Improved performances of organic light-emitting diodes with metal oxide as anode buffer

We demonstrate extremely stable and highly efficient organic light-emitting diodes (OLEDs) based on molybdenum oxide (MoO3) as a buffer layer on indium tin oxide (ITO). The significant features of MoO3 as a buffer layer are that the OLEDs show low operational voltage, high electroluminescence (EL) efficiency and good stability in a wide range of MoO3 thickness. A green OLED with structure of ITO/MoO3/N,N-'-di(naphthalene-1-yl)-N,N-'-diphenyl-benzidene (NPB)/NPB: tris(8-hydroxyquinoline) aluminum (Alq(3)):10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H, 5H, 11H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one (C545T)/Alq(3)/LiF/Al shows a long lifetime of over 50 000 h at 100 cd/m(2) initial luminance, and the power efficiency reaches 15 lm/W. The turn-on voltage is 2.4 V, and the operational voltage at 1000 cd/m(2) luminance is only 6.9 V. The significant enhancement of the EL performance is attributed to the improvement of hole injection and interface stability at anode.

High efficiency tandem organic light-emitting devices with Al/WO3/Au interconnecting layer

An interconnecting layer of Al (2 nm)/WO3 (3 nm)/Au (16 nm) was studied for application in tandem organic light-emitting devices. It can be seen that the Al/WO3/Au structure plays the role of an excellent interconnecting layer. The introduction of WO3 in the connection unit significantly improves the device efficiency as compared to the case of Al/Au. Thus, the current efficiency of the two-unit tandem devices is enhanced by two factors with respect to the one-unit devices. The green two-unit tandem device of indium tin oxide/MoO3/4,4(')-N,N-'-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl(NPB)/tris(8-hydroxylquinoline) aluminum (Alq(3)):10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1]benzopyrano[6,7,8-ij]quinolizin-11-one (C545T)/Alq(3)/LiF/Al/WO3/Au/MoO3/NPB/Alq(3):C545T/Alq(3)/LiF/Al showed a maximum current efficiency of 33.9 cd/A and a power efficiency of 12.0 lm/W.

Effects of doped dye on the charge carrier injection, transport, and electroluminescent performance in polymeric light-emitting diodes

The effects of doped fluorescent dye 4-(dicyanomethylene)-2-i-propyl-6-(1, 1, 7, 7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTI) on the charge carrier injection, transport and electroluminescence (EL) performance in polyfluorene (PFO)-based polymer light-emitting diodes (PLEDs) were investigated by steady-state current-voltage (I-V) characteristics and transient EL measurements. A red EL from DCJTI was observed and the EL performance depended strongly on the DCJTI concentration. The analysis of the steady-state I-V characteristics at different DCJTI concentrations found that three regions was shown in the I-V characteristics, and each region was controlled by different processes depending on the applied electric field. The effect of the dopant concentration on the potential-barrier height of the interface is estimated using the Fowler-Nordheim model. The dopant concentration dependence of the current-voltage relationship indicated clearly the carrier trapping by the DCJTI molecules. The mobility in DCJTI: PFO changed significantly with the DCJTI concentration, and showed a nontrivial dependence on the doping level. The behavior may be understood in terms of the formation of an additional energy disorder due to potential fluctuation caused by the Coulomb interaction of the randomly distributed doping molecules.

Tight intermolecular packing through supramolecular interactions in crystals of cyano substituted oligo(para-phenylene vinylene): a key factor for aggregation-induced emission

Strong supramolecular interactions, which induced tight packing and rigid molecules in crystals of cyano substituent oligo(para-phenylene vinylene) (CN-DPDSB), are the key factor for the high luminescence efficiency of its crystals; opposite to its isolated molecules in solution which have very low luminescence efficiency.

