High‐efficiency organic electroluminescent devices using iridium complex emitter and arylamine‐containing polymer buffer layer

We have developed efficient organic electroluminescent (EL) devices using a phosphorescent material, tris(2‐phenylpyridine) iridium, Ir(ppy)₃, as an emitter material and a polymer buffer layer, tetraphenyldiamine‐containing poly(arylene ether sulfone) (PTPDES) doped with tris(4‐bromophenyl) aminium hexachloroantimonate (TBPAH) as an electron acceptor. In this device, a high external quantum efficiency of 21.6% and a luminous efficiency of 82 lm/W (77 cd/A) at 3.0 V were obtained. These high efficiencies can be explained by high quantum efficiency due to phosphorescent Ir(ppy)₃ and high luminous efficiency realized by the use of the polymer buffer layer. Copyright © 2002 John Wiley & Sons, Ltd.     

Tuning of metal work function with organic carboxylates and its application in top-emitting electroluminescent devices

By fine-tuning of work functions and thus the hole-injection properties of Ag and Al anodes, an electroluminescent device was achieved by using various self-assembled monolayers of organic carboxylate on the electrode surfaces. The IR spectra evidenced different binding behaviors of the carboxylates on Ag and Al. A correlation between the change in work function with the effective dipole moment along the surface normal and the currents in the hole-only devices was observed. These self-assembled-monolayer-modified metals were used as anodes in the fabrication of top-emitting organic light-emitting diodes (TOLEDs). The TOLED with the Ag anode modified by the perfluoroalkanoate exhibited a luminous efficiency as high as 18 cdA(-1), superior to that of the Ag2O-based device. With Al as the anode, the highest luminous efficiency was merely 6 cdA(-1) and decayed rapidly. The poorer EL property and performance of Al-based TOLEDs could be attributed to the weaker ionic bindings of carboxylates on Al and the weaker microcavity effect resulting from the inferior reflectivity of Al as compared to Ag.     

p型结构的高效有机白光器件

制备了一种高效的p型结构的红光有机发光器件.对比发现这种p型结构的器件在亮度、电流密度以及效率等方面都优于普通的器件.将这种p型结构应用到白光器件上,使用红、绿、蓝三种发光材料作为发光层,通过调节它们各自的发射强度来实现白光发射.优化条件后,制得白光器件的最大电流效率和功率效率分别为19.3cd.A-1和12.1lm.W-1,最大亮度可达到31770cd.m-2,在5到11V驱动电压范围内为较纯正的白光,器件的可重复性好.     

Impedance measurements on QLED devices: analysis of high-frequency loop in terms of material properties

Electrochemical impedance spectroscopy is used to study red and green quantum-dot light-emitting diodes devices. The high-frequency loop is interpreted in terms of the thickness, dielectric constant, and resistivity distribution of the hole-injection layer. The analysis employed the device capacitance obtained from a measurement model analysis, the film thickness measured by scanning electron microscopy, and an interpretation of the impedance based on a power-law model. Impedance measurements performed on hole-transport–only devices yielded results that were consistent with the interpretation of the high-frequency capacitive loop in terms of the properties of the hole-injection layer.

     

Carbazole compounds as host materials for triplet emitters in organic light-emitting diodes: polymer hosts for high-efficiency light-emitting diodes

A carbazole homopolymer and carbazole copolymers based on 9,9'-dialkyl-[3,3']-bicarbazolyl, 2,5-diphenyl-[1,3,4]-oxadiazole and 9,9-bis(4-[3,7-dimethyloctyloxy]phenyl)fluorene were synthesized and their electrical and photophysical properties were characterized with respect to their application as host in phosphorescent polymer light-emitting diodes. It is shown that the triplet energy of a polymer depends on the specific connections between its building blocks. Without changing the composition of the polymer, its triplet energy can be increased from 2.3 to 2.6 eV by changing the way in which the different building blocks are coupled together. For poly(9-vinylcarbazole) (PVK), a carbazole polymer often used as host for high-energy triplet emitters in polymer light-emitting diodes, a large hole-injection barrier of about 1 eV exists due to the low-lying HOMO level of PVK. For all carbazole polymers presented here, the HOMO levels are much closer to the Fermi level of a commonly used anode such as ITO and/or a commonly used hole-injection layer such as PEDOT:PSS. This makes high current densities and consequently high luminance levels possible at moderate applied voltages in polymer light-emitting diodes. A double-layer polymer light-emitting diode is constructed comprising a PEDOT:PSS layer as hole-injection layer and a carbazole-oxadiazole copolymer doped with a green triplet emitter as emissive layer that shows an efficacy of 23 cd/A independent of current density and light output.     

