Seebeck Effects in N-Type and P-Type Polymers Driven Simultaneously by Surface Polarization and Entropy Differences Based on Conductor/Polymer/Conductor Thin-Film Devices
Seebeck Effects in N-Type and P-Type Polymers Driven Simultaneously by Surface Polarization and Entropy Differences Based on Conductor/Polymer/Conductor Thin-Film Devices
复制标题
基于导体/聚合物/导体薄膜器件的表面极化和熵差同时驱动的 N 型和 P 型聚合物中的塞贝克效应
DOI：
10.1021/acsnano.5b00589
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发表时间：
2015
期刊：
影响因子：
17.1
通讯作者：
Hu Bin
中科院分区：
文献类型：
--
作者：
Hu Dehua;Liu Qing;Tisdale Jeremy;Lei Ting;Pei Jian;Wang Hsin;Urbas Augustine;Hu Bin
本文利用基于垂直导体/聚合物/导体薄膜器件的n型和p型共轭聚合物IIDT和IIDDT的光诱导分子内电荷转移态，报道了表面极化差和熵差驱动的塞贝克效应。白光100mw /cm2产生电荷转移态时，n型IIDT的Seebeck系数为−898 μV/K， p型IIDDT的Seebeck系数为1300 μV/K，而黑暗条件下的Seebeck系数分别为380和470 μV/K。同时，n型IIDT和p型IIDDT器件的电导率都从黑暗条件下的几乎绝缘状态提高到光激发下的导电状态。巨大的塞贝克效应可归因于以下两种机制。首先，分子内电荷转移态表现出强烈的电子-声子耦合，这导致了高温表面和低温表面之间的极化差异。这种极化差实质上形成了一个温度相关的电场，作为熵差之外的一种新的驱动力，在温差下驱动塞贝克效应发展的高能载流子。其次，分子内电荷转移态在n型IIDT或p型IIDDT中产生负或正的多数载流子（电子或空穴），准备在高低温表面之间驱动以发展塞贝克效应。在极化差和熵差共存的基础上，分子内电荷转移态在n型IIDT和p型IIDDT器件中都能极大地增强塞贝克效应。此外，我们发现当施加光激发产生电荷转移态时，改变电导率可以在极化和熵态之间切换塞贝克效应。因此，在基于有机材料的垂直导体/聚合物/导体薄膜器件中，利用分子内电荷转移态提供了一种开发热电效应的方法。
This paper reports Seebeck effects driven by both surface polarization difference and entropy difference by using photoinduced intramolecular charge-transfer states in n-type and p-type conjugated polymers, namely IIDT and IIDDT, respectively, based on vertical conductor/polymer/conductor thin-film devices. We obtain large Seebeck coefficients of −898 μV/K from n-type IIDT and 1300 μV/K from p-type IIDDT when the charge-transfer states are generated by a white light illumination of 100 mW/cm2, compared with the values of 380 and 470 μV/K in dark condition, respectively. Simultaneously, the electrical conductivities are increased from almost insulating state in dark condition to conducting state under photoexcitation in both n-type IIDT and p-type IIDDT based devices. The large Seebeck effects can be attributed to the following two mechanisms. First, the intramolecular charge-transfer states exhibit strong electron–phonon coupling, which leads to a polarization difference between high and low temperature surfaces. This polarization difference essentially forms a temperature-dependent electric field, functioning as a new driving force additional to entropy difference, to drive the energetic carriers for the development of Seebeck effects under a temperature difference. Second, the intramolecular charge-transfer states generate negative or positive majority carriers (electrons or holes) in the n-type IIDT or p-type IIDDT, ready to be driven between high and low temperature surfaces for developing Seebeck effects. On the basis of coexisted polarization difference and entropy difference, the intramolecular charge-transfer states can largely enhance the Seebeck effects in both n-type IIDT and p-type IIDDT devices. Furthermore, we find that changing electrical conductivity can switch the Seebeck effects between polarization and entropy regimes when the charge-transfer states are generated upon applying photoexcitation. Therefore, using intramolecular charge-transfer states presents an approach to develop thermoelectric effects in organic materials-based vertical conductor/polymer/conductor thin-film devices.