Xing Weilong, Wu Sicheng, Liang Yingying, Sun Yimeng, Zou Ye, Liu Liyao, Xu Wei, Zhu Daoben
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
ACS Appl Mater Interfaces. 2020 Jul 1;12(26):29540-29548. doi: 10.1021/acsami.0c07822. Epub 2020 Jun 22.
Because of the high mobility and Seebeck coefficient, pentacene (PEN) is a promising candidate for organic small-molecule thermoelectric (TE) materials. However, the low intrinsic conductivity impedes its application in thermoelectricity. In this work, hexacyano-trimethylene-cyclopropane (CN6-CP) is employed as the dopant for PEN via constructing bilayer-structured thin films. The almost intact crystallinity and high charge carrier generation efficiency of these interface-doped PEN films ensure their high conductivity. Time of flight secondary ion mass spectrometry was applied to demonstrate the diffusion of dopant molecules into the PEN layer. UV-vis spectral analysis reveals that integral charge transfer happens between the PEN and CN6-CP molecules. The doping process is further characterized by electron spin-resonance, ultraviolet photoelectron spectroscopy, and X-ray photoelectron spectroscopy analysis. Under optimized conditions, the conductivity of the PEN film deposited on the SiO/Si substrate can reach up to 10.1 S cm. To the best of our knowledge, this is the highest conductivity ever reported for doped PEN thin films. The optimal TE performance with a power factor of 36.4 μW m K can be achieved in the PEN/CN6CP thin film with a Seebeck coefficient and conductivity of 199 μV K and 9.2 S cm, respectively. This result shows that interface doping with a strong electron acceptor is a promising approach for optimizing the TE performance of small molecular organic semiconductors.
由于具有高迁移率和塞贝克系数，并五苯（PEN）是有机小分子热电（TE）材料的一个有前途的候选者。然而，其固有的低电导率阻碍了它在热电领域的应用。在这项工作中，通过构建双层结构薄膜，六氰基三亚甲基环丙烷（CN6-CP）被用作PEN的掺杂剂。这些界面掺杂的PEN薄膜几乎完整的结晶度和高电荷载流子产生效率确保了它们的高电导率。采用飞行时间二次离子质谱法来证明掺杂剂分子扩散到PEN层中。紫外可见光谱分析表明，PEN和CN6-CP分子之间发生了整体电荷转移。通过电子自旋共振、紫外光电子能谱和X射线光电子能谱分析对掺杂过程进行了进一步表征。在优化条件下，沉积在SiO/Si衬底上的PEN薄膜的电导率可达到10.1 S/cm。据我们所知，这是掺杂PEN薄膜报道过的最高电导率。在塞贝克系数和电导率分别为199 μV/K和9.2 S/cm的PEN/CN6CP薄膜中可实现功率因子为36.4 μW m⁻¹ K⁻²的最佳TE性能。这一结果表明，用强电子受体进行界面掺杂是优化小分子有机半导体TE性能的一种有前途的方法。
