High Photoluminescence Quantum Efficiency Research Articles

The Rise of Colloidal Quantum Well Light‐Emitting Diodes

AbstractColloidal quantum wells (CQWs) recently become one of the most fascinating optoelectronics and microelectronics materials because of their outstanding properties, including ultranarrow emissions, high photoluminescence quantum efficiencies, and large exciton binding energies. Being a significant CQW application, CQW‐based light‐emitting diode (CQW‐LED) exhibits numerous merits such as extremely high color purity, high device efficiency, solution‐processable preparation, adjustable emission, and excellent compatibility with applied electronics. Herein, the progress of high‐performance CQW‐LEDs is insightfully reviewed, where the innovation of CQW materials as well as the optimization of device engineering are systematically summarized. First, the fundamental concepts in CQW‐LEDs are described, including how to realize CQW emitters, construct CQW‐LED architectures, and understand working mechanisms. Subsequently, various state‐of‐the‐art strategies for developing CQW‐LEDs are highlighted, where material optimizations, charge dynamics (e.g., charge injection, transport, and balance), and exciton behaviors (e.g., exciton generation and recombination) have an important effect on device performances. In the end, current challenges as well as future development opportunities are discussed. This work will present deep insights into achieving high‐performance CQW‐LEDs for next‐generation display, lighting, and optical communication technologies.

Regulating the Spatially Folded Arrangement of Donor and Acceptor Units to Achieve Efficient Orange‐Red Thermally Activated Delayed Fluorescence

Achieving efficient long‐wavelength Organic light‐emitting diodes (OLEDs) remains a challenge due to the energy gap law, which leads to increased non‐radiative decay rates. Herein, a strategy of constructing folded three‐dimensional architectures is proposed to explore new orange‐red thermally activated delayed fluorescence (TADF) emitters with through space charge transfer characteristics. Innovatively, naphthalene is selected as a bridge to connect O‐bridged triphenylamine donor and planar dibenzo[a,c]phenazine acceptor respectively via simple Suzuki‐Miyaura Coupling. In this way, a series of rigid orange‐red emitters with “U”‐shaped, folded “Z”‐shaped and “W”‐shaped configurations are elaborately constructed by modifying end groups, adjusting the numbers of naphthalene and donor, and regulating the linkage sites. The excited state natures and photophysical properties of the emitters can be effectively regulated and optimized by changing three‐dimensional architectures. Finally, the prepared emitter QX36 achieves a lower non‐radiative transition rate, a higher radiative rate and a higher photoluminescence quantum efficiency. Solution‐processed OLEDs based QX36 present the excellent electroluminescent performance with a maximum external quantum efficiency (EQE) of up to 32.3% and EQE of 20.6% at 1000 cd m‐2, which are the leading values of solution‐processed orange‐red OLEDs. This work demonstrates the promising potential of folded TADF emitters for future efficient solution‐processed long‐wavelength OLEDs.

Regulating the Spatially Folded Arrangement of Donor and Acceptor Units to Achieve Efficient Orange-Red Thermally Activated Delayed Fluorescence.

Achieving efficient long-wavelength Organic light-emitting diodes (OLEDs) remains a challenge due to the energy gap law, which leads to increased non-radiative decay rates. Herein, a strategy of constructing folded three-dimensional architectures is proposed to explore new orange-red thermally activated delayed fluorescence (TADF) emitters with through space charge transfer characteristics. Innovatively, naphthalene is selected as a bridge to connect O-bridged triphenylamine donor and planar dibenzo[a,c]phenazine acceptor respectively via simple Suzuki-Miyaura Coupling. In this way, a series of rigid orange-red emitters with "U"-shaped, folded "Z"-shaped and "W"-shaped configurations are elaborately constructed by modifying end groups, adjusting the numbers of naphthalene and donor, and regulating the linkage sites. The excited state natures and photophysical properties of the emitters can be effectively regulated and optimized by changing three-dimensional architectures. Finally, the prepared emitter QX36 achieves a lower non-radiative transition rate, a higher radiative rate and a higher photoluminescence quantum efficiency. Solution-processed OLEDs based QX36 present the excellent electroluminescent performance with a maximum external quantum efficiency (EQE) of up to 32.3% and EQE of 20.6% at 1000 cd m-2, which are the leading values of solution-processed orange-red OLEDs. This work demonstrates the promising potential of folded TADFemitters for future efficient solution-processed long-wavelength OLEDs.

