高性能聚合物光电探测器的分子设计

Owing to their high designability over properties, solution-processibility and flexibility, conjugated polymers have been regarded as a class of prospective materials for new generation optoelectronics. Conjugated polymers can be applied as active materials for photodetectors, which are important for environmental monitoring, data communication, image sensing, and so on. Recently, the performance of polymer photodetectors has been approached to that of their inorganic counterparts. The development of new molecular structure and the rational design of conjugated polymers are essential to further improve the performance of polymer-based photodetectors for practical applications. In this proposal, a side chain modification approach is developed to improve the photodetectivity and other performances of polymer photodetectors. Based on backbones of the polymers with high photovoltaic performance, the specific side chains could tune the surface energy and the interaction between the polymer and the substrate, which would facilitate the effective vertical-phase-segregation of the components in the active layer and selectively control charge injection, leading to the decrease of dark current density. We will focus on conjugated polymers with 3,4-ethylenedioxythiophene (EDOT) and its analogues as side chains, as well as polymers with different surface energy side chains. Optoelectric performance of those polymers will be studied as donor materials in polymer photodetectors. The relationship between molecular structure and optoelectric properties will be revealed, which could benefit the design of the conjugated polymers in related optoelectronic fields.

因其性能的高度可设计性、可溶液处理和柔性轻薄等优势，共轭聚合物是非常有前景的新一代光电材料。共轭聚合物可以作为活性材料应用于光电探测器。它对于环境监测、数据通讯以及图像感应等非常重要。最近聚合物光电探测器在性能上已经逐渐接近无机材料。为进一步提高光电探测器的性能以达到应用水平，发展新的分子设计方向、理性设计共轭聚合物至关重要。本项目拟以具有高效光电转换性能的聚合物的主链结构为基础，通过特定基团修饰侧链策略，来调整聚合物的表面能以及其与衬底的相互作用，促进活性层组分的有效垂直相分离，从而控制电荷的选择性注入，降低暗电流,以提高聚合物光电探测器的光探测度等性能。项目将重点研究3,4-乙撑二氧噻吩及其类似结构以及具有不同表面能的侧链对聚合物材料性能的影响，考察这些聚合物作为光电探测器活性层给体材料时的光电表现，揭示分子结构对共轭聚合物材料的基本性能的影响规律，为有机电子相关方向提供理论设计依据。

与聚合物太阳能电池相似，聚合物光电探测器也通常采用本体异质结结构。这种结构有利于活性材料对光子的吸收和电荷分离，实现高外量子效率（即EQE）和响应率。然而，由于相分离难以控制，异质结结构的二极管性能不佳，造成负偏压下暗电流较大，从而导致噪音升高，探测度下降。本项目主要研究了3,4-乙撑二氧噻吩(EDOT)及其类似结构作为共轭侧链修饰对聚合物光电探测器性能的影响。研究发现基于EDOT侧链的聚合物较噻吩侧链的聚合物，其器件负偏压下的暗电流密度降低了2个数量级以上，而其光伏性能没有显著下降，从而实现了探测度的提高。EDOT侧链聚合物在正极的界面的富集是反向暗电流密度下降的主要原因。其他含氧噻吩共轭侧链修饰也有一定的效果，但不如EDOT。项目成果为高探测度的聚合物光电探测器的开发提供了新的分子设计方法。