Near-Infrared Emission from Organic Light-Emitting Diodes Based on Copper Phthalocyanine with a Periodically Arranged Alq3：CuPc/DCM Multilayer Structure

We demonstrate near-infrared organic light-emitting devices with a periodically arranged tris（8-quinolinolato）aluminum （Alq3）：copper phthalocyanine （CuPc）/4-（dicyanomethylene）-2-methyl-6-（4-dimethylaminost-yry）-4H-pyran （DCM） multilayer structure. DCM and Alq3 doped with CuPc were periodically deposited. Room-temperature electrophosphorescence was observed at about 1.1 μm due to transitions from the first excited triplet state to the singlet ground state （T1 - S0） of CuPc. In this device, we utilize the overlap between the Q band πr - π^＊ at about 625nm of the absorption spectra of CuPc and the PL spectra of the DCM. The near-infrared emission intensity of the CuPc-doped Alq3 device with DCM increases about 2.5 times larger than that of the device without DCM. We attribute the efficiency enhancement to the better overlap between the PL spectra of DCM and the absorption spectra of CuPc.     

Organic Light Emitting Diodes with an Organic Acceptor/Donor Interface Involved in Hole Injection

Organic light emitting diodes with an interface of organic acceptor 3-, 4-, 9-,10-perylenetetracarboxylic dianhydride （PTCDA） and donor copper phthalocyanine （CuPc） involved in hole injection are fabricated. As compared to the conventional device using a 5 nm CuPc hole injection layer, the device using an interface of 10nm PTCDA and 5 nm CuPc layers shows much lower operating voltage with an increase of about 46% in the maximum power efficiency. The enhanced device performance is attributed to the efficient hole generation at the PTCDA/CuPc interface. This study provides a new way of designing hole injection.     

Organic Light-Emitting Diodes with Magnesium Doped CuPc as an Efficient Electron Injection Layer

Bright organic electroluminescent devices are developed using a metal-doped organic layer intervening between the cathode and the emitting layer. The typical device structure is a glass substrate/indium-tin oxide （ITO）/copper phthalocyanine （CuPc）/N,N＇-bis-（1-naphthl）-diphenyl-1,1＇-biphenyl-4,4＇-diamine （NPB）/Tris（8-quinolinolato） aluminum（Alq3）/Mg-doped CuPc/Ag. At a driving voltage of 11 V, the device with a layer of Mg-doped CuPc （1：2 in weight） shows a brightness of 4312cd/m^2 and a current efficiency of 2.52cd/A, while the reference device exhibits 514 cd/m^2 and 1.25 cd/A.     

An Electroluminescence Delay Time Model of Bilayer Organic Light-Emitting Diodes

Based on the mechanism of injection, transport and recombination of the charge carriers, we develop a model to calculate the delay time of electroluminescence （EL） from bilayer organic light emitting diodes. The effect of injection, transport and recombination processes on the EL delay time is discussed, and the relationship between the internal interface barrier and the recombination time is revealed. ＂]~he results show that the EL delay time is dominated by the recombination process at lower applied voltage and by the transport process at higher applied voltage. When the internal interface barrier varies from 0.15 eV to 0.3 eV, the recombination delay time increases rapidly~ while the internal interface barrier exceeds about 0.3eV~ the dependence of the recombination delay time on applied voltage is almost undiversified, which may serve as a guideline for designing of a high-speed EL response device.     

Electroluminescence from Multilayered Diamond/CeF3/SiO2 Films

We report a thin film electroluminescent device with a three-layer structure （diamond/CeF3/SiO2 films）, which has a luminance of 1.5 cd/m^2 at dc voltage 215 V. The electroluminescence spectrum at room temperature shows that the main peaks locate at 527 and 593nm, which are attributed to isolated emission centers of Ce^3＋ ions.     

Blue organic light-emitting diodes with low driving voltage and maximum enhanced power efficiency based on buffer layer MoO3

Blue organic light-emitting devices based on wide bandgap host material, 2-(t-butyl)-9, 10-di-(2-naphthyl) anthracene (TBADN), blue fluorescent styrylamine dopant, p-bis(p-N,N-diphenyl-amino-styryl)benzene (DSA-Ph) have been realized by using molybdenum oxide (MoO₃) as a buffer layer and 4,7-diphenyl-1,10-phenanthroline (BPhen) as the ETL. The typical device structure used was glass substrate/ITO/MoO₃ (5 nm)/NPB (30 nm)/[TBADN: DSA-Ph (3 wt%)](35 nm)/BPhen (12 nm)/LiF (0.8 nm)/Al (100 nm). It was found that the MoO₃∥BPhen-based device shows the lowest driving voltage and highest power efficiency among the referenced devices. At the current density of 20 mA/cm², its driving voltage and power efficiency are 5.4 V and 4.7 Lm/W, respectively, which is independently reduced 46%, and improved 74% compared with those the m-MTDATA∥Alq₃ is based on, respectively. The J-V curves of ‘hole-only’ devices reveal that a small hole injection barrier between MoO₃∥NPB leads to a strong hole injection, resulting low driving voltage and high power efficiency. The results strongly indicate that carrier injection ability and balance shows a key significance in OLED performance.     

