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The multifunctional materials for application in organic light-emitting devices (OLEDs) based on a single structural motif are very desired but quite rare species. Such structures allow simplifying the chemical variety within OLED heterostructures and thus reducing their cost, manufacturing time, and logistic efforts. In this paper, we report the 9-(2,3,5,6-tetrafluoro-4-vinylphenyl)carbazole molecule (Cz4FS) utilized as a fluorescent emitter, host material for quantum dot based OLEDs (QLEDs), acceptor part of the exciplex active layer, and monomer that can be used for the preparation of emissive polymers and copolymers. The external quantum efficiency (EQE) of the corresponding fluorescent OLED based on a Cz4FS single emitter doped into a 1,3-bis(carbazol-9-yl)benzene matrix is 4.2%, which is close to the theoretical limit and maximum brightness at the level of 3600 cd/m2. An OLED based on exciplex emission obtained utilizing Cz4FS as an acceptor demonstrates higher efficiency (5.3%) and much higher brightness near 25 000 cd/m2. A QLED based on Cz4FS as a host for CdSeS/ZnS core-shell quantum dots demonstrates excellent energy transfer from the Cz4FS matrix that results in a clear spectrum of quantum dots with an EQE of 2.3%, maximum of 19 000 cd/m2, and narrow spectral distribution. An OLED based on a Cz4FS-based polymer and copolymer demonstrates not extraordinary efficiency but low-efficiency roll-off in a wide range of current densities.

In the present paper hybrid core-shell InP/ZnS quantum dots were prepared by the one pot synthesis method which does not require additional component injections and which complies more with cost requirements. The synthesized quantum dots were characterized by X-ray diffraction and optical spectroscopy methods. The applicability of the synthesized InP/ZnS core-shell particles in inverted solar cells fabricated with a step-by-step procedure which combines thermal vacuum deposition and spin-coating techniques was investigated. The resulting efficiency of the fabricated inverted solar cell is comparable to that of quantum-dot sensitized TiO2 based solar cells. Therefore, hybrid core-shell InP/ZnS particles can be considered as multifunctional light-harvesting materials useful for implementation in different types of photovoltaic devices, such as quantum dot sensitized solar cells and inverted solar cells. Funding Agencies|Ministry of Education and Science of Ukraine [0121U109506, 0121U107533]; Swedish Research Council [2020-04600]

Organometallic blue fluorescent Zn(II) Schiff base complexes are synthesized and explored computationally in order to use them in organic electroluminescent heterostructures. Characterization of these pyrazolone-based azomethine-zinc complexes was accomplished by various physicochemical techniques to get insight into their applicability as an active layer in light-emitting diodes. All the complexes demonstrate high thermal stability and remarkable photoluminescence both in solution and in the solid state with maximum in the blue region. Quantum chemical calculations of the first exited electronic state and vertical singlet-singlet electronic transitions by means of time-dependent density functional theory calculations and results show that the origin of the luminescence for the target complexes refers to the intraligand charge transfer within the Schiff bases. The constructed light-emitting diodes demonstrate low input voltage (3.2-4.0 V), brightness at a level of 4300-11,600 Cd m(-2), and external quantum efficiency of up to 3.2%, which is a good value for purely fluorescent organic light-emitting diodes. Funding Agencies|Ministry of Education and Science of the Russian FederationMinistry of Education and Science, Russian Federation [FZEG-2020-0030]; Ministry of Education and Science of Ukraine [0121 U107533, 0119 U100259, 0121 U109506]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2018-05973, 2020-04600]; Swedish National Infrastructure for Computing (SNIC) [2020-3-29]

For the first time exploiting sulfobenzimide moiety as an acceptor unit, the new type of donor-sigma-acceptor emitter exhibiting thermally activated delayed fluorescence (TADF) is demonstrated. In different solutions, the synthesized compound emits light resulting from either locally excited carbazole moiety or trough-space charge transfer (exciplex-like) between carbazole and sulfobenzimide units. In the solid state, this emitter demonstrates aggregation-induced emission enhancement and different emission colours due to its different conformations. The mechanoluminescence of the donor-sigma-acceptor compound was observed and studied in detail by experimental and theoretical approaches including single-crystal and powder X-ray analyses. Electroluminescence of the different colours was observed when the compound was utilized as non-doped TADF emitter in rigid and flexible organic light-emitting diodes fabricated on glass or poly(ethylene terephthalate) substrates. The device fabricated on the rigid substrate exhibited the best performance with maximum current efficiency, power efficiency, and external quantum efficiency of 11.0 cd A(-1), 3.0 lm W-1, and 4.3%, respectively.

