Solution-processable small molecules for organic solar cells have attracted intense attention for their advantages of definite molecular structures compared with their polymer counterparts. However, the device efficiencies based on small molecules are still lower than those of polymers, especially for inverted devices, the highest efficiency of which is <9%. Here we report three novel solution-processable small molecules, which contain π-bridges with gradient-decreased electron density and end acceptors substituted with various fluorine atoms (0F, 1F and 2F, respectively). Fluorination leads to an optimal active layer morphology, including an enhanced domain purity, the formation of hierarchical domain size and a directional vertical phase gradation. The optimal morphology balances charge separation and transfer, and facilitates charge collection. As a consequence, fluorinated molecules exhibit excellent inverted device performance, and an average power conversion efficiency of 11.08% is achieved for a two-fluorine atom substituted molecule.

中文翻译：

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氟化使能的最佳形态导致倒置的小分子有机太阳能电池的效率超过11％。

与有机聚合物相比，有机太阳能电池的溶液可加工小分子因其具有确定的分子结构的优势而备受关注。但是，基于小分子的器件效率仍然低于聚合物，特别是对于倒置器件，其最高效率＜9％。在这里，我们报告了三个新颖的可溶液处理的小分子，它们包含具有梯度递减的电子密度的π桥和被各种氟原子（分别为0F，1F和2F）取代的末端受体。氟化导致最佳的活性层形态，包括增强的畴纯度，分层畴尺寸的形成和方向性垂直相渐变。最佳形态平衡了电荷的分离和转移，并促进收费。结果，氟化分子表现出优异的反向器件性能，并且被两个氟原子取代的分子的平均功率转换效率达到11.08％。