Tunable Dopants with Intrinsic Counterion Separation Reveal the Effects of Electron Affinity on Dopant Intercalation and Free Carrier Production in Sequentially Doped Conjugated Polymer Films
Tunable Dopants with Intrinsic Counterion Separation Reveal the Effects of Electron Affinity on Dopant Intercalation and Free Carrier Production in Sequentially Doped Conjugated Polymer Films
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DOI：
10.1002/adfm.202001800
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发表时间：
2020-05-25
影响因子：
19
通讯作者：
Schwartz, Benjamin J.
中科院分区：
文献类型：
--
作者：
Aubry, Taylor J.;Winchell, K. J.;Schwartz, Benjamin J.
掺杂共轭聚合物中的载流子迁移率受到与掺杂剂抗衡离子的库仑相互作用的限制。这使得研究掺杂剂的氧化电位对载流子产生的影响变得复杂，因为不同的掺杂剂与聚合物主链上的极化子具有不同的库仑相互作用。在此，使用基于十二硼烷（DDB）的掺杂剂，其静电屏蔽抗衡离子免受载流子的影响，并且在恒定的尺寸和形状下具有可调的氧化还原电位。DDB掺杂剂由于电荷的空间分离而产生移动的载流子，并且具有更大能量偏移的那些掺杂剂产生更多载流子。中子反射仪表明，掺杂剂渗透到共轭聚合物膜是氧化还原电位驱动。值得注意的是，X射线散射表明，尽管它们的大的2-nm的大小，DDBs插入到结晶聚合物层状小分子，这表明这是任何大小的掺杂剂的优选位置。这些研究结果阐明了为什么掺杂共轭聚合物通常产生整数，而不是部分电荷转移：掺杂剂抗衡离子有效地嵌入到lamydium，远离聚合物主链上的极化子。最后，它表明，红外光谱提供了一种简单的方法来确定极化子迁移率。总体而言，更高的氧化电位导致更高的掺杂效率，对于足以掺杂薄膜结晶不良区域的驱动力，该值达到100%。
Carrier mobility in doped conjugated polymers is limited by Coulomb interactions with dopant counterions. This complicates studying the effect of the dopant's oxidation potential on carrier generation because different dopants have different Coulomb interactions with polarons on the polymer backbone. Here, dodecaborane (DDB)-based dopants are used, which electrostatically shield counterions from carriers and have tunable redox potentials at constant size and shape. DDB dopants produce mobile carriers due to spatial separation of the counterion, and those with greater energetic offsets produce more carriers. Neutron reflectometry indicates that dopant infiltration into conjugated polymer films is redox-potential-driven. Remarkably, X-ray scattering shows that despite their large 2-nm size, DDBs intercalate into the crystalline polymer lamellae like small molecules, indicating that this is the preferred location for dopants of any size. These findings elucidate why doping conjugated polymers usually produces integer, rather than partial charge transfer: dopant counterions effectively intercalate into the lamellae, far from the polarons on the polymer backbone. Finally, it is shown that the IR spectrum provides a simple way to determine polaron mobility. Overall, higher oxidation potentials lead to higher doping efficiencies, with values reaching 100% for driving forces sufficient to dope poorly crystalline regions of the film.