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Author: Ge, Ziyi ×

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    Organic Light-Emitting Diodes Based on Conjugation-Induced Thermally Activated Delayed Fluorescence Polymers: Interplay Between Intra- and Intermolecular Charge Transfer States
    (Lausanne : Frontiers Media, 2019) Li, Yungui; Wei, Qiang; Cao, Liang; Fries, Felix; Cucchi, Matteo; Wu, Zhongbin; Scholz, Reinhard; Lenk, Simone; Voit, Brigitte; Ge, Ziyi; Reineke, Sebastian
    In this work, interactions between different host materials and a blue TADF polymer named P1 are systematically investigated. In photoluminescence, the host can have substantial impact on the photoluminescence quantum yield (PLQY) and the intensity of delayed fluorescence (ΦDF), where more than three orders of magnitude difference of ΦDF in various hosts is observed, resulting from a polarity effect of the host material and energy transfer. Additionally, an intermolecular charge-transfer (CT) emission with pronounced TADF characteristics is observed between P1 and 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T), with a singlet-triplet splitting of 7 meV. It is noted that the contribution of harvested triplets in monochrome organic light-emitting diodes (OLEDs) correlates with ΦDF. For devices based on intermolecular CT-emission, the harvested triplets contribute ~90% to the internal quantum efficiency. The results demonstrate the vital importance of host materials on improving the PLQY and sensitizing ΦDF of TADF polymers for efficient devices. Solution-processed polychrome OLEDs with a color close to a white emission are presented, with the emission of intramolecular (P1) and intermolecular TADF (PO-T2T:P1). © Copyright © 2019 Li, Wei, Cao, Fries, Cucchi, Wu, Scholz, Lenk, Voit, Ge and Reineke.
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    Polymer Featuring Thermally Activated Delayed Fluorescence as Emitter in Light-Emitting Electrochemical Cells
    (Washington, DC : ACS, 2020) Lundberg, Lundberg; Wei, Qiang; Ge, Ziyi; Voit, Brigitte; Reineke, Sebastian; Edman, Ludvig
    Semiconducting polymers that feature thermally activated delayed fluorescence (TADF) can deliver a much desired combination of high-efficiency and metal-free electroluminescence and cost-efficient solution-based fabrication. A TADF polymer is thus a very good fit for the emitting compound in light-emitting electrochemical cells (LECs) because the commonly employed air-stabile and few-layer LEC architecture is well suited for such solution-based fabrication. Herein we report on the first LEC device based on a TADF polymer as the emitting species, which delivers a luminance of 96 cd m-2 at 4 V and a current efficacy of 1.4 cd A-1 and >600 cd m-2 at 6 V, which is competitive with the performance of multilayer organic light-emitting diodes based on the same TADF polymer. We further utilize the established sensitivity of the emission of the TADF polymer to its environment to draw conclusions on the exciton populations in host-guest and host-free TADF LEC devices. Copyright © 2020 American Chemical Society.