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.     

Color Tuning of Avobenzone Boron Difluoride as an Emitter to Achieve Full‐Color Emission

Organic light‐emitting diodes (OLEDs) displaying a wide range of emission colors with emission peaks from 450 to 665 nm using a single emitting material, avobenzone boron difluoride (AVB‐BF₂), are reported. Color tuning is achieved by controlling the aggregation of AVB‐BF₂ and the formation of a “triadic” exciplex of an AVB‐BF₂ dimer and a host molecule. Various electroluminescent devices containing AVB‐BF₂ cover the whole visible light spectrum and a white‐emitting device with CIE coordinates of (0.35, 0.37) is obtained with a single emitting material in a single emissive layer. Furthermore, an exceptionally high external quantum efficiency of nearly 13% is achieved for a green‐emitting OLED because AVB‐BF₂ exhibits thermally activated delayed fluorescence by forming the exciplex.     

Cover Picture: White Electroluminescence from a Single‐Polymer System with Simultaneous Two‐Color Emission: Polyfluorene as the Blue Host and a 2,1,3‐Benzothiadiazole Derivative as the Orange Dopant (Adv. Funct. Mater. 7/2006)

New single‐polymer electroluminescent systems containing two individual emission species—polyfluorenes as a blue host and 2,1,3‐benzothiadiazole derivative units as an orange dopant on the main chain—have been designed and synthesized by Wang and co‐workers on p. 957. The resulting single polymers are found to have highly efficient white electroluminescence with simultaneous blue and orange emission from the corresponding emitting species. A single‐layer device has been fabricated that has performance characteristics roughly comparable to those of organic white‐light‐emitting diodes with multilayer device structures. New single‐polymer electroluminescent systems containing two individual emission species—polyfluorenes as a blue host and 2,1,3‐benzothiadiazole derivative units as an orange dopant on the main chain—have been designed and synthesized. The resulting single polymers are found to have highly efficient white electroluminescence with simultaneous blue (λ_max = 421 nm/445 nm) and orange emission (λ_max = 564 nm) from the corresponding emitting species. The influence of the photoluminescence (PL) efficiencies of both the blue and orange species on the electroluminescence (EL) efficiencies of white polymer light‐emitting diodes (PLEDs) based on the single‐polymer systems has been investigated. The introduction of the highly efficient 4,7‐bis(4‐(N‐phenyl‐N‐(4‐methylphenyl)amino)phenyl)‐2,1,3‐benzothiadiazole unit to the main chain of polyfluorene provides significant improvement in EL efficiency. For a single‐layer device fabricated in air (indium tin oxide/poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonic acid/polymer/Ca/Al), pure‐white electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of (0.35,0.32), maximum brightness of 12 300 cd m^–2, luminance efficiency of 7.30 cd A^–1, and power efficiency of 3.34 lm W^–1 can be obtained. This device is approximately two times more efficient than that utilizing a single polyfluorene containing 1,8‐naphthalimide moieties, and shows remarkable improvement over the corresponding blend systems in terms of efficiency and color stability. Thermal treatment of the single‐layer device before cathode deposition leads to the further improvement of the device performance, with CIE coordinates of (0.35,0.34), turn‐on voltage of 3.5 V, luminance efficiency of 8.99 cd A^–1, power efficiency of 5.75 lm W^–1, external quantum efficiency of 3.8 %, and maximum brightness of 12 680 cd m^–2. This performance is roughly comparable to that of white organic light‐emitting diodes (WOLEDs) with multilayer device structures and complicated fabrication processes.     

长寿命电致发光暗室显示器的光谱研究

长寿命电致发光暗室显示器的光谱研究朱宁，孟宪棫，石磐（天津理工学院光电显示研究室，天津３００１９１）利用感光胶片对特种波长感光灵敏度低和电致发光单色性的特点，作出了系列暗室照明光源和显示器件［１．２．３．４］．根据天津感光胶片公司提出航空胶片生产车间...     

