Metal-free phthalocyanine single crystal: Solvothermal synthesis and near-infrared electroluminescence

A metal-free purple H₂Pc single crystal was synthesized by a facile solvothermal method, and its solubility and near-infrared (NIR) optical properties were also investigated due to its potential applications as a light-emitting layer for OLEDs. The H₂Pc single crystal is insoluble in 1-chlorine naphthalene and other organic solvents. It gives a wide absorption in the range from 620 nm to 679 nm and a wide emission in near 922 nm. As an active light-emitting layer, H₂Pc was employed to fabricate electroluminescent (EL) devices with a structure of ITO/NPB (30 nm)/Alq₃:H₂Pc (30 nm)/BCP (20 nm)/Alq₃ (20 nm)/Al. The emission center is at 936 nm when the H₂Pc doping concentration is 20 wt%. The doping concentration strongly governs the emission intensity. When doping concentration decreases from 10 wt% to 1 wt%, the emission intensity remarkably fades, and simultaneously the emission center undergoes a blue shift.     

Efficient Near-Infrared Electroluminescence from Lanthanide-Doped Perovskite Quantum Cutters

Perovskite nanocrystals (PeNCs) deliver size- and composition-tunable luminescence of high efficiency and color purity in the visible range. However, attaining efficient electroluminescence (EL) in the near-infrared (NIR) region from PeNCs is challenging, limiting their potential applications. Here we demonstrate a highly efficient NIR light-emitting diode (LED) by doping ytterbium ions into a PeNCs host (Yb³⁺ : PeNCs), extending the EL wavelengths toward 1000 nm, which is achieved through a direct sensitization of Yb³⁺ ions by the PeNC host. Efficient quantum-cutting processes enable high photoluminescence quantum yields (PLQYs) of up to 126 % from the Yb³⁺ : PeNCs. Through halide-composition engineering and surface passivation to improve both PLQY and charge-transport balance, we demonstrate an efficient NIR LED with a peak external quantum efficiency of 7.7 % at a central wavelength of 990 nm, representing the most efficient perovskite-based LEDs with emission wavelengths beyond 850 nm.     

Dibenzothiophene Sulfone-Based Ambipolar-Transporting Blue-Emissive Organic Semiconductors Towards Simple-Structured Organic Light-Emitting Transistors

The development of blue-emissive ambipolar organic semiconductor is an arduous target due to the large energy gap, but is an indispensable part for electroluminescent device, especially for the transformative display technology of simple-structured organic light-emitting transistor (SS-OLET). Herein, we designed and synthesized two new dibenzothiophene sulfone-based high mobility blue-emissive organic semiconductors (DNaDBSOs), which demonstrate superior optical property with solid-state photoluminescent quantum yield of 46–67 % and typical ambipolar-transporting properties in SS-OLETs with symmetric gold electrodes. Comprehensive experimental and theoretical characterizations reveal the natural of ambipolar property for such blue-emissive DNaDBSOs-based materials is ascribed to a synergistic effect on lowering LUMO level and reduced electron injection barrier induced by the interfacial dipoles effect on gold electrodes due to the incorporation of appropriate DBSO unit. Finally, efficient electroluminescence properties with high-quality blue emission (CIE (0.179, 0.119)) and a narrow full-width at half-maximum of 48 nm are achieved for DNaDBSO-based SS-OLET, showing good spatial control of the recombination zone in conducting channel. This work provides a new avenue for designing ambipolar emissive organic semiconductors by incorporating the synergistic effect of energy level regulation and molecular-metal interaction, which would advance the development of superior optoelectronic materials and their high-density integrated optoelectronic devices and circuits.     

NARROW BANDWIDTH BRIGHT SCARLET ORGANIC ELECTROLUMINESCENT DEVICE BASED ON N,N'-BIS[4-(N,N-DIMETHYLAMONO)-BENZYLIDENE]-DIAMINOMALEONITRILE DYE

A novel red dye, N, N'-bis[4-(N,N-dimethylamino)-benzylidene]diaminomaleonitrile (BAM), was prepared by reacting diaminomaleonitrile with 4-(N,N-dimethylamino)-benzaldehyde and were characterized by ¹H NMR, UV absorption and photoluminescence. The BAM dye showed an absorption peak wavelength of 530 nm and bright photoluminescence with a peak wavelength at 675 nm. It was used as the doped emitter for fabricating a bright scarlet organic electroluminescent (EL) device. The structure of the double-layer EL device consisted of a hole-transport layer and a luminescent layer between ITO glass and magnesium electrodes. The hole-transport layer was a poly(N-vinylcarbazole) (PVK) film. The luminescent layer consisted of a host material, 8-hydroxyquinoline aluminum (Alq₃), and BAM dye as the dopant. A bright light with the peak of 620 nm and narrow bandwidth of 50 nm was obtained in the device with a maximum luminance of 6230 cd/m². The emission spectra almost unchanged as the luminance increased with increasing injection current and the bias voltage. A tentative explanation from both the electronic distribution viewpoint and the molecular geometric analysis for the narrow bandwidth of this red dye was offered.     

