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A soluble, green-blue fluorescent, pi-extended azatrioxa[8]circulene was synthesized by oxidative condensation of a 3,6-dihydroxycarbazole and 1,4-anthraquinone by using benzofuran scaffolding. This is the first circulene to incorporate anthracene within its carbon framework. Solvent-dependent fluorescence and bright green electroluminescence accompanied by excimer emission are the key optical properties of this material. The presence of sliding pi-stacked columns in the single crystal of dianthracenylazatrioxa[8]circulene is found to cause a very high electron-hopping rate, thus making this material a promising n-type organic semiconductor with an electron mobility predicted to be around 2.26 cm(2) V-1 s(-1). The best organic light-emitting diode (OLED) device based on the dianthracenylazatrioxa[8]circulene fluorescent emitter has a brightness of around 16 000 Cd m(-2) and an external quantum efficiency of 3.3 %. Quantum dot-based OLEDs were fabricated by using dianthracenylazatrioxa[8]circulene as a host matrix material.

In the paper double-channel emission from organic exciplex coupled to fluorescence emission has been shown for the first time. The process has been demonstrated for white emission in light-emitting diodes based on yellow-green organic exciplex combined with organic blue fluorescence emission. Combining the fluorescence emission of mMTDATA with the thermally activated delayed fluorescence exciplex emission from the DPNC/Bphen interface, a highly efficient white OLED has been fabricated. As a result, bright white OLED with a high luminance exceeding 10 000 cd/m2 has been obtained.

A new ambipolar fluorophore, 3,6-di(4,4′-dimethoxydiphenylaminyl)-9-(1-naphthyl)carbazole, was synthesized and its physical properties were studied by differential scanning calorimetry, thermogravimetric analysis, UV-vis absorption, luminescence and photoelectron emission spectroscopy, cyclic voltammetry and a time of flight method. The latter technique indicates that the compound demonstrates bipolar semiconducting properties. Using the synthesized compound as an emissive material, a single-layer OLED with an electroluminescence spectrum containing a voltage-dependent electroplex emission band in the region of 550–650 nm was fabricated. Another OLED was fabricated with an additional electron transporting bathophenanthroline layer that forms a direct interface with the layer of 3,6-di(4,4′-dimethoxydiphenylaminyl)-9-(1-naphthyl)carbazole. A strong exciplex-type band in the electroluminescence spectrum of this OLED with an emission maximum at ca. 540 nm was observed. The electroluminescence spectra of both devices were found to be clearly dependent on the applied bias. This effect can be useful for the development of efficient and colour-tunable OLEDs.

CdTe/CdS core-shell quantum dots were synthesized and implemented into a light emitting device resulting in multi-channel electroluminescence with a light-green emission colour. The main electroluminescence band at about 530 nm corresponds to the emission by the CdTe core (type I core/shell structure), while the next emission band at 595 nm is assigned to the crossed recombination of electrons from the conduction band of the CdS shell and holes from the valence band of the CdTe core (type II core/shell structure). At the same time, the photoluminescence spectrum of the synthesized CdTe/CdS core-shell quantum dots contains only one emission band distinctive for type II structures. This behavior of CdTe/CdS core-shell quantum dots upon the electroexcitation allows the extension of the electroluminescence spectrum in the optical region in a way that is useful for the lighting-source applications. Such multi-channel electroluminescence can most probably also be reproduced in related core-shell systems accounting for size-confinement between the core size and shell thickness.

A new triaryl molecule based on a benzene–benzothiadiazole–benzene core has been applied in a WOLED device. This very simple molecule emits from a combination of emissive states (exciton/electromer/exciplex/electroplex) to give white light with CIE coordinates of (0.38, 0.45) and a colour temperature of 4500 K.

The star-shaped compound tri(9-hexylcarbazol-3-yl) amine (THCA) and 4,7-diphenyl-1,10-phenanthroline (Bphen) were used for the preparation of bilayer and bulk exciplex based organic light emitting diodes (OLEDs) in which THCA and Bphen were selected as donor and acceptor components, respectively. The dependencies of the electroluminescence and impedance characteristics of the exciplex type OLEDs depending on the technologies of the formation of the active layers were studied. The correlations between the appearance of negative differential resistance in current–voltage characteristics and negative capacitance observed at low frequencies in impedance spectra of OLEDs with the resonant tunneling of electrons into THCA through Bphen/THCA barrier and generation–recombination processes in THCA were established.

