Red Organic Light-emitting Diodes Research Articles

Maximization of cytochrome C oxidase enzyme activity by optimizing color conversion from red organic light-emitting diodes

Photobiomodulation (PBM) therapy using red and near-infrared (NIR) light can effectively activate cytochrome C oxidase (CCO) enzyme to promote wound healing in living organisms. To maximize this therapeutic effect, the use of a light source with a spectrum absorbed by the CCO enzyme is necessary. A red/NIR light source optimized for CCO enzyme was obtained by partially color-converting a red organic light-emitting diode with copper indium sulfide/zinc sulfide quantum dots (QDs). To increase color conversion efficiency, the dispersion of QDs was improved by using a fibrous color conversion layer (FCCL). By optimizing the QD content in the FCCL, a red/NIR light source similar to the absorption spectrum of CCO enzyme was obtained with a spectral matching ratio of 81.7 %. When this light source was used in PBM therapy, it was experimentally verified that it showed a much faster wound closure effect compared to general red light, and it was proven that this was due to increased activity of the CCO enzyme. This study is a method of obtaining a red/NIR light source for PBM suitable for a specific enzyme performing a specific function, and is particularly useful due to its excellent form factor of being large, thin, and flexible.

Improvement of electrical characteristics and wet etching procedures for InGaTiO electrodes in organic light-emitting diodes through hydrogen doping

We investigated the effect of hydrogen doping on characteristics of InGaTiO (IGTO) electrode with high conductivity and transmittance during sputtering process. After hydrogen doping, the 300 nm-thick IGTO:H electrode showed lower sheet resistance of 13.79 Ω/square compared to sheet resistance (69.2 Ω/square) of pure IGTO electrode without change of optical transmittance. In addition, wet etching reaction rate of IGTO:H electrode for patterning process was significantly accelerated after hydrogen doping. Possible explanation for hydrogen doping effect on electrical properties and wet etching process of the IGTO:H electrode was suggested. The doped hydrogen influenced the electrical characteristics through the passivation of dangling bonds and oxygen vacancies. Moreover, it significantly impacts crystalline structure, consequently altering the etching rate. Using patterned IGTO:H electrodes, we fabricated red organic light emitting diodes (OLEDs) to show feasibility of the IGTO:H electrodes. External quantum efficiency and current efficiency of the red OLED with IGTO:H (10%) were higher than IGTO electrode without hydrogen doping, indicating that hydrogen doping is an effective method to improve the film properties and IGTO:H electrode can serve as a prospective transparent anode for both flexible and rigid OLEDs.

Rational molecular design of efficient yellow-red dendrimer TADF for solution-processed OLEDs: a combined effect of substitution position and strength of the donors

AbstractThe development of high-performance solution-processed red organic light-emitting diodes (OLEDs) remains a challenge, particularly in terms of maintaining efficiency at high luminance. Here, we designed and synthesized four novel orange-red thermally activated delayed fluorescence (TADF) dendrimers that are solution-processable: 2GCzBP, 2DPACzBP, 2FBP2GCz and 2FBP2DPACz. We systematically investigated the effect of substitution position and strength of donors on the optoelectronic properties. The reverse intersystem crossing rate constant (kRISC) of the emitters having donors substituted at positions 11 and 12 of the dibenzo[a,c]phenazine (BP) is more than 10-times faster than that of compounds substituted having donors substituted at positions 3 and 6. Compound 2DPACzBP, containing stronger donors than 2GCzBP, exhibits a red-shifted emission and smaller singlet-triplet energy splitting, ΔEST, of 0.01 eV. The solution-processed OLED with 10 wt% 2DPACzBP doped in mCP emitted at 640 nm and showed a maximum external quantum efficiency (EQEmax) of 7.8%, which was effectively maintained out to a luminance of 1,000 cd m−2. Such a device∙s performance at relevant display luminance is among the highest for solution-processed red TADF OLEDs. The efficiency of the devices was improved significantly by using 4CzIPN as an assistant dopant in a hyperfluorescence (HF) configuration, where the 2DPACzBP HF device shows an EQEmax of 20.0% at λEL of 605 nm and remains high at 11.8% at a luminance of 1,000 cd m−2, which makes this device one of the highest efficiency orange-to-red HF SP-OLEDs to date.

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.

Narrowband Fluorescent Emitters Based on BN-Doped Polycyclic Aromatic HydrocarbonsforEfficientand Stable Organic Light-emitting Diodes.

Organic light-emitting diodes (OLEDs) using conventional fluorescent emitters are currently attracting considerable interests due to outstanding stability and abundant raw materials. To construct high-performance narrowband fluorophores to satisfy requirements of ultra-high-definition displays, a strategy fusing multi-resonance BN-doped moieties to naphthalene is proposed to construct two novel narrowband fluorophores.Green Na-sBN and red Na-dBN, manifest narrow full-width at half-maxima of 31 nm, near-unity photoluminescence quantum yields and molecular horizontal dipole ratios above 90%. Their OLEDs exhibit the state-of-the-art performances including high external quantum efficiencies (EQE), ultra-low efficiency roll-off and longoperational lifetimes. The Na-sBN-based device achieves EQE as high as 28.8% and remains 19.8% even at luminance of 100,000 cd m-2, and Na-dBN-based device acquires a record-high EQE of 25.2% among all red OLEDs using purefluorescent emitters.

Highly rigid polycyclic acceptors by incorporating quinoxaline and naphthalimideacridine towards red TADF emitters

The development of red thermally activated delayed fluorescence (TADF) emitters with the emission peak above 600 nm remains far behind blue and green emitters. Herein, the highly rigid polycyclic acceptors with strong electron-withdrawing ability, integrated by quinoxaline and 1,8-naphthalimideacridine units, were utilized to construct two new red emitters with emission peak at 640 nm. Both target molecules display the twisted configuration to decrease singlet-triplet splitting energy (ΔEST) for the TADF property. Red organic light-emitting diodes (OLEDs) employing the emitters achieve the maximum external quantum efficiencies of 5.2% with electroluminescence peaks over 600 nm. This work provides a feasible strategy of the new polycyclic acceptors for developing efficient red TADF emitters.

Discrete Mononuclear Platinum(II) Complexes Realize High-Performance Red Phosphorescent OLEDs with EQEs of up to 31.8% and Superb Device Stability.

Designing mononuclear platinum(II) complexes that do not rely on intermolecular aggregation for high-performance red organic light-emitting diodes remains a formidable challenge. In this work, three robust red-emitting Pt(II) complexes w ere created by utilizing a rigid 4-coordination configuration, where the ligands w ere formed by linking electron-donor of triphenylamine (TPA) moieties with electron-acceptor of pyridine, isoquinoline, and/or δ-carboline units. The thermal stability, electrochemical, and photophysical properties of the complexes w ere thoroughly examined. The complexes display efficient red phosphorescence, with high photoluminescence quantum yields and short excited lifetimes. The OLEDs doped with these complexes exhibit high maximum external quantum efficiencies (EQEs) of up to 31.8% with minimal efficiency roll-off even at high brightness. Significantly, the devices demonstrated exceptional long operational lifetime, with a T90 lifetime of over 14000 hours at initial luminance of 1000cd m-2 , indicating the potential for these complexes to be practically utilized. This article is protected by copyright. All rights reserved.

Enhanced light extraction for red organic light emitting diodes via PDMS convex lens based on breath figure method

To inhibit the light loss of substrate mode at the substrate/air interface in organic light emitting diodes (OLEDs), regular porous polystyrene (PS) template was fabricated via the “Breath figure” method. The structure of porous mold was optimized by adjusting the PS solution concentration from 10 to 60 mg/ml and relative humidity from 60% to 80%. The optimal porous PS mold was achieved at 50 mg/ml PS solution under 70% relative humidity. Then, elastic micro-lens arrays based on transparent elastomer polydimethylsiloxane (PDMS) were obtained via a two-step transferring process from the porous PS mold. The projection experiment exhibits excellent focusing effect of the PDMS convex lens relative to the planar PDMS film. These PDMS micro-lens films were in situ fabricated onto the external face of the red OLED device to extract substrate mode light. By using the PDMS micro-lens array with a height of 1.2 μm and a diameter of 6.7 μm, the OLED device demonstrates an enhancement of 32.7%, 35.6%, 46.5%, and 27.6% for maximum luminance, current efficiency, power efficiency, and external quantum efficiency, respectively, without changing its color purity. The device with PDMS micro-lens exhibits a higher intensity than an ideal Lambertian emission pattern, especially at viewing angles from 30° to 60°. It suggests that the introduction of external micro-lens structure significantly improves the light outcoupling efficiency.

Suppression of Dexter Energy Transfer through Modulating Donor Segments of Thermally Activated Delayed Fluorescence Assistant Dopants.

Device degradation in red hyperfluorescent organic light-emitting diodes is primarily caused by exciton energy loss due to Dexter energy transfer (DET) from a thermally activated delayed fluorescence (TADF) assistant dopant to a fluorescent dopant. In this work, the donor segments in the TADF assistant dopants were delicately modulated to suppress DET for high efficiency. The derived benzothienocarbazole donors were introduced to the TADF assistant dopants instead of carbazole, and they accelerated the reverse intersystem crossing of the TADF assistant dopant and managed the DET from the TADF assistant dopant to the fluorescent dopant. As a result, the red TADF-assisted device showed a high external quantum efficiency of 14.7% and improved the device lifetime by 70% compared to a well-known TADF-assisted device.

Flexible, Transparent, High Mobility Amorphous In–Ga–Zn-O Thin Film Transistors Fabricated on Textile

To implement wearable textile displays (WTDs), it is essential that unique properties such as physical and chemical properties, aesthetics, and flexibility of the textile be maintained. Therefore, thin film transistors (TFTs) for WTDs should exhibit excellent electrical properties to enable 4K and 8K high resolution and high frame-rate (>120 Hz) displays while maintaining the properties of textiles. All layers of TFTs were formed by vacuum deposition and oxide-based transparent materials; amorphous In–Ga–Zn-O (a-IGZO), indium tin oxide (ITO), and Al2O3 were used. A transparent and flexible electrode with an ITO/Ag/ITO (IAI) structure was optimized and applied to the source/drain and gate. All processes were performed below 150 °C, and the wet-step was eliminated to prevent physical and chemical deformation of the substrate. The flexible, transparent, high mobility a-IGZO TFTs (FTH TFTs) for WTDs were fabricated on glass, polyethylene terephthalate (PET) film, and textile substrates, respectively. Their electrical performance, transparency, and flexibility were then compared. The textile-based TFTs showed transmittance of 72.98%, high mobility of 11.5 cm2/(V s), and an on/off ratio of 9.28 × 107 even in a low temperature process (<150 °C). In addition, the electrical properties of the textile-based TFTs were maintained despite testing entailing 1000 cycles of bending with a tensile strain of 0.8%. In particular, the FTH TFTs for WTDs were able to stably drive a red organic light-emitting diode on textile.

Design, synthesis, and electroluminescence of red TADF dyes based on cyanophenanthrene

Two rigid electron-deficient cyanophenanthrene frameworks with limited π-conjugation, phenanthrene-9-carbonitrile (CNP) and phenanthrene-9,10-dicarbonitrile (DCNP), are employed as the electron acceptors to construct thermally activated delayed fluorescence (TADF) dyes. The new TADF emitters exhibit long-wavelength emission without strong long-range π-π stacking or interchromophore coupling, as supported by the photophysical and crystallographic results. These unique features are suitable to construct red organic light-emitting diodes (OLEDs). An OLED based on CNP-TPXZ showed an orange-red emission with a peak at 586 nm and a maximum EQE of 8.4%, while that of DCNP-DPXZ exhibited red emission at 614 and a maximum EQE of 6.6%. These results demonstrate that DCNP and CNP are potential electron acceptors for the development of red TADF emitters and OLEDs.

Solution-Processable Pure-Red Multiple Resonance-induced Thermally Activated Delayed Fluorescence Emitter for Organic Light-Emitting Diode with External Quantum Efficiency over 20.

Developing solution-processable red organic light-emitting diodes (OLEDs) with high color purity and efficiency based on multiple resonance thermally activated delayed fluorescence (MR-TADF) is a formidable challenge. Herein, by introducing auxiliary electron donor and acceptor moieties into the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) distributed positions of multiple resonance skeleton simultaneously, an effective strategy to obtain red MR-TADF emitters was represented. The proof-of-the-concept molecule BN-R exhibits a narrowband pure-red emission at 624 nm, with a high luminous efficiency of 94% and a narrow bandwidth of 46 nm. Notably, the fabricated solution-processable pure-red OLED based on BN-R exhibits a state-of-the-art external quantum efficiency over 20% with the Commission Internationale de I'Éclairage coordinates of (0.663, 0.337) and a long operational lifetime (LT50) of 1088 hours at an initial luminance of 1,000 cd m-2.