Cyano‐Substituted Distyrylbenzene Derivative for Laser Media: High Solid‐State Luminescence and Processabilities by Tert‐Butyl Appending Design

AbstractTo create effective organic laser media, it is essential to design molecules with high photoluminescence (PL) quantum efficiency (ΦPL), solubility‐processability for facile crystal resonator formation, and structural tunability. Cyano‐β‐substituted distyrylbenzene (CDSB) is recognized as a potential solid‐luminogen but is limited by its quantum efficiency and solubility toward crystal resonator processability. Herein the rational design for high solid‐state luminescence and processability is demonstrated through designing tertiary‐butyl (tBu)‐appended approach. In contrast, tBu‐appended CDSB, namely tBuC, has good solubility for crystal growth processability and controllability, allowing for the formation of high ΦPL polymorphs. tBuC offers selective growth for (I) green‐emissive platelet crystals or (II) blue‐emissive needle crystals. The ΦPL is 0.72 for I and 0.91 for II. The ΦPL value for II is among the highest in the CDSB series, attributed to the segregated luminescent species based on bulky tBu. Lasing is observed for II due to the above characteristics. The addition of tBu offers a new strategy for crystal engineering toward the realization of laser media although it is a chemically simple approach.

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).

An effective design strategy for thermally activated delayed fluorescence emitters with aggregation-induced emission to enable sky-blue OLEDs that achieve an EQE of nearly 30.

Pure organic thermally activated delayed fluorescence (TADF) materials hold great promise for efficient organic light-emitting diodes (OLEDs), yet developing high-performance blue TADF materials that integrate short delayed lifetime with aggregation-induced emission (AIE) properties remains a significant challenge. In this study, we developed three highly-efficient blue TADF emitters (32clCBP, 32clCXT and 32PclCXT) featuring AIE character by integrating rigid π-extended donors with different acceptors. Notably, the doped 32PclCXT film achieved an exceptionally high photoluminescence quantum efficiency of up to 99% and a short delayed lifetime of 1.4 µs. Furthermore, the fabricated OLEDs based on 32PclCXT exhibited an impressive external quantum efficiency of 29.9% in the sky-blue region, along with low roll-off at high luminance. Therefore, this work establishes a new strategy for developing high-efficiency blue TADF materials and devices.

Strong coupling between a quasi-two-dimensional perovskite and a honeycomb plasmonic nanocone array

Recently organic-inorganic perovskite has been established as a promising platform for achieving room temperature exciton-polaritons, attributable to its superior optical coherence and robust exciton binding energies. However, when interfaced with metallic surfaces, the rapid degradation and quenching effect in perovskite have presented significant challenges, which critically hinders the exploration of light-matter interactions within metallic plasmonic structures. In this study, we report a quasi-two-dimensional lead halide perovskite that demonstrates a pronounced strong coupling phenomenon within an array of aluminum nanocones. The investigated quasi-two-dimensional perovskite structure exhibits high photoluminescence quantum efficiency and improved stability against metallic-induced degradation. Interestingly, the periodical arraying in honeycomb formation of plasmonic structure has advantages in angle-dependent dispersions and the loss neutralizing effectively. Besides, the plasmonic cone lattice characterized by its collective surface lattice resonance, features an exceptionally small mode volume and high quality, enhancing its interaction with the perovskite. A significant Rabi splitting of 243 meV is observed at an incident angle of 30°. The dynamics of the Rabi oscillation is revealed by transient absorption spectra and theoretically analyzed by cavity quantum electrodynamics. This advancement in polariton research paves the way for novel applications, including quantum sources, enhanced photon-electron conversion efficiencies, and low-threshold lasing.