To explore the photophysical properties of coordination compounds with bright blue fluorescence, an azomethin-zinc complex was synthesized and characterized by various techniques (elemental analysi ...

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.

Derivatives of indole and benzo[b]carbazole were prepared by employing efficient regioselective acid-catalysed synthesis of 1H, 1-methyl and 1-naphthylindole with o-phthaldialdehyde. The synthesized compounds were characterized by NMR, IR and mass spectrometries. They form molecular glasses with glass transition temperatures ranging from 86 to 116 °C. Naphthyl-substituted derivatives showed high thermal stabilities with 5% weight loss temperatures of 409 and 413 °C, while their methyl-substituted counterparts exhibited by ca. 90 °C lower 5% weight loss temperatures. Their solutions exhibited blue emission with quantum yields of 67%. Ionization potentials of the compounds estimated by cyclic voltammetry are in the range of 5.49–5.65 eV, while the values obtained using photoelectron emission in air method are in the range of 5.16–5.28 eV. The layers of the compounds exhibited ambipolar charge transport with time-of-flight charge drift mobility values well exceeding 10−3 cm2/(Vs) at high electric fields. Non-doped naphthylindole and benzo[b]carbazole derivative based device emitted deep-blue light with the maximum intensity at 410 nm and CIE of (0.21, 0.16), and it exhibited a maximum external quantum efficiency of 3.4%.

New donor-acceptor and donor-acceptor-donor compounds based on perfluorobiphenyl electron acceptor and diphenylamine or carbazole as electron-donating units were designed, synthesized and characterized. The influence of the nature and number of electron-donating units on thermal, electrochemical and photophysical properties was studied. The compounds exhibited photoluminescence ranging from near-UV to green region. The solid samples of the compounds demonstrated photoluminescence quantum yields in the range from 0.1 to 0.51.2,7-Dimethoxycarbazole-containing compound was characterized by negligible energy gaps between the lowest singlet and triplet states (0.1 eV) and subsequently showed thermally activated delayed fluorescence (TADF). Carbazolyl-substituted perfluorobiphenyl derivatives showed aggregation-induced emission enhancement and high values of the energies of triplet levels (up to 3.08 eV). The derivatives exhibited from moderate to high temperatures of 5% weight loss up to 356 °C. Electron mobility up to 1.2 × 10−4 cm2 V−1 s−1 at electric field of 7 × 105 V/cm was detected for the studied compounds by time-of-flight measurements. One compound with the best combination of the required properties for the OLED hosts was selected for the fabrication of green TADF-based OLED. The device showed maximum external quantum efficiency of 15.1%. Another compound exhibiting efficient TADF demonstrated oxygen sensitivity with non-linear Stern-Volmer curve which was well fitted by two Stern-Volmer constants of 6.54·10−4 and 7.17·10−6 ppm−1.

Derivatives of indolo[3,2-b]carbazole containing differently substituted triphenyl ethenyl moieties were synthesized and characterized as multifunctional materials for optoelectronic devices. A structure-properties relationship of the compounds was studied. Alteration of the substituents of triphenyl ethenyl moiety (H-, Ph-, CN-) afforded to modify thermal, photophysical and charge-transporting properties of the compounds. The synthesized compounds demonstrated high thermal stability with the 5% weight loss temperatures reaching 453 °C. Indolo[3,2-b]carbazoles mono- and disubstituted with tetraphenyl ethenyl groups exhibited polymorphism with two melting peaks at 211/216 °C and 236/245 °C, respectively. Modification of the substitution pattern resulted in the changes of emission of the solid films from blue centered at 471 nm to yellow peaking at 583 nm. Addition of the tetraphenylethylene and triphenyl acrylonitrile fragments resulted in aggregation induced emission (AIE) or aggregation enhanced emission (AEE). The solutions of AIE/AEE-active compounds exhibited low photoluminescence quantum yields which did not reach 1%, while the solid films demonstrated the highly boosted values of 23–35%. Hole mobilities of ca. 10−3 cm2/V × s were observed for tri(tetra)phenyl ethenyl substituted indolo[3,2-b]carbazoles compounds. The compounds containing acrylonitrile moieties exhibited bipolar charge transport with drift mobilities of ca. 10−5 cm2/V × s. The synthesized compounds showed promising electroluminescent properties as fluorescent emitters. OLEDs containing these emitters showed maximum external fluorescent quantum efficiency up to 3.0% and maximum brightness up to 18 800 cd/m2. They also demonstrated lasing properties. Using the most promising compound dissolved in cholesteric liquid crystal, laser beam at 515 nm with full width at half maximum of ca. 3.5 nm was generated.

