Field Of Organic Light-emitting Diodes Research Articles

Spectral narrowing strategiesin multiple resonance thermally activated delayed fluorescencematerials.

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials possess unique advantages of high-efficiency and narrowband emission, which have rapidly occupied an important position in the field of organic light-emitting diodes (OLEDs). In recent years, significant advancements have been made in the development of MR-TADF materials, particularly in achieving spectral narrowing for high-color-purity OLED applications. Based on diverse MR-TADF molecular skeletons, this review summarizes the primary molecular strategies to narrow spectrum by suppressing structural relaxation and intermolecular interactions. Key strategies include π-conjugation extension, increased molecular rigidity, and the introduction of bulky substituents and intramolecular hydrogen bonds. Additionally, effects of these strategies on photophysical properties are discussed. These molecular design strategies are expected to offer valuable insights for the future design of high-efficiency, narrowband OLED emitters.

Carbazolylpyridine (cp)-based tetradentate platinum(II) complexes containing fused 6/5/6 metallocycles.

A series of carbazolylpyridine (cp)-based 6/5/6 Pt(II) complexes featuring tetradentate ligands with nitrogen or oxygen atoms as bridging groups was designed and synthesized, and the bridging nitrogen atoms were derived from acridinyl (Ac), azaaceridine (AAc) and carbazole (Cz). Systematic experimental and theoretical studies reveal that the ligand structures have a significant effect on the electrochemical, photophysical and excited state properties of these complexes. Their oxidation processes mainly occur on the carbazole-Pt moieties, whereas the reduction processes typically occur on the electron-deficient pyridine (Py) moieties. Time-dependent density functional theory (TD-DFT) and natural transition orbital (NTO) calculations reveal that the cp-based Pt(II) complexes have a metal-to-ligand charge transfer (3MLCT) state mixed with ligand-centered (3LC) and intra-ligand charge-transfer (3ILCT) characteristics. Pt(cp-1) shows strong red luminescence with a dominant peak at 611 nm and an excited-state lifetime of 10.7 μs in dichloromethane at room temperature, 602 nm and 10.9 μs in toluene, and 602 nm and 8.2 μs in PMMA films. It also exhibits high photoluminescence quantum efficiencies of 85%, 84% and 60% in dichloromethane, toluene and PMMA, respectively. These studies indicate the potential application of the cp-based Pt(II) complexes as phosphorescent emitters in the field of organic light-emitting diodes (OLEDs).

Improving the Blue Color Purity of Tetradentate Pt(II) Complexes with the Assistance of F⋅⋅⋅H Interaction towards High-Performance Blue Phosphorescent OLEDs with EQE over 33 .

Among the various challenges in the field of organic light-emitting diodes (OLEDs), simultaneously achieving high efficiency, a long lifespan, and a narrow full-width at half maximum (FWHM) in blue OLEDs remains a significant hurdle. Herein, we demonstrate a strategy to improve the color purity of tetradentate Pt(II) complexes with the assistance of ⋅⋅⋅H interaction by incorporating trifluoromethyl (-CF3) groups into the well-known blue tetradentate Pt(II) phosphorescent complex. The results show that the different substitution positions of -CF3 have significantly varying effects on the FWHM values of the complexes; specifically, introducing -CF3 on the benzene ring of carbazole effectively reduces the FWHM, while introducing it on the benzene ring linked to the carbene unit has a minimal impact. When utilized in a mixed host system of SiCzCz/SiTrzCz2, the OLEDs with these new complexes as emitters demonstrated maximum external quantum efficiencies (EQEs) of 27.1 %, 33.8 %, and 27.6 % for PtON-CF3-1, PtON-CF3-2, and PtON-2CF3, respectively, with excellent color purity (CIEy≈0.14 for the PtON-CF3-2 based device). Notably, the device based on PtON-CF3-2 matched the stability of the benchmark PtON-TBBI complex.This work offers an important guideline for the design of high efficient Pt(II) phosphorescent complexes with good blue color purity.

