以聚乙烯亚胺作为电子注入层的聚合物发光器件特性研究

在传统结构与倒置结构的有机发光二极管(LED)的聚合物发光层和阴极之间加入聚乙烯亚胺(PEIE)层能够显著地提高器件的发光效率。通过采用不同厚度的PEIE层的器件发光特性研究表明:PEIE层作为电子注入层(EIL)/空穴阻挡层(HBL)来平衡器件中的电子和空穴浓度,这主要来源于PEIE作为界面偶极层,能有效地降低阴极与发光层之间的电子注入势垒。     

High-efficiency hybrid organic–inorganic light-emitting devices

We report efficient red, orange, green and blue organic–inorganic light emitting devices using light emitting polymers and polyethylenimine ethoxylated (PEIE) interlayer with the respective luminance efficiency of 1.3, 2.7, 10 and 4.1 cd A⁻¹, which is comparable to that of the analogous conventional devices using a low work-function metal cathode. This is enabled by the enhanced electron injection due to the effective reduction of the ZnO work-function by PEIE, as well as hole/exciton-blocking function of PEIE layer. Due to the benign compatibility between PEIE and the neighboring organic layer, the novel phosphorescent organic–inorganic devices using solution-processed small molecule emissive layer show the maximum luminance efficiency of 87.6 cd A⁻¹ and external quantum efficiency of 20.9% at 1000 cd m⁻².     

Study of Configuration Differentia and Highly Efficient,Deep‐Blue,Organic Light‐Emitting Diodes Based on Novel Naphtho[1,2‐d]imidazole Derivatives

Two novel naphtho[1,2‐d]imidazole derivatives are developed as deep‐blue, light‐emitting materials for organic light‐emitting diodes (OLEDs). The 1H‐naphtho[1,2‐d]imidazole based compounds exhibit a significantly superior performance than the 3H‐naphtho[1,2‐d]imidazole analogues in the single‐layer devices. This is because they have a much higher capacity for direct electron‐injection from the cathode compared to their isomeric counterparts resulting in a ground‐breaking EQE (external quantum efficiency) of 4.37% and a low turn‐on voltage of 2.7 V, and this is hitherto the best performance for a non‐doped single‐layer fluorescent OLED. Multi‐layer devices consisting of both hole‐ and electron‐transporting layers, result in identically excellent performances with EQE values of 4.12–6.08% and deep‐blue light emission (Commission Internationale de l'Eclairage (CIE) y values of 0.077–0.115) is obtained for both isomers due to the improved carrier injection and confinement within the emissive layer. In addition, they showed a significantly better blue‐color purity than analogous molecules based on benzimidazole or phenanthro[9,10‐d]imidazole segments.     

Designing a Stable Cathode with Multiple Layers to Improve the Operational Lifetime of Polymer Light‐Emitting Diodes

The short device lifetime of blue polymer light‐emitting diodes (PLEDs) is still a bottleneck for commercialization of self‐emissive full‐color displays. Since the cathode in the device has a dominant influence on the device lifetime, a systematic design of the cathode structure is necessary. The operational lifetime of blue PLEDs can be greatly improved by introducing a three‐layer (BaF₂/Ca/Al) cathode compared with conventional two‐layer cathodes (BaF₂/Al and Ba/Al). Therefore, the roles of the BaF₂ and Ca layers in terms of electron injection, luminous efficiency, and device lifetime are here investigated. For efficient electron injection, the BaF₂ layer should be deposited to the thickness of at least one monolayer (～3 nm). However, it is found that the device lifetime does not show a strong relation with the electron injection or luminous efficiency. In order to prolong the device lifetime, sufficient reaction between BaF₂ and the overlying Ca layer should take place during the deposition where the thickness of each layer is around that of a monolayer.     

Reduction of Tungsten Oxide: A Path Towards Dual Functionality Utilization for Efficient Anode and Cathode Interfacial Layers in Organic Light‐Emitting Diodes

Here, we report on the dual functionality of tungsten oxide for application as an efficient electron and hole injection/transport layer in organic light‐emitting diodes (OLEDs). We demonstrate hybrid polymer light‐emitting diodes (Hy‐PLEDs), based on a polyfluorene copolymer, by inserting a very thin layer of a partially reduced tungsten oxide, WO_2.5, at the polymer/Al cathode interface to serve as an electron injection and transport layer. Significantly improved current densities, luminances, and luminous efficiencies were achieved, primarily as a result of improved electron injection at the interface with Al and transport to the lowest unoccupied molecular orbital (LUMO) of the polymer, with a corresponding lowering of the device driving voltage. Using a combination of optical absorption, ultraviolet spectoscopy, X‐ray photoelectron spectroscopy, and photovoltaic open circuit voltage measurements, we demonstrate that partial reduction of the WO₃ to WO_2.5 results in the appearance of new gap states just below the conduction band edge in the previously forbidden gap. The new gap states are proposed to act as a reservoir of donor electrons for enhanced injection and transport to the polymer LUMO and decrease the effective cathode workfunction. Moreover, when a thin tungsten oxide film in its fully oxidized state (WO₃) is inserted at the ITO anode/polymer interface, further improvement in device characteristics was achieved. Since both fully oxidized and partially reduced tungsten oxide layers can be deposited in the same chamber with well controlled morphology, this work paves the way for the facile fabrication of efficient and stable Hy‐OLEDs with excellent reproducibility.     

