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Author: Krupskaya, Yulia × End date: 2022 × End date: 2022 × Start date: 2022 × Type: Article ×

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    Optical Anisotropy and Momentum-Dependent Excitons in Dibenzopentacene Single Crystals
    (Washington, DC : ACS Publications, 2022) Graf, Lukas; Liu, Fupin; Naumann, Marco; Roth, Friedrich; Debnath, Bipasha; Büchner, Bernd; Krupskaya, Yulia; Popov, Alexey A.; Knupfer, Martin
    High-quality single crystals of the organic semiconductor (1,2;8,9)-dibenzopentacene were grown via physical vapor transport. The crystal structure─unknown before─was determined by single-crystal X-ray diffraction; polarization-dependent optical absorption measurements display a large anisotropy in the ac plane of the crystals. The overall Davydov splitting is ∼110 meV, which is slightly lower than that in the close relative pentacene (120 meV). Momentum-dependent electron energy-loss spectroscopy measurements show a clear exciton dispersion of the Davydov components. An analysis of the dispersion using a simple 1D model indicates smaller electron- and hole-transfer integrals in dibenzopentacene as compared to pentacene. The spectral weight distribution of the excitation spectra is strongly momentum-dependent and demonstrates a strong momentum-dependent admixture of Frenkel excitons, charge-transfer excitons, and vibrational modes.
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    Highly efficient modulation doping: A path toward superior organic thermoelectric devices
    (Washington, DC [u.a.] : Assoc., 2022) Wang, Shu-Jen; Panhans, Michel; Lashkov, Ilia; Kleemann, Hans; Caglieris, Federico; Becker-Koch, David; Vahland, Jörn; Guo, Erjuan; Huang, Shiyu; Krupskaya, Yulia; Vaynzof, Yana; Büchner, Bernd; Ortmann, Frank; Leo, Karl
    We investigate the charge and thermoelectric transport in modulation-doped large-area rubrene thin-film crystals with different crystal phases. We show that modulation doping allows achieving superior doping efficiencies even for high doping densities, when conventional bulk doping runs into the reserve regime. Modulation-doped orthorhombic rubrene achieves much improved thermoelectric power factors, exceeding 20 μW m−1 K−2 at 80°C. Theoretical studies give insight into the energy landscape of the heterostructures and its influence on qualitative trends of the Seebeck coefficient. Our results show that modulation doping together with high-mobility crystalline organic semiconductor films is a previosly unexplored strategy for achieving high-performance organic thermoelectrics.