Polyethyleneimine (PEI) can reduce work function when applied to cathode surface and to improve the drive efficiency of various organic electronic devices. Clarifying the mechanism of the work function reduction is important in developing alternative materials with higher stability. In this paper, a PEI thin film coated on a ZnO layer using all‐atom molecular dynamics simulations is analyzed. The simulations show that the entire PEI thin film induces an electrostatic potential shift of 0.30 eV, whose magnitude and sign are in good agreement with experiments. Further analysis reveals that there are two electric double layers (EDLs) at the ZnO/PEI interface and PEI/vacuum surface and that the latter plays a major role. The coil‐shell conformation of PEI at the PEI/vacuum surface forms the outer EDL and reduces the work function. At the ZnO/PEI interface, on the other hand, the coil‐shell conformation is less dominant because of the Zn‐N interaction and the inner EDL causes a small increase of the work function. This dual EDL model is different from the single EDL model for self‐assembled monolayers in that polymer conformations are essential. The report clarifies the novel polymer‐specific mechanism of work function reduction and opens up the possibility of new cathode modifiers.

中文翻译：

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通过涂覆在氧化锌上的聚乙烯亚胺降低功函数的双电双层模型：全原子分子动力学模拟


聚乙烯亚胺 （PEI） 应用于阴极表面时可降低功函数，提高各种有机电子器件的驱动效率。阐明功函数缩减的机制对于开发具有更高稳定性的替代材料非常重要。在本文中，使用全原子分子动力学模拟分析了涂覆在 ZnO 层上的 PEI 薄膜。模拟结果表明，整个 PEI 薄膜感应出 0.30 eV 的静电电位偏移，其大小和符号与实验非常吻合。进一步分析表明，在 ZnO/PEI 界面和 PEI/真空表面有两个双电层 （EDL），后者起着主要作用。PEI 在 PEI/真空表面的线圈壳构象形成外部 EDL 并降低功函数。另一方面，在 ZnO/PEI 界面处，由于 Zn-N 相互作用，线圈-壳构象不太占主导地位，并且内部 EDL 导致功函数的小幅增加。这种双 EDL 模型与自组装单层的单 EDL 模型不同，因为聚合物构象是必不可少的。该报告阐明了新的聚合物特异性功函数还原机制，并开辟了新的阴极改性剂的可能性。