混合蓝色和绿色发射的高亮度白色有机电致发光器件

使用星形六苯芴类新材料1,2,3,4,5,6-hexakis(9,9-diethyl-9H-fluoren-2-yl)benzene (HKEthFLYPh)分别制备了三种不同结构的有机电致发光器件. 在结构为indium-tin oxide (ITO)/NPB (40 nm)/HKEthFLYPh (10 nm)/Alq3(50 nm)/Mg:Ag (200 nm)的器件中, 获得了两个电致发光谱峰分别位于435 和530 nm处的明亮白光. HKEth-FLYPh是能量传输层; N,N’-bis-(1-naphthyl)-N,N’-diphenyl-(1,1’-biphenyl)-4,4’-diamine (NPB)是空穴传输层和蓝色发光层; tris(8-hydroxyquinoline)aluminum (Alq3)是电子传输层和绿色发光层. 结果表明, 当驱动电压为15 V时, 器件的最大亮度达到8523 cd·m-2; 在5.5 V时, 器件达到最大流明效率为1.0 lm·W-1. 在电压为9 V时, CIE色坐标为(0.29, 0.34). 此外, 通过改变HKEthFLYPh层的厚度, 发现蓝色发射的相对强度随着HKEthFLYPh层厚度的增加而增强.     

一种吡嗪铱(Ⅲ)配合物的晶体结构及光物理性质

合成了一种铱配合物二(4,4'-二氟-5-甲基-2,3-二苯基吡嗪) (乙酰丙酮)合铱[(MDPPF)₂Ir(acac)]的有机电致发光器件(OLED),利用X射线单晶衍射仪测定了该化合物的晶体结构. 利用紫外-可见吸收光谱、发射光谱对其光物理性质进行研究. 结果表明: (MDPPF)₂Ir(acac)的单晶结构属于三斜晶系, P1空间群,晶胞参数a=1.13984(3) nm, b=1.26718(3) nm, c=1.29541(3) nm, α=93.7181(19)°, β=101.638(2)°, γ=110.853(3)°, V=1.69336(7) nm³; (MDPPF)₂Ir(acac)在二氯甲烷溶液中的发射峰为555 nm. 以(MDPPF)₂Ir(acac)为客体材料,制备了结构为ITO/NPB(40 nm)/CBP: (MDPPF)₂Ir(acac)(20 nm)/TPBi(10 nm)/Alq₃ (30 nm)/LiF(1 nm)/Al(100 nm)的一系列不同掺杂浓度器件, 器件的发射峰位于558 nm, 最大亮度达到32700 cd·m^-2,最大电流效率44.3 cd·A^-1, 最大功率效率20.7 lm·W^-1.     

Synthesis and characterization of high Tg carbazole-based amorphous hole-transporting materials for organic light-emitting devices

Novel hole-transporting materials based on carbazole dendrimers, namely G1CBC and G2CBC were synthesized and characterized. They are thermally stable with high glass transition temperatures (T_g) up to 245 °C and exhibit chemically-stable redox processes. Double-layer green OLEDs using these materials as the hole-transporting layer (HTL) with the device configuration of ITO/HTL/Alq3/LiF:Al emit brightly (λ_em 522-534 nm) from the Alq3 layer with a maximum luminance and low turn-on voltage of 15,890 cd/m² and 3.0 V, respectively. Their ability as HTLs in terms of device performance is comparable to the common hole-transporter N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB), however their thermal properties were far greater than both NPB and N,N′-bis(3-methylphenyl)-N,N′-bis(phenyl)benzidine (TPD).     

Bright White Organic Light-emitting Device Based on 1,2,3,4,5,6-Hexakis（9,9-diethyl-9H-fluoren-2-yl）benzene

Organic light-emitting devices(OLEDs) with the structure of indium-tin-oxide(ITO)/N,N'-bis-(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine(NPB)/2,9-dimenthyl-4,7-diphenyl-1,10-phenanthroline(BCP)/tris(8-hydroxyquinoline)aluminum(Alq3)/Mg:Ag or that of ITO/NPB/1,2,3,4,5,6-hexakis(9,9-diethyl-9H-fluoren-2-yl)benzene(HKEthFLYPh)/Alq3/Mg:Ag were studied.White light emission was achieved with the two devices when the thicknesses of BCP and HKEthFLYPh were 1.5 nm(device B) and 5 nm(device II),respectively...     

