Efficient Red Organic Light-emitting Diodes Research Articles

A Tailored TADF Emitter Based on Diphenylacetylene Anthracene Derivatives for Highly Efficient Solution-Processed Pure Red Organic Light-Emitting Diodes.

It holds enormous significance for red thermally activated delayed fluorescence (TADF) emitters to develop organic light-emitting diodes (OLEDs) with high efficiency and high color purity, which remains challenging for highly efficient solution-processed red TADF emitters due to the limitation of severe nonradiative decays. Herein, a red TADF emitter containing space interactions, 4,4'-(9,10-bis(phenylethynyl)anthracene-1,8-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (DBP-2MOTPA), is designed and synthesized, composed of ethynyl as the acceptor and methoxytriarylamine (MOTPA) as the donor. The triphenylamine donor unit decorated with peripheral methoxy units not only improves the solubility for the solution-processed technology but also increases the electron-donating ability. The highly twisted donor-π-acceptor (D-π-A) architecture generates a small energy gap (ΔEST) of 0.14 eV, and the appropriate overlap of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) leads to a supernal photoluminescence quantum yield (ΦPL) of 68%. Consequently, the nondoped device based on DBP-2MOTPA with Commission Internationale de l'Eclairage (CIE) at (0.67, 0.33) exhibits the pure red emission, which satisfies the Rec.1931 standard red gamut (0.67, 0.33) and approaches the Rec.2020 standard (0.71, 0.29). Moreover, the doped devices employing DBP-2MOTPA as the emitter exhibit a maximum external quantum efficiency (EQE) of 6.09%, which is among the effective values in the solution-processed red TADF-OLEDs.

Cyano-substituted Bis((benzothiophen-2-yl)pyridine) (acetylacetonate) iridium complexes for efficient and stable deep red organic light-emitting diodes emitting at 673 nm

This study explores the development of cyano-substituted bis((benzothiophen-2-yl)pyridine) (acetylacetonate) iridium complexes, specifically Ir(btpCN)2(acac), for use in efficient and stable deep red organic light-emitting diodes (OLEDs) emitting at 673 nm. The new emitter, Ir(btpCN)2(acac), was designed to achieve red-shifted emission through strategic cyano substitution at the meta-position of pyridine moiety of btp ligand, leveraging the favorable overlap between its emission spectrum and the absorption spectrum of the exciplex host composed of BCzPh and CN-T2T. The OLED devices employing Ir(btpCN)2(acac) as the emitter exhibited a peak external quantum efficiency (EQE) of 10.2 % and an emission wavelength of 673 nm. Significantly, these devices demonstrated superior operational stability, with a lifetime (LT50) of 190.8 h at an initial luminance of 200 cd m−2, which is among the highest reported for deep-red OLEDs in the literature. This remarkable stability is achieved without compromising the device performance, making Ir(btpCN)2(acac) a highly promising candidate for commercial applications. In addition, the straightforward synthesis process of Ir(btpCN)2(acac) further enhances its potential for widespread use. Overall, our findings highlight the potential of cyano-substituted Ir complexes for creating efficient, stable, and commercially viable deep-red OLEDs. The balanced performance of Ir(btpCN)2(acac) in terms of efficiency, stability, and ease of synthesis marks a significant advancement in the development of OLED technology suitable for phototherapy and other applications requiring reliable deep-red light sources.

New ionic iridium(III) complexes based on methoxyl-modified 1-phenylisoquinoline for solution-processed red organic light-emitting diodes

Three transition-metal phosphorescent iridium(Ⅲ) complexes (Ir1, Ir2, and Ir3) are designed and synthesized with 1-phenylisoquinolines modified by methoxy as the main ligands and o-phenanthroline as the auxiliary ligands. The introduction of different amounts of methoxy can change the luminescence color of the complexes, and Ir1, Ir2, and Ir3 show orange, dark red, and red phosphorescence under the excitation of 365 nm UV lamp, peaking at 588, 648, and 622 nm, respectively. Ionic complexes are conducive to the efficient solution-processed phosphorescent red organic light-emitting diodes (OLEDs). Among the three devices, the Ir2-based device achieved a relatively high external quantum efficiency, current efficiency, and power efficiency of 1.12 %, 0.75 cd/A, and 0.37 lm/W, respectively. These results indicated that polymethoxy-based ionic Ir(III) complexes have great potential for the fabrication of red OLEDs with wet method.