Organic Light‐Emitting Transistors Containing a Laterally Arranged Heterojunction

An approach to produce organic light‐emitting transistors (OLETs) containing a laterally arranged heterojunction structure, which minimizes exciton quenching at the metal electrodes, is described. This device configuration provides an organic light‐emitting diode (OLED) structure where the anode (source) electrode, hole‐transport material (field‐effect material), light‐emitting material, and cathode (drain) electrode are laterally arranged, thus offering a chance to control the electroluminescent intensity by changing the gate bias. Pentacene and tris(8‐quinolinolato)aluminum (Alq₃) are employed as the field‐effect and light‐emitting materials, respectively. The laterally arranged heterojunction structures are achieved by successively inclined deposition of the field‐effect and light‐emitting materials. After deposition of pentacene, a narrow gap of about 10–20 nm between the drain electrode and pentacene was obtained, thereby creating an opportunity to fabricate a laterally arranged heterojunction. In the OLETs, unsymmetrical source and drain electrodes, that is, Au and LiF/Al ones, are used to ensure efficient injection of holes and electrons. Visible‐light emission from OLETs is observed under ambient atmosphere. This result is ascribed to efficient carrier injection and transport, formation of a heterojunction, as well as good luminescence from the organic emissive layer. The device structure serves as an excellent model system for OLETs and demonstrates a general concept of adjusting the charge‐carrier injection and transport, as well as the electroluminescent properties, by forming laterally arranged heterojunctions.     

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.     

基于DOPPP的高效白光OLED器件

采用真空热蒸镀的方法,以荧光染料1-(2,5-d imethoxy-4-(1-pyrenyl)-phenyl)pyrene (DOPPP)为蓝发光 层,5,6,11,2-Tetraphenylnaphthacene (Rubrene)为黄发光层,制备了结构为ITO/m-M TDATA(10nm)/NPB(30nm)/ Rubrene (0.2nm)/ DOPPP (x nm)/TAZ(10nm)/Alq₃(30nm)/LiF(0.5nm)/Al的双发光层的高效白色有机电 致发光器件(OLED)。通过调整DOPPP层的厚度,研究器件的发光性能。当DOPPP层厚小 于25nm时,器件以 黄光发射为主;当DOPPP层厚为25nm时器件的性能最佳,在电流密度为209.18mA/cm²时,获得最 大亮度为9232cd/m²,在电流密度为103.712mA/cm²时获得最大电流效率4.68cd/A, 并随着驱动电压 的升高,器件的色坐标从(0.366,0.365)变化到(0.384,0.399),都在白光的范围之内;当DOPPP层厚度超过25nm时,器件的效率和亮度 都开始下降。     

Solution‐Processed Full‐Color Polymer Organic Light‐Emitting Diode Displays Fabricated by Direct Photolithography

The first full‐color polymer organic light‐emitting diode (OLED) display is reported, fabricated by a direct photolithography process, that is, a process that allows direct structuring of the electroluminescent layer of the OLED by exposure to UV light. The required photosensitivity is introduced by attaching oxetane side groups to the backbone of red‐, green‐, and blue‐light‐emitting polymers. This allows for the use of photolithography to selectively crosslink thin films of these polymers. Hence the solution‐based process requires neither an additional etching step, as is the case for conventional photoresist lithography, nor does it rely on the use of prestructured substrates, which are required if ink‐jet printing is used to pixilate the emissive layer. The process allows for low‐cost display fabrication without sacrificing resolution: Structures with features in the range of 2 μm are obtained by patterning the emitting polymers via UV illumination through an ultrafine shadow mask. Compared to state‐of‐the‐art fluorescent OLEDs, the display prototype (pixel size 200 μm × 600 μm) presented here shows very good efficiency as well as good color saturation for all three colors. The application in solid‐state lighting is also possible: Pure white light [Commision Internationale de l'Éclairage (CIE) values of 0.33, 0.33 and color rendering index (CRI) of 76] is obtained at an efficiency of 5 cd A^–1 by mixing the three colors in the appropriate ratio. For further enhancement of the device efficiency, an additional hole‐transport layer (HTL), which is also photo‐crosslinkable and therefore suitable to fabricate multilayer devices from solution, is embedded between the anode and the electroluminescent layer.     

热处理对白色有机电致发光器件发光性能的影响

为获得优质的有机电致发光器件．它的发射光谱是一个关键的因素。传统的方法是采用红、绿、蓝色多层叠合产生白光,但难以控制各基色的峰值强度。制备了利用混合型聚合物作为白色发光层的单层结构有机电致发光器件((OLED),其制备过程比多层结构器件简单得多。一种热处理方法(180℃,1h)用来控制此类白光OLED中各主要电致发光光谱峰值强度间的比例。经过热处理后,这种白光器件的电致发光光谱很接近于Nichia公司的无机白色发光二极管产品的电致发光光谱。由此可推测器件的色坐标接近于白色等能点,而且其阈值电压比热处理前降低了1V。     

Origin of the Exclusive Ternary Electroluminescent Behavior of BN‐Doped Nanographenes in Efficient Single‐Component White Light‐Emitting Electrochemical Cells

White‐light‐emitting electrochemical cells (WLECs) still represent a significant milestone, since only a few examples with moderate performances have been reported. Particularly, multiemissive white emitters are highly desired, as a paradigm to circumvent phase separation and voltage‐dependent emission color issues that are encountered following host:guest and multilayered approaches. Herein, the origin of the exclusive white ternary electroluminescent behavior of BN‐doped nanographenes with a B₃N₃ doping pattern (hexa‐perihexabenzoborazinocoronene) is rationalized, leading to one of the most efficient (≈3 cd A^?1) and stable‐over‐days single‐component and single‐layered WLECs. To date, BN‐doped nanographenes have featured blue thermally activated delayed fluorescence (TADF). This doping pattern provides, however, white electroluminescence spanning the whole visible range (x/y CIE coordinates of 0.29–31/0.31–38 and average color rendering index (CRI) of 87) through a ternary emission involving fluorescence and thermally activated dual phosphorescence. This temperature‐dependent multiemissive mechanism is operative for both photo‐ and electroluminescence processes and holds over the device lifespan, regardless of the device architecture, active layer composition, and operating conditions. As such, this work represents a new stepping‐stone toward designing a new family of multiemissive white emitters based on BN‐doped nanographenes that realizes one of the best‐performing single‐component white‐emitting devices compared to the prior‐art.     

Highly Efficient Non‐Doped Blue‐Light‐Emitting Diodes Based on an Anthrancene Derivative End‐Capped with Tetraphenylethylene Groups

A novel blue‐emitting material, 2‐tert‐butyl‐9,10‐bis[4‐(1,2,2‐triphenylvinyl)phenyl]anthracene ( TPVAn ), which contains an anthracene core and two tetraphenylethylene end‐capped groups, has been synthesized and characterized. Owing to the presence of its sterically congested terminal groups, TPVAn possesses a high glass transition temperature (155 °C) and is morphologically stable. Organic light‐emitting diodes (OLEDs) utilizing TPVAn as the emitter exhibit bright saturated‐blue emissions (Commission Internationale de L'Eclairage (CIE) chromaticity coordinates of x = 0.14 and y = 0.12) with efficiencies as high as 5.3 % (5.3 cd A^–1)—the best performance of non‐doped deep blue‐emitting OLEDs reported to date. In addition, TPVAn doped with an orange fluorophore served as an authentic host for the construction of a white‐light‐emitting device that displayed promising electroluminescent characteristics: the maximum external quantum efficiency reached 4.9 % (13.1 cd A^–1) with CIE coordinates located at (0.33, 0.39).     

Recent Progress in White Light‐Emitting Electrochemical Cells

Solid‐state white light‐emitting electrochemical cells (LECs) exhibit the following advantages: simple device structures, low operation voltage, and compatibility with inert metal electrodes. LECs have been studied extensively since the first demonstration of white LECs in 1997, due to their potential application in solid‐state lighting. This review provides an overview of recent developments in white LECs, specifically three major aspects thereof, namely, host–guest white LECs, nondoped white LECs, and device engineering of white LECs. Host–guest strategy is widely used in white LECs. Host materials are classified into ionic transition metal complexes, conjugated polymers, and small molecules. Nondoped white LECs are based on intra‐ or intermolecular interactions of emissive and multichromophore materials. New device engineering techniques, such as modifying carrier balance, color downconversion, optical filtering based on microcavity effect and localized surface plasmon resonance, light extraction enhancement, adjusting correlated color temperature of the output electroluminescence spectrum, tandem and/or hybrid devices combining LECs with organic light‐emitting diodes, and quantum‐dot light‐emitting diodes improve the device performance of white LECs by ways other than material‐oriented approaches. Considering the results of the reviewed studies, white LECs have a bright outlook.     

Electrophosphorescent Polyfluorenes Containing Osmium Complexes in the Conjugated Backbone

Electrophosphorescent copolymers have been synthesized by covalent bonding of a red‐emitting osmium complex Os(bpftz), which contains two 3‐trifluoromethyl‐5‐(4‐tert‐butyl‐2‐pyridyl)triazolate (bpftz) cyclometalated ligands, into the backbone of a bipolar polyfluorene (PF) copolymer. Employing these copolymers, a highly efficient red polymer light‐emitting diode has been realised that has an external quantum efficiency of 18.0%, a maximum brightness of 38 000 cd m^?2, and an emission centered at 618 nm. In addition, after incorporating appropriate amounts of green‐emitting benzothiadiazole (BT) and the aforementioned Os(bpftz) into the bipolar PF, an efficient white‐light electroluminescent polymer is obtained that displays simultaneous blue, green, and red emissions.     

界面过渡层对黄光OLED发光性能的影响研究

研究了黄光OLED发光层间加入界面过渡层对OLED发 光性能的影响。实验制备新型黄光OLED的发光层结构为 CBP:R-4B/CBP:Girl:R-4B/CBP:GIrl,对比OLED的发光层结构为CBP:10%R-4B/CBP:10%GIrl、CBP: 10%GIrl/CBP:10%GIrl10%R-4B/CBP:10%R-4B和CBP:10%GIrl/CBP:10%R-4B。结果表明,在对比器 件的发光层界面间加入过渡层可显著提高器件的发光亮度和发光效率,新型器件在13V电压 下、电流密度为40.29mA/cm²时,发光亮度和发光效率分别达到 了11120cd/m²与27.59cd/A,较未加入过渡层的器件分别提 高了265%56.18%。分析认为,过渡层的 加入消除了由不同发光层间严格的界面效应而造成的界面缺 陷,增加了载流子传输速率与激子的复合效率,从而提升了器件的发光性能。     

Above 20% external quantum efficiency in green and white phosphorescent organic light-emitting diodes using an electron transport type green host material

Highly efficient green and white phosphorescent organic light emitting diodes were developed using a green phosphorescent host material based on phenyl substituted spirobifluorene. A high quantum efficiency of 25.3% was achieved in the green phosphorescent device and a high quantum efficiency of 21.6% was obtained in the white device with a stacked emitting structure of deep blue and red:green emitting layers.     

Cover Picture: Solution‐Processed Full‐Color Polymer Organic Light‐Emitting Diode Displays Fabricated by Direct Photolithography (Adv. Funct. Mater. 2/2007)

The first high‐resolution full‐color OLED display based on a direct photolithographic process is presented by Meerholz and co‐workers on p. 191. The cover shows a schematic illustration of the fabrication process, a fluorescence microscope picture demonstrating the micrometer resolution capability of the process, and a picture of the first prototype displaying a test image. Electroluminescent polymers with photoresist‐like properties are the basis of the new process (chemical structure shown in the background). The first full‐color polymer organic light‐emitting diode (OLED) display is reported, fabricated by a direct photolithography process, that is, a process that allows direct structuring of the electroluminescent layer of the OLED by exposure to UV light. The required photosensitivity is introduced by attaching oxetane side groups to the backbone of red‐, green‐, and blue‐light‐emitting polymers. This allows for the use of photolithography to selectively crosslink thin films of these polymers. Hence the solution‐based process requires neither an additional etching step, as is the case for conventional photoresist lithography, nor does it rely on the use of prestructured substrates, which are required if ink‐jet printing is used to pixilate the emissive layer. The process allows for low‐cost display fabrication without sacrificing resolution: Structures with features in the range of 2 μm are obtained by patterning the emitting polymers via UV illumination through an ultrafine shadow mask. Compared to state‐of‐the‐art fluorescent OLEDs, the display prototype (pixel size 200 μm × 600 μm) presented here shows very good efficiency as well as good color saturation for all three colors. The application in solid‐state lighting is also possible: Pure white light [Commision Internationale de l'Éclairage (CIE) values of 0.33, 0.33 and color rendering index (CRI) of 76] is obtained at an efficiency of 5 cd A^–1 by mixing the three colors in the appropriate ratio. For further enhancement of the device efficiency, an additional hole‐transport layer (HTL), which is also photo‐crosslinkable and therefore suitable to fabricate multilayer devices from solution, is embedded between the anode and the electroluminescent layer.     

White Electroluminescence from a Single‐Polymer System with Simultaneous Two‐Color Emission: Polyfluorene as the Blue Host and a 2,1,3‐Benzothiadiazole Derivative as the Orange Dopant

New single‐polymer electroluminescent systems containing two individual emission species—polyfluorenes as a blue host and 2,1,3‐benzothiadiazole derivative units as an orange dopant on the main chain—have been designed and synthesized. The resulting single polymers are found to have highly efficient white electroluminescence with simultaneous blue (λ_max = 421 nm/445 nm) and orange emission (λ_max = 564 nm) from the corresponding emitting species. The influence of the photoluminescence (PL) efficiencies of both the blue and orange species on the electroluminescence (EL) efficiencies of white polymer light‐emitting diodes (PLEDs) based on the single‐polymer systems has been investigated. The introduction of the highly efficient 4,7‐bis(4‐(N‐phenyl‐N‐(4‐methylphenyl)amino)phenyl)‐2,1,3‐benzothiadiazole unit to the main chain of polyfluorene provides significant improvement in EL efficiency. For a single‐layer device fabricated in air (indium tin oxide/poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonic acid/polymer/Ca/Al), pure‐white electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of (0.35,0.32), maximum brightness of 12 300 cd m^–2, luminance efficiency of 7.30 cd A^–1, and power efficiency of 3.34 lm W^–1 can be obtained. This device is approximately two times more efficient than that utilizing a single polyfluorene containing 1,8‐naphthalimide moieties, and shows remarkable improvement over the corresponding blend systems in terms of efficiency and color stability. Thermal treatment of the single‐layer device before cathode deposition leads to the further improvement of the device performance, with CIE coordinates of (0.35,0.34), turn‐on voltage of 3.5 V, luminance efficiency of 8.99 cd A^–1, power efficiency of 5.75 lm W^–1, external quantum efficiency of 3.8 %, and maximum brightness of 12 680 cd m^–2. This performance is roughly comparable to that of white organic light‐emitting diodes (WOLEDs) with multilayer device structures and complicated fabrication processes.     

以Liq∶Rubrene为发光层的白色有机电致发光器件的研制

以蓝色发光材料Liq为主体,以一定的比例掺入黄光染料Rubrene,研制了新型白色有机电致发光器件.调节Rubrene的掺杂比为1.1%时得到近白光器件,色坐标为(0.308,0.347),器件的启亮电压为8V,当外加电压达到25V时,器件发光亮度达3120cd/m2.     

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.     

Light‐Emitting Devices Based on Electrochemiluminescence Gels

Electrochemiluminescence (ECL) is a self‐emission of light from electrochemically excited luminophores via a series of redox reactions. Over the past decade, light‐emitting devices based on gel‐phase ECL active materials, i.e., gel electrolyte composites (referred to as ECL gels) containing an ECL luminophore, electrolyte, and network matrix, have attracted considerable attention as a complementary device platform to conventional electroluminescent devices for low‐cost printable displays and solid‐state light sources. Although the ECL phenomenon is extensively exploited in analytical diagnostics and sensing, the development of printable and fast‐response gel‐type luminescent materials may further expand the potential application of ECL in solid‐state flexible, bendable, and stretchable light‐emitting devices. This review summarizes the operation mechanisms of ECL‐based light‐emitting devices, ECL emitters and electrolytes, engineering strategies for obtaining printable high‐strength/high‐conductivity ECL gels, and emerging applications of gel‐type ECL devices.