Elaboration of the appropriate host materials proved to be not less important for the fabrication of a highly efficient OLED than the design of emitters. In the present work, we show how by simple variation of molecular structure both blue emitters exhibiting delayed fluorescence and ambipolar high triplet energy hosts can be obtained. The compounds with a para-junction revealed higher thermal stability (TID up to 480 °C), lower ionization potentials (5.51–5.60 eV), exclusively hole transport, and higher photoluminescence quantum efficiencies (0.90–0.97). Meta-linkage leads to ambipolar charge transport and higher triplet energies (2.82 eV). Introduction of the accepting nitrile groups in the para-position induces intensive delayed fluorescence via a triplet–triplet annihilation up-conversion mechanism. By utilization of the para-substituted derivative as an emitter and the meta-substituted isomer as the host, a deep-blue OLED with the external quantum efficiency of 14.1% was fabricated.

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 series of TADF emitters with donor-acceptor or donor-acceptor-donor structure containing 2,7-dimethoxycarbazole donor moiety and diphenylsulfone acceptor unit were synthesized and employed in non-doped sky-blue organic light emitting diodes with the external quantum efficiency reaching 9.0%. Thermal, optical and photophysical properties of for D-A and D-A-D compounds containing one or two tert-butyl groups attached to C-3 and C-6 positions of 2,7-dimethoxycarbazole moiety were studied and compared with those of the corresponding compounds containing no tert-butyl groups. Studies of photophysical properties of the compounds confirmed TADF nature of their emission. Computational studies revealed that small modification of the donor moiety could have a significant impact on the TADF mechanism turning it from vibronically induced TADF mediated by the T2 state to the common TADF which occurs through the direct reverse intersystem crossing between the S1 and T1 states. New principle of purposeful of molecular design of TADF emitters with controlled efficiency of reverse intersystem crossing by only small functionalization of donor fragments is proposed.

A new class of carbazole derivatives, with varying degree of core substitution was synthesized and characterized. The presented synthetic route requires mild conditions, starts from low-cost substrates and leads to the formation of the target products with good yields. The optical and electronic properties of the synthesized materials were estimated and supported by DFT calculations. Investigated compounds emit violet light with quantum efficiency reaching 18.2%. Electrochemical and electron photoemission spectroscopy revealed that ionization potentials are in range of 5.10–5.30 eV. Time-of-flight measurements revealed that those compounds have balanced hole and electron mobility in range of 4.27·10−6–8.42·10‐5 cm2/Vs for star-shaped compound and 6.2 × 10−7–6.2 × 10−6 cm2/Vs for linear derivatives. Electroluminescence spectra of the OLED device prepared using the newly synthesized compounds were characterized by broad emission in visible range, resulting in white light generation.

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.

Materials with high triplet energies have attracted great attention for their application in exciplex-based or thermally activated delayed fluorescence-based organic light-emitting diodes. To study the correlation between triplet energy and chemical structure, six compounds with typical donor-acceptor-donor structures were designed, synthesized, and characterized. Through the adjustment of molecular configuration by weakening the strengths of donors and increasing the angles between donors and acceptors, the triplet energies of the materials were gradually increased from 2.5 to 3.0 eV. Three exciplex-based organic light-emitting diodes containing one of the synthesized compounds were fabricated, which exhibited efficient blue, green-yellow, and white thermally activated delayed fluorescence. Blue and green-yellow organic light-emitting diodes exhibited the maximum external quantum efficiencies of 9.1% and 8.3%, respectively. White organic light-emitting diodes showed turn-on voltage of 4.8 V, high maximum luminance of 18474 cdm-2, and maximum external quantum efficiency of 10.6%. Maximum external quantum efficiencies of blue and white organic light-emitting diodes were close to the record values observed for all-exciplex-based blue and white organic light-emitting diodes.

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.