Highly Efficient Near-Infrared Luminescent Radicals with Emission Peaks over 750 nm.

Purely organic molecules exhibiting near-infrared (NIR) emission possess considerable potential for applications in both biological and optoelectronic technological domains, owing to their inherent advantages such as cost-effectiveness, biocompatibility, and facile chemical modifiability. However, the repertoire of such molecules with emission peaks exceeding 750 nm and concurrently demonstrating high photoluminescence quantum efficiency (PLQE) remains relatively scarce due to the energy gap law. Herein, we report two open-shell NIR radical emitters, denoted as DMNA-Cz-BTM and DMNA-PyID-BTM, achieved through the strategic integration of a donor group (DMNA) onto the Cz-BTM and PyID-BTM frameworks, respectively. We found that the donor-acceptor molecular structure allows the two designed radical emitters to exhibit a charge-transfer excited state and spatially separated electron and hole levels with non-bonding characteristics. Thus, the high-frequency vibrations are effectively suppressed. Besides, the reduction of low-frequency vibrations is observed. Collectively, the non-radiative decay channel is significantly suppressed, leading to exceptional NIR PLQE values. Specifically, DMNA-Cz-BTM manifests an emission peak at 758 nm alongside a PLQE of 55 %, whereas DMNA-PyID-BTM exhibits an emission peak at 778 nm with a PLQE of 66 %. Notably, these represent the pinnacle of PLQE among metal-free organic NIR emitters with emission peaks surpassing 750 nm.

Highly Efficient Near‐Infrared Luminescent Radicals with Emission Peaks over 750 nm

AbstractPurely organic molecules exhibiting near‐infrared (NIR) emission possess considerable potential for applications in both biological and optoelectronic technological domains, owing to their inherent advantages such as cost‐effectiveness, biocompatibility, and facile chemical modifiability. However, the repertoire of such molecules with emission peaks exceeding 750 nm and concurrently demonstrating high photoluminescence quantum efficiency (PLQE) remains relatively scarce due to the energy gap law. Herein, we report two open‐shell NIR radical emitters, denoted as DMNA‐Cz‐BTM and DMNA‐PyID‐BTM, achieved through the strategic integration of a donor group (DMNA) onto the Cz‐BTM and PyID‐BTM frameworks, respectively. We found that the donor‐acceptor molecular structure allows the two designed radical emitters to exhibit a charge‐transfer excited state and spatially separated electron and hole levels with non‐bonding characteristics. Thus, the high‐frequency vibrations are effectively suppressed. Besides, the reduction of low‐frequency vibrations is observed. Collectively, the non‐radiative decay channel is significantly suppressed, leading to exceptional NIR PLQE values. Specifically, DMNA‐Cz‐BTM manifests an emission peak at 758 nm alongside a PLQE of 55 %, whereas DMNA‐PyID‐BTM exhibits an emission peak at 778 nm with a PLQE of 66 %. Notably, these represent the pinnacle of PLQE among metal‐free organic NIR emitters with emission peaks surpassing 750 nm.

Pure-Phase Perovskite Quantum Well for Green Light-Emitting Diodes.

Perovskite multiple quantum wells (MQWs) have shown great potential in the field of light-emitting diodes (LEDs). However, the random formation of QWs with varying well widths (n numbers) often leads to suboptimal interface defects and charge transport issues. Here, we reveal that the crystallization sequence of bromide-based perovskite MQWs is large-n QWs preceding small-n QWs. With this insight, we prevent the crystallization of subsequent small-n QWs by reducing the crystallization rate, ultimately resulting in the crystallization of only n = 5 QWs. This reduction in the crystallization rate is achieved through the chemical interaction of dual additives with perovskite constituents. Additionally, the chemical interaction effectively passivates the uncoordinated lead ions defects. Consequently, pure-phase perovskite QWs with a high photoluminescence quantum efficiency of 75% are achieved. The resulting green LEDs achieve a peak external quantum efficiency of 17.1% and a maximum luminance of 29,480 cd m-2, which is attractive for full-color display applications of perovskites.