Dihydrophenazine-derived thermally activated delayed fluorescence emitters for highly efficient orange and red organic light-emitting diodes

Thermally activated delayed fluorescence (TADF) emitters in the long wavelength region usually suffer from severe nonradiative decay according to the energy-gap law, and show relatively large energy split (ΔEST) between the lowest singlet and triplet excited states which compromise efficient up-conversion. Here, we report three orange and red TADF emitters comprising 5, 10-disubstituted phenazine electron-donor and quinoxaline-derived electron-acceptors, which show excellent TADF properties and yield efficient organic light-emitting diodes (OLEDs). These symmetrical acceptor-donor-acceptor (A-D-A) type and rodlike molecules concurrently exhibit high photoluminescence quantum yields up to 85% and fast reverse intersystem crossing. Experimental and theoretical studies reveal that these excellent photophysical properties are attributed the synergistic effect of structural rigidity, steric hindrance and strength of the donor and acceptor units. Doped OLEDs based on these emitters achieved high maximum external electroluminescence quantum efficiencies up to 19.9%, and maximum luminance surpassing 31240 cd/m2.

A reverse intersystem crossing managing assistant dopant for high external quantum efficiency red organic light-emitting diodes

Assistant dopants with reduced Dexter energy transfer rates were designed by replacing the donor moiety of 2,3,5,6-tetra(9H-carbazol-9-yl)terephthalonitrile (4CzTPN) with 5H-benzo[4,5]thieno[3,2-c]carbazole (BTCz).

Modulating up-conversion and non-radiative deactivation to achieve efficient red thermally activated delayed fluorescence emitters

Improving up-conversion and suppressing non-radiative inactivation by employing the novel dibenzothioxanthene acceptor and employing a bulky donor is demonstrated as a new perspective toward highly efficient red organic light-emitting diodes.

The recombination zone adjusted by the gradient doping of TPA-DCPP for efficient and stable deep red organic light emitting diodes.

Deep-red organic light-emitting diodes (DR-OLEDs) or near-infrared organic light-emitting diodes (NIR-OLEDs) have a wide range of applications in real life, such as special light sources for plant growth in agriculture, optical communications, infrared imaging, infrared medical imaging and other fields. However, the device performance of DR-OLEDs is still far behind that of red, green and blue OLEDs. In addition to the well-known energy gap law, the location of the recombination region also has a significant impact on the device performance. If the recombination area is too close to the cathode, the electrons in the electron transport layer will easily cause exciton quenching. In this study, for the first time, we adopted a quantum well-like structure by changing the host (CBP) and guest (TPA-DCPP) thicknesses as the light-emitting layer to manage the position of the recombination zone, and then improved the carrier injection and transportation as well as increased the exciton recombination rate. Furthermore, we introduced a hole trap layer to reduce the current density and suppress the recombination zone movement; finally, we prepared high-brightness and high-efficiency DR-OLEDs based on the TADF material with a wavelength of 674 nm, a maximum brightness of 1151 cd m−2 and a maximum EQE of 4.4%.

A series of novel host materials based on the 10,11-dihydro-5H-dibenzo[b,f]azepine unit for highly efficient green and red organic light-emitting diodes

Highly efficient host materials for green and red OLEDs were developed via the incorporation of 10,11-dihydro-5H-dibenzo[b,f]azepine as a building block.

Highly efficient solution-processed red phosphorescent organic light-emitting diodes employing an interface exciplex host

To cut cost and improve efficiency, an interface exciplex system of NPB/TPBi was employed as a host in solution-processed red phosphorescent organic light-emitting diodes (PhOLEDs).

One-shot triphenylamine/phenylketone hybrid as a bipolar host material for efficient red phosphorescent organic light-emitting diodes

Abstract A new bipolar host material, 2,2′,2′′-tris(diphenylketone)amine (N-DPK) was developed in a one-shot by Ullmann reaction, and characterized by spectroscopic techniques and spatial arrangement was ascertained by single X-ray crystal structure analysis. The compound is possessing C3-symmetry with three diphenylketone units connected to the central nitrogen atom. In this organic architecture, the electron-withdrawing units, phenylketone are incorporated to ortho-position of triphenylamine, electron-donating unit to generate rigidity, which is responsible to reduce the gap between single and triplet energy levels. The material possessed triplet energy (ET) at 2.53 eV, indicating that it could be used as a host material for red phosphorescent organic light-emitting diodes. The OLED device was fabricated with bis(2-methyldibenzo[f,h]quinoxaline)(acetylacetonate)iridium(III) (Ir(MDQ)2acac) and N-DPK, as guest and host, respectively, and 10 wt% doping concentration exhibited good device performance with maximum external quantum efficiency (EQE) of 16.1%.

