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Enhancement of indacenodithiophene–benzothiadiazole copolymer field-effect mobility with MXenes
Jurij Urbančič, Nadiia Pastukhova, Manisha Chhikara, Hu Chen, Iain Mcculloch, Huanhuan Shi, Ali Shaygan Nia, Xinliang Feng, Egon Pavlica, Gvido Bratina, 2022, published scientific conference contribution abstract

Abstract: The predominant mode of charge carrier transport in thin layers of organic semiconductors (OSs) is thermally-activated hopping between localized states. This results in lower charge mobility compared to inorganic semiconductors precluding the use of OSs in high-speed electronic devices. Therefore, significant effort is invested to improve charge carrier mobility of OS thin layers, which form the basis of most of the organic electronic devices. Recent advances in the field of two-dimensional (2D) materials stimulated their use as addition to OS thin layers to boost the charge carrier mobility. MXenes promise to deliver most of the benefits of 2D materials coupled with large scale fabrication capability. Herein we examined Ti3C2X (X is O or OH group termination) MXene, as a candidate to improve charge carrier mobility in thin layer of indacenodithiophene-co-benzothiadiazole (IDTBT), a polymer exhibiting high electron mobility in defect-free crystalline layers. In our work we demonstrate that improvement in electron mobility in solution-cast IDTBT thin layers can be achieved by depositing a non-connected network of MXene flakes at the gate-dielectric/IDBT interface. Bottom-gate field-effect transistors (FETs) comprising of Au electrodes on n-doped silicon wafer covered with 230 nm of thermally deposited SiO2 were prepared and characterized. Charge carrier mobilities determined from transfer characteristics of FETs composing neat IDTBT channels were found to be in the range of 1 - 2×10−2 cm2/Vs. Devices comprising MXene flakes at the interface between SiO2 and IDTBT, instead exhibited a factor of four increase in electron mobility, while preserving the on/off ratio of 104.
Keywords: MXene, IDTBT, charge carrier mobility, OFET
Published in RUNG: 20.10.2022; Views: 1020; Downloads: 9
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Elucidation of Donor:Acceptor Phase Separation in Nonfullerene Organic Solar Cells and Its Implications on Device Performance and Charge Carrier Mobility
Sebastian F. Hoefler, Georg Haberfehlner, Thomas Rath, Andreas Keilbach, Mathias Hobisch, Alexander Dixon, Egon Pavlica, Gvido Bratina, Gerald Kothleitner, Ferdinand Hofer, Gregor Trimmel, 2019, original scientific article

Abstract: In bulk-heterojunction solar cells, the device performance strongly depends on the donor and acceptor properties, the phase separation in the absorber layer, and the formation of a bicontinuous network. While this phase separation is well explored for polymer:fullerene solar cells, only little is known for polymer:nonfullerene acceptor solar cells. The main hurdle in this regard is often the chemical similarity of the conjugated polymer donor and the organic nonfullerene acceptor (NFA), which makes the analysis of the phase separation via atomic force microscopic (AFM) phase images or conventional transmission electron microscopy difficult. In this work, we use the donor polymer PTB7-Th and the small molecule acceptor O-IDTBR as the model system and visualized the phase separation in PTB7-Th:O-IDTBR bulk-heterojunctions with different donor:acceptor ratios via scanning transmission electron microscopy (STEM) high-angle annular dark-field (HAADF) images and electron energy loss spectroscopy (EELS) based elemental mapping, which resulted in a good contrast between the donor and the acceptor despite very low differences in the chemical composition. AFM as well as grazing-incidence wide-angle X-ray scattering (GIWAXS) investigations support the electron microscopic data. Furthermore, we elucidate the implications of the phase separation on the device performance as well as charge carrier mobilities in the bulk-heterojunction layers, and a high performance of the solar cells was found over a relatively broad range of polymer domain sizes. This can be related to the larger domain sizes of the acceptor phase with higher amounts of O-IDTBR in the blend, while the polymer donor phase still forms continuous pathways to the electrode, which keeps the hole mobility at a relatively constant level.
Keywords: nanomorphology bulk-heterojunction scanning transmission electron microscopy organic photovoltaics charge carrier mobility
Published in RUNG: 15.01.2020; Views: 2854; Downloads: 84
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