Fluorene based amorphous hole transporting materials for solution processed organic light-emitting diodes (original) (raw)
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Molecular Crystals and Liquid Crystals, 2016
9,9-Diethylfluorenes substituted with two fluorophenyl, difluorophenyl or trifluorophenyl fragments were synthesized by the multi-step synthetic rout. The materials were characterized by 1 H NMR spectroscopy, mass spectrometry, differential scanning calorimetry and thermogravimetric analyses. Some of the electro-active derivatives could form thin amorphous films and were tested as solution processed hole transporting layers in organic light-emitting diodes with Alq 3 as the emitter and electron transporting material. Some of the electroluminescent devices demonstrated turn voltage of 5.5 V, a maximal photometric efficiency of about 1.0 cd/A and maximum brightness exceeding 960 cd/m 2 .
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
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.
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.
IEEE Journal of Quantum Electronics, 2000
An organic electroluminescent device with a luminous efficiency of 20 lm/W, at 14 cd/m 2 , and an external quantum efficiency of 4.6% has been fabricated using a high hole transport polymer, a small molecule emission layer, and a LiF/Al cathode. The device quantum efficiency can be increased by tuning the ionization potential of the hole-transport moieties. When tested under pulsed voltage mode, in air at room temperature, and without any encapsulation, the device showed a high peak brightness of 4.4 × 10 6 cd/m 2 at 100 A/cm 2 and an efficiency of 4.4 cd/A. Index Terms-Aluminum cathode, efficiency, hole transport layer, ionization potential, luminescence, OLED.
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.
New materials for Organic Light-Emitting Diodes
MRS Proceedings, 1995
ABSTRACTWe have investigated the performance of a class of heterocycles, 5,10-dihetera- 5,10-dihydroindeno[3,2b]indenes, as hole transport agents in simple double heterostructure organic light-emitting diodes with tris(8-hydroxyquinoline)aluminum (Alq). The best of these materials, 5,10-dihydroindolo[3,2b]indole, yields devices with luminance and lifetimes comparable to those obtained using N,N′-di-(3-methylphenyl)-N,N′- diphenyl-4,4′-diaminobiphenyl (TPD) as a hole transporting material.
Organic Electronics, 2007
A series of new fluorene-based alternating polymers (PF-CZ50, PF-DPA50, PF-PXZ50, PF-PZB50) composed of comonomers containing well-known hole-transporting moieties, namely carbazole, diphenylamine, phenoxazine, and phenothiazine, respectively, were synthesized via Suzuki coupling reactions. The molecular structures of the polymers were characterized with 1 H NMR spectroscopy and elemental analysis, and their photophysical, electrochemical, and electroluminescence properties were investigated. The absorption and photoluminescence (PL) emission maxima of the copolymers in the solid state varied depending on which hole-transporting unit was present. Although the polymers' LUMO levels are similar, the differences between their HOMO levels mean they have different hole-transportation properties. Light-emitting devices using the polymers as emitting layers were fabricated with ITO/PEDOT:PSS/polymer/Ca/Al configurations. The emitted light of these polymers ranged from yellowish green to red for the sequence PF-CZ50, PF-DPA50, PF-PXZ50, and PF-PZB50. Especially, PF-PXZ50 and PF-PZB50 emitted almost pure red with good brightness. The planarity of the hole-transporting moieties in the polymers is the main factor affecting the efficiency of these electroluminescence (EL) devices. The planarity of each hole-transporting moiety was calculated by computational analysis using the ab initio Hartree-Fock (HF) with the split-valence 6-31G * basis set. As the magnitude of the non-planarity of the hole-transporting moieties increased, it was found that the EL quantum efficiency of the polymers was enhanced. Compared to PF-CZ50 containing planar carbazole moieties, PF-DPA50 containing a non-planar diphenylamine moiety showed better EL performances without a significant change of the emitting color. In the case of PF-PXZ50 and PF-PZB50, their emission color was red-shifted, and the EL quantum efficiency of their LED devices was enhanced, with respect to the result for PF-CZ50, because of their extra heteroatoms (oxygen and sulfur respectively), which bend the molecules and strengthen their activities as electron donors.