Satisfying both interfacial- and bulk requirements for organic photovoltaics: Bridged-triphenylamines with extended p-conjugated systems as efficient new molecules

© Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/In the domain of organic photovoltaic (OPV) devices, the design of new materials faces the extraordinary challenge to satisfy two opposite requirements: the new materials should exhibit weak intermolecular interactions at the donor-acceptor interface, but strong intermolecular interactions and good charge transport properties in the bulk. In an effort to progress in this direction, here we present three new diphenylethenyl substituted derivatives of methylene-bridged triphenylamine, synthesized by condensation of dimethylmethylene-bridged triphenylamines with 2,2-diphenylacetaldehyde. The synthesized compounds were found to be capable of glass formation with glass transition temperatures in the range of 65–130¿°C. The ionization potentials of these derivatives were found to be in the range of 5.29–5.68¿eV. The time-of-flight hole drift mobilities measured at room temperature well exceeded 10-2¿cm [2]/Vs for all the synthesized compounds. By combining the compounds with fullerene C70 acceptor in bilayer organic solar cells, a power conversion efficiency of 1.9% was obtained. Density functional methods-based calculations indicate that this result can be explained by considering edge-on orientations at the donor-acceptor interface. In this case, the designed architecture of the compounds has an effect to sufficiently “hide” the donor HOMO from a direct and easy contact with C70 LUMO(s), thus maintaining low level of geminate donor-acceptor charge recombination, without losing hole-transport properties in the donor bulk. These two design strategies operate consequently in different parts of the molecules, which is central to the success of the new compounds. Our study shows consequently a possible strategy for a simultaneous improvement of both interfacial- and bulk properties of molecules for OPV applications.Peer ReviewedPostprint (author's final draft

Satisfying both interfacial- and bulk requirements for organic photovoltaics: Bridged-triphenylamines with extended p-conjugated systems as efficient new molecules

© Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/In the domain of organic photovoltaic (OPV) devices, the design of new materials faces the extraordinary challenge to satisfy two opposite requirements: the new materials should exhibit weak intermolecular interactions at the donor-acceptor interface, but strong intermolecular interactions and good charge transport properties in the bulk. In an effort to progress in this direction, here we present three new diphenylethenyl substituted derivatives of methylene-bridged triphenylamine, synthesized by condensation of dimethylmethylene-bridged triphenylamines with 2,2-diphenylacetaldehyde. The synthesized compounds were found to be capable of glass formation with glass transition temperatures in the range of 65–130¿°C. The ionization potentials of these derivatives were found to be in the range of 5.29–5.68¿eV. The time-of-flight hole drift mobilities measured at room temperature well exceeded 10-2¿cm [2]/Vs for all the synthesized compounds. By combining the compounds with fullerene C70 acceptor in bilayer organic solar cells, a power conversion efficiency of 1.9% was obtained. Density functional methods-based calculations indicate that this result can be explained by considering edge-on orientations at the donor-acceptor interface. In this case, the designed architecture of the compounds has an effect to sufficiently “hide” the donor HOMO from a direct and easy contact with C70 LUMO(s), thus maintaining low level of geminate donor-acceptor charge recombination, without losing hole-transport properties in the donor bulk. These two design strategies operate consequently in different parts of the molecules, which is central to the success of the new compounds. Our study shows consequently a possible strategy for a simultaneous improvement of both interfacial- and bulk properties of molecules for OPV applications.Peer Reviewe

Towards Blue AIE/AIEE: Synthesis and Applications in OLEDs of Tetra-/Triphenylethenyl Substituted 9,9-Dimethylacridine Derivatives

Aiming to design blue fluorescent emitters with high photoluminescence quantum yields in solid-state, nitrogen-containing heteroaromatic 9,9-dimethylacridine was refined by tetraphenylethene and triphenylethene. Six tetra-/triphenylethene-substituted 9,9-dimethylacridines were synthesized by the Buchwald-Hartwig method with relatively high yields. Showing effects of substitution patterns, all emitters demonstrated high fluorescence quantum yields of 26–53% in non-doped films and 52–88% in doped films due to the aggregation induced/enhanced emission (AIE/AIEE) phenomena. In solid-state, the emitters emitted blue (451–481 nm) without doping and deep-blue (438–445 nm) with doping while greenish-yellow emission was detected for two compounds with additionally attached cyano-groups. The ionization potentials of the derivatives were found to be in the relatively wide range of 5.43–5.81 eV since cyano-groups were used in their design. Possible applications of the emitters were demonstrated in non-doped and doped organic light-emitting diodes with up to 2.3 % external quantum efficiencies for simple fluorescent devices. In the best case, deep-blue electroluminescence with chromaticity coordinates of (0.16, 0.10) was close to blue color standard (0.14, 0.08) of the National Television System Committee

Derivatives of Phenyl Pyrimidine and of the Different Donor Moieties as Emitters for OLEDs

