Readily synthesised arylamino fumaronitrile for non-doped red organic light-emitting diodes

Bright (maximum 10034 cd m(-2), 455 cd m(-2) at 20 mA cm(-2)) and efficient (maximum 2.4% at 4 mA cm(-2)) red (lambda(max)el 634-636 nm) organic light-emitting diodes employ arylamino-substituted fumaronitrile as the novel host emitter, which is readily prepared and easily purified.     

Quinoline-based aggregation-induced delayed fluorescence materials for highly efficient non-doped organic light-emitting diodes

Three new emitters,namely 10,10'-(quinoline-2,8-diyl)bis(10 H-phenoxazine)(Fene),10,10'-(quinoline-2,8-diyl)bis(10 H-phenothiazine)(Fens) and 10,10'-(quinoline-2,8-diyl)bis(9,9-dimethyl-9,10-dihydroacridine)(Yad),featuring quinoline as a new electron acceptor have been designed and conveniently synthesized.These emitters possessed small singlet-triplet splitting energy(ΔEst) and twisted structures,which not only endowed them show thermally activated delayed fluorescence(TADF)properties but also afforded a remarkable aggregation-induced emission(AIE) feature.Moreover,they also showed aggregation-induced delayed fluorescence(AIDF) property and good photoluminescence(PL) property,which are the ideal emitters for non-doped organic light-emitting diodes(OLEDs).Furthermore,high-performance non-doped OLEDs based on Fene,Fens and Yad were achieved,and excelle nt maximum external quantum efficiencies(EQE_(max)) of 14,9%,13.1% and 17,4%,respectively,were obtained.It was also found that all devices exhibited relatively low turn-on voltages ranging from 3.0 V to3.2 V probably due to their twisted conformation and the AIDF properties.These results demonstrated the quinoline-based emitters could have a promising application in non-doped OLEDs.     

New thermally stable aggregation-induced emission enhancement compounds for non-doped red organic light-emitting diodes

New thermally stable aggregation-induced emission enhancement compounds were synthesized. A non-doped red device showed a maximum brightness of 13,535 cd m(-2), a maximum current efficiency of 6.81 cd A(-1), a maximum power efficiency of 4.96 lm W(-1) and a low turn-on voltage of 4.3 V.     

New electron-donating segment to develop thermally activated delayed fluorescence emitters for efficient solution-processed non-doped organic light-emitting diodes

Thermally activated delayed fluorescent(TADF) materials capable of efficient solution-processed nondoped organic light-emitting diodes(OLEDs) are of important and practical significance for further development of OLEDs. In this work, a new electron-donating segment, 2,7-di(9 H-carbazol-9-yl)-9,9-dimethyl-9,10-dihydroacridine(2 Cz-DMAC), was designed to develop solution-processable non-doped TADF emitters. 2 Cz-DMAC can not only simultaneously increase the solubility of compounds and suppress har...     

Novel iridium complexes as high-efficiency yellow and red phosphorescent light emitters for organic light-emitting diodes

A series of novel biscyclometallated iridium complexes based on spirobifluorene ligands and acetyl acetonate (acac) ancillary ligands have been synthesized and characterized. Their electrochemical properties were investigated by cyclic voltammetry (CV). HOMO, LUMO, and energy band gaps of all the complexes were calculated by the combination of UV-vis absorption spectra and CV results. TGA and DSC results indicated their excellent thermal stability and amorphous structure. All the iridium complexes were fabricated into organic light-emitting devices with the device configuration of ITO/PEDOT:PSS (50 nm)/PVK (50 wt %):PBD (40 wt %):Ir complex (10 wt %) (45 nm)/TPBI (40 nm)/LiF (0.5 nm)/Ca (20 nm)/Ag (150 nm). Yellow to red light emission has been achieved from the iridium complexes guest materials. Complex C1 (yellow light emission) achieved an efficiency of 36.4 cd/A (10.1%) at 198 cd/m² and complex C4 (red light emission) reached external quantum efficiency of 4.6%. The slight decrease of external quantum efficiency at high current density revealed that the triplet-triplet (T₁-T₁) annihilation was effectively suppressed by the new developed complexes.     

