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Understanding the Impact of Film Disorder and Local Surface Potential in Ultraviolet Photoelectron Spectroscopy of PEDOT
Macromolecular Rapid Communications ( IF 4.2 ) Pub Date : 2017-12-06 , DOI: 10.1002/marc.201700533 William A. Muñoz 1 , Xavier Crispin 1 , Mats Fahlman 2 , Igor V. Zozoulenko 1
Macromolecular Rapid Communications ( IF 4.2 ) Pub Date : 2017-12-06 , DOI: 10.1002/marc.201700533 William A. Muñoz 1 , Xavier Crispin 1 , Mats Fahlman 2 , Igor V. Zozoulenko 1
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The spectra of conducting polymers obtained using ultraviolet photoelectron spectroscopy (UPS) exhibit a typical broadening of the tail σUPS ≈ 1 eV, which by an order of magnitude exceeds a commonly accepted value of the broadening of the tail of the density of states σDOS ≈ 0.1 eV obtained using transport measurements. In this work, an origin of this anomalous broadening of the tail of the UPS spectra in a doped conducting polymer, PEDOT (poly(3,4‐ethylenedioxythiophene)), is discussed. Based on the semiempirical approach and using a realistic morphological model, the density of valence states in PEDOT doped with molecular counterions is computed. It is shown that due to a disordered character of the material with randomly distributed counterions, the localized charge carriers in PEDOT crystallites experience spatially varying electrostatic potential. This leads to spatially varying local vacuum levels and binding energies. Taking this variation into account the UPS spectrum is obtained with the broadening of the tail comparable to the experimentally observed one. The results imply that the observed broadening of the tail of the UPS spectra in PEDOT provides information about a disordered spatially varying potential in the material rather than the broadening of the DOS itself.
中文翻译：
了解PEDOT的紫外光电子能谱中的薄膜无序和局部表面电势的影响
使用紫外光电子能谱（UPS）表现出尾σ的典型加宽得到导电聚合物的光谱UPS ≈1电子伏特，其通过一个数量级超过状态σ的密度的尾部的扩大的普遍接受的值DOS使用传输测量获得的≈0.1 eV。在这项工作中，讨论了在掺杂的导电聚合物PEDOT（聚（3,4-乙撑二氧噻吩））中UPS光谱尾部这种异常加宽的起源。基于半经验方法并使用现实的形态学模型，计算了分子抗衡离子掺杂的PEDOT中的价态密度。结果表明，由于材料具有无序分布的抗衡离子的无序特性，PEDOT微晶中的局部电荷载流子会经历空间变化的静电势。这导致空间上变化的局部真空水平和结合能。考虑到这一变化，就可以得到UPS光谱，其尾巴的增宽可与实验观察到的相比。
更新日期：2017-12-06
中文翻译：
了解PEDOT的紫外光电子能谱中的薄膜无序和局部表面电势的影响
使用紫外光电子能谱（UPS）表现出尾σ的典型加宽得到导电聚合物的光谱UPS ≈1电子伏特，其通过一个数量级超过状态σ的密度的尾部的扩大的普遍接受的值DOS使用传输测量获得的≈0.1 eV。在这项工作中，讨论了在掺杂的导电聚合物PEDOT（聚（3,4-乙撑二氧噻吩））中UPS光谱尾部这种异常加宽的起源。基于半经验方法并使用现实的形态学模型，计算了分子抗衡离子掺杂的PEDOT中的价态密度。结果表明，由于材料具有无序分布的抗衡离子的无序特性，PEDOT微晶中的局部电荷载流子会经历空间变化的静电势。这导致空间上变化的局部真空水平和结合能。考虑到这一变化，就可以得到UPS光谱，其尾巴的增宽可与实验观察到的相比。
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