Sterically Hindered Tetradentate [Pt(O^N^C^N)] Emitters with Radiative Decay Rates up to 5.3 × 105 s-1 for Phosphorescent Organic Light-Emitting Diodes with LT95 Lifetime over 9200 h at 1000 cd m-2

Described here are sterically hindered tetradentate [Pt(O^N^C^N)] emitters (Pt-1, Pt-2, and Pt-3) developed for stable and high-performance green phosphorescent organic light-emitting diodes (OLEDs). These Pt(II) emitters exhibit strong saturated green phosphorescence (λmax = 517-531 nm) in toluene and mCP thin films with emission quantum yields as high as 0.97, radiative rate constants (kr) as high as 4.4-5.3 × 105 s-1 and reduced excimer emission, and with a preferential horizontally oriented transition dipole ratio of up to 84%. Theoretical calculations show that p-(hetero)arene substituents at the periphery of the ligand scaffolds in Pt-1, Pt-2, and Pt-3 can i) enhance the spin-orbit coupling (SOC) between the lower singlet excited states and the T1 state, and S0→Sn (n = 1 or 2) transition dipole moment, and ii) introducing additional SOC activity and the bright 1ILCT[π(carbazole)→π*(N^C^N)] excited state (Pt-2 and Pt-3), which are the main contributors to the increased kr values. Utilizing these tetradentate Pt(II) emitters, green phosphorescent OLEDs are fabricated with narrow-band electroluminescence (FWHM down to 36 nm), high external quantum efficiency, current efficiency up to 27.6% and 98.7 cd A-1, and an unprecedented device lifetime (LT95) of up to 9270 h at 1000 cd m-2 under laboratory conditions.

Synthesis and photometric properties of efficient white-emitting phosphor of M-AMG transition metal complexes for OLED applications

Progression in lighting sources mainly depended on new, robust energy-efficient diodes due to their advanced photometric properties. All organic light-emitting sources are constant energy-efficient devices and will be the light of the future. We explore the potential of transition metal complexes by focusing on cobalt(II), nickel(II), and copper (II) with aminoguanidine naphthoate as white phosphors in organic light-emitting diodes (OLEDs). The phosphors synthesized at optimized temperature were characterized structurally and thermally by spectral, thermal, and diffraction techniques. The photophysical studies of the target compound in several organic solvents having divergent polarity were also studied, and the results were exhibited. Photometric properties of the complexes were studied using photoluminescence, CIE (Commission internationale de l'éclairage) chromaticity coordinates, correlated color temperature, color purity, Duv, and TLCI (Television Lighting Consistency Index) to verify the applicability of complexes as phosphors. Excellent luminescence property with a high coloring index for (Cu(2NA-AMG-2H2 O)) opens the advanced avenue for light sources and serves as vital constituents for light-emitting diodes.

Synthesis of green emissive terbium(III) complexes for displays: Optical, electrochemical and photoluminescent analysis

A series of heteroleptic terbium(III) complexes with fluorinated 2-thenoyltrifluoroacetone (TTFA) and other heteroaromatic units have been synthesized. The developed heteroleptic complexes were inspected via elemental study, cyclic voltammetry, thermal analysis and spectroscopic investigations. Optical band-gap data proposed the conducting property of prepared complexes. The photoluminescence emission profiles illustrated peaks based on terbium(III) cation (Tb³⁺ ) positioned at ~617, 586, 546 and 491 nm, imputed to ⁵ D₄ to ⁷ F_J (J = 3,4,5,6) transitions separately. Most intense peak at 546 nm corresponding to ⁵ D₄  → ⁷ F₅ transition is accountable for the green emissive character of developed complexes. The luminous character of complexes reveals the sensitization of Tb³⁺ by ligands. Color parameters further corroborates the green emanation of Tb³⁺ complexes. The photometric characteristics of complexes recommended their usages in designing display devices.

Self-assembly of POSS-Polystyrene Bottlebrush Block Copolymers on an Angle-Robust Selective Absorber for Enhancing the Purity of Reflective Structural Color

A facile approach for improving color purity is explored by the introduction of an angle-robust selective absorber (ARSA) into bottlebrush block copolymer (BBCP)-based one-dimensional (1D) photonic crystals (PCs). The BBCPs of poly[(3-(12-(cis-5-norbornene-exo-2,3-dicarboximido)dodecanoylamino)propyl POSS)-block-(norbornene-graft-styrene)], P_x (x = 1-4), with ultrahigh molecular weights (M_n ∼ 2260 kDa) and low dispersities (D̵ ∼ 1.07) are synthesized by ring-opening metathesis polymerization. The 1D PCs of the lamellar structure are fabricated by self-assembly of the BBCP with different periodicities for full color-generation (blue, green, and red). The optically tailored substrate (i.e., ARSA) is used to modulate the spectral line shape with selective absorption in the near-infrared range. Optical simulation proposes the optimized 1D PC structures on the ARSA, and it provides the reproducibility of the predictable color. The simulated structures are well matched with the experimental results, verifying the enhancement of color saturation even at various incident angles (0-70°).