Nondoped-type White Organic Light-Emitting Diode Using Star-Shaped Hexafluorenylbenzene as an Energy Transfer Layer

White organic light-emitting diodes (WOLEDs) with a structure of indium-tin-oxide (ITO)/N,N'-bis-(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPB)/1,2,3,4,5,6-hexakis(9,9-diethyl-9H-fluoren-2-yl)benzene (HKEthFLYPh)/5,6,11,12 -tetraphenylnaphtacene (rubrene)/tris(8-hydroxyquinoline) aluminum (Alq3)/Mg:Ag were fabricated by vacuum deposition method, in which a novel star-shaped hexafluorenylbenzene HKEthFLYPh was used as an energy transfer layer, and an ultrathin layer of rubrene was inserted between HKEthFLYPh and Alq3 layers as a yellow light-emitting layer instead of using a time-consuming doping process. A fairly pure WOLED with Commissions Internationale De L'Eclairage (CIE) coordinates of (0.32, 0.33) was obtained when the thickness of rubrene was 0.3 nm, and the spectrum was insensitive to the applied voltage. The device yielded a maximum luminance of 4816 cd/m2 at 18 V.     

Synthesis of a highly phosphorescent emitting iridium(III) complex and its application in OLEDs

A rigid ligand benzo[de]benzo[4,5]imidazo[2,1-α]isoquinolin-7-one (biio) was designed and conveniently synthesized, and the corresponding bis-cyclometalated iridium complex (biio)₂Ir(acac) (acac = acetylacetone) was prepared. The light emitting and electrochemical properties of this complex were studied. The complex has the characters of simply synthetic procedure and strong phosphorescence. The electroluminescent device using this complex as dopant was fabricated. The device had the structure of ITO/NPB (40 nm)/Ir complex:CBP (7%, 30 nm)/BCP (15 nm)/Alq₃ (30 nm)/LiF (1 nm)/Al (100 nm). The maximum emission of the device was at 496 nm. The maximum brightness of the device can reach 79640 cd m⁻² with an external quantum efficiency of 12.1% and a maximum current efficiency of 31.7 cd A⁻¹.     

一种新型红色三线态喹喔啉铱(Ⅲ)配合物的合成及发光性质

利用2,3-二苯基喹喔啉和水合三氯化铱(IrCl₃?H₂O)反应, 合成了一种新型喹喔啉铱的配合物[Ir(DPQ)₂(acac)], 通过元素分析, ¹H NMR和HRMS对配合物结构进行了表征, 结果显示得到的是目标化合物. 利用紫外光谱和荧光光谱对配合物的吸收光谱和光致发光光谱进行了研究. 利用该材料作为磷光材料制备了结构为[ITO/NPB(30 nm)/NPB∶7% Ir(DPQ)₂(acac)(25 nm)/PBD (10 nm)/Alq₃ (30 nm)/Mg∶Ag (10∶1)(120 nm)/Ag(10 nm)] 的电致发光器件, 研究了其电致发光光谱. 结果表明, 配合物[Ir(DPQ)₂(acac)]在476和625 nm处存在单重态¹MLCT(金属到配体的电荷跃迁)和三重态³MLCT的吸收峰; 发光光谱结果显示, 在660 nm处有较强的金属配合物三重态的磷光发射; 电致发光光谱显示, 该器件的启动电压是4.25 V, 器件的最大亮度为4910 cd/m², 外量子效率为5.14%, 器件的流明效率为1.12 lm/W, 是一种新型红色磷光材料.     

