Role and Effect of Anions in the Construction of Silver Complexes Based on a Pyridylimidazole Ligand with L‑Type Coordination Vectors and Their Photoluminescence Properties

Three anion-dependent Ag­(I) coordination complexesspecifically, [Ag₂(pyim)₂­(NO₃)₂] (<b>1</b>), {[Ag­(pyim)₂]­·ClO₄·CH₃OH­·(H₂O)_1.25}_<i>n</i> (<b>2</b>), and [Ag₄(pyim)₄]­·(CF₃SO₃)₄ (<b>3</b>)were prepared by the reaction of the corresponding silver salts with a rigid ditopic <i>N</i>-terphenyl-substituted 2-(4-pyridyl)­imidazole (pyim) ligand possessing an “L”-type coordination vector. Complex <b>1</b>, in which the nitrate anion acts as a monodentate terminal ligand, exhibits a discrete cyclic dimer structure, whereas complex <b>2</b>, incorporating a perchlorate anion with weak coordination ability, displays an anion-free one-dimensional (1D) looped chain structure resulting from the Ag sharing of consecutive cyclic dimers. When using a trifluoromethanesulfonate (triflate) as a counteranion with moderate affinity toward the metal center, the resulting complex <b>3</b> exhibits an unusual cyclic tetramer structure. In <b>3</b>, the triflate anions act as bridges between adjacent cyclic tetramers via the weak interaction with the Ag­(I) ions, yielding a parquet-like two-dimensional (2D) framework. All three complexes display violet-blue emission, with maxima ranging from 388 to 396 nm. Furthermore, in solution, complex <b>2</b> exhibits a substantial emission enhancement, resulting in an emission intensity nearly 2 orders of magnitude greater than those of both the free ligand and the two other Ag­(I) complexes, <b>1</b> and <b>3</b>. Counteranions possessing different abilities to coordinate to Ag­(I) play important roles in the structural diversity and photoluminescence properties of <b>1</b>–<b>3</b>

High-Mobility Pyrene-Based Semiconductor for Organic Thin-Film Transistors

Numerous conjugated oligoacenes and polythiophenes are being heavily studied in the search for high-mobility organic semiconductors. Although many researchers have designed fused aromatic compounds as organic semiconductors for organic thin-film transistors (OTFTs), pyrene-based organic semiconductors with high mobilities and on–off current ratios have not yet been reported. Here, we introduce a new pyrene-based p-type organic semiconductor showing liquid crystal behavior. The thin film characteristics of this material are investigated by varying the substrate temperature during the deposition and the gate dielectric condition using the surface modification with a self-assembled monolayer, and systematically studied in correlation with the performances of transistor devices with this compound. OTFT fabricated under the optimum deposition conditions of this compound, namely, 1,6-bis­(5′-octyl-2,2′-bithiophen-5-yl)­pyrene (BOBTP) shows a high-performance transistor behavior with a field-effect mobility of 2.1 cm² V^–1 s^–1 and an on–off current ratio of 7.6 × 10⁶ and enhanced long-term stability compared to the pentacene thin-film transistor

Data File 1: Stable angular emission spectra in white organic light-emitting diodes using graphene/PEDOT:PSS composite electrode

the CIE x- and y-coordinates at different angles (0-70°) Originally published in Optics Express on 01 May 2017 (oe-25-9-9734

Optical Analysis of Power Distribution in Top-Emitting Organic Light Emitting Diodes Integrated with Nanolens Array Using Finite Difference Time Domain

Recently, we have addressed that a formation mechanism of a nanolens array (NLA) fabricated by using a maskless vacuum deposition is explained as the increase in surface tension of organic molecules induced by their crystallization. Here, as another research using finite difference time domain simulations, not electric field intensities but transmitted energies of electromagnetic waves inside and outside top-emitting blue organic light-emitting diodes (TOLEDs), without and with NLAs, are obtained, to easily grasp the effect of NLA formation on the light extraction of TOLEDs. Interestingly, the calculations show that NLA acts as an efficient light extraction structure. With NLA, larger transmitted energies in the direction from emitting layer to air are observed, indicating that NLAs send more light to air otherwise trapped in the devices by reducing the losses by waveguide and absorption. This is more significant for higher refractive index of NLA. Simulation and measurement results are consistent. A successful increase in both light extraction efficiency and color stability of blue TOLEDs, rarely reported before, is accomplished by introducing the highly process-compatible NLA technology using the one-step dry process. Blue TOLEDs integrated with a <i>N</i>,<i>N</i>′-di­(1-naphthyl)-<i>N</i>,<i>N</i>′-diphenyl-(1,1′-biphenyl)-4,4′-diamine NLA with a refractive index of 1.8 show a 1.55-times-higher light extraction efficiency, compared to those without it. In addition, viewing angle characteristics are enhanced and image blurring is reduced, indicating that the manufacturer-adaptable technology satisfies the requirements of highly efficient and color-stable top-emission displays

Healing Graphene Defects Using Selective Electrochemical Deposition: Toward Flexible and Stretchable Devices

