Department of Materials Science and Engineering and The Shenzhen Key Laboratory for Printed Organic Electronics , South University of Science and Technology of China , No. 1088, Xueyuan Road , Shenzhen , Guangdong 518055 , China.
Department of Physical Chemistry , University of Málaga , Campus de Teatinos s/n , Málaga 29071 , Spain.
J Am Chem Soc. 2018 May 16;140(19):6095-6108. doi: 10.1021/jacs.8b02144. Epub 2018 Apr 20.
Development of high-performance unipolar n-type organic semiconductors still remains as a great challenge. In this work, all-acceptor bithiophene imide-based ladder-type small molecules BTI n and semiladder-type homopolymers PBTI n ( n = 1-5) were synthesized, and their structure-property correlations were studied in depth. It was found that Pd-catalyzed Stille coupling is superior to Ni-mediated Yamamoto coupling to produce polymers with higher molecular weight and improved polymer quality, thus leading to greatly increased electron mobility (μ). Due to their all-acceptor backbone, these polymers all exhibit unipolar n-type transport in organic thin-film transistors, accompanied by low off-currents (10-10 A), large on/off current ratios (10), and small threshold voltages (∼15-25 V). The highest μ, up to 3.71 cm V s, is attained from PBTI1 with the shortest monomer unit. As the monomer size is extended, the μ drops by 2 orders to 0.014 cm V s for PBTI5. This monotonic decrease of μ was also observed in their homologous BTI n small molecules. This trend of mobility decrease is in good agreement with the evolvement of disordered phases within the film, as revealed by Raman spectroscopy and X-ray diffraction measurements. The extension of the ladder-type building blocks appears to have a large impact on the motion freedom of the building blocks and the polymer chains during film formation, thus negatively affecting film morphology and charge carrier mobility. The result indicates that synthesizing building blocks with more extended ladder-type backbone does not necessarily lead to improved mobilities. This study marks a significant advance in the performance of all-acceptor-type polymers as unipolar electron transporting materials and provides useful guidelines for further development of (semi)ladder-type molecular and polymeric semiconductors for applications in organic electronics.
高性能单极性 n 型有机半导体的发展仍然是一个巨大的挑战。在这项工作中，我们合成了基于全受体噻吩亚胺的梯型小分子 BTI n 和半梯型均聚物 PBTI n（n=1-5），并深入研究了它们的结构-性能关系。研究发现，Pd 催化的 Stille 偶联优于 Ni 介导的 Yamamoto 偶联，可得到具有更高分子量和改善聚合物质量的聚合物，从而大大提高了电子迁移率（μ）。由于其全受体骨架，这些聚合物在有机薄膜晶体管中均表现出单极性 n 型传输特性，同时具有低漏电流（10-10 A）、大的导通/关断电流比（10）和小的阈值电压（约 15-25 V）。单体单元最短的 PBTI1 的μ最高，达到 3.71 cm V s。随着单体尺寸的增大，μ降低了 2 个数量级，达到 PBTI5 的 0.014 cm V s。这种μ的单调下降在其同系物 BTI n 小分子中也得到了观察。这种迁移率下降的趋势与薄膜中无序相的演变很好地吻合，这可以通过拉曼光谱和 X 射线衍射测量来揭示。梯型结构单元的扩展似乎对薄膜形成过程中结构单元和聚合物链的运动自由度有很大的影响，从而对薄膜形貌和电荷载流子迁移率产生负面影响。结果表明，合成具有更多扩展梯型骨架的结构单元不一定会导致迁移率的提高。这项研究标志着全受体型聚合物作为单极性电子传输材料的性能取得了重大进展，为进一步开发（半）梯型分子和聚合物半导体在有机电子中的应用提供了有用的指导。
