H-carbazol-9-yl)triphenylamine conjugated with different carbazole or triphenylamine derivatives have been readily synthesized by Suzuki coupling reactions. The resulting compounds showed good thermal stabilities with high glass transition temperatures between 148 and 165 °C. The introduction of HTMs 3b and 3c into the standard devices ITO/HATCN/NPB/HTMs 3 (indium tin oxide/dipyrazino(2,3-f:2',3'-h)quinoxaline…
Journal of Applied Physics, 2014
Electrical transport in thermally stable 2, 7-bis [N, N-bis (4-methoxy-phenyl) amino]-9, 9-spirobifluorene (MeO-Spiro-TPD) thin films has been investigated as a function of temperature and organic layer thickness. ITO/MeO-Spiro-TPD interface was found to be injection limited and has been studied in detail to find barrier height for hole injection. The thickness of tetrafluoro-tetracyano-quinodimethane thin films were optimized to be used as hole injection buffer layer which resulted in switching of charge transport mechanism from injection limited to space charge limited conduction above a critical thickness of 3 nm. Hole mobility has been measured using transient space charge limited conduction (SCLC), field dependent SCLC, and top contact transistor characteristics. The charge carrier transport in interface modified hole only devices was analysed using Gaussian disorder model. The thermal stability of MeO-Spiro-TPD has been investigated by atomic force microscopy and X-ray diffraction studies. The study indicates a thermally stable and highly efficient hole transport material for application in organic semiconductor based devices. V
Organic Electronics, 2009
This paper describes the synthesis of three triaryldiamine derivatives presenting two thermally polymerizable trifluorovinyl ether groups that can be polymerized through thermal curing to form perfluorocyclobutyl (PFCB) polymers. These PFCB polymers, studied using time-of-flight techniques for the first time, exhibited remarkable non-dispersive holetransport properties, with values of l h of ca. 10 À4 cm 2 V À1 s À1 . When we employed these thermally polymerized polymers as hole-transport layers (HTLs) in electroluminescence devices containing tris(8-hydroxyquinolate) aluminum (Alq 3 ) as the emission layer, we obtained high current densities (ca. 3400 mA cm À2 ), impressive brightnesses (5 Â 10 4 cd m À2 ), and high external quantum efficiencies (EQEs = 1.43%). These devices exhibited the same turn-on voltage, but higher EQEs, relative to those incorporating the vacuum-processed model compound N,N 0 -di(1-naphthyl)-N,N 0 -diphenylbenzidine (a-NPD) (EQE = 1.37%) as the HTL under the same device structure.
Organic Electronics, 2020
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Synthetic Metals, 2011
Phenyl or naphthyl substituted 9-(2,2-diphenylvinyl)carbazoles were synthesized by the multi-step synthetic route. The materials were examined by various techniques including thermogravimetry, differential scanning calorimetry, and electron photoemission technique. These derivatives were also tested as hole-transporting materials in bilayer OLEDs with Alq 3 as the emitter. The devices exhibited promising overall performance with a turn-on voltage of 3.2 V, a maximal photometric efficiency of about 4.8 cd/A and maximum brightness of 12,400-13,100 cd/m 2 .