Using fluorene to lock electronically active moieties in thermally activated delayed fluorescence emitters for high-performance non-doped organic light-emitting diodes with suppressed roll-off

Thermally activated delayed fluorescence (TADF) emitters with aggregation-induced emission (AIE) features are hot candidates for non-doped organic light-emitting diodes (OLEDs), as they are highly emissive in solid states upon photoexcitation. Nevertheless, not every AIE-TADF emitter in the past had guaranteed decent efficiencies in non-doped devices, indicating that the AIE character alone does not necessarily afford ideal non-doped TADF emitters. As intermolecular electron-exchange interaction that involves long-lived triplet excitons plays a dominant role in the whole quenching process of TADF, we anticipate that it is the main reason for the different electroluminescence performances of AIE-TADF emitters. Therefore, in this work, we designed two TADF emitters SPBP-DPAC and SPBP-SPAC by modifying a reported less successful emitter BP-DPAC with extra fluorenes to increase intermolecular distances and attenuate this electron-exchange interaction. With the fluorene lock as steric hindrance, SPBP-DPAC and SPBP-SPAC exhibit significantly higher exciton utilization in non-doped films due to the suppressed concentration quenching. The non-doped OLEDs based on SPBP-DPAC and SPBP-SPAC show an excellent maximum external quantum efficiency (EQE) of 22.8% and 21.3% respectively, and what''s even more promising is that ignorable roll-offs at practical brightness (e.g., 1000 and 5000 cd m⁻²) were realized. These results reveal that locking the phenyl rings as steric hindrance can not only enhance the molecular rigidity, but also cause immediate relief of concentration quenching, and result in significant performance improvement under non-doped conditions. Our approach proposes a feasible molecular modification strategy for AIE-TADF emitters, potentially increasing their applicability in OLEDs.

Two TADF emitters were developed by modifying a reported less successful emitter BP-DPAC with fluorene to suppress concentration quenching. Their non-doped OLEDs displayed excellent EQEs of 22.8% and 21.3% with well-suppressed roll-off.     

Carbazole compounds as host materials for triplet emitters in organic light-emitting diodes: polymer hosts for high-efficiency light-emitting diodes

A carbazole homopolymer and carbazole copolymers based on 9,9'-dialkyl-[3,3']-bicarbazolyl, 2,5-diphenyl-[1,3,4]-oxadiazole and 9,9-bis(4-[3,7-dimethyloctyloxy]phenyl)fluorene were synthesized and their electrical and photophysical properties were characterized with respect to their application as host in phosphorescent polymer light-emitting diodes. It is shown that the triplet energy of a polymer depends on the specific connections between its building blocks. Without changing the composition of the polymer, its triplet energy can be increased from 2.3 to 2.6 eV by changing the way in which the different building blocks are coupled together. For poly(9-vinylcarbazole) (PVK), a carbazole polymer often used as host for high-energy triplet emitters in polymer light-emitting diodes, a large hole-injection barrier of about 1 eV exists due to the low-lying HOMO level of PVK. For all carbazole polymers presented here, the HOMO levels are much closer to the Fermi level of a commonly used anode such as ITO and/or a commonly used hole-injection layer such as PEDOT:PSS. This makes high current densities and consequently high luminance levels possible at moderate applied voltages in polymer light-emitting diodes. A double-layer polymer light-emitting diode is constructed comprising a PEDOT:PSS layer as hole-injection layer and a carbazole-oxadiazole copolymer doped with a green triplet emitter as emissive layer that shows an efficacy of 23 cd/A independent of current density and light output.     

Alkoxy encapsulation of carbazole-based thermally activated delayed fluorescent dendrimers for highly efficient solution-processed organic light-emitting diodes

Two n-butoxy-encapsulated dendritic thermally activated delayed fluorescent(TADF) emitters(namely O-D1 and O-D2) with the first-/second-generation carbazoledendrons are designed and synthesized via C—N coupling between carbazoledendrons and 2,4,6-tris(4-bromophenyl)-1,3,5-triazine core.It is found that,compa red with the commo nly-used tert-butyl groups,the use of n-butoxy encapsulation groups can lead to smallersinglet-triplet energy gap for the dendrimers,producing stronger TADF effect together with faster reverse intersystem crossing process.Solution-processed TADF organic light-emitting diodes(OLEDs) utilizingalkoxy-encapsulated dendrimers O-D1 and O-D2 as emitters exhibitstate-of-the-art device efficiency withthe maximum external quantum efficiency up to 16.8% and 20.6%,respectively,which are ～1.6 and～2.0 times that of the tert-butyl-encapsulated counterparts.These results suggest that alkoxy encapsulation of the carbazole-based TADF dendrimers can be a promising approach for developing highly efficient emitters for solution-processed OLEDs.     

