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Crystalline structure, molecular motion and photocarrier formation in thin films of monodisperse poly(3-hexylthiophene) with various molecular weights

Polymer Journal volume 55, pages 497–505 (2023)Cite this article

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Abstract

A better understanding of the carrier formation process for semiconducting polymers, especially in thin films, is essential for designing and constructing highly functionalized polymeric optoelectronic devices. Here, the effects of aggregation states and thermal molecular motion on photocarrier formation in melt-crystallized thin films of monodispersed poly(3-hexylthiophene) (P3HT) are discussed. Grazing incidence X-ray diffraction measurements revealed that the crystalline ordering in the films was greatly influenced by the molecular weight (MW) of P3HT. In contrast, dynamic mechanical analysis (DMA) revealed that the MW had no significant effects on the α1 relaxation process, which corresponded to the twisting motion of thiophene rings in the crystalline phase unless the MW was quite small. Femtosecond transient absorption (TAS) spectroscopy showed that better crystalline ordering led to the direct formation of polarons (P) from hot excitons at room temperature. Once the temperature went beyond Tα1, at approximately 310 K, the P formation process from polaron pairs (PP) was activated. Thus, it can be claimed that the P formation for P3HT could be regulated by the thermal molecular motion in addition to the crystalline structure. The knowledge obtained here should be useful for a better molecular design of semiconducting polymers that can be applied to optoelectronic devices.

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Acknowledgements

This work was supported by JSPS KAKENHI for Scientific Research (B) (No. JP20H02790) to KT and Scientific Research (B) (No. JP20H02802) to DK from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan. We are also thankful for the support from the JST-Mirai Program (JPMJMI18A2) (K.T.). GIWAXD measurements were carried out at BL03XU at SPring-8 constructed by the Consortium of the Advanced Softmaterial Beamline (FSBL) (Proposal No. 2016A7225, 2016B7273, and 2021A7217).

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  1. Department of Applied Chemistry, Kyushu University, 744 Motooka Nishi-ku, Fukuoka, 819-0395, Japan

    Daisuke Kawaguchi, Yudai Ogata & Keiji Tanaka

  2. Center for Polymer Interface and Molecular Adhesion Science, Kyushu University, 744 Motooka Nishi-ku, Fukuoka, 819-0395, Japan

    Daisuke Kawaguchi & Keiji Tanaka

  3. Department of Applied Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8603, Japan

    Ayano Higasayama & Yushu Matsushita

  4. Diffraction and Scattering Group I, Diffraction and Scattering Division, Center for Synchrotron Radiation Research, Japan Synchrotron Radiation Research Institute (JASRI), Hyogo, 679-5148, Japan

    Taizo Kabe

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Kawaguchi, D., Higasayama, A., Ogata, Y. et al. Crystalline structure, molecular motion and photocarrier formation in thin films of monodisperse poly(3-hexylthiophene) with various molecular weights. Polym J 55, 497–505 (2023). https://doi.org/10.1038/s41428-022-00713-0

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