(Invited) Designing Solution-Processed Photonic Light- and Heat-Management Structures for Solution-Processable and Printable Organic Optoelectronic Devices

An ever-increasing interest in the development and application of innovative optical and optoelectronic devices places greater emphasis for the advancement of new smart and functional materials that are readily processable. Significant progress has already been realized in the fields of organic light-emitting diodes (OLEDs) and photovoltaic cells (OPVs) through development of novel semiconducting materials. Here we discuss developments and advancements in materials design towards photonic structures that aid and improve light management in organic and inorganic/organic hybrid devices, with focus on solar cells. Specifically, we present a novel inorganic/organic hybrid material that is produced in a one-pot synthesis and is solution processable, and can manipulated to exhibit a refractive index of 1.5 to up to 2.05. The material is of very low optical loss and, thus, can be readily integrated into efficient photonic structures. We cover systems targeted for use in light in-coupling structures, anti-reflection coatings, and beyond. Extension to architectures for heat management, important for a broad range of photovoltaic device platforms, including inorganic, inorganic/organic hybrid and organic devices, will also be presented.

Recent progress in high-performance thermally activated delayed fluorescence exciplexes based on multiple reverse intersystem crossing channels

In the field of organic light-emitting diodes (OLEDs), exciplex materials with thermally activated delayed fluorescence (TADF) characteristics have garnered significant attention in recent years owing to their potential for high fluorescence efficiency, primarily achieved through the reverse intersystem crossing (RISC) process. By converting non-radiative triplet states to radiative singlet states, the RISC process can effectively regulate exciton behavior, resulting in the harvest of triplet excitons and the improvement of luminescence efficiency. Recently, multi-RISC strategies have been developed to further enhance the performance of TADF exciplex materials and devices. In this paper, we review these research progress in this area. We classify molecular design strategies according to the composition of exciplexes, discuss the design principles and energy-harvesting mechanism of high-performance TADF exciplexes based on multi-RISC strategies, and prospect their further research and development. The progressive endeavors summarized in this review may inspire further research on material design and device fabrication, and promote the development of OLED applications.

Enhancing the emissive film quality: A new role of TADF materials for high-performance blue perovskite light-emitting diodes

Thermally activated delayed fluorescence (TADF) materials are widely used in the field of organic light-emitting diodes (OLEDs) because they can capture both singlet and triplet excitons for light emission. However, only scare attention has been paid to the application of TADF materials in perovskite LEDs (PeLEDs) and the understanding of effects of TADF materials in PeLEDs is limited. In this study, a new role of TADF materials for achieving high-quality perovskite films to enhance the performance of PeLEDs is emphasized. TADF materials are introduced into quasi-2D blue PeLEDs to assist in the crystallization of perovskites during film annealing and ensure the formation of high-quality films with reduced defects, enhancing device performance. Additionally, a step-like hole transport layer has been constructed to reduce the hole transport barrier, which can further enhance the performance of PeLEDs. The resultant blue PeLEDs exhibits an external quantum efficiency of 5.44 %, which is 12.7-fold higher than that of the control device. Furthermore, a turn-on voltage of 2.6 V is achieved, which is the lowest for TADF-based blue PeLEDs. The findings may not only unlock a new role of TADF materials in blue PeLEDs, but also provide an alternative pathway to achieve high-performance PeLEDs.

