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<p>In organic semiconductors, elucidation of structures in the amorphous thin films is important because it determines crucial factors for device performance. The amorphous structures determine densities of states, electronic couplings, and reorganization energies, all of which affect current and light-emitting characteristics of devices. However, due to the amorphous nature, the detailed molecular-level structure, especially the distribution, has not been well characterized. Here, we fabricate organic amorphous thin films by molecular dynamic simulations mimicking the experimental deposition process. The simulation clearly exhibits that the molecules are oriented with a broad distribution with respect to the substrate; the average orientation successfully reproduced the experiments quantitatively. We also conduct charge transport simulations. The horizontal molecular orientation results in an increase in hole mobility as in the experiment. The origin of the increased mobility in horizontally oriented systems is found to be the narrowing of the site energy distribution and the reduction of pairs with exceptionally large electronic couplings.</p>

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Predictions of molecular orientation and charge mobility in organic vacuum-deposited thin films by multiscale simulation

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  • 出版模式：

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  • 发表日期：

    2025年6月5日

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  • Kuraudo Ishihara,
  • Hironori Kaji

摘要

In organic semiconductors, elucidation of structures in the amorphous thin films is important because it determines crucial factors for device performance. The amorphous structures determine densities of states, electronic couplings, and reorganization energies, all of which affect current and light-emitting characteristics of devices. However, due to the amorphous nature, the detailed molecular-level structure, especially the distribution, has not been well characterized. Here, we fabricate organic amorphous thin films by molecular dynamic simulations mimicking the experimental deposition process. The simulation clearly exhibits that the molecules are oriented with a broad distribution with respect to the substrate; the average orientation successfully reproduced the experiments quantitatively. We also conduct charge transport simulations. The horizontal molecular orientation results in an increase in hole mobility as in the experiment. The origin of the increased mobility in horizontally oriented systems is found to be the narrowing of the site energy distribution and the reduction of pairs with exceptionally large electronic couplings.