Simultaneous Tuning of Alkyl Chains and End Groups in Non-fused Ring Electron Acceptors for Efficient and Stable Organic Solar Cells
Dou Luo, Zhengyan Jiang, Chengwei Shan, Lanqing Li, Chenghao Duan, Qian Liu, Zhaojin Wang, Kai Wang, Baomin Xu, Aung Ko Ko Kyaw
Abstract
Fine-tuning the alkyl chains and end groups of non-fused ring electron acceptors (NFREAs) plays vital roles in the promotion of charge transfer (CT) and power conversion efficiency (PCE). In this work, we developed a series of A–D–A′–D–A-type NFREAs, which possess the same terminals (A), the cyclopentadithiophene unit (D), and the thieno[3,4-c]pyrrole-4,6-dione (A′). Despite the subtle difference in side chains and halogenated end groups, the six acceptors exhibit a considerable difference in the efficiency and device stability of the organic solar cells (OSCs). Among the molecules, chlorinated NFREAs show a broader light absorption than the fluorinated ones do. Compared with C8C8–4F (1-octylnonyl and fluorination) and C6C4–4Cl (2-butyloctyl and chlorination), C8C8–4Cl (1-octylnonyl and chlorination) exhibits a lower highest occupied molecular orbital level, higher electron mobility, and denser molecular packing. The OSCs based on PM6:C8C8–4Cl yield the best PCE of 14.11%, which is attributed to the faster charge transport, high miscibility, and preferable morphology. Moreover, the PM6:C8C8–4Cl devices retain 91.1% of the initial PCE after being placed in air with 67% relative humidity for 50 days. This work shows that the simultaneous optimization of side chains and end groups facilitates the CT and improves the stability in the OSCs, offering a novel view into the molecular design of A–D–A′–D–A-type NFREAs.