掺杂发光有机电致磷光器件工作原理及主体材料

本文总结了基于掺杂发光的有机电致磷光器件(PhOLED)中磷光材料被激发的途径及机理,并指出不同主体材料对器件性能的不同影响.全面介绍了小分子主体材料研究的新进展及它们在PhOLEDs器件中的运用.比较和讨论了基于各种不同性质主体材料的器件性能,指出主体材料选择策略.同时讨论了各类主体材料的分子结构、热稳定性、三线态能级、载流子迁移率及HOMO/LUMO能级之间的关系,揭示了上述特性对器件性能影响.     

Recent progress in thermally activated delayed fluorescence emitters for nondoped organic light-emitting diodes

Nondoped organic light-emitting diodes (OLEDs) have drawn immense attention due to their merits of process simplicity, reduced fabrication cost, etc. To realize high-performance nondoped OLEDs, all electrogenerated excitons should be fully utilized. The thermally activated delayed fluorescence (TADF) mechanism can theoretically realize 100% internal quantum efficiency (IQE) through an effective upconversion process from nonradiative triplet excitons to radiative singlet ones. Nevertheless, exciton quenching, especially related to triplet excitons, is generally very serious in TADF-based nondoped OLEDs, significantly hindering the pace of development. Enormous efforts have been devoted to alleviating the annoying exciton quenching process, and a number of TADF materials for highly efficient nondoped devices have been reported. In this review, we mainly discuss the mechanism, exciton leaking channels, and reported molecular design strategies of TADF emitters for nondoped devices. We further classify their molecular structures depending on the functional A groups and offer an outlook on their future prospects. It is anticipated that this review can entice researchers to recognize the importance of TADF-based nondoped OLEDs and provide a possible guide for their future development.

The mechanism, exciton leaking channels, and reported molecular design strategies of TADF emitters for high-performance nondoped OLEDs are summarized. Their molecular structures depending on the functional A groups are further classified.     

Molecular hosts for triplet emitters in organic light-emitting diodes and the corresponding working principle

This paper summarizes the mechanism and routes for excitation of triplet emitters in dopant emission based phosphorescent organic light-emitting diodes (PhOLEDs), providing a comprehensive overview of recent progress in molecular hosts for triplet emitters in PhOLEDs. Particularly, based on the nature of different hosts, e.g., hole transporting, electron transporting or bipolar materials, in which the dopant emitters can be hosted to generate phosphorescence, the respective device performances are summarized and compared. Highlights are given to the relationships among the molecular structure, thermal stability, triplet energy, carrier mobility, molecular orbital energy level and their corresponding device performances.     

A single-molecule excimer-emitting compound for highly efficient fluorescent organic light-emitting devices

A pyrene-containing single-molecule excimer-emitting compound, 1,8-bis(pyren-2-yl)naphthalene (BPyN), was synthesized. With BPyN as a host emitter, C545T-based green OLEDs were fabricated, exhibiting high efficiencies of 22 lm W(-1), 22 cd A(-1) and 6.2% external quantum efficiency (EQE) at 100 cd m(-2), and 19 lm W(-1), 22 cd A(-1) and 6.2% EQE at 1000 cd m(-2).     

Dendritic macromolecules for organic light-emitting diodes

The general concepts, design criteria, and physical parameters, such as component placement and electroluminescence, that relate to the construction of OLED devices are described, followed by a discussion of the current literature detailing the use of branched and dendritic materials as the key electroluminescent elements of single- and multi-layered fabricated devices. Their configurations, efficiencies, emission intensities, and molecular structural implications are also delineated and discussed. This critical review should appeal to researchers in the synthetic, material, and physical sciences (122 references).     

Phosphorescent dyes for organic light-emitting diodes

This article presents general concepts that have guided important developments in our recent research progress regarding room-temperature phosphorescent dyes and their potential applications. We first elaborate the theoretical background for emissive metal complexes and the strategic design of the chelating C-linked 2-pyridylazolate ligands, followed by their feasibility in functionalization and modification in an aim to fine-tune the chemical and photophysical properties. Subsequently, incorporation of 2-pyridylazolate chromophores is illustrated in the synthesis of the highly emissive, charge-neutral Os, Ru, Ir, and Pt complexes. Insights into their photophysical properties are gained from spectroscopy, relaxation dynamics, and theoretical approaches, from which the lowest-lying excited states, competitive radiative decay, and radiationless processes are then analyzed in detail. In view of applications, their potentials for OLEDs have been evaluated. The results, in combination with the fundamental basis, give a conceptual design contributed to the future advances in the field of OLEDs.     