Organic electroluminescent device with aromatic amine-containing polymer as a hole transport layer (II): Poly(arylene ether sulfone)-containing tetraphenylbenzidine

Organic electroluminescent devices were fabricated using a poly(arylene ether sulfone)-containing tetraphenylbenzidine (PTPDES) and tris(8-quinolinolato)-aluminum(III) complex, Alq, as the hole transport layer and the electron-transporting emitter layer, respectively. A device structure of glass substrate/indium—tin oxide (ITO)/PTPDES/Alq/Mg : Ag was employed. Hole injection from ITO through the PTPDES layer to the Alq layer and concomitant electroluminescence from the Alq layer were observed. Bright green light with a luminance of 14,000 cd/m² was observed at a drive voltage of 14 V, indicating that the polymer possesses a high hole mobility and a high electron-blocking capability.     

氧化石墨烯掺杂PEDOT:PSS作为空穴注入层对有机发光二极管发光性能的影响

研究了氧化石墨烯(GO)掺杂聚(3,4-亚乙二氧基噻吩):聚(苯乙烯磺酸) (PEDOT:PSS)作为空穴注入层对有机发光二极管发光性能的影响. 在PEDOT:PSS水溶液中掺入GO, 经过湿法旋涂和退火成膜后, 不仅提高了空穴注入层的空穴注入能力和导电率, 透光率也得到了相应的提高, 从而使得有机发光二极管(OLED)器件的发光性能得到了提升. 通过优化GO掺杂量发现, 当GO掺杂量为0.8%(质量分数)时, 空穴注入层的透光率达到最大值(96.8%), 此时获得的OLED器件性能最佳, 其最大发光亮度和最大发光效率分别达到17939 cd·m^-2和3.74 cd·A^-1. 与PEDOT:PSS 作为空穴注入层的器件相比, 掺杂GO后器件的最大发光亮度和最大发光效率分别提高了46.6%和67.6%.     

Novel Hyperbranched Phthalocyanine as a Hole Injection Nanolayer in Organic Light‐Emitting Diodes

A novel organic hyperbranched copper phthalocyanine was synthesized for use as a hole injection nanolayer on ITO in organic light‐emitting diodes (OLEDs). This material is soluble in organic solvents which allows for processing under anhydrous conditions, unlike water based conventional polymer hole injection layer materials such as poly(3,4‐ethylenedioxythiophene)(PEDOT)/polystyrene sulfonate (PSS). The hyperbranched layer increased the luminous efficiency and brightness of single layer OLED devices, in addition to reducing current leakage which causes crosstalk in panel devices, compared to devices prepared from PEDOT/PSS. Therefore, this material is more suitable for OLED applications due to its processing and performance advantages over conventional commercial conducting polymer compositions.

     

Novel liquid crystalline organic semiconducting oligomers incorporating N-heterocyclic carbazole moieties for fluorescent OLEDs

A novel class of nematic liquid crystalline organic semiconducting oligomers incorporating N-heterocyclic carbazole moieties has been synthesised using simple and highly efficient reaction pathways. The electroluminescent colour of these novel oligomers can be varied in a controlled manner by molecular design. The values of the ionisation potential and the electron affinity of these electroluminescent oligomers can also be matched by structural design to the Highest Occupied Molecular Orbital (HOMO) energy level of the electron-blocking layer and the Lowest Unoccupied Molecular Orbital (LUMO) energy level of electron-transporting layer in the Organic light emitting diodes to create low charge-injection barriers for electrons and holes, respectively leading to electroluminescence with an efficacy up to 4.1 cd A^?1.     

Architectural and structural optimization of the protective polymer layer for enhanced targeting

Using Monte Carlo simulations we study the influence of ligand architecture (valence, branching length) and structure (polydispersity) of a flat protective polymer layer on the accessibility of its functional groups and efficiency of receptor targeting. Two types of receptor surfaces were considered: the surface homogeneously covered with receptors and the surface containing a finite number of receptor sites. We found that multivalent ligands provide a larger density of targeting groups on the periphery of the layer compared to monovalent ligands for the same overall number of targeting groups per polymer layer. Because of their cooperativity in binding, multivalent ligands were also considerably more efficient in binding to both types of receptor surfaces. With an increase of ligand valence the number of functional groups attached to receptors noticeably increases. Short-branched divalent ligands show an especially high cooperativity in binding to closely packed receptors. However, in the case of immobile receptors separated by a finite distance from each other, the average distance between the functional groups belonging to the same short divalent ligand is too small to reach different receptors simultaneously and the receptor binding is less efficient than in the monovalent ligand case. Using a bidisperse protective polymer layer formed by short nonfunctional polymers and long functionalized polymers considerably increases the fraction of functional groups on the periphery of the layer. Simulations of receptor binding confirm the high efficiency of receptor targeting by bidisperse polymer layers, which is achieved by means of larger compressibility and higher capability of the ligands to reach out compared to the corresponding monodisperse layers. The concepts of multivalent ligands and a bidisperse protective polymer layer each have their own advantages which can be combined for an enhanced targeting effect.     

