Xiaowei Zhan’s group, from College of Engineering at Peking University, made new progress in nonfullerene acceptors for organic solar cells (OSCs), revealed butterfly effects in fused-ring electron acceptors (FREAs) and proposed bottom-up design of high-performance FREAs (J. Am. Chem. Soc., DOI: 10.1021/jacs.0c09800).
Since 2006, the Zhan group has been working on nonfullerene acceptors and pioneered the concept of FREAs, represented by the landmark molecule ITIC (Adv. Mater., 2015, 27, 1170–1174, cited 1880 times). Molecular design of FREAs generally adopts a top-down strategy that emphasizes final molecular structure of FREAs while overlooks starting materials and synthesis. However, subtle changes on the starting materials may significantly perturb the chemical structures, physical properties and photovoltaic performance of the resultant FREAs.
Very recently, Zhan’s group revealed butterfly effects in FREAs and presented bottom-up design of high-performance FREAs. They designed and synthesized a series of FREAs based on naphthalene-fused octacyclic cores (NOICs). NOICs have the same end groups and side chains, as well as similar fused-ring cores. The butterfly effects, arising from different methoxy positions in the starting materials, impact design of the final FREAs, as well as their molecular packing, optical and electronic properties, charge transport, film morphology and performance of OSCs. The binary-blend devices based on this NOIC series show power conversion efficiencies varying from 7.15% to 14.1%, due to the different intrinsic properties of the NOIC series, morphologies of blend films, and voltage losses of devices. These results indicate that the butterfly effects resulting from small differences in the starting materials significantly affect the properties of the final FREAs, underscoring the need for bottom-up design for high-performance FREAs.
The research work was supported by the National Nature Science Foundation of China and Basic Research Promotion Project of Peking University.
Molecular structures and device performance of the NOIC series.