Novel phosphorescent neutral iridium(III) complex with the steric hindrance for highly efficient red organic light-emitting diodes

A novel and highly efficient thiophenquinolone-based red iridium(III) complex bearing a bulky fluorophenyl moiety is designed and synthesized. The complex shows intensive red phosphorescence (596 nm with shoulder at 642 nm), high photoluminescence efficiency (0.62) and broad full width at half maximum (81 nm). The bulky fluorophenyl moiety introduced into the complex could improve the efficiency of electroluminescence with the maximum current efficiency, power efficiency and the external quantum efficiency up to 29.0 cd/A, 30.4 lm/W and 17.6% due to the effective steric hindrance in solid states.     

Solution-processable single-material molecular emitters for organic light-emitting devices

This tutorial review presents some recent developments in the design, synthesis and implementation of organic solution-processable molecular fluorophores for non-doped electroluminescent [corrected] devices. After a brief presentation of the basic principles of operation and main characteristics of electroluminescent devices, some examples of active emitters representative of the main classes of non-doped molecular electrofluorophores will be discussed. Emphasis is placed on the relationships between the molecular structure and the electronic properties of molecular emitters, in which high photoluminescence efficiency, synthetic accessibility and processability are combined by design with additional functions such as hole and/or electron injection and transport.     

Productive harvesting of triplet excitons in anthracene-based emitters toward high-performance deep-blue nondoped organic light-emitting diodes

Developing efficient deep-blue non-doped organic light-emitting diodes (OLEDs) is of great significance in practical applications. Here, two highly efficient asymmetric anthracene-based fluorescent emitters, 1-phenyl-2-(4-(10-(4-(2-phenyl-1H-phenanthro[9,10-d]imidazole-1-yl)phenyl)anthracen-9-yl)phenyl)-1H-phenanthro [9,10-d]imidazole (PPI-An-NPPI) and 1-phenyl-2-(4-(10-(4-(2,4,5-triphenyl-1H-imidazole-1-yl)phenyl) anthracen-9-yl)phenyl)-1H-phenanthro[9,10-d]imidazole (PPI-An-NPIM), have been designed and synthesized by introducing large steric hindrance imidazole moieties to regulate molecular excited states and photophysical properties. Experimental data show that they have high photoluminescence efficiencies, good thermal stabilities, and suitable energy levels for carrier injection. Theoretical calculations present that their high-lying excited states exhibit dominant locally excited-state characteristics with enhancing oscillator strength compared with anthracene core. The calculated transition dipole moments data show that two molecules are preferentially oriented along the horizontal direction. In addition, some hot exciton mechanism-like channels are also observed and confirmed, which are beneficial for the productive triplet-singlet exciton conversion. The non-doped OLED using PPI-An-NPPI as the emitting layer achieves a maximum external quantum efficiency (EQE_max) of 7.75% and Commission Internationale de L’Eclairage (CIE) coordinates of (0.15, 0.11), whereas PPI-An-NPIM gives a better color purity of CIE (0.14, 10) with an EQE_max of 7.48%. Moreover, all devices exhibit an insignificant efficiency roll-off at high luminescence and still yield an EQE of 7.61% and 7.14% at 1,000 cd/m². This work provides an interesting insight into developing efficient deep-blue fluorescent emitters for high-performance non-doped OLEDs.     

Fused-seven-ring anthracene derivative with two sulfur bridges for high performance red organic light-emitting diodes

A fused-seven-ring anthracene derivative with two sulfur bridges, benzobisthioxanthene (BTA), was synthesized, facilely. OLEDs employing BTA as the emitter exhibited bright (maximum 40,752 cd m(-2)) and efficient red emission (CIE, x = 0.64, y = 0.36) with a luminous efficiency of 4.4 cd A(-1).     

A solution-processable phosphonate functionalized deep-blue fluorescent emitter for efficient single-layer small molecule organic light-emitting diodes

Based on a p-type scaffold, a novel solution-processable phosphonate functionalized deep-blue fluorescent emitter has been designed and synthesized. The corresponding non-doped single-layer SMOLED shows a peak current efficiency of 0.76 cd A(-1) with CIE coordinates of (0.15, 0.09), which is about three orders of magnitude higher than that of the prototype with tert-butyl substituents.     

High efficiency mer-iridium complexes for organic light-emitting diodes

We have developed a new process at high vacuum (5 x 10(-5) Torr) and high temperature (300 degrees C) to produce meridional iridium complexes from the dimer; interestingly, mer-Ir(m-ppy)(3) overthrows the concept of poor efficiency and shows excellent efficiency which is almost equal to that of fac-Ir(ppy)(3), fac-Ir(m-ppy)(3) and (ppy)(2)Ir(acac).