Indolocarbazole Derivatives for Highly Efficient Organic Light‐Emitting Diodes

AbstractSince the discovery of the organic light‐emitting diode (OLED), scientists worldwide have dedicated extensive efforts to enhance the efficiency and reliability of devices, striving for superior performance. Various molecular structures have undergone structural modifications to assess their suitability in achieving the desired outcomes. This review focuses on indolo[3,2,1‐jk]carbazole (ICz), a building block that has garnered considerable attention within the OLED community. The rigid and fused ICz core induces a multiresonance effect through an alternating distribution of frontier molecular orbitals. Notably, ICz‐based thermally activated delayed fluorescence emitters exhibit a full width at half maximum below 20 nm, ensuring high color purity, and boast an external quantum efficiency above 30%, comparable to state‐of‐the‐art narrow‐emitting boron–nitrogen‐type materials. Furthermore, the ICz core is a building block in host and metal complexes, enhancing stability, efficiency, and color purity. Consequently, the ICz core is promising as a central component in host and emitters, improving OLED device performance. This review aims to succinctly summarize studies on ICz‐based organic materials within the OLED field, offering insights into future perspectives regarding developing and applying ICz‐derived organic compounds.

Syntheses of multi-resonance frameworks towards narrowband organic light-emitting diodes.

Multi-resonance (MR)-type organic emitters are highly attractive in the field of organic light-emitting diodes because of their narrowband emission and thermally activated delayed fluorescence (TADF) properties. Compared with conventional TADF emitters, MR-featured emitters have more complex chemical structures and building logics. The core structures of MR emitters are MR frameworks, i.e., polyaromatic frameworks, precisely embedded with electron-donating and electron-withdrawing atoms/groups. Generally, electron-donating units can be easily introduced through the dedicated design of the precursors/intermediates, while integrating electron-withdrawing units is the key point and bottleneck for the synthesis of the MR framework. In this review, we briefly summarize the synthetic strategies of MR frameworks, focusing on the means of introducing various electron-withdrawing atoms/groups, which will aid the further exploration of MR-TADF emitters and their applications in OLEDs.

The third strategy: modulating emission colors of organic light-emitting diodes with UV light during the device fabrication process

A novel strategy is proposed to modulate emission colors of OLEDs without synthesizing different emitters or relying on molecular aggregation or concentration effects, which theoretically enables OLEDs to achieve infinite emission colors.

Effect of substituents in tuning the inter- and intra-molecular interactions in the dinuclear Pt(II) complexes

Substituents play a vital role in the formation of inter- and intra-molecular interactions in the Pt(II) complexes, especially Pt···Pt interactions have a tendency to tune the emission wavelength and the efficiency which has the potential applications in the field of organic light-emitting diodes (OLEDs). In this regard, the pyridazine-based bidentate ligands L1 (-CH3) and L2 (-CF3) are designed and synthesized. Subsequently, the ligands are carefully utilized for the preparation of dinuclear Pt(II) complexes 1 and 2. Complexes were analyzed by various analytical and spectroscopic studies and further confirmed by single crystal X-ray studies, which revealed both complexes show much shortened intra-molecular Pt···Pt distance (2.903 Å in 1 and 2.883 Å in 2) which helps to tune the emission towards the NIR region (up to 850 nm). Further, both complexes show various intermolecular interactions which lead to the formation of a multi-dimensional framework. Complexes 1 and 2 show strong emission at 705 nm and 725 nm, respectively, and further, DFT and TD-DFT studies were performed which confirms that complexes 1 and 2 show strong MMLCT character.

Synthesis, characterization and photo-physical studies of naphthalamide-based Ir(III) complexes

Interest in tuning the emission towards deep-red (DR) and near-infrared (NIR) regions is enhanced due to their fascinating applications in the field of organic light-emitting diodes (OLEDs), night-vision display and bio-imaging. In this regard, Naphthalimide based bidentate chromophoric ligand (L1, NIPy, 2‑butyl‑6-(pyridin-2-yl)-1H-benzo[de]isoquinoline-1,3(2H)‑dione) was utilized to prepare the DR emitting Ir(III) complexes [Ir(L1)2(L2)] (1) and [Ir(L1)2(L3)] (2) where L2 = 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridine and L3 = 1-(4-fluorophenyl)-3-methyl-1H-3λ4-imidazole). Complexes have been characterized by various analytical and spectroscopic methods, and 2 was further confirmed by a single crystal X-ray diffraction method. Strong intermolecular π···π interactions between the naphthalamide units in complex 2 lead to the formation of a multi-dimensional framework. These complexes show emissions in the range of 650–700 nm at room temperature, which extends up to the near-infra-red region (800 nm). The photophysical studies were supported by DFT and TD-DFT calculations. These types of naphthalimide-based Ir(III) complexes tend to show emissions in the NIR region which has potential applications in the field of photodynamic therapy and OLEDs.