Light Emitting Diodes Prepared from Terbium‐Immobilized Polyurea Chelates

Abstract

This article describes the synthesis and application of poly(1,4‐phenylene‐2,6‐pyridylurea) (MCPU) as a charge transporting and rare earth metal chelating host matrix for organic light emitting diodes (OLEDs). The chelation between MCPU and Terbium (Tb³⁺) (the rare earth metal used in this study), is facile in nature and persists in thin films obtained by spin coating onto various substrates. Multiple polymer chelating moieties at each Tb ion site may derive from MCPU repeat units from a single polymer chain or two polymer chains, and their respective structures are proposed. The emissive properties of these films in the presence and absence of Terbium (Tb³⁺) were characterized by steady state UV‐VIS absorption spectroscopy and photoluminescence (PL) spectroscopy. The PL emission from Tb(MCPU) films indicate contribution from both the host MCPU and the Tb ions. The incorporation of these films in OLEDs employing different device architectures yields electroluminescence spectra, which show the characteristic emission of the Tb ions but no emission from the host polymer matrix. Although these devices are not optimized, they exhibit an order of magnitude higher external quantum efficiency as compared to that of conventional aluminum tris 8‐hydroxyquinoline (Alq₃) based OLEDs, at low current densities.     

Synthesis,structure, and luminescence of rhenium(I) complexes with substituted bipyridines

Two new rhenium(I) complexes chelated by a substituted 2,2′-bipyridine with general formula Re(CO)₃LCl, where L?=?6?-(2″-methoxyphenyl)-2,2′-bipyridine (L₁ ) and 6?-(4″-diphenylaminophenyl)-2,2′-bipyridine (L₂ ), are synthesized and characterized by IR, NMR, and elemental analysis. Structure of 1 was determined by single-crystal X-ray crystallography, revealing that rhenium is six-coordinate octahedral. The electrochemical, photophysical, and thermal properties of the two rhenium(I) complexes were investigated. Electroluminescent devices were fabricated by doping 1 in polymer blend host of poly(vinylcarbazole) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole using simple solution spin-coating technique. The device exhibits a maximum current efficiency of 2.97?cd?A^?1 and peak brightness in excess of 2390?cd?m^?2.     

Polycyclic aromatic hydrocarbon-bridged coumarin derivatives for organic light-emitting devices

Three biscoumarin dyes bridged by polycyclic aromatic bridges (anthracen, pyrene and dibenzo[g,p]chrysene) were prepared as the emissive materials for the application of organic light-emitting devices. The relationship between their structures, photophysical properties, electrochemical properties and performances of organic light-emitting devices are described. The multilayered doped devices with a configuration of ITO/NPB (20 nm)/TBADN: biscoumarin compound (x wt%, 30 nm)/TPBi (30 nm)/Liq (2 nm)/Al (100 nm) have been successfully fabricated by vacuum-deposition method. All the devices showed green emission with high electroluminescent efficiencies. Especially, the device based on the compound containing pyrene as a bridge group at 7% doping concentration showed the best performance with a maximum brightness of 10552 cd/m², maximum luminous efficiency of 5.39 cd/A and maximum external quantum efficiency (EQE) of 2.35%.     

Electroluminescence of colloidal ZnSe quantum dots

The article reports a green chemical synthesis of colloidal ZnSe quantum dots at a moderate temperature. The prepared colloid sample is characterised by UV-vis absorption spectroscopy and transmission electron microscopy. UV-vis spectroscopy reveals as-expected blue-shift with strong absorption edge at 400 nm and micrographs show a non-uniform size distribution of ZnSe quantum dots in the range 1-4 nm. Further, photoluminescence and electroluminescence spectroscopies are carried out to study optical emission. Each of the spectroscopies reveals two emission peaks, indicating band-to-band transition and defect related transition. From the luminescence studies, it can be inferred that the recombination of electrons and holes resulting from interband transition causes violet emission and the recombination of a photon generated hole with a charged state of Zn-vacancy gives blue emission. Meanwhile electroluminescence study suggests the application of ZnSe quantum dots as an efficient light emitting device with the advantage of colour tuning (violet-blue-violet).     

The enhanced performance of organic light-emitting diodes by using PCBM as the anode modification layer

[6,6]-Phenyl C₆₁ butyric acid methyl ester (PCBM) is used to modify an indium tin oxide (ITO)-coated substrate. Organic light-emitting diodes (OLEDs) using PCBM as the anode modification layer are fabricated. The dependence of performance on different PCBM thicknesses is also investigated. When the thickness of the PCBM film is appropriate, the brightness and efficiency of OLEDs are enhanced, which is attributed to an enhanced hole injection and an improved carrier balance. The enhancement of hole injection was ascribed to the formation of a dipole layer at the anode/organic interface.     

新型可溶性酞菁的合成和光致发光及电致发光性质

以3(4)-硝基邻苯二腈和对甲氧基苯酚为原料, 经过两步反应合成了α(β)-四(4-甲氧基苯氧基)酞菁锌, 通过谱学方法和元素分析表征了其结构. 比较研究其溶液和旋涂膜的紫外可见光谱、光致发光光谱和固体薄片的光致发光光谱. 并以其旋涂膜为发光层制备了电致发光器件, 研究其电致发光性质. 结果表明, 固态酞菁材料与其溶液的荧光发射波长相比均向长波方向移动了145 nm以上, 而且都有不同程度的宽展. 在固态下β-位取代酞菁荧光发射波长红移的程度比α-位取代酞菁大. 电致发光光谱的发射波长和其旋涂膜的光致发光光谱的发射波长基本一致, 大约在856和862 nm左右. 在固态下酞菁分子排列紧密, 分子间相互作用增强导致了荧光发射波长的巨大红移.