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- ItemModulating the luminance of organic light-emitting diodes: Via optical stimulation of a photochromic molecular monolayer at transparent oxide electrode(Cambridge : RSC Publ., 2020) Ligorio, Giovanni; Cotella, Giovanni F.; Bonasera, Aurelio; Zorn Morales, Nicolas; Carnicella, Giuseppe; Kobin, Björn; Wang, Qiankun; Koch, Norbert; Hecht, Stefan; List-Kratochvil, Emil J.W.; Cacialli, FrancoSelf-assembled monolayers (SAMs) deposited on bottom electrodes are commonly used to tune charge carrier injection or blocking in optoelectronic devices. Beside the enhancement of device performance, the fabrication of multifunctional devices in which the output can be modulated by multiple external stimuli remains a challenging target. In this work, we report the functionalization of an indium tin oxide (ITO) electrode with a SAM of a diarylethene derivative designed for optically control the electronic properties. Following the demonstration of dense SAM formation and its photochromic activity, as a proof-of-principle, an organic light-emitting diode (OLED) embedding the light-responsive SAM-covered electrode was fabricated and characterized. Optically addressing the two-terminal device by irradiation with ultraviolet light doubles the electroluminescence. The original value can be restored reversibly by irradiation with visible light. This expanded functionality is based on the photoinduced modulation of the electronic structure of the diarylethene isomers, which impact the charge carriers' confinement within the emissive layer. This approach could be successfully exploited in the field of opto-communication technology, for example to fabricate opto-electronic logic circuits. © 2020 The Royal Society of Chemistry.
- ItemOligothiophene-Based Phosphonates for Surface Modification of Ultraflat Transparent Conductive Oxides(Weinheim : Wiley-VCH, 2020) Timpel, Melanie; Nardi, Marco V.; Wegner, Berthold; Ligorio, Giovanni; Pasquali, Luca; Hildebrandt, Jana; Pätzel, Michael; Hecht, Stefan; Ohta, Hiromichi; Koch, NorbertThe self-assembly of electroactive organic molecules on transparent conductive oxides is a versatile strategy to engineer the interfacial energy-level alignment and to enhance charge carrier injection in optoelectronic devices. Via chemical grafting of an aromatic oligothiophene molecule by changing the position of the phosphonic acid anchoring group with respect to the organic moiety (terminal and internal), the direction of the main molecular dipole is changed, i.e., from parallel to perpendicular to the substrate, to study the molecular arrangement and electronic properties at the organic–inorganic interface. It is found that the observed work function increase cannot solely be predicted based on the calculated molecular dipole moment of the oligothiophene-based phosphonates. In addition, charge transfer from the substrate to the molecule has to be taken into account. Molecular assembly and induced electronic changes are analogous for both indium-tin oxide (ITO) and zinc oxide (ZnO), demonstrating the generality of the approach and highlighting the direct correlation between molecular coverage and electronic effects. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim