Watts Kristen E, Neelamraju Bharati, Moser Maximilian, McCulloch Iain, Ratcliff Erin L, Pemberton Jeanne E
Department of Chemistry and Centre for Plastic Electronics, Imperial College London, London, U.K.
KSC, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia.
J Phys Chem Lett. 2020 Aug 20;11(16):6586-6592. doi: 10.1021/acs.jpclett.0c01673. Epub 2020 Aug 3.
The prototypical system for understanding doping in solution-processed organic electronics has been poly(3-hexylthiophene) (P3HT) p-doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (FTCNQ). Multiple charge-transfer states, defined by the fraction of electron transfer to FTCNQ, are known to coexist and are dependent on polymer molecular weight, crystallinity, and processing. Less well-understood is the loss of conductivity after thermal annealing of these materials. Specifically, in thermoelectrics, FTCNQ-doped regioregular (rr) P3HT exhibits significant conductivity losses at temperatures lower than other thiophene-based polymers. Through detailed spectroscopic investigation of progressively heated P3HT films coprocessed with FTCNQ, we demonstrate that this diminished conductivity is due to formation of the nonchromophoric, weak dopant HFTCNQ. This species is likely formed through hydrogen abstraction from the α aliphatic carbon of the hexyl chain at the 3-position of thiophene rings of rr-P3HT. This reaction is eliminated for polymers with ethylene glycol-containing side chains, which retain conductivity at higher operating temperatures. In total, these results provide a critical materials design guideline for organic electronics.
用于理解溶液处理有机电子器件中掺杂情况的典型体系是用2,3,5,6-四氟-7,7,8,8-四氰基对苯二醌二甲烷（FTCNQ）进行p型掺杂的聚（3-己基噻吩）（P3HT）。由向FTCNQ转移电子的比例所定义的多个电荷转移态已知是共存的，并且取决于聚合物分子量、结晶度和加工过程。这些材料经热退火后电导率的损失则较难理解。具体而言，在热电学中，FTCNQ掺杂的区域规整（rr）P3HT在低于其他噻吩基聚合物的温度下表现出显著的电导率损失。通过对与FTCNQ共处理的逐步加热的P3HT薄膜进行详细的光谱研究，我们证明这种电导率降低是由于形成了非发色性的弱掺杂剂HFTCNQ。这种物质可能是通过从rr-P3HT噻吩环3位己基链的α脂肪族碳上夺取氢而形成的。对于带有含乙二醇侧链的聚合物，这种反应被消除，这些聚合物在较高的工作温度下仍保持电导率。总的来说，这些结果为有机电子学提供了关键的材料设计指导方针。
