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Molecular orientation and thermal stability of thin-film organic semiconductors
Organic Electronics ( IF 3.2 ) Pub Date : 2020-11-06 , DOI: 10.1016/j.orgel.2020.106014
Han-Nan Yang , Shou-Jie He , Tao Zhang , Jia-Xiu Man , Yongbiao Zhao , Nan Jiang , Deng-Ke Wang , Zheng-Hong Lu

Molecular orientation in organic semiconductors plays a critical role in maximizing external quantum efficiencies of organic light-emitting diodes. It was generally believed that the molecular packing of organic semiconductors is either amorphous or liquid-crystal-like with a preferred molecular orientation distributed uniformly throughout the film. In this paper, however, we report that the orientation of organic molecules in physical-vapor deposited films varies drastically depending on thickness. The thermal stability of the molecular network, measured by its characteristic glass transition temperature, also varies as a function of the film thickness. Based on a two-layered film-structure model, we propose a simple function to quantify the molecular dipole orientation S parameter as a function of film thickness. This function describes well experimental data. In addition to contributing to external quantum efficiency, the molecular orientation parameter S is found to have a strong impact on disruptive change in material density after thermal anneal and glass transition.



中文翻译:

薄膜有机半导体的分子取向和热稳定性

有机半导体中的分子取向在最大化有机发光二极管的外部量子效率中起着至关重要的作用。通常认为,有机半导体的分子堆积是无定形的或液晶状的,优选的分子取向均匀地分布在整个膜中。然而,在本文中,我们报道了物理气相沉积膜中有机分子的取向随厚度的变化而急剧变化。分子网络的热稳定性,通过其特征性的玻璃化转变温度来衡量,也随薄膜厚度而变化。基于两层膜结构模型,我们提出了一个简单的函数来量化分子偶极子方向S参数与膜厚度的函数关系。该功能描述了很好的实验数据。除了有助于提高外部量子效率外,还发现分子取向参数S对热退火和玻璃化转变后材料密度的破坏性变化有很大影响。

更新日期:2020-11-17
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