Maximum External Quantum Efficiency Research Articles

Superbly Efficient and Stable Ultrapure Blue Phosphorescent Organic Light-Emitting Diodes with Tetradentate Pt(II) Complex with Vibration Suppression Effect.

Blue phosphorescent organic light-emitting diodes (PHOLEDs) are on the brink of commercialization for decades. However, the external quantum efficiency (EQE) and operational lifetime of PHOLEDs are not yet reached industrial standards. Here, a novel tetradentate Pt(II) emitter with a spirofluorene onto the carbazole unit that minimizes the vibration modes, corresponding to the structural relaxation during the de-excitation, called the vibration suppression effect is reported. This modification reduces the intensity of the second peak in the spectrum and Shockley-Read-Hall recombination by blocking direct hole injection into the emitter while enhancing Förster resonance energy transfer, resulting in 451h of LT50 (the time until a 50% decrease in initial luminance at 1000cdm-2) and 25.1% of the maximum EQE (EQEmax). Thanks to the vibration suppression effect, an extremely narrow full width at half a maximum of 22nm is obtained. In phosphor-sensitized thermally activated delayed fluorescent OLED, ultra-pure blue emission with Commission internationale de l'Eclairage (CIE) coordinates of (0.136, 0.096) is obtained with 28.1% of EQEmax. Furthermore, 50.3% of the EQEmax and 589h of LT70 are simultaneously recorded with the two-stack tandem PHOLED, which is the highest EQEmax among 2-tandem and bottom-emission PHOLEDs with CIEy<0.15.

Effect of magnesium doping on NiO hole injection layer in quantum dot light-emitting diodes

Abstract This study reports on the fabrication of quantum dot light-emitting diodes (QLEDs) with an ITO/Ni1−x Mg x O/SAM/TFB/QDs/ZnMgO/Al structure and investigates the effects of various Mg doping concentrations in NiO on device performance. By doping Mg into the inorganic hole-injection layer NiO (Ni1−x Mg x O), we improved the band alignment with the hole-injection layer through band tuning, which enhanced charge balance. Optimal Mg doping ratios, particularly a Ni0.9Mg0.1O composition, have demonstrated superior device functionality, underscoring the need for fine-tuned doping levels. Further enhancements were achieved through surface treatments of Ni0.9Mg0.1O with UV-Ozone (UVO) and thermal annealing (TA) of the ZnMgO electron transport layer. Consequently, by optimizing Mg-doped NiO in QLED devices, we achieved a maximum external quantum efficiency of 8.38 %, a brightness of 66,677 cd/m2, and a current efficiency of 35.31 cd/A, indicating improved performance. The integration of Mg-doped NiO into the QLED structure resulted in a device with superior charge balance and overall performance, which is a promising direction for future QLED display technologies.

Efficient thermally activated delayed fluorescence materials from symmetric anthraquinone derivatives for high-performance red OLEDs

Constructing efficient red thermally activated delayed-fluorescence (TADF) materials for high-performance organic light-emitting diodes (OLEDs) remains challenging due to the formidable barrier of energy gap law. In this work, a design strategy of connecting two donor units to the adjacent positions of electron acceptor is proposed for creating red luminescent materials, and four Y-shaped TADF molecules consisting of strong electron-withdrawing anthraquinone (AQ) acceptor and triphenylamine or acridine-based donors are designed and synthesized. They exhibit strong red emissions (604−618 nm) in toluene solutions and orange/red emissions (566−608 nm) with good photoluminescence quantum yields (43−68%) in doped films, and enjoy small singlet-triplet energy gaps (0.02−0.10 eV) and fast reverse intersystem crossing processes (1.5–7.3 × 105 s−1), which are attributed to the unique Y-shape structure. A maximum external quantum efficiency of 19.5% with an electroluminescence peak at 616 nm is achieved for AQ-PTPA-based red doped device, representing the highest level for red TADF-OLEDs based on AQ acceptor in the literature. This work can provide guidance for the design of efficient red delayed-fluorescence molecules for the application in OLEDs.

