A solution-processable triphenylamine-fluorene host for exciplex based white phosphorescent organic light-emitting diodes
30 Oct 2014-Journal of Materials Chemistry C (The Royal Society of Chemistry)-Vol. 2, Iss: 45, pp 9754-9759
TL;DR: In this article, a triphenylamine-fluorene oligomer with macro-spirocyclic structure was designed and prepared as a host for exciplex based white phosphorescent organic light-emitting diodes (white PhOLEDs), in which only iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2)picolinate (FIrpic) was employed as the dopant.
Abstract: A novel triphenylamine-fluorene oligomer with macro-spirocyclic structure was designed and prepared as a host for exciplex based white phosphorescent organic light-emitting diodes (white PhOLEDs), in which only iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2)picolinate (FIrpic) was employed as the dopant. The device exhibited a comparatively high performance with a maximum luminance and current efficiency of 14 213 cd m−2 and 22.6 cd A−1, respectively.
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TL;DR: In this paper, two self-host dendrimers with TADF nature were designed and synthesized for solution-processed non-oped fluorescent organic light-emitting diodes (OLEDs).
Abstract: Two self-host dendrimers TZ-Cz and TZ-3Cz with TADF nature were designed and synthesized for solution-processed nondoped fluorescent organic light-emitting diodes (OLEDs). The first and second generation carbazole dendrons were conveniently introduced into the TADF core through non-conjugated aliphatic chains, which favourably make the fluorescence of the core independent of the peripheral dendrons. Photophysical investigation showed that the prevalent concentration quenching effect of the TADF materials can be effectively restrained by the encapsulation of the emissive core. Moreover, the key role of the end-capping moieties on the molecular frontier orbital of the dendrimers was revealed by electrochemical testing and theoretical calculations. Solution-processed OLEDs featuring TZ-3Cz as the host-free emitter achieved a superior external quantum efficiency of 10.1%, which is almost ten times higher than that of the emissive core TZ (1.09%). Thus, a facile strategy to design a solution-process with highly emissive self-host TADF materials for nondoped OLEDs by flexible alkyl chain is demonstrated.
60 citations
TL;DR: In this paper, a series of novel triphenylamine-based small molecular hole transport materials (HTMs) are reported for solution processed organic light-emitting devices (OLEDs).
Abstract: A series of novel triphenylamine-based small molecular hole transport materials (HTMs) are reported for solution processed organic light-emitting devices (OLEDs). The character of this series of HTMs, denoted as TPD(BTPA)n (n = 1, 2, 4), is connecting the flexible moieties of butadiene bridged triphenylamine (BTPA) to N,N,N′,N′-tetraphenyl-[1,1′-biphenyl]-4,4′-diamine (TPD). The glass transition temperature and crystallization temperature (Tg and Tc) showed a proportional relationship with the number of BTPA moieties. The Tg value of TPD(BTPA)4 can be up to 125.5 °C, which is higher than most of the reported small molecular HTMs (Tg: 54–116 °C). The TPD(BTPA)4 spincoated film showed an outstanding thermal stability which remained amorphous even when annealed at 110 °C, for 48 h. This indicated that the breaking of the planar molecular structure with BTPA moieties can suppress intermolecular stacking. The solution processed OLEDs with 8-hydroxyquinoline aluminum (Alq3) as emission and electron transport layers showed high stability at high operation current (>400 mA cm−2). The OLED with TPD(BTPA)4 achieved a maximum current efficiency of 5.83 cd A−1 (at the operation current density > 400 mA cm−2), which is higher than the maximum current efficiency of most evaporation and solution processed OLEDs in identical structures.
38 citations
TL;DR: Observations indicated that developing a single polymer with the generated exciplex emission can be a novel and effective molecular design strategy toward highly stable and efficient white polymer light-emitting diodes.
Abstract: In this Article, we designed and synthesized a series of polyfluorene derivatives, which consist of the electron-rich 4,4′-(9-alkyl-carbazole-3,6-diyl)bis(N,N-diphenylaniline) (TPA-Cz) in the side chain and the electron-deficient dibenzothiophene-5,5-dioxide (SO) unit in the main chain. The resulting copolymer PF-T25 that did not comprise the SO unit exhibited blue light-emission with the Commission Internationale de L’Eclairage coordinates of (0.16, 0.10). However, by physically blending PF-T25 with a blue light-emitting SO-based oligomer, a novel low-energy emission correlated to exciplex emerged due to the appropriate energy level alignment of TPA-Cz and the SO-based oligomers, which showed extended exciton lifetime as confirmed by time-resolved photoluminescent spectroscopy. The low-energy emission was also identified in copolymers consisting of SO unit in the main chain, which can effectively compensate for the high-energy emission to produce binary white light-emission. Polymer light-emitting diodes...