Structural Changes and Differences in Intrinsic Photoluminescence of Four Cationic Two-Dimensional Lead Halide Frameworks Modulated by Synthesis Temperature.

Luminescent hybrid organolead halide materials with cationic inorganic frameworks and high chemical inertness have demonstrated broad application prospects in the visible light region. However, the corresponding relationship between structural changes and luminescence properties in such materials needs further clarification. Here, for the first time, we have successfully synthesized [Pb2X3](PDAH)(H2O) (X = Cl or Br, PDAH = C7H4NO4) single crystals via a facile hydrothermal method and then obtained [Pb11X14](PDA)4 (X = Cl or Br, PDA = C7H3NO4) at higher temperatures. The different synthesis temperatures resulted in significant differences in the luminescence properties of the two groups of structures. X-ray crystallography revealed the different degrees of distortion of the PbII centers' coordination environment between the two structures, which would significantly affect the electron-phonon coupling process under excited states and ultimately affect the emission properties originating from self-trapped excitons (STEs) of the two materials. In addition, density functional theory (DFT) calculations indicate that the two structures have different band gap characteristics due to the different proportions of inorganic and organic components, which also affect the optoelectronic properties of the two groups of materials. It is also worth mentioning that the broadband orange-light emission of [Pb11Br14](PDA)4 with a high photoluminescence quantum efficiency (PLQE) of 86% endows it with potential applications in WLEDs.

Design and synthesis of efficient red space-confined thermally activated delayed fluorescence emitter

Design and synthesis of efficient red space-confined thermally activated delayed fluorescence emitter

A zero-dimensional perovskite with high-efficiency luminescence and transient response for advanced information encryption

A zero-dimensional perovskite with high-efficiency luminescence and transient response for advanced information encryption

Highly efficient In(I) doped Cs3Cu2I5 single crystals for light-emitting diodes and gamma spectroscopy applications

Highly efficient In(I) doped Cs3Cu2I5 single crystals for light-emitting diodes and gamma spectroscopy applications

Intramolecular Hydrogen Bonding Rigidifying Flexible Bridge for Solution- and Vacuum-Processed TSCT-TADF Emitters.

To realize strong donor-acceptor face-to-face stacking for efficient through-space charge transfer-type thermally activated delayed fluorescence, a conceptually new design strategy is proposed to couple flexible bridges with adequate rigidity via built-in intramolecular hydrogen bonds (IHBs). The resulting emitter ACE-CN has a planarized benzyl methyl ether bridge self-anchored by the C-H···O IHB and shows a high photoluminescence quantum efficiency of 93%. The solution- and vacuum-processed devices exhibited high external quantum efficiencies of 11.8% and 24.7%, respectively.

Steric Control of Luminescence in Phenyl-Substituted Trityl Radicals.

Triphenylmethyl (trityl) radicals have shown potential for use in organic optoelectronic applications, but the design of practical trityl structures has been limited to donor/radical charge-transfer systems due to the poor luminescence of alternant symmetry hydrocarbons. Here, we circumvent the symmetry-forbidden transition of alternant hydrocarbons via excited-state symmetry breaking in a series of phenyl-substituted tris(2,4,6-trichlorophenyl)methyl (TTM) radicals. We show that 3-fold phenyl substitution enhances the emission of the TTM radical and that steric control modulates the optical properties in these systems. Simple ortho-methylphenyl substitution boosts the photoluminescence quantum efficiency from 1% (for TTM) to 65% at a peak wavelength of 612 nm (for 2-T3TTM) in solution. In the crystalline solid state, the neat 2-T3TTM radical shows a remarkably high photoluminescence quantum efficiency of 25% for emission peaking at 706 nm. This has implications in the design of aryl-substituted radical structures where the electronic coupling of the substituents influences variables such as emission, charge transfer, and spin interaction.