Efficient Top-Emitting Polymer Light-Emitting Diodes Using Chromium as Anode

We demonstrate a high eftlciency top-emitting polymer light-emitting diode （TPLED） with chromium （Cr） taking as the anode. The TPLED structure is Cr/poly-3, 4-ethylenedioxythiophene （PEDOT：PSS）/poly [2-（4-3＇,7＇- dimethyloctyloxy）-phenyl]-p-phenylenevinylene） （P-PP V） /Ba/Ag. The Cr （ 100 nm） anode is prepared by sputterdepositing in a vacuum chamber. It is found that the device emissive properties are affected dramatically by the thickness of both PEDOT：PSS and the Ag cathode. Optimized thicknesses of PEDOT：PSS and Ag layer are 60nm and 15nm, respectively. The diode exhibits excellent electroluminescence （EL） properties, such as a turn-on voltage of 3.32 V, luminous eftlciency of 4.41 cd/A and luminance of 6989cd/m^2 at driving voltage of about 9 V.     

Efficient Phosphorescent Organic Light Emitting Diodes Using FITCNQ as the Indium-Tin-Oxide Modification Layer

A phosphorescent organic light emitting diode by using tetrafluorotetracyanoquinodimethane （F4 TCNQ） as the indium-tin-oxide modification layer and 4,4＇-bis（earbazol-9-yl）biphenyl （CBP） as the hole transporting layer is reported. CBP doped with a green phosphorescent dopant, tris（2-（p-tolyl）pyridine） iridium（III） （Ir（mppy）3） is used as the emission layer in this device, and the maximum current efficiency of 31.3 cd/A is achieved. Further- more, low efficiency roll-off of 10.4% is observed with device luminance increasing from 100 cd/m2 （29. 7 cd/A） to lO000 cd/m2 （26.5 cd/A）. It is demonstrated that a charge-generation area is formed at F4 TCNQ/CBP interface, which will benefit hole injection into the hole transporting layer. Moreover, use of the CBP hole transporting layer will benefit the low efficiency roll-off by broadening triplet exciton formation, as well as by avoiding accumulation of unbalanced carrier at the hole transporting layer/emission layer interface.     

Enhanced Efficiency of Polymer： Fullerene Bulk Heterojunction Solar Cells with the Insertion of Thin TiO2 Layer near the LiF/A1 Electrode

The insertion layer of TiO2 between polymer-fullerene blend and LiF/AI electrode is used to enhance the shortcircuit current Isc and fill factor （FF）. The solar cell based on the blend of poly[2-methoxy-5-（2＇-ethylhexyloxy）- 1,4-phenylenevinylene] （MEH-PPV） and C60 with the modifying layer of TiO2 （about 20nm） shows the open- circuit Voc of about 0.62 V, short circuit current Isc of about 2.35 mA/cm^2, filling factor FF of about 0.284, and the power conversion efficiency （PCE） of about 2.4% under monochromatic light （50Onto） photoexcitation of about 17mW/cm^2. Compared to ceils without the TiO2 layer, the power conversion efficiency increases by about 17.5%. Similar effect is also obtained in cells with the undoped MEH-PPV structure of ITO/PEDOT：PASS/MEH- PPV/（TiO2）LiF/AI. The improved solar cell performance can be attributed to enhanced carrier extraction efficiency at the active layer/electrode interfaces when TiO2 is inserted.     

Organic Light-Emitting Devices with a LiF Hole Blocking Layer

We introduce a thin LiF layer into tris-8-hydroxyquinoline aluminium （Alq3 ） based bilayer organic light-emitting devices to block hole transport. By varying the thickness and position of this LiF layer in Alq3, we obtain an electroluminescent efficiency increase by a factor of two with respect to the control devices without a LiF blocking layer. By using a 10nm dye doped Alq3 sensor layer, we prove that LiF can block holes and excitons effectively. Experimental results suggest that the thin LiF layer may be a good hole and exciton blocking layer.     