Series of compounds consisting of carbazole arms and 1,3,5-triazine core linked by amino group were synthesized and characterized. The clear relationship between electrochemical properties, quantum efficiency, charge transport properties and structure were estimated. The exciplex-forming properties of the synthesized compound as donor, and two known exciplex-forming acceptors 4,7-diphenyl-1,10-phenanthroline (Bphen) and 2,2′,2"-(1,3,5-benzenetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) where predicted and investigated. It was shown that the star-shaped configuration of the compound 3CzNCprovides the best exciplex OLED performance with EQE up to 6.84%.

The bicarbazole derivative 4,4'-(9H, 9'H-[3,3'-bicarbazole]-9,9'-diyl) bis(3-(trifluoromethyl) benzonitrile), denoted as pCNBCzoCF(3), was synthesized and tested for white OLED applications. pCNBCzoCF3 demonstrated an extremely small value of the singlet-triplet energy gap that caused intensive thermally activated delayed fluorescence (TADF). In addition, this compound is able to form exciplex-type excited states at the interface with star-shaped 4,40,400-tris[phenyl(m-tolyl) amino] triphenylamine (m-MTDATA). Combining the TADF emission of pCNBCzoCF3 with the exciplex emission from the pCNBCzoCF(3) m-MTDATA interface, we fabricated a number of highly efficient "warm-white'' OLEDs, the electroluminescence of which was close to candle emission. The best device demonstrated a very high brightness of 40 900 Cd m(-2) (at 15 V), current efficiency of 53.8 Cd A(-1) and power efficiency of 19.3 lm W-1, while the external quantum efficiency reached 18.8%. The fabricated devices demonstrated high emission characteristics even for the standard test at 1000 Cd m(-2) (current efficiency of 46.2 Cd A(-1), power efficiency of 10.6 lm W-1, EQE of 17.0%). QC 20180223

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.

New carbazole-substituted N-annelated perylenes with different linking topologies of the chromophores were synthesized and their physical properties were studied with various experimental techniques including thermogravimetric analysis, differential scanning calorimetry, UV-vis, fluorescence and photoelectron emission spectroscopies and cyclic voltammetry. The synthesized materials exhibit extremely high thermal stability with 5% weight loss temperatures ranging from 400 to 457 °C. Photoluminescence quantum yields of the solid films of the compounds range from 33 to 51%. The ionization potentials of the solid samples established by the electron photoemission technique were found to be in the range of 5.14–5.53 eV. Using the newly synthesized compounds as emissive materials, efficient organic light-emitting diodes (OLEDs) were fabricated with the emission pattern covering the broad visible region from 475 to 675 nm. Bright green OLEDs exhibited luminance exceeding 62 000 cd m−2 and external quantum efficiency reaching 4.2%.

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.

Different donor-acceptor-donor (D-A-D) and donor-π-bridge-acceptor-π-bridge-donor (D-π-A-π-D) systems based on a quinoxaline acceptor are compared. A significant difference in electrochemical and photophysical properties was found depending on molecular structure. A luminescence shift from 539 nm up to 671 nm was observed upon extension of conjugation length. The studied compounds were tested in fluorescent organic light emitting diodes (OLEDs) demonstrating an external quantum efficiency up to 4.5% for a deep red non-doped device and 7% when doped into an exciplex host device. A quantum-chemical interpretation of the electroluminescence spectra for the fabricated OLEDs was carried out including modelling of excimers and exciplexes.

Two new carbazole-containing aromatic imides were synthesized by three-step synthetic pathway with the moderate yields up to 76%. The compounds were investigated theoretically. TD-DFT computational studies revealed low singlet-triplet energy differences. The compounds were found to have relatively high thermal stability with 5% mass loss temperatures in the range of 280–310 °C. Phthalimide-based compound exhibited aggregation-induced emission enhancement and thermally activated delayed fluorescence with photoluminescence quantum efficiency of 20% in the solid state. Structure-properties relationship of this compound was investigated and it was found that charge-transfer through space mechanism is responsible for the emission. Series of green-emitting doped and non-doped electroluminescent devices were fabricated based on the carbazole-phthalimide derivative were fabricated to reveal best-performing mCP-doped device demonstrating maximum external quantum efficiency of 2.4% with current efficiency of 6.6 cd/A and power efficiency of 4.0 lm/W with maximum brightness of 8300 cd/m2.

In order to apply the vacuum deposited polyaniline (PAN) films as sensitive to pH level elements of fibril — optic sensors (FOS) a technology of polymer deposition has been developed. It gives a possibility to obtaining the conducting emeraldine form of PAN by means of the known methods of proton doping. Effect of vacuum deposition temperature on the refractive index and spectral characteristics of the films has been established. Based on the PAN films optical response on the hydrogen index of medium the FOS of the pH level has been worked out.