36 citations
TL;DR: In this article, a high triplet energy electron transporting material 1,3,5-tris(diphenylphosphoryl)benzene (TPO) was successfully designed and synthesized to form an efficient exciplex with the commonly used hole transporting molecule tris(4-carbazoyl-9-ylphenyl)amine (TCTA).
30 citations
TL;DR: A novel bipolar oligomer (TPA-PO)3 was prepared as a host material for efficient blue phosphorescent organic light-emitting diodes (OLEDs) and achieved a maximum current efficiency and maximum luminance with a relatively low efficiency roll-off.
24 citations
References
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TL;DR: In this article, a host material doped with the phosphorescent dye PtOEP (PtOEP II) was used to achieve high energy transfer from both singlet and triplet states.
Abstract: The efficiency of electroluminescent organic light-emitting devices1,2 can be improved by the introduction3 of a fluorescent dye. Energy transfer from the host to the dye occurs via excitons, but only the singlet spin states induce fluorescent emission; these represent a small fraction (about 25%) of the total excited-state population (the remainder are triplet states). Phosphorescent dyes, however, offer a means of achieving improved light-emission efficiencies, as emission may result from both singlet and triplet states. Here we report high-efficiency (≳90%) energy transfer from both singlet and triplet states, in a host material doped with the phosphorescent dye 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II) (PtOEP). Our doped electroluminescent devices generate saturated red emission with peak external and internal quantum efficiencies of 4% and 23%, respectively. The luminescent efficiencies attainable with phosphorescent dyes may lead to new applications for organic materials. Moreover, our work establishes the utility of PtOEP as a probe of triplet behaviour and energy transfer in organic solid-state systems.
7,023 citations
TL;DR: Blue phosphorescence approaching the theoretical efficiency has also been achieved, which may overcome the final obstacle against the commercialization of full color display and white light sources from phosphorescent materials.
Abstract: Although organic light-emitting devices have been commercialized as flat panel displays since 1997, only singlet excitons were emitted. Full use of singlet and triplet excitons, electrophosphorescence, has attracted increasing attentions after the premier work made by Forrest, Thompson, and co-workers. In fact, red electrophosphorescent dye has already been used in sub-display of commercial mobile phones since 2003. Highly efficient green phosphorescent dye is now undergoing of commercialization. Very recently, blue phosphorescence approaching the theoretical efficiency has also been achieved, which may overcome the final obstacle against the commercialization of full color display and white light sources from phosphorescent materials. Combining light out-coupling structures with highly efficient phosphors (shown in the table-of-contents image), white emission with an efficiency matching that of fluorescent tubes (90 lm/W) has now been realized. It is possible to tune the color to the true white region by changing to a deep blue emitter and corresponding wide gap host and transporting material for the blue phosphor. In this article, recent progresses in red, green, blue, and white electrophosphorescent materials for OLEDs are reviewed, with special emphasis on blue electrophosphorescent materials.
1,240 citations
TL;DR: This critical review focuses on small-molecular organic host materials as triplet guest emitters in PhOLEDs, using typical hole and electron transport materials used in OLEDs.
Abstract: Phosphorescent organic light-emitting diodes (PhOLEDs) unfurl a bright future for the next generation of flat-panel displays and lighting sources due to their merit of high quantum efficiency compared with fluorescent OLEDs. This critical review focuses on small-molecular organic host materials as triplet guest emitters in PhOLEDs. At first, some typical hole and electron transport materials used in OLEDs are briefly introduced. Then the hole transport-type, electron transport-type, bipolar transport host materials and the pure-hydrocarbon compounds are comprehensively presented. The molecular design concept, molecular structures and physical properties such as triplet energy, HOMO/LUMO energy levels, thermal and morphological stabilities, and the applications of host materials in PhOLEDs are reviewed (152 references).
1,072 citations
627 citations
TL;DR: In this article, the authors reviewed the device structures adopted to achieve high performance solution processed organic light-emitting diodes, the development of solution processable small molecules, and the comparisons of the different nature of the films and devices fabricated by solution-process or vacuum deposition.
Abstract: Organic light-emitting diodes (OLEDs) based on vacuum deposited small molecules have undergone significant progress since the first efficient double-layered OLEDs were reported in 1987 by Tang and Van Slyke. Recently, solution processed small molecular OLEDs are also drawing more and more research attention, as such a technology combines advantages of the facile synthesis of small molecules and the low-cost solution process like polymers. The performance of OLEDs made by solution process is gradually catching up with their vacuum deposited counterparts. This feature article will review the device structures adopted to achieve high performance solution processed OLEDs, the development of solution processable small molecules, and the comparisons of the different nature of the films and devices fabricated by solution-process or by vacuum deposition. Finally, the prospects and remaining problems will be discussed.
565 citations