Rational design of narrowband deep blue MR-TADF dendrimers for high performance solution-processed all fluorescence white OLEDs

Developing solution-processable deep-blue multiple resonances thermally activated delayed fluorescence (MR-TADF) is a formidable challenge. Here, we using a convergent synthesis process successfully developed a series of MR-TADF dendrimers based on C=O/N resonant core (QAO). The alkyl chain alternate-linked functional dendrons not only ensure the narrow-band deep-blue emission but also enable the dendrimers with aggregation-induced emission enhancement (AIEE) properties, which efficiently mitigate the aggregation-induced exciton quenching (ACQ) and obnoxious spectral redshift broadening effect. Notably, the solution-processed deep blue MR-TADF OLEDs achieved a maximum external quantum efficiency (EQE) of 13.5 % and CIE of (0.15, 0.12) with an electroluminescence peak below 450 nm. Further using such dendrimer as a sensitizer for white OLEDs resulted in an optimized high EQE of 18.9 % and a high color-rendering index (CIR) of 81.1 for two and three optical components of white emissions, which are among the highest values of previously reported solution-processed all-fluorescence white OLEDs. This is the first attempt to construct white OLED based on an MR-TADF emitter and the satisfactory results indicate that the flexible dendron engineering strategy can effectively develop high-performance narrow band deep-blue MR-TADF for wide-color gamut display and high CIR white OLEDs.

Narrowband Emission in Pt(II) Complexes via Ligand Engineering for Blue Phosphorescent Organic Light‐Emitting Diodes

AbstractIn this study, three stable tetradentate Pt(II) complexes are synthesized and characterized, namely, Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu, tailored for blue phosphorescent organic light‐emitting diodes to realize high‐efficiency and narrowband emissions via ligand engineering. Biphenyl (Pt‐biPh) or tert‐butyl‐modified biphenyl (Pt‐biPh5tBu and Pt‐biPh4tBu) is introduced into the carbene unit of the ligand to control the intermolecular interactions between the Pt(II) phosphors. Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu exhibit high photoluminescence quantum yields of 74%, 84%, and 92% with exciton lifetimes of 2.2, 2.3, and 2.5 µs, respectively, demonstrating rapid and efficient light emission. Furthermore, Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu show maximum external quantum efficiency (EQE) values of 18.1%, 19.0%, and 21.8%, respectively. Pt‐biPh5tBu and Pt‐biPh4tBu exhibit narrowband emission with a full width at half maximum of 21 nm owing to the small vibrational emission because of their sterically hindered and bulky ligand structures. Moreover, phosphor‐sensitized thermally activated delayed fluorescence devices employing a Pt‐biPh4tBu sensitizer achieve a high EQE of 28.6%. In particular, Pt‐biPh4tBu performs better than the state‐of‐the‐art phosphor as the sensitizer of the blue phosphor‐sensitized thermally activated delayed fluorescence devices in terms of the EQE.

C60 Functionalized Single‐Walled Carbon Nanotube‐based Phototransistor for Efficient Detection of Visible Light Under Appropriate Gate Electrostatics

AbstractThe current study concerns highly reliable visible light sensing by C60 fullerene functionalized single‐walled carbon nanotube (SWCNT) based phototransistor. The absorbance of visible light (532 nm) increases significantly due to the formation of an interlink between the SWCNT network and C60 clusters. Photogenerated excess electrons in SWCNT are trapped by the C60 clusters and increase the effective hole concentrations in the SWCNT channel, which eventually improves the photoconductive gain. C60‐SWCNT channel is further integrated into the back gated field effect transistor (FET) structure in which 90 nm SiO2 dielectric thickness is used. The responsivity toward visible light is further enlarged with appropriate negative gate electrostatic. In order to ensure the morphological and structural behavior of C60‐SWCNT, various microscopic and spectroscopic characterizations are performed. The C60‐SWCNT phototransistor exhibits responsivity of 1.219 A W−1 at Vgs = – 21 V. The detectivity and rise/fall time of C60‐SWCNT came around to be 2.34 × 1010 Jones, 86.42 ms/3.35 ms at the same Vgs. The maximum external quantum efficiency (EQE) of the C60‐SWCNT phototransistor is very high, ≈274%. In the overall study, a comprehensive discussion is introduced on the effect of variable gate potential on the performance of the C60‐SWCNT phototransistor.

Dipole-assisted hole injection for efficient blue quantum dot light-emitting diodes

Quantum dot light-emitting diodes (QLEDs) present commercial potential and application prospects in both lighting and display technologies. Blue quantum dots (QDs) possess a substantial bandgap and a profound valence band. The significant potential barrier between blue quantum dots and the hole transport layer leads to an imbalance in charge transfer, thereby adversely impacting the device performance. Self-assembled monolayers are attractive for carrier transport. Here, a dynamic self-assembly method is introduced, doping [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) into Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) to form electric dipoles at interfaces, realizing better energy level alignment and hole injection rate. The maximum external quantum efficiency rises from 8.77% to 17.26% with 2PACz: PEDOT:PSS strategy, representing a twofold enhancement. This result demonstrates that small molecules undergo dynamic self-assembled bilateral motions during crystallization process, aligning energy levels and passivating interfacial trap states, thereby endowing blue QLEDs with high brightness and high efficiency. This work offers a viable pathway for broader applications of blue QLEDs.