2-对联苯-8-羟基喹啉锌的合成及其应用于新型白光OLED

合成了一种全新的有机发光材料2-对联苯-8-羟基喹啉锌(Zn[2-(p-biPh)-8-Q-O]₂), 通过¹H NMR, UV-Vis等对配合物的结构进行表征. 利用该材料制备了新型白光有机电致发光器件(OLED), 其结构为: ITO/NPB (N,N'-双(1-萘基)-N,N'-二苯基-1,1'-二苯基-4,4'-二胺)/BCP (2,9-二甲基-4,7-二苯基-1,10-菲咯啉)/Zn[2-(p-biPh)-8-Q-O]₂/Al. 通过调节空穴阻挡层BCP的厚度, 实现了NPB(蓝光发射)和Zn[2-(p-biPh)-8-Q-O]₂(黄光发射)作为器件双发光层的有效复合, 并研究了其发光机理. 当BCP层的厚度为2.0 nm时, 获得了稳定的白色发光; 该器件在6 V电压下启亮, 20 V电压时最大发光亮度达到130 cd/m², 电流效率为0.224 cd/A.     

Enantiomer separation of rac-2,2′-dihydroxy-1,1′-binaphthyl (BNO) by inclusion complexation with racemic or achiral ammonium salts and a novel transformation of a 1:1:1 racemic complex of BNO, Me4N·Cl and MeOH into a conglomerate complex in the solid state

The complete simultaneous and mutual enantiomer resolution of 2,2′-dihydroxy-1,1′-binaphthyl (BNO) and N-(3-chloro-2-hydroxypropyl)-N,N,N-trimethylammonium chloride, Me₃N⁺CH₂CH(OH)CH₂Cl·Cl⁻ into their enantiomers by inclusion complexation between their racemates in EtOH in the presence of a chiral seed crystal is reported. The enantiomer resolution of the rac-BNO was also accomplished easily by inclusion complexation with achiral ammonium salts, N-(2-hydroxyethyl)-N,N,N-trimethylammonium chloride, Me₃N⁺CH₂CH₂OH·Cl⁻ and tetramethylammonium chloride, Me₄N⁺·Cl⁻. Inclusion complexation of the rac-BNO with Me₃N⁺ CH₂CH₂OH·Cl⁻ gave only a 1:1 conglomerate inclusion complex but not a racemic complex. Recrystallization of the rac-BNO and an equimolar amount of Me₄N⁺·Cl⁻ from MeOH (7 ml) and MeOH (15 ml) gave a 1:1:1 racemic complex, BNO·Me₄N⁺·Cl⁻·MeOH and a 1:1 conglomerate complex, BNO·Me₄N⁺·Cl⁻, respectively. Novel transformation of the former racemate into the latter conglomerate occurred by heating or by exposure to MeOH vapor in the solid state.     

Synthesis and characteristics of bis(2,4-dimethyl-8-quinolinolato)(triphenylsilanolato)aluminum (III): A potential hole-blocking material for the organic light-emitting diodes

A new five-coordinated bis(2,4-dimethyl-8-quinolinolato)(triphenylsilanolato)aluminum (III) (24MeSAlq) material, having bulky substituents, was prepared in one-step reaction and was characterized. The photoluminescent (PL) spectrum of 24MeSAlq shows the largest hypsochromic shift exhibiting the maximum wavelength at the peak of 461 nm among the blue-emitting q₂AlOR-type complexes (q = 8-quinolinolato ligand and OR = aryloxy or alkoxy ligand) reported. The deep blue device composed of ITO/2-TNATA (60 nm)/NPB (15 nm)/24MeSAlq (20 nm)/Alq₃ (45 nm)/LiF (1 nm)/Al (100 nm), which uses 24MeSAlq as a hole-blocking layer and applies a principle efficiently confining an exciton recombination zone into a hole transporting layer, shows the maximum electroluminescent (EL) at the peak of 446 nm originating from the NPB emissive layer. This is attributed to an excellent hole-blocking property due to the high HOMO (highest occupied molecular orbital) energy level (6.14 eV).     

Spectroscopic and structural characterization of Na2[(VO)2(ttha)]·8H2O (ttha = triethylenetetraamine-N,N,N′,N″,N′″,N′″-hexaacetate): Interpreting the results with density functional theory