采用复合空穴注入层提高有机电致发光器件的性能

制备了以Ag/SAM/m-MTDATA为复合空穴注入层的NPB/Alq₃双层异质结发光器件,研究了器件的性能并与传统的器件进行了对比。考察了银膜厚度的变化对器件性能的影响。研究了光谱窄化以及微腔效应对器件的影响。研究结果表明:在ITO表面制备4-FTP自组装单分子膜修饰的5 nm厚的金属银膜,可以在保持阳极透明性的基础上,增强空穴的注入,改善界面的形貌,进而提高器件性能。制备的ITO/Ag/SAM/m-MTDATA/NPB/Alq₃/LiF/Al器件的启亮电压为4 V,最 大电流效率为6.9 cd/A, 最大亮度为34 680 cd/m²(12 V);优于以ITO为阳极的对比器件(25 300 cd/m² @12 V)。     

Photovoltaic Cells with TiO2 Nanocrystals and Conjugated Polymer Composites

Various compositional photovoltaic cells based on the blend of poly(3-hexylthiophene) (P3HT) as donors and TiO₂ nanocrystals as acceptors are fabricated and investigated. It is demonstrated that the blend ratio of P3HT and TiO₂ nanocrystals could greatly influence the performance of the photovoltaic cells. The maximum of 0.411% in power conversion efficiency under AM 1.5, 100mW/cm², and 44.4% of fill factor are obtained in the solar cell with the blend weight ratio 1:1 of P3HT and TiO₂ nanocrystals. The function of nanocrystal composition is discussed in terms of the results of photoluminescence spectroscopy, atomic force microscopy, transmission electron microscopy, and charge transport I-V curve.     

非掺杂型高效绿色磷光有机电致发光器件

在空穴传输层TCTA与电子传输层TPBi之间引入磷光染料Ir(ppy)3超薄发光层,制备了结构为ITO/MoO_3(2 nm)/NPB(40 nm)/TCTA(10 nm)/Ir(ppy)3(xnm)/TPBi(40 nm)/LiF(1 nm)/Al(80 nm)的非掺杂磷光有机电致发光器件。通过调控非掺杂发光层的厚度,详细研究了Ir(ppy)3层厚度对器件性能的影响。实验结果表明,当非掺杂发光层厚度为0.2 nm时,器件的性能最好,器件的亮度、效率和外量子效率分别达到26 350 cd·m~(-2)、42.9 cd·A~(-1)和12.9%。研究结果表明,采用超薄的非掺杂发光层可以简化器件结构和制备工艺,获得高效率的OLED器件。     

Nonlinear electrical properties and DC accelerated aging characteristics of ZnO-Pr6O11-CoO-Cr2O3-Dy2O3-based varistors

The nonlinear electrical properties and stability against DC accelerated aging stress of various varistors, which are composed of ZnO-Pr₆O₁₁-CoO-Cr₂O₃-Dy₂O₃ (ZPCCD)-based ceramics, was investigated as a function of Dy₂O₃ content. The varistors with Dy₂O₃ exhibited a high nonlinear exponent above 30, compared with that without Dy₂O₃. The varistor with 0.5 mol% Dy₂O₃ exhibited the highest nonlinearity, with a nonlinear exponent of 66.6 and a leakage current of 1.2 μA. Furthermore, this varistor showed the high stability, in which the variation rate of varistor voltage, of nonlinear exponent, and of leakage are −1.9, −10.5, and +275.0%, respectively, under DC accelerated aging stress, 0.95 V_1 mA/150 °C/24 h.     

Role of TiO2 Nanotube on Improvement of Performance of Hybrid Photovoltaic Devices

The performance of TiO₂ nanotubes in bulk heterojunction of poly (2-methoxy-5-(2'-ethylhexyloxy)-1, 4-phenylenevinylene) (MEH-PPV)/TiO₂ nanotubes is investigated. The transport properties are studied by using the time-of-flight technique (TOF). The carrier mobilities of both holes and electrons are not improved for the MEH-PPV:TiO₂ composites compared with the pristine MEH-PPV. However, photoluminescence under the influence of the electric field indicates that the dissociation of excitons in the MEH-PPV:TiO₂ composites, which is facilitated by photoinduced charge transfer, only requires a smaller electric field.     

