Observation of spontaneous orientation polarization in evaporated films of organic light-emitting diode materials
Observation of spontaneous orientation polarization in evaporated films of organic light-emitting diode materials
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DOI：
10.1016/j.orgel.2018.04.026
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发表时间：
2018-07
影响因子：
3.2
通讯作者：
K. Osada;K. Goushi;H. Kaji;C. Adachi;H. Ishii;Y. Noguchi
中科院分区：
文献类型：
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作者：
K. Osada;K. Goushi;H. Kaji;C. Adachi;H. Ishii;Y. Noguchi
有机半导体薄膜中的分子取向决定了器件性能。特别是，永久偶极矩（PDM）沿表面法线方向的自发取向会在堆叠多层器件的异质界面处感应出极化电荷，并且界面电荷主导电荷积累和注入特性。自发取向偏振（SOP）已在几种有机半导体材料的“随机取向”薄膜中观察到，并且可能是许多常见材料所固有的。在此，我们报告了另外 11 种有机发光二极管材料分子，包括热激活延迟荧光发射器、水平定向发射器和电子传输器，在其蒸发薄膜中表现出 SOP。实验结果清楚地表明，SOP 经常出现在“水平取向”薄膜和“随机取向”薄膜中。影响 SOP 形成的因素按照每个 PDM 的品质因数进行了讨论。我们发现强烈的分子间相互作用往往会降低品质因数。此外，我们还提出了 SOP 对器件性能的影响。
The molecular orientation in organic semiconductor films determines device performances. In particular, the spontaneous orientation of a permanent dipole moment (PDM) along the surface normal direction induces a polarization charge at the hetero-interfaces of stacked multilayer devices, and the interface charge dominates the charge accumulation and injection properties. Spontaneous orientation polarization (SOP) has been observed in the “randomly oriented” films of several organic semiconductor materials, and is potentially inherent in many common materials. Herein, we report that 11 additional molecules of organic light-emitting diode materials, including thermally activated delayed fluorescence emitters, and horizontally oriented emitters and electron transporters, exhibit SOP in their evaporated films. The experimental results clearly indicate that SOP frequently occurs in “horizontally oriented” films as well as “randomly oriented” films. The factors contributing to SOP formation are discussed in terms of the figure of merit per PDM. We found that strong intermolecular interactions tend to reduce the figure of merit. Moreover, we suggest the impact of SOP on device performances.