The development of novel small-molecule donor is crucial for achieving highly efficient small-molecule organic solar cells (SM-OSCs). In this study, two small-molecule donors, B3TR and B2, were designed and synthesized. In comparison to B3TR, the skeleton of B2 includes an additional benzo[1,2-b:4,5-b']dithiophene (BDT) unit, but lacks two alkylated thiophene units. Although both small-molecule donors exhibit similar absorption profiles in solution, B2 demonstrates stronger crystallinity and lower energetic disorder than B3TR. When blended with the non-fullerene acceptor BTP-eC9, the B2:BTP-eC9 film exhibits a smaller π-π distance and a more favorable bulk heterojunction morphology. Interestingly, with an increase in solvent vapor annealing (SVA) time, B3TR shows a significant redshift in the absorption edge in the B3TR:BTP-eC9 film and an upshifted HOMO level. In contrast, B2 does not exhibit redshifts in the absorption edge in the B2:BTP-eC9 film and maintains an unchanged HOMO level. Consequently, the as-cast B3TR:BTP-eC9-based device achieves a PCE of 2.36%, with an open-circuit voltage (VOC) of 0.870 V. After SVA treatment, the B3TR:BTP-eC9-based SM-OSC attains a PCE of 14.8% with a significantly reduced VOC of 0.809 V. In contrast, the as-cast B2:BTP-eC9-based device exhibits a significantly high PCE of 9.8% with a VOC of 0.876 V. After SVA treatment, the B2:BTP-eC9-based device produces a superior PCE of 17.1%, with a slightly reduced VOC of 0.861 V. This study indicates that the development of highly crystalline donor materials is one of the promising strategies for achieving high-performance SM-OSCs.

中文翻译：

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高结晶供体使小分子有机太阳能电池的效率超过 17%

新型小分子供体的开发对于实现高效小分子有机太阳能电池（SM-OSC）至关重要。在本研究中，设计并合成了两种小分子供体B3TR和B2。与B3TR相比，B2的骨架包含一个额外的苯并[1,2-b:4,5-b']二噻吩（BDT）单元，但缺少两个烷基化噻吩单元。尽管两种小分子供体在溶液中表现出相似的吸收曲线，但 B2 比 B3TR 表现出更强的结晶度和更低的能量无序。当与非富勒烯受体 BTP-eC9 共混时，B2:BTP-eC9 薄膜表现出更小的 π-π 距离和更有利的本体异质结形貌。有趣的是，随着溶剂蒸气退火 (SVA) 时间的增加，B3TR:BTP-eC9 薄膜中的吸收边显示出显着的红移，并且 HOMO 能级上移。相比之下，B2:BTP-eC9 薄膜中的吸收边没有出现红移，并保持不变的 HOMO 能级。因此，基于 B3TR:BTP-eC9 的铸态器件的 PCE 为 2.36%，开路电压 (VOC) 为 0.870 V。经过 SVA 处理后，基于 B3TR:BTP-eC9 的 SM-OSC 达到PCE 为 14.8%，VOC 显着降低为 0.809 V。相比之下，基于 B2:BTP-eC9 的铸态器件表现出 9.8% 的显着高 PCE，VOC 为 0.876 V。经过 SVA 处理后，B2 ：基于 BTP-eC9 的器件产生了 17.1% 的优异 PCE，VOC 略有降低，为 0.861 V。这项研究表明，开发高度结晶的供体材料是实现高性能 SM-OSC 的有前途的策略之一。