The roles of zinc selenide sandwiched between organic layers and its applications in white light-emitting diodes

In this paper, the roles of zinc selenide (ZnSe) sandwiched between organic layers, i.e. organic/ZnSe/aluminum quinoline (Alq₃), have been studied by varying device structure. A broad band emission was observed from ITO/poly(N-vinylcarbazole)(PVK)(80 nm)/ZnSe(120 nm)/ Alq₃(15 nm)/Al under electric fields and it combined the emissions from the bulk of PVK, ZnSe and Alq₃, however, emission from only Alq₃ was observed from trilayer device ITO/N,N^′-bis-(1-naphthyl)-N,N^′-diphenyl-1, 1^′-biphenyl-4, 4^′-diamine (NPB) (40 nm)/ZnSe(120 nm)/ Alq₃(15 nm)/Al. Consequently the luminescence mechanism in the ZnSe layer is suggested to be charge carrier injection and recombination. By thermal co-evaporating Alq₃ and 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), we get white light emission with a Commission Internationale de l’E clairage (C.I.E) co-ordinates of (0.32, 0.38) from device ITO/PVK(80 nm)/ZnSe(120 nm)/ Alq₃:DCJTB(0.5 wt% DCJTB)(15 nm)/Al at 15 V and the device performs stably with increasing applied voltages.     

Effect of laser-etched indium tin oxide on optoelectrical properties of organic light-emitting diodes

This study investigated how laser and wet etching methods of ITO substrates affect the optoelectrical properties of OLEDs. Experimental results indicated that the OLED with a laser-etched ITO substrate has a lower driving voltage than that with a wet-etched ITO substrate. According to scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements, the ITO etching methods yielded different surface morphologies of ITO pattern edges. The lower luminance of the OLED with a laser-etched ITO substrate is attributable to the fringe at the edge of ITO pattern, which causes a high local electric field resulting in the recrystallization of organic materials.     

Optimized Performances of Thick Film Organic Lighting-Emitting Diodes

The performance of organic light-emitting diodes (OLEDs) with thick film is optimized. The alternative vanadium oxide (V₂O₅) and N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) layers are used to enhance holes in the emissive region, and 4,7-dipheny-1,10-phenanthroline (Bphen) doped 8-tris-hydroxyquinoline aluminium (Alq₃) is used to enhance electrons in the emissive region, thus ITO/V₂O₅ (8nm)/NPB (52nm)/V₂O₅ (8nm)/NPB (52nm)/Alq₃ (30 and 45nm)/Alq₃:Bphen (30wt%, 30 and 45nm)/LiF (1nm)/Al (120nm) devices are fabricated. The thick-film devices show the turn-on voltage of about 3V and the maximal power efficiency of 4.5lm/W, which is 1.46 times higher than the conventional thin-film OLEDs.     

Electroluminescence of a Multi-Layered Organic Light-Emitting Diode Utilizing Trans-4-[p-[N-methyl-N-(hydroxymethyl)amino]styryl]-N-Methylphridinium Tetraphenylborate as the Active Layer

Employing an organic dye salt of trans-4-[p-[N-methyl-N-(hydroxymethyl)amino]styryl]-N-methylphridinium tetra\-phenylborate (ASPT) as the active layer, 8-hydrocyquinoline aluminium (Alq₃) as the electron transporting layer and N,N’-diphenyl-N,N’-bis(3-methylphenyl)-[1,1’-biphenyl]-4,4’-diamine (TPD) as the hole transporting layer, respectively, we fabricate a multi-layered organic light-emitting diode and observe the colour tunable electroluminescence (EL). The dependence of the EL spectra on the applied voltage is investigated in detail, and the recombination mechanism is discussed by considering the variation of the hole-electron recombination region.     

Efficient White Light Emission Using a Single Copolymer with Red and Green Chromophores on a Conjugated Polyfluorene Backbone Hybridized with InGaN-Based Light-Emitting Diodes

We report an efficient white-light emission based on a single copolymer/InGaN hybrid light-emitting diode. The single copolymer consists of a conjugated polyfluorene backbone by incorporating 2,1,3-benzothiadiazole （BT） and 4,7-bis（2-thienyl）-2,1,3-benzothiadiazole （DBT） as green and red light-emitting units, respectively. For the single copolymer/InGaN hybrid device, the Commission Internationale de 1＇Eclairage （CIE） coordinates, color temperature Tc and color rendering index Ra at 20mA are （0.323,0.329）, 5960K and 86, respectively. In comparison with the performance of red eopolymer PFO-DBT15 （DOF：DBT=85：15 with DOF being 9＇9- dioctylfluorene） and green copolymer PFO-BT35 （DOF：BT=-65：35） blend/InGaN hybrid white devices, it is concluded that the chemically doped copolymer hybridized device shows a higher emission intensity and spectral stability at a high driving current than the polymer blend.