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.

Red organic light-emitting diodes based photobiomodulation therapy enabling prominent hair growth

Red organic light-emitting diodes based photobiomodulation therapy enabling prominent hair growth

Two new red-emitting ternary europium(III) complexes with high photoluminescence quantum yields and exceptional performance in OLED devices.

Two new organo-europium complexes (OEuCs) [Eu(btfa)3(Bathphen)] (OEuC-1) and [Eu(tta)3(Bathphen)] (OEuC-2) where btfa and tta are the anions of 4,4,4-trifluoro-1-phenyl-1,3-butanedione and 2-thenoyltrifluoroacetone while Bathphen = Bathophenanthroline have been synthesized and characterized. Both complexes in the solid state exhibit strong red emissions with photoluminescence quantum yields (PLQYs) of 80% ± 10%. These complexes were tested as dopants in the emitting layer (EML) to fabricate red organic light emitting diodes (R-OLEDs). Through device engineering involving the amalgamation of appropriate host materials and complexes, we have achieved exceptional overall R-OLED performance for an OEuC-2 based device, with maximum current efficiency (CEmax) = 9.91 cd A-1, maximum power efficiency (PEmax) = 9.15 lm W-1, maximum external quantum efficiency (EQEmax.) = 6.24%, brightness (B) of 545 cd m-2, and (CIE)x,y = 0.620, 0.323 at J = 10 mA cm-2.

High-efficiency and stable red to near-infrared organic light-emitting diodes using dinuclear platinum(ii) complexes

High-performance red and NIR organic light-emitting diodes (OLEDs) have been achieved using highly robust and phosphorescent diplatinum(ii) complexes featuring strong intramolecular Pt–Pt and π–π interactions.

Multifaceted Sulfone-Carbazole-Based D-A-D Materials: A Blue Fluorescent Emitter as a Host for Phosphorescent OLEDs and Triplet-Triplet Annihilation Up-Conversion Electroluminescence.

Electroluminescence (EL) from the singlet-excited (S1) state is the ideal choice for stable, high-performing deep-blue organic light-emitting diodes (OLEDs) owing to the advantages of an adequately short radiative lifetime, improved device durability, and low cost, which are the most important criteria for their commercialization. Herein, we present the design and synthesis of three donor-acceptor-donor (D-A-D)-configured deep-blue fluorescent materials (denoted as TC-1, TC-2, and TC-3) composed of a thioxanthone or diphenyl sulfonyl acceptor and phenyl carbazolyl donor. These systems exhibit strong deep-blue photoluminescence (422-432 nm) in solutions and redshifted emission (472-486 nm) in thin films. The solid-state photoluminescence quantum yield (PLQY) was estimated to be 78 and 94% for TC-2 and TC-3, respectively. TC-2 and TC-3 possess good molecular packing and large molecular cross-sectional areas, which not only improves the PLQY but enhances the triplet-triplet annihilation up-conversion (TTAUC) efficiency of fluorescent emitters. Furthermore, both compounds were applied as an acceptor for confirming their TTAUC property using bis(2-methyldibenzo[f,h]quinoxaline)(acetylacetonate)iridium(III) (Ir(MDQ)2acac) as the sensitizer. Non-doped OLEDs based on TC-2 and TC-3 exhibit blue EL in the 461-476 nm range. In particular, TC-3 exhibits a maximum external quantum efficiency (EQEmax) of 5.1%, and its EL maximum is 476 nm. In addition, the three emitters were employed as hosts in red OLEDs using bis(1-phenylisoquinoline)(acetylacetonate)iridium(III) (Ir(piq)2acac) as the phosphorescent dopant. The red phosphorescent OLEDs based on TC-1, TC-2, and TC-3 achieve excellent EQEmax values of 21.6, 22.9, and 21.9%, respectively, and peak luminance efficiencies of 12.0, 14.0, and 12.3 cd A-1. These results highlight these fluorophores' versatility and promising prospects in practical OLED applications.