We fabricated a yellow organic light-emitting diode (OLED) based on the star-shaped donor compound tri(9-hexylcarbazol-3-yl)amine, which provides formation of the interface exciplexes with the iridium(III) bis[4,6-difluorophenyl]-pyridinato-N,C2']picolinate (FIrpic). The exciplex emission is characterized by a broad band and provides a condition to realize the highly effective white OLED. It consists of a combination of the blue phosphorescent emission from the FIrpic complex and a broad efficient delayed fluorescence induced by thermal activation with additional direct phosphorescence from the triplet exciplex formed at the interface. The fabricated exciplex-type device exhibits a high brightness of 38 000 cd/m(2) and a high external quantum efficiency.

In the present work we have demonstrated double-channel emission from organic exciplexes coupled to inorganic nanoparticles. The process is demonstrated by yellow-green emission in light-emitting diodes based on organic exciplexes hybridized with perovskite-type dispersed BaZrO3 nanoparticles. Such double-channel emission provides a broadening of the electroluminescence spectrum and a resultant yellow-green emission color of the device. We have realized an energy transfer from the exciplexes arranged by the interface between two organic layers and the spherical-shaped BaZrO3 nanoparticles randomly deposited on the organic interface constructed of the tris(4-carbazoyl-9-ylphenyl)amine and 4,7-diphenyl-1,10-phenanthroline molecules. The fabricated device exhibits a current efficiency value of 3.88 C d/A, maximum brightness of 3465 cd/m2 (at 15 V), and external quantum efficiency of about 1.26%. In order to estimate the efficiency of the energy transfer from the exciplex to the BaZrO3 nanoparticles we have applied the Förster model for the dipole-dipole energy transfer accounting for the mutual overlap of the exciplex emission spectrum and the absorption spectrum of the BaZrO3 nanoparticles.

The occurrence of light induced ambipolar conductivity in organic transistors based on 1,7-bis(9-ethyl-3-carbazolyl) N,N′-2-ethyl hexyl perylene bisimide (BCEHPB) was studied. It is shown that under illumination the output characteristics are transformed into superposition of standard saturated behavior for one carrier at high gate voltage and a superlinear current increase at low gate voltage and high source–drain voltage due to injection of the opposite (hole) carrier. The influence of injection of holes from metal electrodes by impedance spectroscopy barrier structure BCEHPB/Ag was studied to explain this effect. Increasing the injection of holes in the transistor under illumination can be interpreted as a result of the devastation of the interface trap states.

A three-terminal organic light-emitting device with a periodic interrupted middle electrode is developed to allow for an adjustable emission color. The emission results from three independent light-emitting diodes with one diode utilizing exciplex emission. An equivalent electrical circuit is suggested taking the current–voltage characteristics and the direction of current flow through the organic structure into account. Two diodes are formed between the embedded middle electrode and the LiF/Al top and ITO bottom electrode, respectively, and the third diode utilizes that part of the device without the middle-electrode exhibiting exciplex emission. It will be shown that the spectrum of the emitted light can be tuned from blue to orange by controlling the applied potentials to the device terminals.

We have found that the structures based on ITO/tri(9-hexylcarbazol-3-yl)amine/Ca/Al fabricated by means of vacuum deposition generate acoustic oscillations when pulse voltage is applied. Impedance spectroscopy study indicates the presence of significant inductive response, which is the result of significant energy barriers at the semiconductor-metal interface. We assume that a very heterogeneous spatial distribution of the electric field at the organic/metal interface and the noncoplanarity of the molecules cause the electrostriction effect in the structures.

We demonstrate the fabrication and properties of an near ultraviolet organic light emitting diode (UV OLED) that contains 2,7-di(9-carbazolyl)-9-(2-ethylhexyl)carbazole organic emitting layer and aluminum-doped magnesium zinc oxide (ZnMgO:Al) layer as transparent electrode. The obtained ZnMgO:Al layer is transparent for the wavelengths longer than 325 nm and has low resistivity of the order of 10-3 Ωcm. The UV OLED device turns on at the applied voltage of 9 V.