The preparation and properties of chromium oxide nanolayers on semiconducting matrices

Ultrathin chromium oxide layers (nanostructures) were synthesized on the (100) and (110) silicon and gallium arsenide surfaces by molecular layering (atom layer deposition). Technological factors were shown to influence the main rules governing nanolayer formation, nanolayer composition, and some electric nanolayer characteristics.     

Enhancing the device performance of a blue light‐emitting copolymer using CdSe/ZnS quantum dots

An alternating triarylamine‐functionalized fluorene‐based copolymer synthesized using a Suzuki–Miyaura cross‐coupling procedure is used as blue emitting layer in polymer light‐emitting diodes (PLEDs). Subsequently, the effects of CdSe/ZnS quantum dots (QDs) on the optoelectronic properties of the copolymer are investigated. Therefore, CdSe/ZnS QDs are embedded into the copolymer matrix and hybrid PLEDs are fabricated. The devices comprised of CdSe/ZnS QDs reveal enhanced performances, yielding about 3.4 times more luminous efficiency than that of the device without QDs. Further enhancement is achieved by using electron transport layer; the luminous efficiency rose from 0.065 to 1.740 cd A^?1 for the hybrid PLEDs, corresponding to a superb 27‐fold intensification of the efficiency. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 147–156     

Non-Aufbau Principle to Achieve High Stability Organic Luminescence Radicals

To solve the problem of stability of organic luminescence radicals, Li et al. proposed a new kind of organic luminescence radicals with non-Aufbau electronic structure by using donor-acceptor molecular structure. The stability of this kind of radicals was greatly improved and the high luminous efficiency was maintained. Using a non-Aufbau radical as the emission layer of an OLED, the maximum external efficiency of 5.3% has been achieved, which is among the highest efficiencies for pure organic near-intrared electroluminescence. This work has been published online in the Nature Materials on July 22,2019.     

反构造原理策略实现高稳定有机发光自由基

To solve the problem of stability of organic luminescence radicals, Li et al. proposed a new kind of organic luminescence radicals with non-Aufbau electronic structure by using donor-acceptor molecular structure. The stability of this kind of radicals was greatly improved and the high luminous efficiency was maintained. Using a non-Aufbau radical as the emission layer of an OLED, the maximum external efficiency of 5.3% has been achieved, which is among the highest efficiencies for pure organic near-infrared electroluminescence. This work has been published online in the Nature Materials in July 22, 2019.     

Structure of ultrathin polyethylene layers in multilayer films

The crystalline structures of “microlayer” and “nanolayer” polyethylene have been examined in coextruded films comprised of alternating layers of high-density polyethylene and polystyrene. Transmission electron microscopy (TEM), small-angle x-ray scattering (SAXS), and wide-angle x-ray scattering (WAXS) reveal that microlayer polyethylene, where the layer thickness is on the order of several microns, crystallizes with the normal unoriented lamellar morphology. In nanolayer films, where the film thickness of tens of nanometers is on the size scale of molecular dimensions, lamellae are oriented with the long axes perpendicular to the extrusion direction in a row-nucleated morphology similar to structures described in the literature. The lamellae are partially twisted about the long axes. The preferred twist angles of ±40° orient the lamellar surfaces normal to the layer surface. The row-nucleated morphology imparts highly anisotropic mechanical properties to the nanolayer polyethylene.     

Synthesis of Bi-O- and Bi-V-O-containing Nanolayers by Ionic Deposition

A possibility of preparing Bi₂O₃ and BiVO₄ nanolayers by ionic deposition on the silica surface was shown for the first time. The influence of the concentration and pH of reactant solutions and of the number of ionic deposition cycles on the kinetics of the nanolayer growth was studied. The conditions were determined for the formation of a nanolayer by a reaction in a layer of ions sorbed on the surface. The thickness of the synthesized layers was determined by ellipsometry. The layer compositions were studied by X-ray spectral microanalysis, X-ray photoelectron spectroscopy, and UV and IR Fourier transform spectroscopy. The structure of the layers was studied by powder X-ray diffraction.     