Structure-property investigation of two red TADF isomers with different D-A conjugation for superior exciton utilization

In this text, by linking a phenoxazine donor (D) into different positions of the 11,12-diphenyldipyrido[3,2-a:2′,3′-c]phenazine acceptor (A), Two novel red thermally activated delayed fluorescence (TADF) isomers, PPZBP and BPZPP, were designed and synthesized. The different connection modes bring different steric hindrance between D and A segments, which lead to tunable conjugation of the whole molecule, resulting in the change of locally excited triplet (3LE) state. Beneficial from the suitable conjugation, PPZBP shows better energy level alignments than BPZPP for superior triplet up conversion. PPZBP-based red organic light-emitting diode realizes a higher EQE of 22.0% than that (14.8%) of the BPZPP-based one. This work not only demonstrates the importance of controlling D-A conjugations on the 3LE states and the resultant influences on RISC rates, it also gives a deep insight into preferred design strategies for high-efficiency red TADF emitters.

UV-ozone treated Ti3C2Tx-MXene nanosheets as hole injection layer for organic light-emitting diodes

In this work, we successfully synthesized Ti3C2Tx-MXene nanosheets with a lateral dimension of 1 ∼ 2 μm by using wet-chemical etchant and sonication-assisted liquid-phase exfoliation method. After UV-ozone treatment, the work function for Ti3C2Tx-MXene nanosheets was adjusted to 5.14 eV well matching to indium tin oxide (ITO) anode (4.80 eV). Using Ti3C2Tx-MXene nanosheets as hole injection layer (HIL), Ir(ppy)3-based green organic light-emitting diodes (OLEDs) were fabricated, and the resulting devices exhibit a low turn-on voltage of 3.0 V and the high current efficiency, power efficiency and external quantum efficiency of 72.79 cd/A, 54.44 lm/W and 20.34 %, which are obviously better than these of 67.38 cd/A, 50.38 lm/W and 18.65 % for PEDOT:PSS-based reference device. Further, FIrpic- and Ir(pq)2acac-based blue and red OLEDs with Ti3C2Tx-MXene nanosheets HIL were demonstrated, which also show the significantly improved device efficiency of 44.56 cd/A, 32.44 lm/W and 22.07 % for blue device and 39.17 cd/A, 38.54 lm/W and 21.90 % for red device than these for corresponding PEDOT:PSS-based devices, proving the universal applicability of Ti3C2Tx-MXene nanosheets as HIL in OLEDs. The higher performance for Ti3C2Tx-MXene nanosheets-based devices can be attributed to the appropriate work function, high transmittance, high carrier mobility and good film forming property for Ti3C2Tx-MXene nanosheets. This is the first report about the MXene using as HIL in OLEDs, which opens up a new way to develop high-performance holes injection materials for solution-processed OLEDs.

Multiplying the efficiency of red thermally activated delayed fluorescence emitter by introducing intramolecular hydrogen bond

As one of the three primary colors, red organic light-emitting diodes (OLEDs) are indispensable in practical applications. However, red emitters are generally subject to severe non-radiative exciton loss due to their narrow energy gap. In this work, three new thermally activated delayed fluorescence (TADF) emitters were developed, namely 4-(acenaphtho[1,2-b]quinoxalin-9-yl)-N,N-diphenylaniline (TPA-AP), 4-(acenaphtho[1,2-b]pyrido[2,3-e]pyrazin-10-yl)-N,N-diphenylaniline (TPA-APy), and 4-(acenaphtho[1,2-b]pyrazino[2,3-e]pyrazin-9-yl)-N,N-diphenylaniline (TPA-APm), employing a series of finely modified acenaphtho[1,2-b]quinoxaline (AP) derivatives as acceptor units. Among three TADF emitters, an intramolecular hydrogen bond is formed between the donor (D) and acceptor (A) units in TPA-APm. Consequently, the overlap of the frontier molecular orbitals (FMOs) of TPA-APm can increase appropriately, and the fluorescence radiative rate (kF) of TPA-APm is nearly twofold than that of TPA-AP and TPA-APy. Furthermore, the non-radiative decay rate (knr) of TPA-APm is less than that of TPA-AP and TPA-APy by an order of magnitude, which is attributed to the improved molecular rigidity caused by intramolecular hydrogen bond. As a result, TPA-APm-based OLEDs achieved a multiplied external quantum efficiency (EQE) of 21.1% with the electroluminescence peak at 590 nm, comparing to only 7.0% and 11.5% for the TPA-AP-based and TPA-APy-based devices, respectively. These results demonstrate appropriate intramolecular hydrogen bond can suppress the influence of non-radiative decay by simultaneously enhancing molecular rigidity and facilitating the fluorescence process, and have great potential in the design of efficient red TADF emitters.