An ambipolar BODIPY derivative for a white exciplex OLED and cholesteric liquid crystal laser toward multifunctional devices

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

Spin- and Voltage-dependent emission from Intra- and Intermolecular TADF OLEDs

Organic light emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) utilize molecular systems with a small energy splitting between singlet and triplet states. This can either be realized in intramolecular charge transfer states of molecules with near-orthogonal donor and acceptor moieties or in intermolecular exciplex states formed between a suitable combination of individual donor and acceptor materials. Here, we investigate 4,4'-(9H,9'H-[3,3'-bicarbazole]-9,9'-diyl)bis(3-(trifluoromethyl) benzonitrile) (pCNBCzoCF3), which shows intramolecular TADF but can also form exciplex states in combination with 4,4',4''-tris[phenyl(m-tolyl)amino]triphenylamine (m-MTDATA). Orange emitting exciplex-based OLEDs additionally generate a sky-blue emission from the intramolecular emitter with an intensity that can be voltage-controlled. We apply electroluminescence detected magnetic resonance (ELDMR) to study the thermally activated spin-dependent triplet to singlet up-conversion in operating devices. Thereby, we can investigate intermediate excited states involved in OLED operation and derive the corresponding activation energy for both, intra- and intermolecular based TADF. Furthermore, we give a lower estimate for the extent of the triplet wavefunction to be >1.2 nm. Photoluminescence detected magnetic resonance (PLDMR) reveals the population of molecular triplets in optically excited thin films. Overall, our findings allow us to draw a comprehensive picture of the spin-dependent emission from intra- and intermolecular TADF OLEDs.Comment: 9 pages, 5 figure

The energy structure of free electrons for semiconductor in the field of cylindrical symmetry

The energetic structure of semiconductor free electrons in the field of cylindrical symmetry whose radial part is a sum of two components, which depend on radial coordinate according to quadratic and biquadratic laws has been studied. The quantization conditions for energy in this field are found and the importance of both quadratic and biquadratic component quantum state formation is analyzed. It is shown that these states can be described by generalized degenerated hypergeometric functions. It is revealed that presence of the biquadratic component is important for the structure of energy levels

Photoelectric properties of ₂O₃-pGaSe-pInSe cascade heterostructures

Cascade heterostructure of nGa₂O₃-pGaSe-pInSe was created, and a corresponding band energy diagram was built. Electrical and photoelectric properties of this structure were investigated. Due to isotype pGaSe-pInSe heterojunction the photosensitivity spectrum of nGa₂O₃-pGaSe-pInSe heterostructure extends up to 1.2 eV in IR range as referred to the photosensitivity spectrum of anisotype nGa₂O₃-pGaSe heterojunction

Photovoltaic properties of a heterostructure on the basis of porous silicon and polyaniline

An electric junction between porous silicon (n-type conductivity) and conductive polyaniline (p-type conductivity) has been made by electrochemical polymerization of aniline on the porous silicon surface. This heterostructure has been found to exhibit rectifying І-V characteristics. Under illumination, a considerable increase of the current is observed with a reverse bias. The structure photosensitivity is defined mainly by two barriers, namely, by the polymer/porous silicon interphase and the porous silicon/crystalline silicon barrier.Электрический контакт между пористым кремнием с n-типа проводимостью и проводящим полианилином с проводимостью p-типа изготовлен путем электрохимической полимеризации анилина на поверхности пористого кремния. Найдено, что такая гетероструктура демонстрирует выпрямляющие І-V характеристики. При освещении наблюдалось значительное повышение тока при обратном смещении. Фоточувствительность структуры преимущественно определяется двумя барьерами: интерфазой полимер-пористый кремний и пористый кремний-монокристаллический кремний.Електричний контакт мiж поруватим кремнiєм з n-типу провiднiстю i електропровiдним полiмером - полiанiлiном з провiднiстю p-типу створено шляхом електрохiмiчної полiмеризацiї анiлiну на поверхнi поруватого кремнiю. 3найдено, що така гетероструктура демонструє випрямляючi І-V характеристики. При освiтленнi спостерiгалося значне пiдвищення струму при зворотному змiщеннi. Фоточутливiсть структури переважно визначається двома бар'єрами: iнтерфазою полiмер-поруватий кремнiй та поруватий кремнiй-монокристалiчний кремнiй

Thermally Activated Delayed Fluorescence in Organic Semiconductors and Its Application in Light-Emitting Diodes

The presence of the effect of thermally activated delayed fluorescence (TADF) in organic light-emitting materials (emitters), manifested in the "collecting" of triplet excitons in organic semiconductor complexes that do not contain noble metals, creates excellent prerequisites for the application of TADF materials in the technology of manufacturing organic light-emitting diodes (OLED). The significant progress in solving theoretical and technical problems, achieved in the process of development of highly efficient TADF materials, paves the way for the formation of the future of organic electronics. This review presents the analyses of the nature of the long-term fluorescence generation mechanism at the molecular level and the up-to-date strategies for designing TADF donor-acceptor materials, as well as exciplex intermolecular complexes. Special attention is focused on the analysis of TADF emitter ambipolar materials with a highly twisted, rigid molecular structure, which reveal a tendency towards the multi-channel emission mechanisms and their implementation in a variety of OLED structure architectures