Asymmetric tris-heteroleptic iridium(III) complexes towards blue phosphorescence: Synthesis, photophysics and OLED application

The development of blue phosphorescent iridium(III) complexes has been a formidable challenge in the field of organic light-emitting diodes (OLEDs). Unlike the conventional blue Ir-complex structure of symmetric tri-/bis-cyclometalated coordination geometry, we herein report a new configuration of [Ir(C1^N1)(C2^N2)(LX)]-tris-heteroleptic Ir(III) complex, where C1^N1 and C2^N2 denote two different main ligands, and LX stands for a third ancillary ligand. By the new configuration, two asymmetric blue iridium complexes, namely dfbpy-Ir-dfppy and dfppy-Ir-dfbpy, were designed and synthesized, displaying the highly desirable blue emission peaks at 450 nm and 452 nm, respectively. Based on the two new emitters, the blue OLEDs exhibited good performances with the maximum external quantum efficiency (EQEmax) reaching 8.5% and CIE(x, y) coordinates of (0.21, 0.31). This study provides a new strategy for efficient blue iridium complexes through reasonably engineering the asymmetric tris-heteroleptic Ir-complex configuration.

Rational design of hybridized local and charge-transfer (HLCT) emitters towards blue OLEDs with high luminance and low efficiency roll-off

Organic blue emitters have been get more and more attention by scientists and industries in the field of organic light-emitting diodes (OLEDs). The design of efficient blue emitters, especially deep-blue ones, is still a challenge because of their intrinsic wide band-gaps and unbalanced carrier mobilities. Herein, two donor‒π‒acceptor (D‒π‒A) type molecules with phenanthro[9,10-d]imidazole (PI) as A and pyridinyl as π-bridge were designed and synthesized by fine-turning the D moieties, namely mPTPA and mP3PCZ, respectively. Theoretical calculation and single-crystal analysis showed that there exist intramolecular hydrogen bond (IHB) interactions inducing small torsion angles between pyridinyl and adjacent phenyls. The rigid 9-phenyl-9H-carbazole (PCZ) and IHB interactions makes mP3PCZ exhibiting planar configuration along the long-axis of the molecule, which could increase the orbital overlap and oscillator strength (fos). The solvatochromic effect manifested that both two emitters have hybridized local and charge-transfer (HLCT) characteristics, and the excited state of mP3PCZ exhibited LE-dominated HLCT state which is beneficial for high photoluminescence efficiency. Ultimately, the non-doped devices based on mPTPA and mP3PCZ achieved maximum luminance larger than 12000 cd m−2. Furthermore, the doped device based on mP3PCZ exhibited maximum external quantum efficiency of 5.14% with low efficiency roll-off, and with the corresponding deep-blue Commission international de l’éclairage (CIE) coordinate of (0.166, 0.085).

Highly Twisted TADF Molecules and Their Applications in OLEDs.

Thermally activated delayed fluorescence (TADF) materials have attracted great potential in the field of organic light-emitting diodes (OLEDs). Among thousands of TADF materials, highly twisted TADF emitters has become a hotspot in recent years. Compared with traditional TADF materials, highly twisted TADF emitters tend to show multi-channel charge transfer characters and form rigid molecular structures. This is advantageous for TADF materials as non-radiative decay processes can be suppressed to facilitate efficient exciton utilization. Accordingly, OLEDs with excellent device performances have also been reported. In this review, we have summarized the recent progress of highly twisted TADF materials and related devices, and overviewed the molecular design strategies, photophysical studies and the performances of OLED devices. In addition, the challenges and perspectives of highly twisted TADF molecules and relative OLEDs are also discussed.

