Thomas Elayne M, Davidson Emily C, Katsumata Reika, Segalman Rachel A, Chabinyc Michael L
Materials Department, University of California, Santa Barbara, California 93106, United States.
Department of Chemical Engineering, University of California, Santa Barbara, California 93106, United States.
ACS Macro Lett. 2018 Dec 18;7(12):1492-1497. doi: 10.1021/acsmacrolett.8b00778. Epub 2018 Dec 6.
Predicting the interactions between a semiconducting polymer and dopant is not straightforward due to the intrinsic structural and energetic disorder in polymeric systems. Although the driving force for efficient charge transfer depends on a favorable offset between the electron donor and acceptor, we demonstrate that the efficacy of doping also relies on structural constraints of incorporating a dopant molecule into the semiconducting polymer film. Here, we report the evolution in spectroscopic and electrical properties of a model conjugated polymer upon exposure to two dopant types: one that directly oxidizes the polymeric backbone and one that protonates the polymer backbone. Through vapor phase infiltration, the common charge transfer dopant, F-TCNQ, forms a charge transfer complex (CTC) with the polymer poly(3-(2'-ethyl)hexylthiophene) (P3EHT), a conjugated polymer with the same backbone as the well-characterized polymer P3HT, resulting in a maximum electrical conductivity of 3 × 10 S cm. We postulate that the branched side chains of P3EHT force F-TCNQ to reside between the π-faces of the crystallites, resulting in partial charge transfer between the donor and the acceptor. Conversely, protonation of the polymeric backbone using the strong acid, HTFSI, increases the electrical conductivity of P3EHT to a maximum of 4 × 10 S cm, 2 orders of magnitude higher than when a charge transfer dopant is used. The ability for the backbone of P3EHT to be protonated by an acid dopant, but not oxidized directly by F-TCNQ, suggests that steric hindrance plays a significant role in the degree of charge transfer between dopant and polymer, even when the driving force for charge transfer is sufficient.
由于聚合物体系中固有的结构和能量无序性，预测半导体聚合物与掺杂剂之间的相互作用并非易事。尽管有效电荷转移的驱动力取决于电子供体和受体之间有利的能级差，但我们证明，掺杂的效果还依赖于将掺杂剂分子掺入半导体聚合物薄膜的结构限制。在此，我们报告了一种模型共轭聚合物在暴露于两种掺杂剂类型时的光谱和电学性质的演变：一种直接氧化聚合物主链，另一种使聚合物主链质子化。通过气相渗透，常见的电荷转移掺杂剂F-TCNQ与聚合物聚（3-（2'-乙基）己基噻吩）（P3EHT）形成电荷转移络合物（CTC），P3EHT是一种与特征明确的聚合物P3HT具有相同主链的共轭聚合物，其最大电导率为3×10 S/cm。我们推测，P3EHT的支化侧链迫使F-TCNQ位于微晶的π面之间，导致供体和受体之间发生部分电荷转移。相反，使用强酸HTFSI使聚合物主链质子化，可将P3EHT的电导率提高到最大4×10 S/cm，比使用电荷转移掺杂剂时高2个数量级。P3EHT主链能够被酸掺杂剂质子化，但不能被F-TCNQ直接氧化，这表明空间位阻在掺杂剂与聚合物之间的电荷转移程度中起着重要作用，即使电荷转移的驱动力足够。
