Zhang Yuan, Wang Qi, Hu Fengyang, Wang Yuhao, Wu Di, Wang Rongbin, Duhm Steffen
Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, Suzhou 215123, People's Republic of China.
Jiangsu Key Laboratory of Advanced Negative Carbon Technologies, Soochow University, Suzhou 215123, People's Republic of China.
ACS Phys Chem Au. 2023 Feb 20;3(3):311-319. doi: 10.1021/acsphyschemau.2c00073. eCollection 2023 May 24.
The conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is used in a manifold of electronic applications, and controlling its conductivity is often the key to attain a superior device performance. To that end, solvent additives like Triton, ethylene glycol (EG), or dimethyl sulfoxide (DMSO) are regularly incorporated. In our comprehensive study, we prepare PEDOT:PSS thin films with seven different additive combinations and with thicknesses ranging from 6 to 300 nm on indium-tin-oxide (ITO) substrates. We utilize X-ray photoelectron spectroscopy (XPS) to access the PSS-to-PEDOT ratio and the PSS-to-PSSH ratio in the near-surface region and ultraviolet photoelectron spectroscopy (UPS) to get the work function (WF). In addition, the morphology and conductivity of these samples are obtained. We found that the WF of the prepared thin films for each combination becomes saturated at a thickness of around 50 nm and thinner films show a lower WF due to the inferior coverage on the ITO. Furthermore, the WF shows a better correlation with the PSS-to-PSSH ratio than the commonly used PSS-to-PEDOT ratio as PSS can directly affect the surface dipole. By adding solvent additives, a dramatic increase in the conductivity is observed for all PEDOT:PSS films, especially when DMSO is involved. Moreover, adding the additive Triton (surfactant) helps to suppress the WF fluctuation for most films of each additive combination and contributes to weaken the surface dipole, eventually leading to a lower and thickness-independent WF.
导电聚合物聚（3,4 - 乙撑二氧噻吩）：聚（苯乙烯磺酸盐）（PEDOT:PSS）被用于多种电子应用中，控制其电导率通常是实现卓越器件性能的关键。为此，常加入诸如 Triton、乙二醇（EG）或二甲基亚砜（DMSO）等溶剂添加剂。在我们的综合研究中，我们在氧化铟锡（ITO）衬底上制备了具有七种不同添加剂组合且厚度范围为6至300纳米的PEDOT:PSS薄膜。我们利用X射线光电子能谱（XPS）来获取近表面区域的PSS与PEDOT的比例以及PSS与PSSH的比例，并利用紫外光电子能谱（UPS）来得到功函数（WF）。此外，还获得了这些样品的形态和电导率。我们发现，对于每种组合的制备薄膜，其功函数在厚度约为50纳米时达到饱和，并且较薄的薄膜由于在ITO上的覆盖较差而显示出较低的功函数。此外，由于PSS可直接影响表面偶极，功函数与PSS与PSSH的比例比常用的PSS与PEDOT的比例具有更好的相关性。通过添加溶剂添加剂，观察到所有PEDOT:PSS薄膜的电导率都有显著增加，尤其是当涉及DMSO时。此外，添加添加剂Triton（表面活性剂）有助于抑制每种添加剂组合的大多数薄膜的功函数波动，并有助于减弱表面偶极，最终导致较低且与厚度无关的功函数。