Construction of Concentration Quenching‐Resistant Multi‐Resonance TADF Emitters via Positional Isomerization for OLEDs

AbstractMultiple resonance thermally activated delayed fluorescence (MR‐TADF) emitters are promising for high‐definition organic light‐emitting diodes (OLEDs) due to their high exciton utilization and color purity. However, strong interchromophore interactions cause most MR‐TADF emitters with planar structures to aggregate at high doping concentrations, leading to degraded efficiencies. Herein, using benzenesulfonyl‐functionalized dibenzothiophene sulfoximine with steric effects, three MR‐TADF emitters (2SBN, 3SBN, and 4SBN) are synthesized by coupling the classic DtBuCzB skeleton at different sites. Three emitters exhibit green or blue‐green emission with full width at half maximum (FWHM) values less than 29 nm and photoluminescence quantum yields exceeding 90%. OLEDs based on 2SBN, 3SBN, and 4SBN achieve high maximum external quantum efficiency (EQEmax) values of 30.1%, 27%, and 33.8%, respectively, at a 5 wt.% doping concentration. Notably, due to the distorted conformation of 4SBN and suppressed intermolecular interaction, the OLED remains high EQEmax of 28.9% at a doping concentration of 20 wt.%. These results demonstrate the feasibility of molecular design to modulate spatial conformations via positional isomerism to develop MR‐TADF emitters with reduced concentration quenching.

A Self‐Assembling Molecule for Improving the Mobility in PEDOT:PSS Hole Transport Layer for Efficient Perovskite Light‐Emitting Diodes

AbstractPoly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), the most widely used hole injection layer (HIL) for perovskite light‐emitting diodes (PeLEDs), has a large hole injection energy barrier and easy charge separation at PEDOT:PSS/perovskite layer. Here, a self‐assembling molecule (SAM) called (2‐(3,6‐dimethoxy‐9H‐carbazol‐9‐yl)ethyl) phosphonic acid (MeO‐2PACz) is introduced as an interlayer between PEDOT:PSS and perovskite to overcome the limitations of PEDOT:PSS HIL. The MeO‐2PACz interlayer facilitated hole injection due to the reduced hole injection energy barrier and the improved hole mobility, enhanced photoluminescence (PL) due to the prevented charge transfer from perovskite into PEDOT:PSS, and reduced interface trap density due to the passivation of methoxy and carbazole group toward perovskite. As a result, PeLEDs with MeO‐2PACz interlayer has greatly enhanced maximum luminance (Lmax = 17,310 cd m−2) and reduced leakage current, resulting in higher maximum external quantum efficiency (EQEmax = 21.50%) compared to pristine Control device (EQEmax of 4.82%).

Modulating Charge‐Transfer Excited States of Multiple Resonance Emitters via Intramolecular Covalent Bond Locking

AbstractAdvanced multiple resonance thermally activated delayed fluorescence (MR‐TADF) emitters with high efficiency and color purity have emerged as a research focus in the development of ultra‐high‐definition displays. Herein, we disclose an approach to modulate the charge‐transfer excited states of MR emitters via intramolecular covalent bond locking. This strategy can promote the evolution of strong intramolecular charge‐transfer (ICT) states into weak ICT states, ultimately narrowing the full‐width at half‐maximum (FWHM) of emitters. To modulate the ICT intensity, two octagonal rings are introduced to yield molecule m‐DCzDAz‐BNCz. Compounds m‐CzDAz‐BNCz and m‐DCzDAz‐BNCz exhibit bright light‐green and green fluorescence in toluene, with emission maxima of 504 and 513 nm, and FWHMs of 28 and 34 nm, respectively. Sensitized organic light‐emitting diodes (OLEDs) employing emitters m‐CzDAz‐BNCz and m‐DCzDAz‐BNCz exhibit green emission with peaks of 508 and 520 nm, Commission Internationale de L'Eclairage (CIE) coordinates of (0.12, 0.65) and (0.19, 0.69), and maximum external quantum efficiencies (EQEs) of 30.2 % and 32.6 %, respectively.