Na₂[(V^IVO)₂(ttha)]·8 H₂O (ttha = triethylenetetraamine–N,N,N′,N″,N′″,N′″–hexaacetate ion), prepared by treating [VO(H₂O)₅][(VO)₂(ttha)]·4 H₂O with Na₆(ttha), has been characterized by single crystal X-ray diffraction, infrared spectroscopy, UV–Vis absorption spectroscopy, electron spin resonance spectroscopy, and modeled by density functional theory (DFT). The X-ray structure revealed a distorted octahedral geometry around each vanadium center. The electronic absorption spectrum of [(VO)₂(ttha)]²⁻ (aq) features absorptions at ca. 200 nm (ε > 13900 L mol⁻¹ cm⁻¹), 255 nm (ε = 3480 L mol⁻¹ cm⁻¹), 586 nm (ε = 33 L mol⁻¹ cm⁻¹), and 770 nm (ε = 38 L mol⁻¹ cm⁻¹). The time-dependent density functional theory (TDDFT) calculated electronic absorption spectrum was remarkably similar to the actual spectrum, and TDDFT predicts absorption peaks at 297, 330, 458, 656, and 798 nm. TDDFT assigned the peak at 798 nm to be the α spin HOMO → LUMO transition. Hence, the peak at 770 nm in the actual spectrum is most likely the α spin HOMO → LUMO transition. Moreover, the TDDFT calculations revealed that the α spin HOMO and LUMO are partly comprised of d orbitals on both vanadium centers, and the first derivative electron spin resonance spectrum also suggests that the two unpaired electrons in [(VO)₂(ttha)]²⁻ are localized near the vanadium centers.     

Isophorone－based Fluorescent Dopant for Red Organic Electrolumi－nescence Device

lsophorone-based red fluorescent compound 3-(dicyanomethy-lene ) -5, 5-dimethyi- 1- [ 2- ( N-ethyl-3-carbazyi ) ethylene ] cyciohe-xene (DCDCC) was synthesized for use in organic Hght-emit-ring diodes (OLEDs). DCDCC was characterized by narrow emission in photoluminescence with full.width at half-maximum of only 50 nm in solution and in thin solid film of 70 nm width. devices with configuration of ITO/NPB/Alq3:DCDCC/Alq3/Mg: Ag were fabricated utilizing DCDCC as dopant emitter. An efficient red emission peaked at 612 nm was obtained for the device with 1% (wt.%) DCDCC in Alq3. The maximum luminance and current efficiency were as high as 3700 cd/m^2 at 14 V and 1.25 cd/A at 150 mA/cm^2, respective-ly.     

Luminescence and electroluminescence of bis (2-(benzimidazol-2-yl) quinolinato) zinc. Exciplex formation and energy transfer in mixed film of bis (2-(benzimidazol-2-yl) quinolinato) zinc and N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine

The absorption and emission properties of benzimidazol-2-yl-quinoline (BIQ) and bis (2-(benzimidazol-2-yl) quinolinato) zinc (ZnBIQ) a new emitter used for organic light emitting device (OLED) were reported. Exciplexes are observed for ZnBIQ with N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) system, in both electro- and photoluminescent processes. The identification of exciplex emission in co-evaporated and multi-layer ZnBIQ thin film was reported for the first time. The optical formation of the exciplex involves the excitation of a single molecule, followed by the relaxation of that exciton into a lower energy exciplex state. Both BIQ and ZnBIQ possess very high thermal stabilities and can be purified by subliming under the high vacuum condition. Devices consisting of ZnBIQ as the emitting layer have been fabricated, and the emission spectra of ZnBIQ-base devices gave a voltage-dependent spectrum, with the red emission observed (3-7 V), switching over to strong white emission as the bias was raised.     

New hole-transport polyurethanes applied to polymer light-emitting diodes

Polymeric light-emitting diodes (PLEDs) using high-performance hole-transport polyurethanes (PUs) have been fabricated. The PUs were prepared from the condensation polymerization of (E, E)-1,4-bis(2-hydroxystyryl)benzene, an oligo para-phenylene-(E)-vinylene (OPV) unit, with toluene diisocyanate (TDI), isophorone diisocyanate (IPDI) or dicyclohexylmethane 4,4′-diisocyanate (H₁₂MDI), respectively. The condensation polymerization was end-capped with 4-tert-butylphenol as the terminal group. The PLED having the PU layer inserted between PEDOT:PSS (HIL) and MEH-PPV (EML) demonstrated superior current efficiency and low turn-on voltage when comparing to the reference devices of ITO/MEH-PPV(50 nm)/Ca(10 nm)/Ag(100 nm) as well as ITO/PEDOT:PSS(30 nm)/MEH-PPV(50 nm)/Ca(10 nm)/Ag(100 nm). In particularly, the best device performance was realized with the PU of OPV-IPDI as the hole-transport layer, resulting 53 times and 2.72 times of current efficiency enhancement as well as 1.5 V and 1 V voltage reduction of the turn-on voltage, respectively, when compared against the reference devices. Besides, our experiments also showed that the PU polymer could also be applied for flexible PLED with similar performance enhancement. Based on the promising results, we concluded that OPV-IPDI was a good hole-transport material for light-emitting diode application.     