Crystal Structure and Optical Properties of ZnO:Ce Nano Film

ZnO and cerium-doped ZnO on a glass substrate have been prepared by the sol–gel method using the spin coating technique and water bath growth process. Ce-doping concentration on film structure, morphology, and optical properties is investigated. The result indicated that the hexagonal wurtzite ZnO with high crystalline quality formed on the substrate. The crystal parameters a and c decreased, crystal size increased, and the compressive strain formed after Ce-doping. Formed un-, 3%, 6%, 12% Ce-doped ZnO film has a spherical shape with a size between 8.6–31, 14–52, 18–56, and 20–91 nm, respectively. All films had good absorption of 300–400 nm ultraviolet light, in particular, the absorption of near ultraviolet (370–400 nm) increased after doping of Ce. The transmittance of light between 400–800 nm decreased with Ce-doping concentration. The band gap energy increased after Ce-doping reaching better optical behavior for preparing ZnO heterostructured thin-film. All film emitted intense blue emission under 375 nm excitation at room temperature. This indicated the film can have application in optoelectronic devices.

High-Performance Narrowband Pure-Red OLEDs with External Quantum Efficiencies up to 36.1% and Ultralow Efficiency Roll-Off

High-color-purity blue and green organic light-emitting diodes (OLEDs) have been resolved thanks to the development of B/N-based polycyclic multiple resonance (MR) emitters. However, due to the derivatization limit of B/N polycyclic structures, the design of red MR emitters remains challenging. Herein, a series of novel red MR emitters is reported by para-positioning N-π-N, O-π-O, B-π-B pairs onto a benzene ring to construct an MR central core. These emitters can be facilely and modularly synthesized, allowing for easy fine-tuning of emission spectra by peripheral groups. Moreover, these red MR emitters display excellent photophysical properties such as near-unity photoluminescence quantum yield (PLQY), fast radiative decay rate (k_r ) up to 7.4 × 10⁷ s^-1 , and most importantly, narrowband emission with full-width at half-maximum (FWHM) of 32 nm. Incorporating these MR emitters, pure red OLEDs sensitized by phosphor realize state-of-the-art device performances with external quantum efficiency (EQE) exceeding 36%, ultralow efficiency roll-off (EQE remains as high as 25.1% at the brightness of 50 000 cd m^-2 ), ultrahigh brightness over 130 000 cd m^-2 , together with good device lifetime.

Photoluminescence behavior of Eu3+ doped XAl2O4(X = Mg, Ca, Sr and Ba) phosphors: a comparative study

In this work, the Eu³⁺doped stuffed tridymite type structure of alkaline earths aluminate i.e. XAl₂O₄(X = Mg, Ca, Sr and Ba) phosphor materials have been synthesized by conventional high temperature solid state reaction method at 1623 K. The Samples were structurally and morphologically characterized by x-ray diffraction (XRD) and Scanning electron microscope (SEM) measurements. The vibrational behavior of the phosphor samples were investigated by Fourier transform infrared (FTIR) measurements. The phosphor samples emit intense red emission in 610-615 nm range due to⁵D₀ → ⁷F₂transition of Eu³⁺ion on excitation with charge transfer band (CTB) wavelength arising due to Eu³⁺-O^2-and also by the discrete bands of Eu³⁺ions .The decay time of⁵D₀level of Eu³⁺ion were recorded on excitation with 393 nm and by the CTB wavelength for all the four samples. The optimized 1 mol% Eu³⁺doped CaAl₂O₄phosphor exhibits optimum emission intensity and color purity under the excitation with 393 nm than others. The decay time is also found to be larger in the case of Eu³⁺doped CaAl₂O₄phosphor sample. Therefore, Eu³⁺doped CaAl₂O₄phosphor may be promising material for red color light emitting applications and white light generation.

Enhancing the Performance of Quasi-2D Perovskite Light-Emitting Diodes Using Natural Cyclic Molecules with Distinct Phase Regulation Behaviors

In this study, two natural small molecules, α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD), are used as additives to improve the performance of quasi-2D PEA₂Cs_n-1Pb_nBr_3n+1 (n = 3, herein) PeLEDs. Both of them are shown to efficiently passivate the quasi-2D perovskite films to afford improved film quality and morphology, but they exhibit distinct phase regulation behaviors possibly due to their different pore sizes. It reveals that α-CD effectively suppresses the formation of the low-n phases (n ≤ 2), while β-CD better regulates the phase with a medium-n value (n = 3). Because of effectively suppressing the formation of low-n phases, the CD-assisted quasi-2D perovskite films possess facilitated exciton energy transfer and reduced nonradiative recombination. Consequently, the optimized α-CD-derived PeLED shows the highest luminance (L_max) of 37,825 cd/m² with an external quantum efficiency (EQE) of 3.81%, while the β-CD-derived PeLED delivers a lower L_max of 24,793 cd/m² with an EQE of 3.09%. Compared to the pristine device, L_max is enhanced by 6.3 and 3.8 times for α-CD- and β-CD-based PeLEDs, respectively, and EQE is enhanced by ∼4.8 times for both devices; besides, both CD-assisted devices also exhibit improved color purity and a lower bias dependency of electroluminescent intensity.