Achieving deep red to near-infrared emission in dinuclear platinum (II) complexes with the donor-π-acceptor-type cyclometalated ligand

A novel deep red-emitting dinuclear platinum (II) complex, (TPA2niq)2Pt2(C8OXT)2, featuring a donor-π-acceptor (D-π-A) type ligand, was synthesized and characterized. Here, TPA2niq represents the 4-(tert-butyl)-N-(4-(tert-butyl)phenyl)-N-(4-(6-(isoquinolin-1-yl)naphthalen-2-yl)phenyl)aniline unit, while C8OXT was the abbreviation for the bridging ligand 5-(4-octyloxyphenyl)-1,3,4-oxadiazole-2-thiol. Its photophysical, electrochemical, and electroluminescent characteristics were primarily studied. It was found that (TPA2niq)2Pt2(C8OXT)2 exhibited a saturated deep red emission with a peak at 686 nm in dichloromethane. Furthermore, the (TPA2niq)2Pt2(C8OXT)2-doped polymer electroluminescent devices (PLEDs), fabricated through a solution process, exhibited outstanding electroluminescence (EL) properties, with an emission peak at 684 nm, a maximum external quantum efficiency (EQE) of 3.78%, and a maximum radiant emittance of 4478 mW/Sr/m2. By incorporating the D-π-A type ligand into the dinuclear platinum (II) complex, the PLEDs achieved efficient deep red emission.

Highly Efficient, Low-Roll-Off, Red, "Hot Exciton" Organic Light-Emitting Diodes Promoted by the Heavy-Atom Effect of Selenium.

It is important to attain red hot exciton materials applicable in highly efficient organic light-emitting diodes with low-efficiency roll-off, but their development is restricted by the energy gap law. Herein, the sulfur atom was replaced by a heavier selenium atom based on benzothiadiazole to obtain a new benzoselenadiazole acceptor with a heavy atom effect and stronger electron-withdrawing ability. Two novel red hot exciton materials named BSe-DtBuTPA and BSe-2PhCz-d24 were designed and synthesized based on the benzoselenadiazole unit. Benefiting from the heavy-atom effect of selenium and the small ΔES1T2, both emitters exhibited ultrafast high-lying reverse intersystem crossing rate constants (7.00 × 107 and 1.17 × 107 s-1). The devices based on BSe-DtBuTPA and BSe-2PhCz-d24 demonstrated maximum external quantum efficiencies of 4.81 and 7.15% with emission peaks at 653 and 596 nm, respectively. The device based on deep-red BSe-DtBuTPA exhibited negligible efficiency roll-off of 18.5% at 10000 cd/m2.

Efficient solution-processed near-infrared organic light-emitting diodes with a binary-mixed electron transport layer

A binary-mixed electron transport layer (ETL) has been reported for constructing solution-processable near-infrared organic light-emitting diodes (NIR OLEDs). Relative to the single-component ETL, the binary-mixed ETL composed of PDINN:TPBi can enhance the carrier transport capacity, reduce device impedance, and weaken fluorescence quenching of the emitting layer. By carefully selecting an appropriate luminescent material Y5 (a nonfullerene electron acceptor in organic solar cells) and precisely fine-tuning the molecular aggregation in active layer using a mixed solvent, the morphology is optimized and luminescence performance is enhanced, resulting in efficient NIR OLEDs with an emission peak at 890 nm. The experiment showcases a Y5-based near-infrared OLED with a maximum radiance of 34.9 W sr-1 m-2 and a maximum external quantum efficiency of 0.50%, which is among the highest values reported for non-doped fluorescent NIR OLEDs with an emission peak over 850 nm.

Boron cluster-based TADF emitter via through-space charge transfer enabling efficient orange-red electroluminescence

Thermally activated delayed fluorescence (TADF) materials driven by a through-space charge transfer (TSCT) mechanism have garnered wide interest. However, access of TSCT-TADF molecules with long-wavelength emission remains a formidable challenge. In this study, we introduce a novel V-type D-A-D-A' emitter, Trz-mCzCbCz, by using a carborane scaffold. This design strategically incorporates carbazole (Cz) and 2,4,6-triphenyl-1,3,5-triazine (Trz) as donor and acceptor moieties, respectively. Theoretical calculations alongside experimental validations affirm the typical TSCT-TADF characteristics of this luminogen. Owing to the unique structural and electronic attributes of carboranes, Trz-mCzCbCz exhibits an orange-red emission, markedly diverging from the traditional blue-to-green emissions observed in classical Cz and Trz-based TADF molecules. Moreover, bright emission in aggregates was observed for Trz-mCzCbCz with absolute photoluminescence quantum yield (PLQY) of up to 88.8%. As such, we have successfully fabricated five organic light-emitting diodes (OLEDs) by utilizing Trz-mCzCbCz as the emitting layer. It is important to note that both the reverse intersystem crossing process and the TADF properties are profoundly influenced by host materials. The fabricated OLED devices reached a maximum external quantum efficiency (EQE) of 12.7%, with an emission peak at 592 nm. This represents the highest recorded efficiency for TSCT-TADF OLEDs employing carborane derivatives as emitting layers.