Rational design of quinoxaline-based bipolar host materials for highly efficient red phosphorescent organic light-emitting diodes.

Two novel bipolar carbazole/diphenylquinoxaline-based host materials 3-(2,3-diphenylquinoxalin-6-yl)-9-phenyl-9H-carbazole (M1) and 3-(4-(2,3-diphenylquinoxalin-6-yl)phenyl)-9-phenyl-9H-carbazole (M2) have been rationally designed and synthesized. The phenyl spacer between the functionalized quinoxaline moiety and the carbazole moiety is also introduced to investigate its influence on their photophysical properties. The chemical structures, and thermal, photophysical and electrochemical properties of the two host materials were characterized and explored in detail. Red phosphorescent light-emitting diodes with M1 and M2 as hosts were prepared to explore their electroluminescent properties. Both M1 and M2 host-based red devices exhibit outstanding electroluminescent performance. For example, two red devices all realize good red emission with the maximum at 594 nm, the maximum external quantum efficiency and luminance can reach 14.66% and 28 619 cd m−2 for M1-based devices and 15.07% and 28 818 cd m−2 for M2-based devices, indicating compounds M1 and M2 designed in this work have potential applications in the development of high-performance monochrome and white OLEDs.

A thermally activated delayed fluorescence exciplex to achieve highly efficient and stable blue and green phosphorescent organic light-emitting diodes.

The development of a thermally activated delayed fluorescence (TADF) exciplex with high energy is of great significance in achieving highly efficient blue, green, and red organic light-emitting diodes (OLEDs) for use in full-color displays and white lighting. Highly efficient and stable blue and green phosphorescent OLEDs were demonstrated by employing a TADF exciplex (energy: 2.9 eV) based on 4-substituted aza-9,9′-spirobifluorenes (aza-SBFs). Blue PhOLEDs demonstrated a maximum current efficiency (CE) of 47.9 cd A−1 and an external quantum efficiency (EQE) of 22.5% at 1300 cd m−2 (2.5 times the values of aza-SBF-based systems), with the best blue PhOLED demonstrating a CE, power efficiency (PE) and EQE of 60.3 cd A−1, 52.7 lm W−1, and 26.2%, respectively. Green PhOLEDs exhibited a CE of 78.1 cd A−1 and EQE of 22.5% at 9360 cd m−2, with the best green PhOLED exhibiting a maximum CE, PE, and EQE of 87.4 cd A−1, 101.6 lm W−1, and 24.5%, respectively. The device operational lifetime was improved over 17-fold compared to reference devices because of the high thermal stability of the materials and full utilization of the TADF exciplex energy, indicating their potential for application in commercial OLEDs.

The roles of thermally activated delayed fluorescence sensitizers for efficient red fluorescent organic light-emitting diodes with D–A–A type emitters

The roles of thermally activated delayed fluorescence sensitizers (4CzIPN and OSTFCN) are investigated by developing two red D–A–A type chromophores.

Efficient solution-processed red organic light-emitting diode based on an electron-donating building block of pyrrolo[3,2-b]pyrrole

Abstract An electron-rich moiety, pyrrolo[3,2-b]pyrrole, has been used as a new donor block in organic lighting-emitting diodes (OLEDs). Combined with a strong electron-withdrawing group of 2,1,3-benzothiadiazole, a novel red fluorophore BTZPP was synthesized. The solution-processed red-emitting device based on BTZPP showed encouraging performances with external quantum efficiency of up to 3.4%. This evidently indicates that the pyrrolo[3,2-b]pyrrole group can be a promising electron-donating moiety for enriching the material types and promoting the development of OLEDs.

Functionalized Quinazolines and Pyrimidines for Optoelectronic Materials

Background: Quinazolines, the important group of benzodiazines, are widely known in medicinal chemistry due to their broad spectrum of biological activities. Notably, extensive research on the synthesis and application of quinazoline derivatives for electronic devices, luminescent elements, photoelectric conversion elements, and image sensors has been published recently. Objective: This review reports luminescent small molecules and chelate compounds including a quinazoline or pyrimidine ring in their scaffold highlighting their applications related to photo- and electroluminescence. Conclusion: It is clear from the review of the topic that the incorporation of quinazoline and pyrimidine fragments into π-extended conjugated systems is of great value for the creation of novel optoelectronic materials. Polyhalogen derivatives represent the major starting materials for polysubstituted fluorescent quinazolines. Electroluminescent properties of aryl(hetaryl)substituted quinazolines with π-extended conjugated systems proved to be the most important. Incorporation of benzimidazole, carbazole, triphenylene or triphenylamine fragments into quinazoline scaffold allows fabricating materials for organic light-emitting diodes, including white OLEDs and highly efficient red phosphorescent organic light-emitting diodes. Moreover, arylvinylsubstituted quinazolines are of great interest as potential structures for nonlinear optical materials and for colorimetric pH sensors. Iridium complexes based on 2-aryl(thienyl) quinazoline or pyrimidine derivatives represent high-efficiency phosphorescent materials for OLEDs. Pyrimidine push-pull systems are of considerable importance as potential photosensitizers for dye-sensitized solar cells. Pyrimidine derivatives bearing phenylacridine or phenylphenoxazine fragments at the positions 4 and 6 are capable to function as thermally activated delayed fluorescence emitters.