A new interface engineering method is demonstrated for the preparation of an efficient white organic light-emitting diode (WOLED) by embedding an ultrathin layer of the novel ambipolar red emissive compound 4,4-difluoro-2,6-di(4-hexylthiopen-2-yl)-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene (bThBODIPY) in the exciplex formation region. The compound shows a hole and electron mobility of 3.3 × 10-4 and 2 × 10-4 cm2 V-1 s-1, respectively, at electric fields higher than 5.3 × 105 V cm-1. The resulting WOLED exhibited a maximum luminance of 6579 cd m-2 with CIE 1931 color coordinates (0.39; 0.35). The bThBODIPY dye is also demonstrated to be an effective laser dye for a cholesteric liquid crystal (ChLC) laser. New construction of the ChLC laser, by which a flat capillary with an optically isotropic dye solution is sandwiched between two dye-free ChLC cells, provides photonic lasing at a wavelength well matched with that of a dye-doped planar ChLC cell.

New stable WOLEDs based on pi-extended azatrioxa[8]circulenes have been fabricated. Combining the own blue emission of the azatrioxa[8] circulenes with the yellow-green emission of the "m-MTDATA:azatrioxa[8]circulene'' exciplex a broad visible region, from 400 to 700 nm, is covered. The so constructed WOLEDs exhibit a luminance exceeding 23 700 cd m(-2) and an external quantum efficiency reaching 3%. QC 20170613

International audience; A new biscarbazoloanthracene consisting of nine fused aromatic rings, including two pyrrole units, has been obtained in a straightforward and convergent synthesis. Computational chemistry and conformational analysis revealed that the semiconductor's molecule is not planar, the two carbazole moieties being helical twisted from the plane of the anthracene unit. Photophysical and electrochemical measurements showed that this angular fused heteroacene has a low lying HOMO energy level with a wide band gap despite its extended π-conjugated molecular framework. Based on its relatively low-lying HOMO level, the semiconductor promises a high environmental stability in comparison to other related linear fused acenes and heteroacenes. The biscarbazoloanthracene has been applied as the light emitting layer in a white light emitting diode (WOLED). It is proposed that the white OLED feature is due to dual light emission properties from the active semiconductor layer being based on both the molecular luminescence of the small molecule and a discrete excimer emission made possible by suitable aggregates in the solid state. Noteworthy, this is the first reported example of such a behavior observed in a small molecule heteroacene rather than an oligomer or a polymer.

Star-shaped carbazole-based compounds were synthesized by the Buchwald–Hartvig method. The materials were examined by various experimental and theoretical methods, including differential scanning c...

We performed impedance spectroscopy studies on intercalated multilayer structures of type-layered inorganic semiconductor (gallium selenide and indium selenide)/organic semiconductors (N,N′-dimethyl-3,4,9,10-perylenetetracarboxylic diimide), which revealed the appearance of low-frequency inductive response as a result of intercalation of organic semiconductors (OS) into inorganic semiconducting layers. A current–voltage characteristic has the shape of Coulomb steps with a step 0.32 V that are blurred due to superimposition of electric field and illumination. An applied electric field and illumination during the introduction of OS leads to the formation of electrets and photoelectret states that modify polarisation and photoprocesses in accordance with the conductivity type of nonorganic matrix.

Impedance spectroscopy studies performed for intercalated multilayer structures of the type of a layered inorganic semiconductor (InSe)/conducting polymer (PEDOT:PSS) revealed low-frequency inductive response and the growth of dielectric permeability in megahertz region together with the decrease of dielectric loss angle down to one as a consequence of the conducting polymer intercalation into semiconducting layers. A model describing the unusual current–voltage characteristic is proposed.

The electroluminescent device ITO/CuI/3,6-di(9-carbazolyl)-9-(2-ethylhexyl)carbazole(TCz1)/Ca/Al in which TCz1 for the first time was used as the emitting layer, was fabricated by means of vacuum deposition. The device emits blue light with a peaks at 388 and 406 nm at 4.5 V, with high current efficiency values (11.5 cd/A) and external quantum efficiency (1.72%).