Graphene produced by chemical-vapor-deposition inevitably has defects such as grain boundaries, pinholes, wrinkles, and cracks, which are the most significant obstacles for the realization of superior properties of pristine graphene. Despite efforts to reduce these defects during synthesis, significant damages are further induced during integration and operation of flexible and stretchable applications. Therefore, defect healing is required in order to recover the ideal properties of graphene. Here, the electrical and mechanical properties of graphene are healed on the basis of selective electrochemical deposition on graphene defects. By exploiting the high current density on the defects during the electrodeposition, metal ions such as silver and gold can be selectively reduced. The process is universally applicable to conductive and insulating substrates because graphene can serve as a conducting channel of electrons. The physically filled metal on the defects improves the electrical conductivity and mechanical stretchability by means of reducing contact resistance and crack density. The healing of graphene defects is enabled by the solution-based room temperature electrodeposition process, which broadens the use of graphene as an engineering material

Conductivity Enhancement of Nickel Oxide by Copper Cation Codoping for Hybrid Organic-Inorganic Light-Emitting Diodes

We demonstrate a Cu­(I) and Cu­(II) codoped nickel­(II) oxide (NiO_<i>x</i>) hole injection layer (HIL) for solution-processed hybrid organic-inorganic light-emitting diodes (HyLEDs). Codoped NiO_<i>x</i> films show no degradation on optical properties in the visible range (400–700 nm) but have enhanced electrical properties compared to those of conventional Cu­(II)-only doped NiO_<i>x</i> film. Codoped NiO_<i>x</i> film shows an over four times increased vertical current in comparison with that of NiO_<i>x</i> in conductive atomic force microscopy (c-AFM) configuration. Moreover, the hole injection ability of codoped NiO_<i>x</i> is also improved, which has ionization energy of 5.45 eV, 0.14 eV higher than the value of NiO_<i>x</i> film. These improvements are a consequence of surface chemical composition change in NiO_<i>x</i> due to Cu cation codoping. More off-stoichiometric NiO_<i>x</i> formed by codoping includes a large amount of Ni vacancies, which lead to better electrical properties. Density functional theory calculations also show that Cu doped NiO model structure with Ni vacancy contains diverse oxidation states of Ni based on both density of states and partial atomic charge analysis. Finally, HyLEDs of Cu codoped NiO_<i>x</i> HIL have higher performance comparing with those of pristine NiO_<i>x</i>. The current efficiency of devices with NiO_<i>x</i> and codoped NiO_<i>x</i> HIL are 11.2 and 15.4 cd/A, respectively. Therefore, codoped NiO_<i>x</i> is applicable to various optoelectronic devices due to simple sol–gel process and enhanced doping efficiency

Unraveled Face-Dependent Effects of Multilayered Graphene Embedded in Transparent Organic Light-Emitting Diodes

With increasing demand for transparent conducting electrodes, graphene has attracted considerable attention, owing to its high electrical conductivity, high transmittance, low reflectance, flexibility, and tunable work function. Two faces of single-layer graphene are indistinguishable in its nature, and this idea has not been doubted even in multilayered graphene (MLG) because it is difficult to separately characterize the front (first-born) and the rear face (last-born) of MLG by using conventional analysis tools, such as Raman and ultraviolet spectroscopy, scanning probe microscopy, and sheet resistance. In this paper, we report the striking difference of the emission pattern and performance of transparent organic light-emitting diodes (OLEDs) depending on the adopted face of MLG and show the resolved chemical and physical states of both faces by using depth-selected absorption spectroscopy. Our results strongly support that the interface property between two different materials rules over the bulk property in the driving performance of OLEDs

Efficient Large-Area Transparent OLEDs Based on a Laminated Top Electrode with an Embedded Auxiliary Mesh

To realize transparent organic light-emitting diodes (OLEDs), a top electrode should have excellent optical, electrical, and mechanical properties. Conventionally, transparent conductive oxides and semitransparent metal have been widely used for transparent top electrodes, but they have several fundamental drawbacks. We herein report efficient large-area inverted transparent OLEDs using a vacuum-laminated top electrode with an embedded metal mesh. The laminated device with 1 mm pitch exhibits superior optical properties including a high transmittance of 75.9% at 550 nm, a low reflectance of 12.0% at 550 nm, and spectrally flat characteristics over the entire visible region and shows nearly ideal Lambertian angular emission characteristics with little angular color shift in both directions. Moreover, the lowered sheet resistance of 4 Ω/sq originating from the embedded metal mesh (1 mm pitch) led to efficient and uniform emission characteristics. As a result, the device shows a relatively high maximum current efficiency of 50.3 cd/A (bottom: 24.5 cd/A; top: 25.8 cd/A) and a maximum external quantum efficiency of 15.3% (bottom: 7.9%; top: 7.4%), which surpasses all previously reported values based on a laminated top electrode. In addition, we successfully demonstrate its potential as a large-area transparent top electrode in various optoelectronic devices through a large-area transparent OLED segment panel (45 × 90 mm², diagonal length of 70.2 mm in the active area) with a laminated top electrode