非富勒烯异构受体的堆积排列及光伏性能研究

    为了满足人类日益增长的发展需求，寻找和开发绿色可再生能源已迫在眉睫。有机太阳能电池由于其价格低廉、质轻体薄、颜色多样以及可实现建筑一体化处理等优点在新能源材料中逐渐崭露头角。在近20年的努力下，有机太阳能电池的光电转化效率从不到1%迅速提高至超过18%，展现出巨大的发展潜力。其中设计新型的非富勒烯受体材料成为推动电池快速发展的有效策略之一。然而，在发展材料的同时，还需深入研究材料的内在作用机理，尤其是其分子堆积排列和聚集行为对电荷传输的影响，进而帮助设计和开发性能更优异的受体。本论文设计并合成了一系列非富勒烯受体，尤其是结构相似但性能差异较大的异构体，通过单晶衍射等技术手段研究结构与性能之间的关系以及对光伏性能的影响。

    在A-D-A体系，研究了单氯取代对分子性能的影响。实现了端基IC-Cl-m的定位分离，并基于此构筑了氯取代位置异构体ITIC-2Cl-δ和ITIC-2Cl-γ。通过单晶分析可知ITIC-2Cl-δ为线性堆积结构，而ITIC-2Cl-γ为三维网络堆积结构，形成的矩形网络传输通道提供了更多的电子跳跃节点。因此基于ITIC-2Cl-γ的器件获得了更高的光电转化效率（13%）。这表明，即使是单纯的氯取代位置异构，对于提高器件的转换效率也是非常有效的。为进一步探索氯代异构的作用，还合成了对称性不同的位置异构体ITIC-2Cl-β和a-ITIC-2Cl，对其分子堆积排列和光伏性能进行了研究。结果表明不对称策略同样可以诱导分子形成三维网络传输结构，进而表现为更高的迁移率以提高器件的电流和填充因子。本研究通过调整氯原子在端基的取代位置实现了分子堆积模式的转变，从而影响其本身的物理化学性质及其对应的器件性能。

    在A-D-A-D-A体系，进一步研究双氯取代的作用。合成了双氯代位置异构体BTIC-BO4Cl-βγ和BTIC-BO4Cl-βδ。单晶结果表明BTIC-BO4Cl-βδ具有更好的分子平面性，更短的π∙∙∙π距离和更小结合能，形成了最紧密的三维网络堆积结构。基于其的器件实现了更高的迁移率、更少的电荷复合和更低的非辐射能量损失,这导致更高的转化效率17.04%得以实现。研究表明分子排列堆积方式的变化，特别是三维网络骨架大小的变化，对电荷传输有很大的影响，并最终反映在器件效率的差异上。此外，还对此体系三维网络骨架大小的原因进行了分析：与氮原子相连的烷基链的不同导致了分子堆积模式的转变，乙基己基取代的分子形成了大框架的疏松结构，而丁基辛基取代的分子形成了小框架的紧密结构。这影响了三维网络骨架的大小，对应着材料堆积有序性的变化，因此产生了性能差异。

    在氯代的基础上，进一步研究了三氟甲基化对性能的影响。结合上述异构化策略构筑了超窄带隙分子BTIC-CF₃-γ。BTIC-CF₃-γ的单晶结构揭示了此体系的分子堆积与A-D-A体系的区别：协同的H/J聚集形成椭圆形框架的三维网络堆积结构。制备成电池器件后，BTIC-CF₃-γ的转化效率为15.59%，远高于基于氟和氯取代受体器件的效率（13.61%和13.16%），这得益于其红移的吸收和异构化策略带来的相纯度提升。结果表明三氟甲基化是设计窄带隙受体的有效策略。在此基础上与上述氯代策略结合，得到了更高结晶性但仍保持良好溶解性的不对称受体BTIC-2Cl-γCF₃。基于此材料，甲苯处理的二元器件的转化效率达到了16.31%。当PC₇₁ThBM加入后，使转化效率进一步提升至17.12%。此外，制备的半透明器件转化效率为13.06%，光透过率为24.45%，这在建筑一体化的生产中展现出潜在的应用价值。结合氯代和三氟甲基化的不对称策略使材料达到了较理想的聚集状态，具有合适的结晶性且在绿色溶剂中可加工的能力。

    除上述位置异构策略外，还研究了其他同分异构策略。其一，官能团异构：合成了端基官能团异构体BTIC-OCOMe和BTIC-COOMe，制备成器件后，乙酰氧基和甲氧基甲酰基取代体系的光电转化效率分别为8.32%和13.25%，差异主要可归因于三方面：吸收光谱，分子能级和激子拆分效率等。这是对端基位置异构研究的补充。其二，核异构：合成了核顺反异构体BDT_tIC-γCl和BDT_cIC-γCl。理论计算表明两者的能级分布差异较大，表现为吸收光谱的不同。因此，基于BDT_cIC-γCl的器件实现了7.61%的转化效率，比基于BDT_tIC-γCl器件的效率（0.71%）有很大提升。此外，BDT_cIC-γCl纯膜和共混膜中存在更有序的分子堆积，这与其更高的迁移率相符，从而在器件中获得更高的电流。这是对核位置异构研究的补充，有助于对受体材料核设计的理解。

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