Sulfur-Decorated Nonaromatic Amine Emitters Towards Efficient Triplet Exciton Utilization in Organic Light-Emitting Diodes.

Purely organic compounds served as promising materials for organic electronics have intrigued extensive research focuses owing to their unique photophysical and electronic properties. In the field of organic light-emitting diodes (OLEDs), the utilization of triplet excitons is of great significance for realizing high-performance devices. In contrast to the traditional aromatic amine-based counterparts, sulfur atom with a high-level outer orbit simultaneously provides powerful electron-donating ability and striking spin-orbit coupling effect to facilitate the utilization of theoretically spin-forbidden triplet excitons, demonstrating great prospect in constructing highly emissive purely organic emitters for OLED applications. Herein, we summarize the currently developed sulfur-decorated nonaromatic amine-based emitters exhibiting attractive photoelectronic characteristics, and gain insight into the understanding of molecular design and photophysical processes of these emitters, providing new perspectives for enriching the existing luminescent material systems and designing high-performance emitters.

Exploring the Electroluminescent Applications of Imidazole Derivatives.

Recently, the fields of organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LECs) have improved tremendously with regard to tunable emission, efficiency, brightness, and thermal stability. Imidazole derivatives are excellent deep blue-green light-emitting layers in the OLED or LEC devices. This Review summarizes the major breakthroughs of various electroluminescence (EL) layers with imidazole-containing organic or organometallic derivatives, the molecular design principles, and their light-emitting performances as effective EL materials. The highly tunable chemical structures and flexible molecular design strategies of imidazole-based compounds are advantages that provide great opportunities for researchers. They can provide a good basis for the design and development of new EL materials with narrower emission and higher efficiency. Moreover, imidazole compounds have demonstrated breakthrough performances in thermally activated delayed fluorescence (TADF) properties where triplet excitons are utilized to inhibit anti-intersystem quenching, showing great promise in breaking the theoretical external quantum efficiencies (EQE) limits in traditional fluorescent devices.

The construction of white-light-emitting anisotropic hydrogel

In this work, hybrid anisotropic hydrogel is developed through dispersing carbon quantum dots, ultrahigh magnetic nanoparticle-coated alumina (Fe/Al2O3) platelets in acrylamide aqueous solution in the assistance of magnetic field, then fix the oriented structure via gelation. The aligned Fe/Al2O3 platelets result in formation of anisotropic structure, thus endows the hydrogels mechanical anisotropy and fluorescent anisotropy. White-light emission is obtained via varying the weight ratio of yellow-emitting ZnO QDs and blue-emitting N,S-CDs. This strategy not only enriches the mechanical/fluorescent dual anisotropic soft materials, but also have great potential application in the fields of organic light-emitting diodes, nonlinear optics and field effect transistors.

New Fields, New Opportunities and New Challenges: Circularly Polarized Multiple Resonance Thermally Activated Delayed Fluorescence Materials.

Circularly polarized luminescence (CPL) materials that concurrently exhibit high efficiency and narrowband emission are extremely promising applications in 3D and wide color gamut display. By merging the CPL optical property and multiple resonance (MR) induced thermally activated delayed fluorescence (TADF) characteristic into one molecule, a new strategy, namely CP-MR-TADF, is proposed to generate organic emitters with CPL activity, TADF and narrowband emission. High-performance red, green and blue CP-MR-TADF emitters have been developed following this strategy. Herein, the present status and progress of CP-MR-TADF materials in the field of organic light-emitting diodes (OLEDs) is summarized. Finally, for this rapidly growing new research field, the future opportunities are forecasted and the present challenges are discussed.

