School of Chemical Engineering, Purdue University , 480 Stadium Mall Drive, West Lafayette, Indiana 47907, United States.
ACS Appl Mater Interfaces. 2015 Aug 26;7(33):18195-200. doi: 10.1021/acsami.5b05860. Epub 2015 Aug 14.
Polymer thermoelectric devices are emerging as promising platforms by which to convert thermal gradients into electricity directly, and poly(3,4-ethylene dioxythiophene) doped with poly(styrenesulfonate) (
PSS) is a leading candidate in a number of these thermoelectric modules. Here, we implement the stable radical-bearing small molecule 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO-OH) as an intermolecular dopant in order to tune the electrical conductivity, thermopower, and power factor of
PSS thin films. Specifically, we demonstrate that, at moderate loadings (∼2%, by weight) of the open-shell TEMPO-OH molecule, the thermopower of
PSS thin films is increased without a marked decline in the electrical conductivity of the material. This effect, in turn, allows for an optimization of the power factor in the composite organic materials, which is a factor of 2 greater than the pristine
PSS thin films. Furthermore, because the loading of TEMPO-OH is relatively low, we observe that there is little change in either the crystalline nature or surface topography of the composite films relative to the pristine
PSS films. Instead, we determine that the increase in the thermopower is due to the presence of stable radical sites within the
PSS that persist despite the highly acidic environment that occurs due to the presence of the poly(styrenesulfonate) moiety. Additionally, the oxidation-reduction-active (redox-active) nature of the TEMPO-OH small molecules provides a means by which to filter charges of different energy values. Therefore, these results demonstrate that a synergistic combination of an open-shell species and a conjugated polymer allows for enhanced thermoelectric properties in macromolecular systems, and as such, it offers the promise of a new design pathway in polymer thermoelectric materials.
聚合物热电设备作为一种有前途的平台，能够直接将热梯度转化为电能，而聚（3,4-亚乙基二氧噻吩）掺杂聚（苯乙烯磺酸盐）（PEDOT：PSS）是许多这些热电模块中的领先候选者。在这里，我们实施了稳定的自由基小分子 4-羟基-2,2,6,6-四甲基哌啶-1-氧自由基（TEMPO-OH）作为一种分子间掺杂剂，以调节 PEDOT：PSS 薄膜的电导率、热电势和功率因数。具体而言，我们证明，在适度负载（约 2%，重量）的开壳 TEMPO-OH 分子下，PEDOT：PSS 薄膜的热电势增加，而材料的电导率没有明显下降。这种效应反过来又允许在复合有机材料中优化功率因数，这是原始 PEDOT：PSS 薄膜的两倍。此外，由于 TEMPO-OH 的负载相对较低，我们观察到复合薄膜的结晶性质或表面形貌相对于原始 PEDOT：PSS 薄膜几乎没有变化。相反，我们确定热电势的增加是由于在存在聚（苯乙烯磺酸盐）部分时，PEDOT：PSS 中存在稳定的自由基位。此外，TEMPO-OH 小分子的氧化还原活性（氧化还原活性）性质提供了一种过滤不同能量值电荷的方法。因此，这些结果表明，开壳物种和共轭聚合物的协同组合允许在大分子系统中增强热电性能，并且为聚合物热电材料的新设计途径提供了希望。