Highly Emissive Luminogens Based on Imidazo[1,2‐a]pyridine for Electroluminescent Applications

A search for novel organic luminogens led us to design and synthesize some N‐fused imidazole derivatives based on imidazo[1,2‐a]pyridine as the core and arylamine and imidazole as the peripheral groups. The fluorophores were synthesized through a multicomponent cascade reaction (A³ coupling) of a heterocyclic azine with an aldehyde and alkyne, followed by Suzuki coupling and a multicomponent cyclization reaction. All of the compounds exhibited interesting photophysical responses, especially arylamine‐containing derivatives, which displayed strong positive solvatochromism in the emission spectra that indicated a more polar excited state owing to an efficient charge migration from the donor arylamine to the imidazo[1,2‐a]pyridine acceptor. The quantum yields ranged from 0.2 to 0.7 and depended on the substitution pattern, most notably that based on the donor group at the C2 position. Moreover, the influence of general and specific solvent effects on the photophysical properties of the fluorophores was discussed with four‐parameter Catalán and Kamlet–Taft solvent scales. The excellent thermal, electrochemical, and morphological stability of the compounds was explored by cyclic voltammetry, thermogravimetric analysis, and AFM methods. Furthermore, to understand the structure, bonding, and band gap of the molecules, DFT calculations were performed. The performance of the electroluminescence behavior of the imidazo[1,2‐a]pyridine derivative was investigated by fabricating a multilayer organic light‐emitting diode with a configuration of ITO/NPB (60 nm)/EML (40 nm)/BCP (15 nm)/Alq₃ (20 nm)/LiF (0.5 nm)/Al(100 nm) (ITO=indium tin oxide, EML=emissive layer, BCP=2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline, Alq₃=tris(8‐hydroxyquinolinato)aluminum), which exhibited white emission with a turn‐on voltage of 8 V and a brightness of 22 cd m^?2.     

Perfluoro-1,3,5-tris(p-oligophenyl)benzenes: Amorphous Electron-Transport Materials with High-Glass-Transition Temperature and High Electron Mobility

Perfluoro-1,3,5-tris(p-quaterphenyl)benzene (PF-13Y) and perfluoro-1,3,5-tris(p-quinquephenyl)benzene (PF-16Y) have been synthesized and characterized. They showed higher glass transition temperatures compared with perfluoro-1,3,5-tris(p-terphenyl)benzene (PF-10Y). Organic light-emitting diodes were fabricated using these materials as the electron-transport layers. PF-13Y and -16Y are better electron transporters than PF-10Y. The electron mobilities of PF-10Y and Alq₃ were measured by the time-of-flight technique. PF-10Y showed higher electron mobilities (10⁻⁴ cm²/V s) and weaker electric field dependence compared with Alq₃.     

Red Phosphorescent Bis‐Cyclometalated Iridium Complexes with Fluorine‐, Phenyl‐, and Fluorophenyl‐Substituted 2‐Arylquinoline Ligands

Red phosphorescent iridium(III) complexes based on fluorine‐, phenyl‐, and fluorophenyl‐substituted 2‐arylquinoline ligands were designed and synthesized. To investigate their electrophosphorescent properties, devices were fabricated with the following structure: indium tin oxide (ITO)/4,4′,4′′‐tris[2‐naphthyl(phenyl)amino]triphenylamine (2‐TNATA)/4,4′‐bis[N‐(1‐naphthyl)‐N‐phenylamino]biphenyl (NPB)/4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl (CBP): 8 % iridium (III) complexes/bathocuproine (BCP)/tris(8‐hydroxyquinolinato)aluminum (Alq₃)/8‐hydroxyquinoline lithium (Liq)/Al. All devices, which use these materials showed efficient red emissions. In particular, a device exhibited a saturated red emission with a maximum luminance, external quantum efficiency, and luminous efficiency of 14200 cd m^?2, 8.44 %, and 6.58 cd A^?1 at 20 mA cm^?2, respectively. The CIE (x, y) coordinates of this device are (0.67, 0.33) at 12.0 V.     