Carrier radiation distribution in organic light-emitting diodes

This paper is based on the analysis of white organic electroluminescent device electroluminescent spectrum to explain the regular pattern of carrier radiation distribution.It has proved electron that is injected from cathode is satisfied with the regularity of radiation distribution on the organic emitting layer.This radiation distribution is related to several factors,such as electron injection capabilities,applied electrical field intensity,carrier mobility,etc.The older instruction design is ITO/2-TNATA/NPB/ADN:DCJTB:TBPe/Alq3/cathode.Get to change electron injector capabilities through using different cathode and also find electroluminescent spectrum to produce significant changes.Simultaneously,electron radiation quantity has some limitation,and electroluminescent spectrum reflects that spectral intensity does not change anymore when the ratio of cathode dopant to a saturated state on the organic emitting layer.It also shows the same spectrum variational phenomenon while changing the applied electrical field intensity.To put forward of the carrier radiation distribution is good for organic light emitting diode (OLED) luminescence properties analysis and research.     

单层OLED器件模型的MATLAB分析计算

近年来有机发光二极管(OLED)的工业应用特别是在平板显示器中的应用已被广泛研究.OLED发光是分别由阴极和阳极注入的电子和空穴在发光层中复合的结果.单层结构是OLED器件的基础.为了提高OLED器件的性能,需要详细理解电荷载流子的注入过程.借助MATLAB求解了无量纲单层OLED器件模型,介绍了有关分析计算方法和技巧.综合利用MATLAB提供的符号求解常微分方程、绘图等命令,可使工作量大为减少.该方法具有编程简单,使用方便、实用性强等特点.     

A high performance inverted organic light emitting diode using an electron transporting material with low energy barrier for electron injection

A high performance inverted green emission organic light emitting diode with a maximum external quantum efficiency of 20% and a maximum power efficiency of 80 lm/W was realized by properly selecting an electron transporting material to have no energy barrier for electron injection between the n-doped electron transporting layer (n-ETL) and the ETL. Based on the energy levels and the current density–voltage characteristics of electron only devices, we demonstrate that the interface between an n-ETL and an ETL even in homo-junction is as important as the interface between the cathode and the n-ETL for efficient electron injection into an emitting layer.     

High‐Performance All‐Polymer White‐Light‐Emitting Diodes Using Polyfluorene Containing Phosphonate Groups as an Efficient Electron‐Injection Layer

We report an efficient non‐doped all‐polymer polymer white‐light‐emitting diode (PWLED) with a fluorescent three‐color, white single polymer as an emissive layer, an ethanol‐soluble phosphonate‐functionalized polyfluorene (PF‐EP) as an electron‐injection/electron‐transport layer, and LiF/Al as a cathode, respectively. The all‐polymer PWLED achieves a peak external quantum efficiency of 6.7%, a forward viewing luminous efficiency of 15.4 cd A^?1 and a power efficiency of 11.4 lm W^?1, respectively, at a brightness of 347 cd m^?2 with Commission Internationale d’Eclairage coordinates of (0.37, 0.42) and color rendering index of 85, which is the best results among the non‐doped PWLEDs. Moreover, this kind of PWLED not only shows excellent color stability, but also achieves high brightness at low voltages. The brightness reaches 1000, 10000, and 46830 cd m^?2 at voltages of 4.5, 5.4, and 7.5 V, respectively. The significant enhancement of white‐single‐polymer‐based PWLEDs with PF‐EP/LiF/Al to replace for the commonly used Ca/Al cathode is attributed to the more efficient electron injection at PF‐EP/LiF/Al interfaces, and the coordinated protecting effect of PF‐EP from diffusion of Al atoms into the emissive layer and exciton‐quenching near cathode interfaces. The developed highly efficient non‐doped all‐polymer PWLEDs are well suitable for solution‐processing technology and provide a huge potential of low‐cost large‐area manufacturing for PWLEDs.     