Charge Transfer as the Key Parameter Affecting the Color Purity of Thermally Activated Delayed Fluorescence Emitters

The key factors determining the emission bandwidth of thermally activated delayed fluorescence (TADF) are investigated by combining computational and experimental approaches. To achieve high internal quantum efficiencies in a metal-free organic light-emitting diode via TADF, the first triplet (T₁) to first singlet (S₁) reverse intersystem crossing is promoted by configuring molecules in an electron donor-acceptor (D-A) alternation with a large dihedral angle, which results in a small energy gap (ΔE_ST) between S₁ and T₁ levels. This allows for effective non-radiative up-conversion of triplet excitons to singlet excitons that fluoresce. However, this traditional molecular design of TADF results in broad emission spectral bands (full-width at half-maximum = 70-100 nm). Despite reports suggesting that suppressing the D-A dihedral rotation narrows the emission band, the origin of emission broadening remains elusive. Indeed, our results suggest that the intrinsic TADF emission bandwidth is primarily determined by the charge transfer character of the molecule, rather than its propensity for rotational motion, which offers a renewed perspective on the rational molecular design of organic emitters exhibiting sharp emission spectra.

Water Passivation of Perovskite Nanocrystals Enables Air-Stable Intrinsically Stretchable Color-Conversion Layers for Stretchable Displays

Conventional organic light-emitting devices without an encapsulation layer are susceptible to degradation when exposed to air, so realization of air-stable intrinsically-stretchable display is a great challenge because the protection of the devices against penetration of moisture and oxygen is even more difficult under stretching. An air-stable intrinsically-stretchable display that is composed of an intrinsically-stretchable electroluminescent device (SELD) integrated with a stretchable color-conversion layer (SCCL) that contains perovskite nanocrystals (PeNCs) is proposed. PeNCs normally decay when exposed to air, but they become resistant to this decay when dispersed in a stretchable elastomer matrix; this change is a result of a compatibility between capping ligands and the elastomer matrix. Counterintuitively, the moisture can efficiently passivate surface defects of PeNCs, to yield significant increases in both photoluminescence intensity and lifetime. A display that can be stretched up to 180% is demonstrated; it is composed of an air-stable SCCL that down-converts the SELD's blue emission and reemits it as green. The work elucidates the basis of moisture-assisted surface passivation of PeNCs and provides a promising strategy to improve the quantum efficiency of PeNCs with the aid of moisture, which allows PeNCs to be applied for air-stable stretchable displays.

Narrow Bandpass and Efficient Semitransparent Organic Solar Cells Based on Bioinspired Spectrally Selective Electrodes

The visual aesthetic that involves color, brightness, and glossiness is of great importance for building integrated photovoltaics. Semitransparent organic solar cells (ST-OSCs) are thus considered as the most promising candidate due to their superiority in transparency and efficiency. However, the realization of high color purity with narrow bandpass transmitted light usually causes the severely suppressed transparency in ST-OSCs. Herein, we present a spectrally selective electrode (SSE) by imitating the integrating strategy of beetle cuticle for achieving narrow bandpass ST-OSCs with high efficiency and long-term stability. The proposed SSE allows for efficient light-selective passage, leading to tunable narrow bandpass transmitted light from violet to red. An optimized power conversion efficiency of 15.07% is achieved for colorful ST-OSCs, which exhibit color purity close to 100% and a peak transmittance approaching 30%. Long-term stability is also improved for ST-OSCs made with this SSE due to the light-rejecting and the moisture-blocking abilities. The realization of bright and colorful ST-OSCs also indicates the application potential of SSEs in light-emitting diodes, lasers, and photodetectors.