We report on stable in time organic photovoltaic devices based on metal-phthalocyanine structures, which were formed by vacuum deposition of nickel phthalocyanine (NiPc). The reported stability is due to ultra-thin zinc oxide (ZnO) layer formed at low temperature on top of the structure (beneath the metal contact) by atomic layer deposition (ALD) technique. We performed comparative analysis of current density–voltage characteristics and frequency dependencies of the impedance for freshly made ITO/NiPc/ZnO/Al and ITO/NiPc/Al devices and after storage during one month in air. We conclude that introducing of ultra-thin ZnO film into under-cathode region of ITO/NiPc/Al structure provides long-term protection of NiPc films from atmospheric effects.

With the purpose of developing organic photosensitive cells with a wide photosensitivity spectrum and improved photogeneration characteristics, an ITO/pentacene/DiMe-PTCDI/Al heterostructure formed by alternate vacuum deposition of pentacene and perylene N,N′-dimethyl-3,4,9,10-perylenetetracarboxylic diimide (DiMe-PTCDI) derivative films on the ITO substrate was studied. The effect of the heterostructure’s formation conditions on its spectral photosensitivity and photovoltaic properties was also studied. An analysis of current-voltage characteristics and frequency dependences of the impedance showed that the current through the heterojunction is controlled by thermionic emission with an ideality factor of 1.5–2.2, and the heterostructure can be simulated by an equivalent circuit consisting of two series elements representing the heterostructure bulk and space charge region.

The effect of an integrated polymer on the luminescence characteristics of porous silicon (PS)-conducting polymer (CP) heterostructures has been studied. Both n-(100) and p-type (111) PS has been employed in order to prepare the heterostructures. To obtain the integrated polymer layers (polyaniline, polymethoxyaniline, polyphenylacetylene, poly-para-phenylene, poly-N-epoxy-propylcarbazol), the methods of electrochemical polymerization, vacuum deposition, and spin coating have been used. The obtained structures were studied using atom force microscopy and were examined as to the capability to photoluminescence (PL) and cathodoluminescence (CL). It has been found that the presence of a CP layer on the PS surface preserves the “red” PL, but weakens it to 50–90%. The CL spectra of the obtained heterostructures allow us to suggest their capability of electroluminescence in the visible region of the spectrum.

The investigation of heterojunctions based on conductive polymer PPA or PAN and InSe has been reported. The temperature dependence of the saturation current was carried out to obtain the barrier height of the investigated structures. The barrier height ϕ0 has been found to be equal to 0.6 eV and 0.83 eV for InSe-PPA and InSe-PAN, respectively. For the InSe-PPA heterostructure, the higher power conversion efficiency than that for the InSe-PAN heterostructure at a light intensity of 50 mW/cm2 has been obtained.

To improve the injection of charge carriers from ITO electrode into the molecular semiconductor in the pentacene-based photovoltaic structures, we propose introducing an additional transport copper iodide (CuI) layer with high conductivity. The organic flexible barrier based on ITO/CuI/pentacene/Al was fabricated using flexible polyethyleneterephtalate substrate with conductive ITO layer by vacuum deposition technique. CuI films, annealed at the temperature of 523 K, exhibited optical transmittance ∼80% in the wavelength range 400–900 nm, minimum resistivity about 1.8 × 103 Ω/sq, and developed surface. They were used for fabrication of photosensitive barrier structure on the basis of pentacene.

The organic solar cell based on poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS)/pentacene (Pc) was fabricated using a flexible polyethyleneterephthalate (PET) substrate coated with conductive ITO layer and aluminum contact film formed on a Pc layer by electron beam deposition. The performed investigations of current–voltage characteristics indicate that the devices operate like Schottky diodes. Under illumination of an ITO/PEDOT:PSS/Pc/Al multilayer structure the photovoltaic effect is measured with open circuit voltages up to 0.5 V, short circuit current of 0.6 μA and fill factor 0.2. The spectral-photocurrent excitation profile covers a full range of visible light (380–700 nm).

We demonstrate the fabrication and properties of an near ultraviolet organic light emitting diode (UV OLED) that contains 2,7-di(9-carbazolyl)-9-(2-ethylhexyl)carbazole organic emitting layer and aluminumdoped magnesium zinc oxide (ZnMgO:Al) layer as transparent electrode. The obtained ZnMgO:Al layer is transparent for the wavelengths longer than 325 nm and has low resistivity of the order of 10−3 Ωcm. The UV OLED device turns on at the applied voltage of 9 V.

Cataloged from PDF version of article. The results of an experimental study of the electroluminescent device made of ITO/CuI/2,6-di-tert-butyl-4-(2,5-diphenyl-3,4-dihydro-2H-pyrazol-3-yl)-phenol (HPhP)/3,6-Di(9-carbazolyl)-9-(2ethylhexyl) carbazole (TCz1)/Ca:Al with efficacy up to 10.63 cd/A are presented. HPhP provides blue emission with a peak wavelength at 445 nm. The layer of TCz1 acts as an electron-transporting layer. In the framework of density functional theory (DFT) approach the geometry configuration and energy levels of HPhP are found being in a good agreement with spectral and cyclic voltammogram data. (C) 2011 Elsevier B.V. All rights reserved.

Structural and optical characteristics of polyaniline films of different thickness obtained on the surface of optically transparent SnO2 electrode by means of electrochemical polymerization method have been investigated. It is found that the increase in thickness of films from 140 to 540 nm leads to crystal formation increase in optical density in the spectral range of 650-800nm. Polyaniline films obtained under optimal conditions show stable optical response and can be used as sensing elements of optical sensors.

As results of the carried out investigation of vacuum deposited polyaniline (PAN) films, it was found that the index of refraction of deposited films changes with the change in the angle of incidence of laser light; in other words, PAN films are optically anisotropic. In particular, if the deposition temperature Tα=1800C, the minimum and maximum refraction indeces are 1.810 and 1.758 respectively; when Tα=3600C, they are 1.785 and 1.754 respectively; and when Tα=4000C, they are 1.786 and 1.755 respectively. Such results show that the rate of films deposition increases with the increase in deposition temperature; in particular, when Tα=3600C and the deposition time is 40 minutes, the film thickness d=353 nm; when Tα=4000C and the deposition time is the same, the thickness was 400 nm. As results, by means of variation in PAN films deposition technology, it is possible to control optical characteristics of films, and thin has a wide range of application. Due to redox reactions index was also observed. Such films are of prospects as active elements of integral and fiber optical devices.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The construction of fibre-optic pH sensor on the base of fibre-optic and polyaniline as sensitive materials was proposed.

Taking into account that ionic-doped liquid crystals are conductive and the conductance depends on dopant concentration, we suggested using ionic-doped liquid crystals as a electrolytic medium in a described configuration of cell. The application of an ionic doped liquid crystal as electrolytic medium in electrochromic device were investigated. Polyaniline is a conductive polymer and has electrochromic effect in an electrolytic medium under the applied voltage. The spectral investigation of the electrochromic effect of polyaniline was carried out in a new cell. The spectral dependences of such structure were presented on paper. An appearance of electrochromic effect was observed in a structure SnO2 -- liquid crystal -- polyaniline -- SnO2.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have studied electroluminescence and impedance properties of exciplex-type organic light-emitting devices (OLEDs) based on 4,4,4″ - tris[3- methylphenyl (phenyl)-...

In the current study we demonstrate an application of four previously synthesized 1,7-diphenyl-substituted BODIPY species for inverted photovoltaic cells and for organic light-emitting devices (OLEDs). Depending on the type of substituents or annulation of the pyridone rings these dyes exhibit spectral properties in the full visible region up to the near-infrared wavelengths. All the studied compounds show very strong visible absorption that can be ascribed to the low lying LUMO levels making them electronically suitable as acceptors for many donor materials. The best fabricated inverted photovoltaic device based on the BODYPI-core derivatives demonstrates a power conversion efficiency equal to 1.36% which is close to previously published reports for related species. Two kinds of deep red OLEDs (doped and undoped) with narrow electroluminescence spectra (full width at half maximum up to 45 nm) have been fabricated. Maximum brightness of 3900 cd m−2 and an external quantum efficiency by 2.3% were achieved for the best OLED structure.