Amino N‐Oxide Functionalized Conjugated Polymers and their Amino‐Functionalized Precursors: New Cathode Interlayers for High‐Performance Optoelectronic Devices

A series of amino N‐oxide functionalized polyfluorene homopolymers and copolymers (PNOs) are synthesized by oxidizing their amino functionalized precursor polymers (PNs) with hydrogen peroxide. Excellent solubility in polar solvents and good electron injection from high work‐function metals make PNOs good candidates for interfacial modification of solution processed multilayer polymer light‐emitting diodes (PLEDs) and polymer solar cells (PSCs). Both PNOs and PNs are used as cathode interlayers in PLEDs and PSCs. It is found that the resulting devices show much better performance than devices based on a bare Al cathode. The effect of side chain and main chain variations on the device performance is investigated. PNOs/Al cathode devices exhibit better performance than PNs/Al cathode devices. Moreover, devices incorporating polymers with para‐linkage of pyridinyl moieties exhibit better performance than those using polymers with meta‐linked counterparts. With a poly[(2,7‐(9,9‐bis(6‐(N,N‐diethylamino)‐hexyl N‐oxide)fluorene))‐alt‐(2,5‐pyridinyl)] (PF6NO25Py) cathode interlayer, the resulting device exhibits a luminance efficiency of 16.9 cd A^?1 and a power conversion efficiency of 6.9% for PLEDs and PSCs, respectively. These results indicate that PNOs are promising new cathode interlayers for modifying a range of optoelectronic devices.     

Investigation on the Low Luminous Efficiency in a Polymer Light‐Emitting Diode with a High Work‐function Cathode by Soft Contact Lamination**

This article reports the main origin of the low luminescent efficiency in hole‐dominant polymer light‐emitting diodes by controlling the hole injection and by chemically modifying the cathode by molecular monolayers. Since molecular modification of the top electrode is impossible when one deposits the electrode using a vacuum deposition method, this study was performed using a soft contact lamination technique to form electrical contacts on top of the emissive layer. The top electrode was chemically modified with an alkane thiol self‐assembled monolayer (SAM) to act as an interfacial spacer layer between the emitting layer and the cathode. Herein, it is reported that, contrary to common belief, a high device quantum efficiency can be achieved from the dominantly hole‐transporting device with a high work‐function cathode (like Au) by facilitating more hole injection from the anode in the device with low population of exciton quenching channels near the cathode.     

载流子平衡的低压高效有机白光器件

研究了结构为ITO/m-MTDATA:x%4F-TCNQ/NPB/TBADN:EBDP:DCJTB/Bphen:Liq/LiF/Al的有机白光电致发光器件(WOLED)。分别在ITO与NPB间加入高迁移率的m-MTDATA:4F-TCNQ来增强器件的空穴注入,在阴极和发光层间加入高迁移率的Bphen:Liq层增强器件的电子注入,降低驱动电压,提高器件效率。同时,由于注入的电子和空穴数量偏离平衡,器件的效率也会受到影响。实验中,通过调节4F-TCNQ的掺杂浓度来调控空穴的注入和传输,使载流子达到高度平衡。器件的最大电流效率和流明效率分别达到了9.3cd/A和4.6 lm/W。     

Inverted Solution Processable OLEDs Using a Metal Oxide as an Electron Injection Contact.

A new type of bottom‐emission electroluminescent device is described in which a metal oxide is used as the electron‐injecting contact. The preparation of such a device is simple. It consists of the deposition of a thin layer of a metal oxide on top of an indium tin oxide covered glass substrate, followed by the solution processing of the light‐emitting layer and subsequently the deposition of a high‐workfunction (air‐stable) metal anode. This architecture allows for a low‐cost electroluminescent device because no rigorous encapsulation is required. Electroluminescence with a high brightness reaching 5700 cd m^–2 is observed at voltages as low as 8 V, demonstrating the potential of this new approach to organic light‐emitting diode (OLED) devices. Unfortunately the device efficiency is rather low because of the high current density flowing through the device. We show that the device only operates after the insertion of an additional hole‐injection layer in between the light‐emitting polymer (LEP) and the metal anode. A simple model that explains the experimental results and provides avenues for further optimization of these devices is described. It is based on the idea that the barrier for electron injection is lowered by the formation of a space–charge field over the metal‐oxide–LEP interface due to the build up of holes in the LEP layer close to this interface.     

Optimization of polymer light emitting devices using TiOx electron transport layers and prism sheets

The internal and external efficiency of polymer light emitting devices were found can be simultaneously improved by insertion a high refractive index material, titanium oxide (TiO_x), to the emission layer and a prism sheet attached to the substrate. The TiO_x layer increased the internal efficiency due to a better electron injection and hole confinement. However, it led a wider angular emission profile with more photons trapped in the substrate. By using the prism sheet, those trapped light was efficiently coupled to the air. The extraction efficiency enhancement was increased from 33.1% to 54.4% and the overall current efficiency was improved up to 86%.     