Organic photovoltaic cells with near infrared absorption spectrum

Organic photovoltaic cells with a strong absorption spectrum in the near infrared region were fabricated with the structure of indium tin oxide (ITO)/zinc phthalocynine (ZnPc)/lead phthalocynine (PbPc)/C-60/Al. PbPc has a broad and strong absorption, while the organic films of PbPc/C-60 showed an additional new absorption peak at 900 nm. The absorption in the near infrared region can harvest more photons to invert into photocurrent. Moreover, the introduction of ZnPc thin layer between ITO and PbPc further improved the new absorption peak and the collection of hole carriers at the electrode ITO, which increased the power conversion efficiencies to 1.95% and short-circuit current density to 9.1 mA/cm(2) under AM 1.5 solar spectrum.

Preparation of In2O3 ceramic nanofibers by electrospinning and their optical properties

Electrospinning was employed to fabricate polymer-ceramic composite fibers from solutions containing polyvinyl pyrrolidone (PVP) and In(NO3)(3)center dot 4(1)/2H2O. Upon firing the composite fibers at 800 degrees C, In2O3 fibers with diameters ranging from 200 to 400 nm were synthesized. This indium oxide calcined at 800 degrees C is a body-centered cubic cell. The photoluminescence (PL) properties of the as-formed In2O3 nanofibers were investigated. The In2O3 nanofibers show a strong PL emission in the ultraviolet (UV) region under shorter UV light irradiation.

Charge ordering induced metal-semiconductor transition in Ag2BiO3: A first-principles study

Accurate ab initio density-functional calculations are performed to investigate the relationship of the ground-state crystal structures and electronic properties of Ag2BiO3 compound. The results indicate that Ag2BiO3 in Pnna phase, in which the bismuth atoms occupy the same Wyckoff positions, exhibits metallic conductivity, while in Pnn2 and Pn phases, Ag2BiO3 exhibits semiconducting character, which is in agreement with the experimental results. Charge ordering is indeed induced by the crystal inversion twin in the Pnn2 phase compared with the Pnna phase. In the low temperature phase Pn, the charge ordering is similar to that of Pnn2 phase although it is more distorted in Pn phase. In addition, the calculation indicates that the charge ordering is caused in the 6s electron rearrangement.

Oriented growth and luminescence of ZnO : Eu films prepared by sol-gel process

A series of Eu3+-doped ZnO films have been prepared by a sol-gel method. These films were characterized by X-ray diffraction (XRD) and photoluminecent spectra (PL). Effects of synthetic parameters, such as annealing atmosphere, temperature and concentration of doped ions, on the highly oriented crystal growth were studied in detail. The crystalline structures of films annealed in vacuum have a wurtzite symmetry with highly c-axis orientation. A characteristic D-5(0) -> F-7(J)(J = 1, 2, 3 and 4) red emission is observed due to energy transfer from the ZnO host to the doped Eu3+ in the c-oriented ZnO films.

Enhancement of the electrooxidation of ethanol on Pt-Sn-P/C catalysts prepared by chemical deposition process

In this paper, five Pt3Sn1/C catalysts have been prepared using three different methods. It was found that phosphorus deposited on the surface of carbon with Pt and Sn when sodium hypophosphite was used as reducing agent by optimization of synthetic conditions such as pH in the synthetic solution and temperature. The deposition of phosphorus should be effective on the size reduction and markedly reduces PtSn nanoparticle size, and raise electrochemical active surface (EAS) area of catalyst and improve the catalytic performance. TEM images show PtSnP nanoparticles are highly dispersed on the carbon surface with average diameters of 2 nm. The optimum composition is Pt3Sn1P2/C (note PtSn/C-3) catalyst in my work. With this composition, it shows very high activity for the electrooxidation of ethanol and exhibit enhanced performance compared with other two Pt3Sn1/C catalysts that prepared using ethylene glycol reduction method (note PtSn/C-EG) and borohydride reduction method (note PtSn/-B). The maximum power densities of direct ethanol fuel cell (DEFC) were 61 mW cm(-2) that is 150 and 170% higher than that of the PtSn/C-EG and PtSn/C-B catalyst.