Molecular Engineering to Achieve AIE-active Fluorophore with Near-infrared (NIR) Emission and Temperature-sensitive Property.

Near-infrared organic small molecule luminescent materials have the advantages of easy modification, high quantum efficiency, good biological affinity, and color adjustability; thus, have promising application prospects in the fields of photoelectric devices, sensitive detection, photodynamic therapy, and biomedical imaging. However, traditional organic luminescent molecules have the problems of short emission wavelength, aggregation-causing emission quenching, and low quantum yield. Herein, we successfully synthesized four D-π-A-D light-emitting molecules based on electron-withdrawing malonitrile group and different electron-donating arylamine groups. These compounds showed satisfactory solvatochromism, aggregation-induced emission, red and near-infrared fluorescence, high photoluminescence quantum efficiency and temperature response properties. This successful example of molecular engineering provides a valuable reference for the development of advanced NIR materials with AIE and temperature-sensitive properties.

High-Brightness Blue Polariton Organic Light-Emitting Diodes.

Polariton organic light-emitting diodes (POLEDs) use strong light-matter coupling as an additional degree of freedom to tailor device characteristics, thus making them ideal candidates for many applications, such as room temperature laser diodes and high-color purity displays. However, achieving efficient formation of and emission from exciton-polaritons in an electrically driven device remains challenging due to the need for strong absorption, which often induces significant nonradiative recombination. Here, we investigate a novel POLED architecture to achieve polariton formation and high-brightness light emission. We utilize the blue-fluorescent emitter material 4,4'-Bis(4-(9H-carbazol-9-yl)styryl)biphenyl (BSBCz), which exhibits strong absorption and a highly horizontal transition-dipole orientation as well as a high photoluminescence quantum efficiency, even at high doping concentrations. We achieve a peak luminance of over 20,000 cd/m2 and external quantum efficiencies of more than 2%. To the best of our knowledge, these values represent the highest reported so far for electrically driven polariton emission from an organic semiconductor emitting in the blue region of the spectrum. Our work therefore paves the way for a new generation of efficient and powerful optoelectronic devices based on POLEDs.

Performance-improved narrowband near-ultraviolet emission from a simple butyl and cyanogen substituted indolocarbazole

High-efficiency narrowband near-ultraviolet (NUV) organic light-emitting diodes with high color purity have currently encountered great challenges. Here, using butyl (Bu) and cyanogen (CN) substituted strategy in the simplest polycyclic aromatic hydrocarbons of indolocarbazole (ICz), two simple emitters of BuICz and BuICzCN were demonstrated. This simple strategy was observed to enable both emitters to realize NUV emission at 380–381 nm with a small full width at half maximum (FWHM) of 21–23 nm and high photoluminescent quantum efficiency of 50%–59% in toluene solution. Furthermore, the BuICzCN doped devices exhibited a slightly blueshifted narrowband NUV electroluminescence at 388 nm with a small FWHM of 32.3 nm but a higher external quantum efficiency of 3.92% in comparison with the BuICz doped devices. This work provides a path to realize high-performance narrow-band NUV emission.

Enhancing Light Out-coupling in Perovskite Light-Emitting Diodes through Plasmonic Nanostructures.

Perovskite light-emitting diodes (PeLEDs) have emerged as promising candidates for lighting and display technologies owing to their high photoluminescence quantum efficiency and high carrier mobility. However, the performance of planar PeLEDs is limited by the out-coupling efficiency, predominantly governed by photonic losses at device interfaces. Most notably, the plasmonic loss at the metal electrode interfaces can account for up to 60% of the total loss. Here, we investigate the use of plasmonic nanostructures to improve the light out-coupling in PeLEDs. By integrating these nanostructures with PeLEDs, we have demonstrated an effectively reduced plasmonic loss and enhanced light out-coupling. As a result, the nanostructured PeLEDs exhibit an average 1.5-fold increase in external quantum efficiency and an ∼20-fold improvement in device lifetime. This finding offers a generic approach for enhancing light out-coupling, promising great potential to go beyond existing performance limitations.