Stabilized Blue Emission from Polymer–Dielectric Nanolayer Nanocomposites

Blue‐light‐emitting polymer (polyfluorene)/dielectric nanolayer nanocomposites were prepared by the solution intercalation method and employed in an electroluminescent (EL) device. Their photoluminescence (PL) and electroluminescence characteristics demonstrates that the interruption of interchain interaction in intercalated organic/inorganic hybrid systems reduces the low‐energy emission that results from keto‐defects. By reducing the probability that the excitons initially generated on the polyfluorenes will find keto‐defects, both the color purity and the luminescence stability were improved. Furthermore, the dielectric nanolayers have an aspect ratio of about five hundred, and therefore act as efficient exciton blocking layers and barriers to oxygen diffusion, producing a dramatic increase in the device stability. A nanocomposite device with a Li:Al alloy cathode gave a quantum efficiency of 1.0 %(ph/el), which corresponds to an approximate five times enhancement compared to the neat polymer device. The nanocomposite emitting layer is considered to have a pseudo‐multiple quantum well structure.     

Fluorescent deep-blue and hybrid white emitting devices based on a naphthalene–benzofuran compound

We report the synthesis, photophysics and electrochemical properties of naphthalene–benzofuran compound 1 and its application in organic light emitting devices. Fluorescent deep-blue emitting devices employing 1 as the emitting dopant embedded in 4-4′-bis(9-carbazolyl)-2,2′-biphenyl (CBP) host show the peak external quantum efficiency of 4.5% and Commission Internationale d’Énclairage (CIE) coordinates of (0.15, 0.07). Hybrid white devices using fluorescent blue emitting layer with 1 and a phosphorescent orange emitting layer based on an iridium-complex show the peak external quantum efficiency above 10% and CIE coordinates of (0.31, 0.37).     

柔性有机电致发光器件的寿命

综述了柔性有机电致发光器件(FOLED)的研究现状和发展趋势;针对提高其寿命问题的研究,选择和比较了聚合物、金属箔片、超薄玻璃3种柔性衬底材料的优缺点及发展概况;结合本课题组的实验分析,说明设计并选择合理的器件结构、发光材料和阴极材料对延长器件的使用寿命非常有效;提高FOLED寿命的另一重要步骤是减少水蒸汽和氧气向器件内部的渗透,最后也简介了以聚合物和超薄玻璃为衬底材料的器件封装方法。     

电极用金属的功函数对OLED发光性能的影响

OLED是一种主动发光器件，影响器件发光性能的因素很多，如电子流与空穴流间的平衡、发光层内电子与空穴的有效复合、外部注入非平衡载流子的能力等。外部注入非平衡载波子的能力与金属－半导体的界面特性有关。本文基于热电子发射理论论述了电极用金属的功函数与非平衡载流子注入的关系，说明其对OLED发光性能的影响。     

Achieving Highly Efficient Fluorescent Blue Organic Light‐Emitting Diodes Through Optimizing Molecular Structures and Device Configuration

Based on the results of first‐principles calculations of the electronic properties of blue light‐emitting materials, the molecular structures of oligofluorenes are optimized by incorporating electron‐withdrawing groups into the molecules to balance hole and electron injection and transport for organic light‐emitting diodes (OLEDs). The result is a remarkable improvement in the maximum external quantum efficiency (EQE) of the undoped device from 2.0% to 4.99%. Further optimization of the device configurations and processing procedures, e.g., by changing the thickness of the emitting layer and through thermal annealing treatments, leads to a very high maximum EQE of 7.40% for the undoped sky‐blue device. Finally, by doping the emitter in a suitable host material, 4,4’‐bis(carbazol‐9‐yl)biphenyl (CBP), at the optimal concentration of 6%, pure blue emission with extremely high maximum EQE of 9.40% and Commission Internationale de l’Eclairage (CIE) coordinates of (0.147, 0.139) is achieved.     

Highly Efficient Hole Injection Using Polymeric Anode Materials for Small‐Molecule Organic Light‐Emitting Diodes

A novel, highly efficient hole injection material based on a conducting polymer polythienothiophene (PTT) doped with poly(perfluoroethylene‐perfluoroethersulfonic acid) (PFFSA) in organic light‐emitting diodes (OLEDs) is demonstrated. Both current–voltage and dark‐injection‐current transient data of hole‐only devices demonstrate high hole‐injection efficiency employing PTT:PFFSA polymers with different organic charge‐transporting materials used in fluorescent and phosphorescent organic light‐emitting diodes. It is further demonstrated that PTT:PFFSA polymer formulations applied as the hole injection layer (HIL) in OLEDs reduce operating voltages and increase brightness significantly. Hole injection from PTT:PFFSA is found to be much more efficient than from typical small molecule HILs such as copper phthalocyanine (CuPc) or polymer HILs such as polyethylene dioxythiophene: polystyrene sulfonate (PEDOT‐PSS). OLED devices employing PTT:PFFSA polymer also demonstrate significantly longer lifetime and more stable operating voltages compared to devices using CuPc.