Synthesis and characterization of electroactive and biodegradable ABA block copolymer of polylactide and aniline pentamer

A triblock copolymer PLA-b-AP-b-PLA (PAP) of polylactide (PLA) and aniline pentamer (AP) with the unique properties of being both electroactive and biodegradable is synthesized by coupling an electroactive carboxyl-capped AP with two biodegradable bihydroxyl-capped PLAs via a condensation reaction. Three different molecule weight PAP copolymers are prepared. The PAP copolymers exhibit excellent electroactivity similar to the AP and polyaniline, which may stimulate cell proliferation and differentiation. The electrical conductivity of the PAP2 copolymer film (similar to 5 x 10(-6) S/cm) is in the semiconducting region. Transmission electron microscopic results suggest that there is microphase separation of the two block segments in the copolymer, which might contribute to the observed conductivity. The biodegradation and biocompatibility experiments in vitro prove the copolymer is biodegradable and biocompatible. Moreover, these new block copolymer shows good solubility in common organic solvents, leading to the system with excellent processibility. These biodegradable PAP copolymers with electroactive function thus possess the properties that would be potentially used as scaffold materials for neuronal or cardiovascular tissue engineering.

White electroluminescence from a single-polymer system with simultaneous two-color emission: Polyfluorene as blue host and 2,1,3-benzothiadiazole derivatives as orange dopants on the side chain

Four single polymers with two kinds of attachment of orange chromophore to blue polymer host for white electroluminescence (EL) were designed. The effect of the side-chain attachment and main-chain attachment on the EL efficiencies of the resulting polymers was compared. The side-chain-type single polymers are found to exhibit more efficient white EL than that of the main-chain-type single polymers. Based on the side-chain-type white single polymer with 4-(4-alkyloxy-phenyl)-7-(4-diphenylamino-phenyl)-2,1,3-benzothiadiazoles as the orange-dopant unit and polyfluorene as the blue polymer host, white EL with simultaneous orange (lambda(max) = 545 nm) and blue emission (lambda(max) = 432 nm/460 nm) is realised. A single-layer device (indium tin oxide/poly(3,4-ethylenedioxythiophene)/polymer/Ca/Al) made of these polymers emits white light with the Commission Internationale de l'Eclairage coordinates of (0.30,0.40), possesses a turn-on voltage of 3.5 V, luminous efficiency of 10.66 cd A(-1), power efficiency of 6.68 lm W-1, and a maximum brightness of 21240 cd m(-2).

Synthesis and characterization of white-light-emitting polyfluorenes containing orange phosphorescent moieties in the side chain

Two orange phosphorescent iridium complex monomers, 9-hexyl-9-(iridium (III)bis(2-(4'-fluorophenyl)-4-phenylquinoline-N, C-2')(tetradecanedionate-11,13))-2,7-dibromofluorene (Br-PIr) and 9-hexyl-9-(iridium(III)bis(2-(4'-fluorophenyl)-4-methylquinoline-N, C-2')(tetradecanedionate-11,13))-2,7-dibromofluorene (Br-MIr), were successfully synthesized. The Suzuki polycondensation of 2,7-bis(trimethylene boronate)-9,9-dioctylfluorene with 2,7-dibromo-9,9-dioetylfluorene and Br-Plr or Br-MIr afforded two series of copolymers, PIrPFs and MIrPFs, in good yields, in which the concentrations of the phosphorescent moieties were kept small (0.5-3 mol % feed ratio) to realize incomplete energy transfer. The photoluminescence (PL) of the copolymers showed blue- and orange-emission peaks. A white-light-emitting diode with a configuration of indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/PIr05PF (0.5 mol % feed ratio of Br-PIr)/Ca/Al exhibited a luminous efficiency of 4.49 cd/A and a power efficiency of 2.35 lm/W at 6.0 V with Commission Internationale de L'Eclairage (CIE) coordinates of (0.46, 0.33). The CIE coordinates were improved to (0.34, 0.33) when copolymer MIr10PF (1.0 mol % feed ratio of Br-MIr) was employed as the white-emissive layer. The strong orange emission in the electroluminescence spectra in comparison with PL for these kinds of polymers was attributed to the additional contribution of charge trapping in the phosphorescent dopants.