Design and performance of sulfur and selenium-substituted triarylboron D3-A TADF emitters for OLED applications

This study presents the design, synthesis, and comprehensive theoretical and photophysical analysis of two new D3-A type thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diode (OLED) applications. Utilizing a triarylboron core as the electron-accepting group and phenothiazine (PTZ) or phenoselenazine (PSZ) as electron-donating units, the molecules BTP-S and BTP-Se were developed. The D3-A structure supports the separation of frontier molecular orbitals (FMOs), leading to minimized singlet-triplet energy gaps (ΔEST), which are crucial for the TADF mechanism. Density functional theory (DFT) calculations presented that BTP-S and BTP-Se exhibit band gaps (Eg) of 2.52 and 3.23 eV, respectively, with BTP-S showing an ΔEST value as low as 0.007 eV for the S1-T1 transition at the lowest energy conformation. Photophysical studies revealed high photoluminescence quantum yields (PLQYs) for both compounds, with BTP-S achieving up to 85 % in mCP films and BTP-Se up to 59 %. In vacuum-processed OLEDs, BTP-S achieved a maximum external quantum efficiency (EQE) of 25.3 %, a current efficiency (ηc) of 195.8 cd/A, and a maximum luminance (Lmax) of 17356 cd/m2, while BTP-Se reached an EQE of 7.5 %, an ηc of 132.19 cd/A, and an Lmax of 16826 cd/m2 likely limited by the contributions of a folded-donor conformer enabled by the Se substitution. These findings underscore the impact of donor unit selection and conformation on the TADF characteristics, and provide valuable insights for designing high-performance OLED materials.

Gold Coordination-Accelerated Multi-Resonance TADF Emission for Efficient Solution-Processible Ultrapure Deep-Blue OLEDs.

Multi-resonance (MR) type emitters have emerged as highly promising candidates for high-resolution organic light-emitting diodes (OLEDs). However, thermally activated delayed fluorescence (TADF) emissions with simultaneous short excited state lifetimes and ultrapure blue color (a CIEy close to 0.046 and an emission peak > 440 nm) have rarely been obtained for MR emitters. Herein, we report a design of dual gold-coordinated MR molecules to achieve efficient and short-lived ultrapure blue TADF emission. The dinuclear Au(I) complex, namely iPrAuBN, shows a narrowband deep-blue emission with a peak maximum of 448 nm and a full width at half maximum (FWHM) of 29 nm in doped film. The coordination with two Au atoms significantly shortens the delayed fluorescence lifetime to 7.8 μs in comparing with 60.6 μs for the organic analogue. Solution-processed OLED doped with iPrAuBN demonstrates an ultrapure blue electroluminescence with a peak maximum of 442 nm, a FWHM of 19 nm, Commission International de l'Éclairage (CIE) coordinates of (0.154, 0.036), and a maximum external quantum efficiency of 14.8%.

Robust Sandwich-Structured Thermally Activated Delayed Fluorescence Molecules Utilizing 11,12-Dihydroindolo[2,3-a]carbazole as Bridge.

Constructing folded molecular structures is emerging as a promising strategy to develop efficient thermally activated delayed fluorescence (TADF) materials. Most folded TADF materials have V-shaped configurations formed by donors and acceptors linked on carbazole or fluorene bridges. In this work, a facile molecular design strategy is proposed for exploring sandwich-structured molecules, and a series of novel and robust TADF materials with regular U-shaped sandwich conformations are constructed by using 11,12-dihydroindolo[2,3-a]carbazole as bridge, xanthone as acceptor, and dibenzothiophene, dibenzofuran, 9-phenylcarbazole and indolo[3,2,1-JK]carbazole as donors. They hold outstanding thermal stability with ultrahigh decomposition temperatures (556-563 oC), and exhibit fast delayed fluorescence and excellent photoluminescence quantum efficiencies (86%-97%). The regular and close stacking of acceptor and donors results in rigidified molecular structures with efficient through-space interaction, which are conducive to suppressing intramolecular motion and reducing reorganized excited-state energy. The organic light-emitting diodes (OLEDs) using them as emitters exhibit excellent electroluminescence performances, with maximum external quantum efficiencies of up to 30.6%, which is a leading value for the OLEDs based on folded TADF emitters. These results demonstrate the proposed strategy of employing 11,12-dihydroindolo[2,3-a]carbazole as bridge for planar donors and acceptors to construct efficient folded TADF materials is applicable.