Two derivatives of phenyl pyrimidine as acceptor unit and triphenylamino or 4,4′-dimethoxytriphenylamino donor groups were designed and synthesized as emitters for organic light-emitting diodes (OLEDs) aiming to utilize triplet excitons in the electroluminescence. Thermogravimetric analysis revealed high thermal stability of the compounds with 5% weight loss temperatures of 397 and 438 °C. The theoretical estimations and photophysical data show the contributions of local excited and charge transfer states into emission. The addition of the methoxy groups led to the significant improvement of hole-transporting properties and the bathochromic shift of the emission from blue to green-blue spectral diapason. It is shown that mixing of the compounds with the organic host results in facilitation of the delayed emission. The singlet–triplet energy splitting was found to be too big for the thermally activated delayed fluorescence. No thermal activation of the long-lived emission was detected. No experimental evidence for triplet–triplet annihilation and room temperature phosphorescence were detected making the hot exciton mechanism the most probable one. The OLEDs based on the compounds reached the maximum external quantum efficiency of up to 10.6%

Single-Molecular White Emission of Organic Thianthrene-Based Luminophores Exhibiting Efficient Fluorescence and Room Temperature Phosphorescence Induced by Halogen Atoms

Because of the contradiction of the efficiencies of fluorescence (FL) and room temperature phosphorescence (RTP) under ambient conditions, achievement of the molecular design of efficient monomolecular white emission resulting from the overlapping of FL and RTP is attractive but very challenging. With the aim of obtaining efficient white emission from a single organic molecule, phenyl-(thianthren-2-yl)-methanone and its tan derivatives with halogen atoms are developed. Single-molecular white emitters are investigated by experimental and theoretical approaches including steady-state and time-resolved spectroscopy, X-ray analyses, and density functional theory calculations. Photoluminescence quantum yields (PLQYs) of white emission of the molecular dispersion of phenyl-(thianthren-2-yl)-methanone in the rigid host ZEONEX at room temperature are significantly enhanced from 19 to 84% after the removal of oxygen. Based on the results of X-ray analysis of the single crystal, the high PLQY values are partly attributed to the absence of pi-pi intermolecular interactions and the low number of weak van der Waals intermolecular stacking due to the strong bending of heterocyclic thianthrene moiety and the high dihedral angle between thianthrene and benzoyl groups. The structural peculiarities of the newly synthesized thianthrene derivatives may result in the development of even more efficient organic monomolecular white emitters

Exciplex-Enhanced Singlet Emission Efficiency of Nondoped Organic Light Emitting Diodes Based on Derivatives of Tetrafluorophenylcarbazole and Tri/Tetraphenylethylene Exhibiting Aggregation-Induced Emission Enhancement

Two derivatives of tetrafluorophenylcarbazole and tri/tetraphenylethylene displaying aggregation-induced emission enhancement were synthesized and investigated by theoretical and experimental tools. The synthesized compounds exhibit efficient emission in solid state with fluorescence intensity maxima at 511 and 502 nm and photoluminescence quantum yields of 57 and 27%. They exhibit high thermal stability with 5% weight loss temperatures of 362 and 314 °C and glass-forming properties with glass-transition temperatures of 112 and 80 °C. Ionization potentials measured by photoelectron emission spectrometry were found to be comparable (5.83 and 5.87 eV). The layers of the compounds showed bipolar charge-transporting properties with balanced electron and hole mobilities reaching 10^–3 cm²/V s at high electric fields. Exciplex-host-based OLEDs containing one or two emitting layers of tetraphenylethenyl-containing emitter were fabricated and showed more than 50% higher external quantum efficiency as compared to that of the corresponding nondoped device. The best nondoped OLED containing the synthesized emitter showed turn-on voltage of 9.1 V, maximum brightness of 11 800 cd/m², maximum current efficiency of 4.5 cd/A, and external quantum efficiency of ca. 1.7%. The best modified device, with exciplex-based host layer showed turn-on voltage of 9.1 V, maximum brightness of 16 300 cd/m², maximum current efficiency of 7.3 cd/A, and external quantum efficiency of ca. 2.6%

Interfacial versus Bulk Properties of Hole-Transporting Materials for Perovskite Solar Cells: Isomeric Triphenylamine-Based Enamines versus Spiro-OMeTAD

International audienc

Structure and Spectral Properties of Thianthrene and Its Benzoyl-Containing Derivatives

The IR absorption spectra of the recently synthesized series of benzoyl-containing thianthrene derivatives were studied in the context of their structural identification. Geometry optimizitation of the ground singlet state by density functional theory (DFT) calculations with the gradient and Hessian search were performed for thianthrene molecule in the framework of the C2v symmetry restriction. The excited singlet and triplet states of thianthrene were found to be distorted along the b3u vibrational mode of the D2h point group, as well as the ground state, which leads to the non-planar batterfly-like structure (C2v). But the excited states require additional symmetry reduction; they are closer to planarity but have no symmetry elements. Optimized ground states structure for the thianthrene-benzoyle molecule and its four derivatives with fluoro-substituents and different substitution positions were analysed through complete assignment of all their vibrational modes and comparison with experimental infrared absorption spectra. A good agreement between experimental data and DFT calculated IR spectra provides additional structural support to results of the X-ray diffraction analysis of all synthesized compounds. The Hirshfeld surfaces analysis of the crystalline 3-fluorobenzoylthianthrene (T3F) was performed in order to analyze intermolecular interactions in T3F crystal. It indicates the presence of weak CH...F, CH...S and CH...O intermolecular contacts, stabilizing the crystal structure of T3F. The CH...O interactions appear in the IR spectrum of T3F crystal as two vibrational modes with frequencies 3084 and 3078 cm-1. The intermolecular interactions CH...F and CH...S do not affect the IR spectrum of T3F