Highly efficient red fluorescent organic light-emitting diodes by sorbitol-doped PEDOT:PSS

This work shows a promising approach to improve device performance by optimizing the electron transport and hole injection layers for tetraphenyldibenzoperiflanthene (DBP):rubrene-based red fluorescent organic light-emitting diodes (OLEDs). We compared the effect of two electron transport layers (ETLs), and found that the rubrene/bathophenanthroline (Bphen) ETL-based OLED showed a much higher external quantum efficiency (EQE) (4.67%) than the Alq3 ETL-based OLED (EQE of 3.08%). The doping ratio of DBP in rubrene was tuned from 1.0 wt% to 4.5 wt%, and the 1.5 wt%-DBP:rubrene-based OLED demonstrated the highest EQE of 5.24% and lowest turn-on voltage of 2.2 V. Atomic force microscopy images indicated that 1.5 wt% DBP-doped rubrene film exhibited a regular strip shape, and this regular surface was favorable to the hole and electron recombination in the emitting layer. Finally, the sorbitol-doped poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was used to further improve the EQE; doping with 6 wt% sorbitol achieved the highest current efficiency of 7.03 cd A−1 and an EQE of 7.50%. The significantly enhanced performance implies that the hole injection is a limiting factor for DBP:rubrene-based red fluorescent OLEDs.

Efficient management of excitons in red and white organic light-emitting diodes by employing blue thermally activated delayed fluorescent emitter based acridine/sulfone derivative as the host

Abstract Highly efficient red and white organic light-emitting diodes (OLEDs) employing blue thermally activated delayed fluorescent (TADF) emitter of mSOAD based acridine/sulfone derivative as the host are realized by efficient management for singlet and triplet excitons. The red OLEDs reach a high maximum current efficiency, power efficiency and EQE of 32.7 cd A−1, 31.0 lm W−1 and 20.3%, respectively. And the white OLEDs with different dopant concentrations exhibit ultra-high color stability of ±(0.008, 0.001), ±(0.000, 0.003) and ±(0.002, 0.005), respectively. Meantime, the high efficiencies are also achieved with maximum current efficiencies, power efficiencies and EQEs of 28.2–32.0 cd A−1, 26.3–30.5 lm W−1 and 12.2–17.4%, respectively. The analysis of energy level and transient decay characteristics demonstrate the excellent device performances are mainly stemmed from the sufficient confinement for charges and excitons and efficient energy transfer from the TADF host to dopant.

High efficiency red phosphorescent organic light-emitting diodes with low dopant concentration, low roll-off and long lifetime based on a novel host material with thermally activated delayed fluorescent properties

Abstract High cost of phosphors, efficiency roll-off and short lifetime are the main factors that limited phosphorescent organic light-emitting diodes' (PHOLED) application. In this work, we report red emission PHOLED with low dopant concentration, low efficiency roll-off and long operation lifetime based on a novel host material 2,4-bisbiphenyl-6-(12-phenylindole[2,3 -a]carbazole-11-yl)-1,3,5-triazine (BBPICT), with thermally activated delayed fluorescent (TADF) properties. The devices displayed a maximum external quantum efficiency of 20.9% and low efficiency roll-off of 1.7% at 1000 cd m−2, and the operation lifetime of the device at a brightness of 1000 cd m−2 is 1390 h.

Thermally activated delayed fluorescence sensitizer for D–A–A type emitters with orange-red light emission

Two novel red emitters were integrated with a thermally activated delayed fluorescence sensitizer to achieve highly efficient red organic light-emitting diodes.

9-Silafluorene and 9-germafluorene: novel platforms for highly efficient red phosphorescent organic light-emitting diodes

De novo molecular platforms have been applied to build host materials for highly efficient PHOLEDs. A 9-silafluorene derivative was studied for the first time as a host and an external quantum efficiency of over 28% was achieved successfully in red PHOLEDs.