PbS/CdS-sensitized mesoscopic SnO2 solar cells for enhanced infrared light harnessing

Metal oxide semiconductors with lower lying conduction band minimum and superior electron mobility are essential for efficient charge separation and collection in PbS-sensitized solar cells. In the present study, mesoscopic SnO(2) was investigated as an alternative photoanode to the commonly used TiO(2) and examined comprehensively in PbS-sensitized liquid junction solar cells. To exploit the capability of PbS in an optimized structure, cascaded nPbS/nCdS and alternate n(PbS/CdS) layers deposited by a successive ionic layer adsorption and reaction method were systematically scrutinized. It was observed that the surface of SnO(2) has greater affinity to the growth of PbS compared with TiO(2), giving rise to much enhanced light absorption. In addition, the deposition of a CdS buffer layer and a ZnS passivation layer before and after a PbS layer was found to be beneficial for efficient charge separation. Under optimized conditions, cascaded PbS/CdS-sensitized SnO(2) exhibited an unprecedented photocurrent density of 17.38 mA cm(-2) with pronounced infrared light harvesting extending beyond 1100 nm, and a power conversion efficiency of 2.23% under AM 1.5, 1 sun illumination. In comparison, TiO(2) cells fabricated under similar conditions showed much inferior performance owing to the less efficient light harnessing of long wavelength photons. We anticipate that the systematic study of PbS-sensitized solar cells utilizing different metal oxide semiconductors as electron transporters would provide useful insights and promote the development of semiconductor-sensitized mesoscopic solar cells employing panchromatic sensitizers.     

White electroluminescent single‐polymer achieved by incorporating three polyfluorene blue arms into a star‐shaped orange core

A series of star‐like dopant/host single‐polymer systems with a D‐A type star‐shaped orange core and three blue polyfluorene arms were designed and synthesized. Through tuning the doping concentration of the orange core and thermal annealing treatment of white polymer light‐emitting diodes based on them, highly efficient white electroluminescence has been achieved. A typical single‐layer device (ITO/PEDOT:PSS/polymer/Ca/Al) realized pure white emission with a luminous efficiency of 16.62 cd A^?1, an external quantum efficiency of 6.28% and CIE coordinates of (0.33, 0.36) for S‐WP‐002TPB3 containing 0.02 mol % orange core. The high efficiency of the devices could be mainly attributed to the suppressed concentration quenching of the dopant units, more efficient energy transfer from polymer host to orange dopant and thermal annealing‐induced α‐phase polyfluorene (PF) self‐dopant in amorphous PF host. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

CdS量子点敏化ZnO纳米棒阵列电极的制备和光电化学性能

采用连续式离子层吸附与反应法制备了CdS量子点敏化的ZnO纳米棒电极.应用扫描电子显微镜(SEM)、X射线衍射(XRD)和透射电子显微镜(TEM)对CdS量子点/ZnO纳米棒电极的形貌、晶型和颗粒尺寸进行了分析和表征;采用光电流-电位曲线和光电流谱研究了不同CdS循环沉积次数及不同沉积浓度对复合电极的光电性能影响.结果表明,前驱体浓度都为0.1mol·L-1且沉积15次敏化后的ZnO纳米棒阵列电极光电性能最好.与单纯的ZnO纳米棒阵列电极和单纯的CdS量子点电极相比,其光电转换效率显著提高,单色光光子-电流转换效率(IPCE)在380nm处达到76%.这是因为CdS量子点可以拓宽光的吸收到可见光区,并且在所形成的界面上光生载流子更容易分离.荧光光谱实验进一步说明了光电增强的原因是,两者间形成的界面中表面态大大减少,有利于减少光生电子和空穴的复合.     

Alkali metal salts doped pluronic block polymers as electron injection/transport layers for high performance polymer light-emitting diodes

A series of alkali metal salts doped pluronic block copolymer F127 were used as electron injection/transport layers (ETLs) for polymer light-emitting diodes with poly[2-(4-(3′,7′-dimethyloctyloxy)-phenyl)-p-phenylenevinylene] (P-PPV) as the emission layer. It was found that the electron transport capability of F127 can be effectively enhanced by doping with alkali metal salts. By using Li2CO3 (15%) doped F127 as ETL, the resulting device exhibited improved performance with a maximum luminous efficiency (LE) of 13.59 cd/A and a maximum brightness of 5529 cd/m2, while the device with undoped F127 as ETL only showed a maximum LE of 8.78 cd/A and a maximum brightness of 2952 cd/m2. The effects of the doping concentration, cations and anions of the alkali metal salts on the performance of the resulting devices were investigated. It was found that most of the alkali metal salt dopants can dramatically enhance the electron transport capability of F127 ETL and the performance of the resulting devices was greatly improved.