Luminescent supramolecular polymers: Cd2+-directed polymerization and properties

A family of supramolecular polymers was prepared via Cd2+-directed self-assembly polymerization of his (2,2':6',2 ''-terpyridine)-based ligand monomers, using oligofluorenes and triphenylamine as bridges under mild conditions. The polymers were fully characterized using thermogravimetric analysis, inherent viscosity, electrochemical measurements, UV-visible spectroscopy, photoluminescence (PL) and electroluminescence (EL). Polymers with oligofluorenes as spacers exhibited blue emission (434-442 nm) in dimethyl acetamide (DMAc) solution, while polymers with triphenylamine as spacer presented an emission peak at 494 nn in DMAc solution. Complexation polymerization of bis(2,2':6',2 ''-terpyridine)-based ligand monomers with cadmium(II) improved fluorescence quantum yields dramatically, and the film PL quantum yields of these polymers were about 0.38-0.54. Single-layer light-emitting diodes were fabricated with the configuration indium tin oxide (ITO)/polymer/Ca/Al; the EL showed green emission and the onset voltages of the devices were 8-11 V.

Two- and three-dimensional Au nanoparticle/CoTMPyP self-assembled nanotructured materials: Film structure, tunable electrocatalytic activity, and plasmonic properties

Two- and three-dimensional Au nanoparticle/[tetrakis(N-methylpyridyl)porphyrinato]cobalt (CoTMPyP) nanostructured materials were prepared by "bottom-up" self-assembly. The electrocatalytic and plasmonic properties of the Au nanoparticle/CoTMPyP self-assembled nanostructured materials (abbreviated as Au/CoTMPyP SANMs) are tunable by controlled self-assembly of the An nanoparticles and CoTMPyP on indium tin oxide (ITO) electrode. The electrocatalytic activity of the Au/CoTMPyP SANMs can be tuned in two ways. One way is that citrate-stabilized An nanoparticles are positioned first on ITO surface with tunable number density, and then positively charged CoTMPyP ions are planted selectively on these gold sites. The other way is that An nanoparticles and CoTMPyP are deposited by virtue of layer-by-layer assembly, which can also tune the amount of the as-deposited electrocatalysts. FE-SEM studies showed that three-dimensional SANMs grow in the lateral expansion mode, and thermal annealing resulted in both surface diffusion of nanoparticles and atomic rearrangement to generate larger gold nanostructures with predominant (I 11) facets.

微芯片毛细管电泳电化学/电化学发光同时检测药物分子

提出了基于毛细管电泳芯片的电化学和电化学发光同时检测技术.在此芯片系统中,三联吡啶钌Ru(bpy)2+3[Tris(2,2'-bypiridyl) ruthenium(Ⅱ)]既作为电化学发光(ECL)检测所需的发光试剂与被分析物反应,生成激发态的Ru(bpy)2+3*,从而产生电化学发光信号;又具有催化作用参与电极表面的电化学反应,从而得到增强的电流响应.电化学信号与电化学发光信号同时产生并被分别纪录,从而实现了电化学和电化学发光的同时检测.这种芯片由两部分构成,分别是带有分离和进样通道的聚二甲基硅氧烷(PDMS)层和ITO(Indium tin oxide)工作电极底片.PDMS层与ITO电极底片采用可逆键合的方式组成芯片,该芯片大大简化了操作过程,提高了发光信号的采集效率.在整个实验过程中,ITO电极表现出良好的稳定性,可长时间多次使用.选用山莨菪碱和氧氟沙星两种药物分子作为被分析物,对芯片系统性能进行了表征.