Paracyclophane-based bipolar near-ultraviolet emitters showing advanced circularly polarized luminescent properties

<p>As linking unit, [2.2]paracyclophane (PCP) has been inserted in between electron-donating groups (<em>i.e.</em> carbazole and 10<em>H</em>-phenoxazine) and electron-accepting groups (<em>i.e.</em> triphenyl-1,3,5-triazine and diphenylsulfone) to prepare a series of linear bipolar racemic near-ultraviolet (NUV) emitters owing to the planar chirality associated with the PCP. In toluene, the racemic bipolar PCP-based emitters can show emission wavelength in the range of 400-444 nm. Critically, very small Commission Internationale de L��Eclairage (CIE) chromaticity coordinate of y value of 0.03 has been achieved for the photoluminescent spectra of these bipolar racemic NUV emitters in solution. The PCP-based bipolar emitters can show efficient NUV emission with photoluminescent quantum yields (PLQY) of <em>ca.</em> 0.5 in doped mCP film. In addition, the enantiomers of the NUV emitters have been obtained to show obvious circular dichroism (CD) behavior and circularly polarized luminescence (CPL). The absorption asymmetric factor (<em>g</em><sub>abs</sub>) of <em>ca.</em> 4.4��10<sup>-4</sup> and photoluminescent asymmetric factor (<em>g</em><sub>PL</sub>) of <em>ca.</em> 1.5��10<sup>-3</sup> can be achieved by the PCP-based NUV enantiomers. After doped in the emission layer of organic light-emitting diodes (OLEDs), efficient NUV and deep blue-emitting OLEDs have been constructed. The NUV OLEDs based on the racemic emitters can achieve forward-viewing maximum external quantum efficiency (<em>��</em><sub>ext</sub>) of 5.03% and electroluminescence (EL) peak at 404 nm with CIE<sub>y</sub> of 0.05, while the OLEDs with deep blue emission can show <em>��</em><sub>ext</sub> of 4.12% and EL peak at 412 nm with CIE<sub>y</sub> of 0.08. Furthermore, the NUV chiral enantiomers can bring <em>��</em><sub>ext</sub> of 5.25% and EL peak at 404 nm with CIE<sub>y</sub> of 0.05, while the deep blue chiral enantiomers can give <em>��</em><sub>ext</sub> of 4.40% and EL peak at 412 nm with CIE<sub>y</sub> of 0.08. Clearly, these encouraging EL data show the great potential of these linear PCP-based bipolar emitters in the field of OLEDs.</p>

A Review on the Milestones of Blue Light-Emitting Materials in India

Since 1987 in the field of optoelectronics, organic light-emitting diodes (OLEDs) have secured their position because of their extreme use in panels of lighting applications such as TV and smartphone displays. At present, OLEDs are at top-notch position in the lighting market for their promising features. The field of OLEDs is rapidly growing day by day in academia and industry due to the success of OLEDs in the form of excellent efficiency, feasible methods, excellent lifetime, color purity, and superb device architecture. As a result, OLEDs are new profitable leading devices of the 21st century. However, the OLED industry has evolved in optoelectronics in the last 30 years and is advancing rapidly just because of the development in OLED materials (fluorescent, phosphorescent, thermally activated delayed fluorescent, and blue light-emitting materials). Blue light-emitting materials have achieved incredible popularity nationally and internationally. At the international level, USA, Japan, Korea, and Germany are at the top of the list in the production of OLEDs. India has also seen rapid progress in OLED development in the last 12 years and details of research in blue OLEDs by key players of India are involved in this report.1 Introduction1.1 OLED Construction1.2 Working of OLED2 OLED Development2.1 Historical Background of OLED2.1.1 International Status2.1.2 National Status3 Progress of Blue Emitters in India4 Present Scenario of Blue OLEDs5 Conclusions and Outlook