Initial Growth Mode, Nanostructure, and Molecular Stacking of a ZnPc:C60 Bulk Heterojunction

Authors

  • Hyo Jung Kim,

    Corresponding author
    1. Department of Materials Science and Engineering and OLED Center, Seoul National University, Seoul 151-744, Republic of Korea
    • Department of Materials Science and Engineering and OLED Center, Seoul National University, Seoul 151-744, Republic of Korea
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  • Ji Whan Kim,

    1. Department of Materials Science and Engineering and OLED Center, Seoul National University, Seoul 151-744, Republic of Korea
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  • Hyun Hwi Lee,

    Corresponding author
    1. Pohang Accelerator Laboratory, POSTECH, Pohang, Gyungbuk 790-784, Republic of Korea
    • Pohang Accelerator Laboratory, POSTECH, Pohang, Gyungbuk 790-784, Republic of Korea.
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  • Byeongdu Lee,

    1. X-ray Science Division, Argonne National Laboratory, Argonne, IL 60439 USA
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  • Jang-Joo Kim

    Corresponding author
    1. Department of Materials Science and Engineering and OLED Center, Seoul National University, Seoul 151-744, Republic of Korea
    • Department of Materials Science and Engineering and OLED Center, Seoul National University, Seoul 151-744, Republic of Korea
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Abstract

The initial growth modes of ZnPc films is examined, revealing the previously undescribed nanoscale crystal structure evolution and the nanograins of the ZnPc:C60 mixed layers in the thin films. Initially, the ZnPc molecules are stacked in the preferred γ(200) configuration, similar to the structures of CuPc. The ZnPc thin film growth display 2D planar to 3D island growth after the initial compressive strain had relaxed in films 7–8 MLs thick. 3D island formation decreases the prevalence of the preferred ordering in the γ(200) crystals. The ZnPc films consist of randomly distributed ellipsoid nanograins during the initial growth stages. The ellipsoid nanograins transition to an ordered state later in the growth process. Insertion of C60 changes the preferred molecular stacking of ZnPc, and β(100) forms in the ZnPc:C60 layers fabricated at room temperature, which is usually observed at high annealing temperatures (200 °C) in a single ZnPc film. The ellipsoid ZnPc nanograins also retain their shapes in the ZnPc:C60 mixed layers. The formation of β(100) and the presence of ellipsoid nanograins in the mixed layer are related to improvements relative to planar devices in the organic photovoltaic device performance.

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