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.

The starburst carbazole derivative and phosphorescent bis-cyclometalated iridium(III) complex (IC2) were used for the preparation of multilayered “warm-white” organic light-emitting diodes (OLEDs), the emission spectra of which are modulated by the thickness of the phosphorescent layer. It was shown that the electroluminescence spectra of the fabricated devices are more extended into the visible region compared with the photoluminescence spectra of both component materials. The observed extension of the electroluminescence spectra can be assigned to the phosphorescent emission of the low-energy exciplex formed at the interface of the emissive layers. The quantum-chemical calculations performed by the DFT and (TD) DFT methods support the formation of the low-energy triplet exciplex at the interface of the IC2 layer and the neighboring layer of the starshaped carbazole-based compound, (4,4′,4″-tris[3-methylphenyl(phenyl)amino] triphenylamine, tri(9-hexylcarbazol-3-yl)amine (THCA). Indeed, the triplet excite...

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.

Four derivatives of 3,6-bis(indol-1-yl)-9-phenylcarbazole were synthesized by Ullmann-type coupling including those having methoxy groups at the different positions. Thermal, optical and photophysical properties of the synthesized materials were studied. All the synthesized 3,6-bis(indol-1-yl)-9-phenylcarbazoles are capable of glass formation with the glass transition temperatures ranging from 77 to 95 °C. They exhibit high thermal stability with the 5% weight loss temperatures ranging from 393 to 459 °C. Photoluminescence spectra of the dilute solutions of 3,6-bis(indol-1-yl)-9-phenylcarbazoles are characterized by two well-resolved vibrational peaks at ca. 390 nm and 405 nm. The solid films of the materials also exhibit well-resolved vibrational peaks, however the wavelengths of the maxima are red-shifted by ca. 10 nm. 3,6-Bis(indol-1-yl)-9-phenylcarbazoles were tested in the single-layer organic light emitting diodes as active materials and in phosphorescent light emitting diodes as host materials of emitting layers in combination with Ir(Fppy) 3 as a guest phosphor. Blue single-layer electroluminescent and electrophosphorescent devices with current efficiencies of 3.7–4.1 cd/A and 10.8–12.6 cd/A respectively were fabricated.

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

Phosphorescent bis-cyclometallated iridium (III) complexes based on 2-phenyl-1,2,3-benzotriazole with additional donoric diphenylamine or carbazole moieties were synthesized, studied and tested as phosphorescent materials in the single-layer phosphorescent organic light emitting diodes. These single-layer devices were fabricated employing a simple technological approach, based upon the simultaneous vacuum deposition from one crucible of host material and the corresponding phosphorescent 1,2,3-triazole-based iridium complexes. Red and orange electrophosphorescent single-layer devices with current efficiencies of 5.3 cd/A and 6.8 cd/A respectively are reported. Results of the impedance spectroscopy suggest that the proposed method of formation of the working layer provides homogeneous distribution of molecular guest in the matrix of host.

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.

We studied structural and optical properties of 5′ replaced pyrazoline by hindered phenol 2,6-di-tert.-butyl-4-(2,5-diphenyl-3,4-dihydro-2H-pyrazol-3-yl)-phenol (HPhP) films for application in organic light-emitting diode (OLED) as a hole transport layer (HTL). Analysis of impedance and current–voltage characteristics of ITO/HPhP/Al structure has shown that the current is limited by a space charged region with exponential distribution of traps near Fermi level. Characteristics of electroluminescence structure ITO/HPhP/Alq3/poly(ethylene glycol) dimethyl ether/Al was studied and analyzed. We performed the comparative analysis of luminescence time decay in two types of electroluminescent devices with HTL from pyrazolines derivative with hindered phenol and without it. We showed that hindered phenol in HTL slows down the degradation processes in OLED.

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%).

This work describes the electrical characteristics of thin film sandwich cells with vanadyl phthalocyanine complex as a photoactive material in air and in water vapors. The characteristics are altered by the incorporation of an ultrathin metallic layer in phthalocyanine, so that the cells with the aluminum layer in the presence of mixed water/ammonia vapors may generate a significant output power in dark. The effect is assigned to the contribution of mobile ions appeared owing to electrochemical reactions at the metallic interlayer.

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.