A novel fabrication technique and new conjugated polymers for multilayer polymer light-emitting diodes

We report a novel fabrication technique for multilayer light-emitting diodes composed of new polyoxadiazole, POD, conjugated polymers for the first time. The fabrication technique called vapor deposition polymerization is described. Chemical modification of monomers brought about the enhancement of reactivity and the production of high molecular weight of POD. Emission color with photoexcitation was controllable from violet-blue to green by varying the chemical structures of PODs. It was found that PODs could be employed as either electroluminescent or carrier-injecting layers by the optimization of the device structure. Two types of bilayer devices, which are constructed with POD/tris (8-quinolinoato) aluminum, Alq₃, and with two POD layers with different chemical structures, were investigated. Carrier injection begins in the POD/Alq₃ bilayer device near 7 V, and the device emitted green light from Alq₃. The maximum luminance of the POD/Alq₃ device reached 3500 cd/m². The POD/POD bilayer device emitted blue light with maximum luminance of 21 cd/m². Electroluminescence spectra of the devices coincided with photoluminescence spectra of each emitting material used. © 1997 John Wiley & Sons, Ltd.     

Synthesis of regio- and stereoselective alkoxy-substituted spirobifluorene derivatives for blue light emitting materials

Three new octyloxy substituted spirobifluorenes, 2,7-diphenyl-3′,6′-bis(octyloxy)-9,9′-spirobifluorene (DPBSBF, 1a), 2,7-dibiphenyl-3′,6′-bis(octyloxy)-9,9′-spirobifluorene (DBBSBF, 1b) and 2,7-diterphenyl-3′,6′-bis(octyloxy)-9,9′-spirobifluorene (DTBSBF, 1c) were prepared. All the compounds had been fully characterized by ¹H and ¹³C NMR, UV-Vis, DSC, mass spectrometry and gave satisfactory elemental analyses. They possessed good solubility in common organic solvents and good homogeneous film formation. The optical energy band gap of DBBSBF was 3.27 eV between the HOMO energy level, 5.85 eV, measured by UPS and the LUMO, 2.58 eV, calculated from absorption spectrum. A blue organic light emitting diode (OLED) based on the structure of ITO/TPD (60 nm)/DBBSBF (40 nm)/Alq₃ (20 nm)/LiF (1 nm)/Al (100 nm) showed good performance. The luminance of 3125 cd/m² was observed at a drive voltage of 12.8 V and the colour coordinate in CIE chromaticity was (0.14, 0.12). The external quantum efficiency was obtained to be 2.8% at 100 cd/m².     

A novel oligothiophene derivative as a hole‐transport with emitting material for OLED

A novel oligothiophene derivative containing the triphenylamine moiety with high glass transition temperature (T_g; 135 °C), 5,5′‐{bis[4‐di(4‐thiophenyl)amino]phenyl}‐2,2′‐bithiophene (TTPA‐dimer) was synthesized by the dimerization of tris[4‐(2‐thienyl)phenyl]amine (TTPA) with a palladium catalysis. Some types of electroluminescent (EL) devices that use the amorphous material for a hole‐ and an electron‐transporting with an emitting layer were fabricated. These devices emitted a bright green‐yellowish light (λ_emi; around 510 nm) with a small full width at half maximum (FWHM) rather than that of Alq₃. The single layer EL device showed a maximum luminance of 221 cd/m² at 8 V (0.06 lm/W at 100 cd/m²). On the other hand, the double layer (TTPA‐dimer/Alq₃) EL device that used Alq₃ as the electron transport material was increased up to 10830 cd/m² at 12 V (0.89 lm/W at 300 cd/m²) and with a lower turn‐on voltage (3.2 V at 0.1 cd/m²) than other types of EL devices. Copyright © 2003 John Wiley & Sons, Ltd.