Design Strategy of Anthracene-Based Fluorophores toward High-Efficiency Deep Blue Organic Light-Emitting Diodes Utilizing Triplet-Triplet Fusion

In contrast to the red and green regions, conventional fluorescent emitters continue to serve as blue emitters in commercialized organic light-emitting diodes. Many researchers have studied anthracene moieties as blue emitters, given their appropriate energy levels and good emission properties. We herein report two new deep blue-emitting anthracene derivatives that include p-xylene as moieties connecting the anthracene cores to side groups. We enhanced the efficiency by maximizing triplet-triplet fusion (TTF) without sacrificing emission color. The large steric hindrance imposed by the methyl groups of p-xylene creates a perpendicular geometry between p-xylene and the neighboring aromatic rings. Any extension of π-conjugation is thus disrupted, and the isolated core anthracene moiety emits a deep blue color with a high photoluminescence quantum yield. Moreover, the extensive steric hindrance suppresses vibration and rotation because the molecules are rigid. The high horizontal dipole ratio attributable to the large aspect ratio increases the outcoupling efficiency of the emitted light. Furthermore, the charge mobility and triplet harvesting ability are enhanced by decreasing the bulkiness of the side groups. Molecular dynamics simulation revealed that the bulkiness of the side group significantly impacted molecular density, which in turn affected the charge transport and TTF. We used two molecules, 2PPIAn (containing a phenyl side group) and 4PPIAn (containing a terphenyl side group), to form nondoped emission layers that exhibited maximum external quantum efficiencies of 8.9 and 7.1% with Commission Internationale de L'Eclairage coordinates of (0.150, 0.060) and (0.152, 0.085), respectively.

Efficient and High-Color-Purity Light-Emitting Diodes Based on In Situ Grown Films of CsPbX3 (X = Br, I) Nanoplates with Controlled Thicknesses

We report a facile solution-based approach to the in situ growth of perovskite films consisting of monolayers of CsPbBr₃ nanoplates passivated by bulky phenylbutylammonium (PBA) cations, that is, two-dimensional layered PBA₂(CsPbBr₃)_n-1PbBr₄ perovskites. Optimizing film formation processes leads to layered perovskites with controlled n values in the range of 12-16. The layered perovskite emitters show quantum-confined band gap energies with a narrow distribution, suggesting the formation of thickness-controlled quantum-well (TCQW) structures. The TCQW CsPbBr₃ films exhibit smooth surface features, narrow emission line widths, low trap densities, and high room-temperature photoluminance quantum yields, resulting in high-color-purity green light-emitting diodes (LEDs) with remarkably high external quantum efficiencies (EQEs) of up to 10.4%. The solution-based approach is extended to the preparation of TCQW CsPbI₃ films for high-color-purity red perovskite LEDs with high EQEs of up to 7.3%.

Improved Efficiency and Enhanced Color Quality of Light-Emitting Diodes with Quantum Dot and Organic Hybrid Tandem Structure

Light-emitting diodes based on organic (OLEDs) and colloidal quantum dot (QLEDs) are widely considered as next-generation display technologies because of their attractive advantages such as self-emitting and flexible form factor. The OLEDs exhibit relatively high efficiency, but their color saturation is quite poor compared with that of QLEDs. In contrast, the QLEDs show very pure color emission, but their efficiency is lower than that of OLEDs currently. To combine the advantages and compensate for the weaknesses of each other, we propose a hybrid tandem structure which integrates both OLED and QLED in a single device architecture. With ZnMgO/Al/HATCN interconnecting layer, hybrid tandem LEDs are successfully fabricated. The demonstrated hybrid tandem devices feature high efficiency and high color saturation simultaneously; for example, the devices exhibit maximum current efficiency and external quantum efficiency of 96.28 cd/A and 25.90%, respectively. Meanwhile, the full width at half-maximum of the emission spectra is remarkably reduced from 68 to 44 nm. With the proposed hybrid tandem structure, the color gamut of the displays can be effectively increased from 81% to 100% NTSC. The results indicate that the advantages of different LED technologies can be combined in a hybrid tandem structure.

Isomeric Thermally Activated Delayed Fluorescence Emitters for Color Purity-Improved Emission in Organic Light-Emitting Devices

To improve the color purity of thermally activated delayed fluorescence (TADF) emitters, two isomeric compounds, oPTC (5'-(phenoxazin-10-yl)-[1,1':3',1″-terphenyl]-2'-carbonitrile) and mPTC (2'-(phenoxazin-10-yl)-[1,1':3',1″-terphenyl]-5'-carbonitrile), were designed and synthesized with same skeleton but different molecular restrictions. Both compounds exhibit similar highest occupied molecular orbital and lowest unoccupied molecular orbital distributions and energy levels, photophysical properties in nonpolar cyclohexane solution, and high external quantum efficiencies (19.9% for oPTC and 17.4% for mPTC) in the devices. With the increased molecular space restriction induced by the additional phenyl substitutions at meta-position of the cyano group from mPTC to oPTC, much weaker positive solvatochromic effect is observed for mPTC. And the color purity of emission from mPTC (full width at half-maximum (fwhm) of 86 nm) is also improved contrasted with that of oPTC (fwhm of 97 nm) in the devices. These results prove that increased restriction of the molecular structure is a simple and effective method to improve the color purity of the TADF emitters.