High‐Efficiency Hybrid White Organic Light‐Emitting Diodes with Extremely Low Efficiency Roll‐Off and Superior Color Stability Enabled by an Emitting System with Imidazole‐Biphenyl Derivatives

AbstractHybride white organic light‐emitting diodes (WOLEDs) have experienced great success as a prospective technology for the new generation lighting source. Nevertheless, WOLEDs exhibiting excellent effciency and good color stability at high operation brightness are still rare. Herein, a simple but efficient blue molecule, pyrenoimidazole‐biphenyl (PPyIM), which exhibits promising external quantum efficiency (EQE) of 7.6% and 7.2% at the luminescence of 1000 −and 5000 cd m−2 in nondoped blue OLED, is first developed. And then, phenanthroimidazole‐biphenyl (PPIM) with analogous molecular skeleton of PPyIM is chosen as the host of phosphorescent dye PO‐01, and the resulting doped device achieves excellent EQE of 26.5% at the high luminescence of 5000 cd m−2. Furthermore, adopting PPyIM as nondoped blue emissive layer, the two‐color hybrid WOLED exhibites stable warm white emission with CIE coordinates of (0.454, 0.439), color rendering index (CRI) of 45, and correlated color temperature (CCT) of 2996 K. The maximum EQE reaches 23.5%, and the EQE still maintains 21.2% even at the luminance of 5000 cd m−2. Notably, this device exhibits exceptionally stable warm white emission, the CIE coordinates variation is only (0.004, 0.003) in the wide luminance range from 400 to 10000 cd m−2, representing the best outcome for hybrid WOLEDs to date.

High‐Lying Triplet Excitons Utilization of Silole Derivatives Enables their Efficiency Breakthrough in OLEDs

AbstractSiloles are routinely studied in the application of organic light‐emitting diodes (OLEDs) due to their high performances of solid‐state fluorescence property and carrier mobility. The structures of siloles used in electroluminescence device reported so far can only utilize singlet excitons, limiting the device efficiency and commercialization. Seeking to build appliable molecular structures to achieve triplet excitons utilization in silole‐core emitters, two derivatives are designed, Silole‐1DPA‐TRZ and Silole‐1Cz‐TRZ, in which electron acceptor of triazine (TRZ) together with electron donors of diphenylamine (DPA) and carbazole (Cz) modified at 1‐position of silole unit form silole‐D‐A structures. This special molecular design, for the first time, enables triplet excitons harvest via high‐lying reverse intersystem crossing (hRISC) process in silole derivatives with hybridized local and charge‐transfer (HLCT) characteristics. Experimental and theoretical studies show that relative to a stronger charge transfer state of Silole‐1Cz‐TRZ, a more equal local excitation/charge transfer distribution in the HLCT state of Silole‐1DPA‐TRZ is realized, making its application in silole‐based OLED with an efficiency breakthrough of ≈9.1% maximum external quantum efficiency (EQEmax).

Saturated Red Electrophosphorescence From Novel Pyridinopyridazine‐Based Iridium Complexes

ABSTRACTTwo isomeric homoleptic Ir(III) complexes with pyridinopyridazine derivative ligands were prepared first. Due to its stronger intramolecular hydrogen bonding and intermolecular interactions, complex IrPPM has a higher decomposition temperature (5% weight loss) of 387°C than IrPPP (354°C). They have similar UV–Vis absorption and photoluminescence spectra in CH2Cl2 solution with photoluminescence peaks around 635–636 nm. However, the emission peak of IrPPM in neat powder obviously red‐shifted to 652 nm, and that of IrPPP blue‐shifted to 626 nm. Simultaneously, complex IrPPM has a lower photoluminescence quantum yield of 0.3 than IrPPP (0.5). Efficient saturated red OLED devices are developed with Commission Internationale de L'Eclairage color coordinates of (0.67, 0.32) and (0.66, 0.32), respectively. The maximum external quantum efficiencies of both devices exceed 11%. These results demonstrate the great potential of pyridinopyridazine derivatives for developing new iridium complexes for OLED applications.