Non-fullerene acceptors with branched side chains and improved molecular packing to exceed 18% efficiency in organic solar cells

• Published in: Nature energy Vol. 6; no. 6; pp. 605 - 613
• Main Authors: Li, Chao, Zhou, Jiadong, Song, Jiali, Xu, Jinqiu, Zhang, Huotian, Zhang, Xuning, Guo, Jing, Zhu, Lei, Wei, Donghui, Han, Guangchao, Min, Jie, Zhang, Yuan, Xie, Zengqi, Yi, Yuanping, Yan, He, Gao, Feng, Liu, Feng, Sun, Yanming
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.06.2021; Nature Publishing Group
• Subjects: 639/301/299; 639/4077/909/4101/4096/946; Chain branching; Chains; Charge transport; Design; Economics and Management; Efficiency; Energy; Energy Policy; Energy Storage; Energy Systems; Fullerenes; Molecular chains; Morphology; Packing; Photovoltaic cells; Photovoltaics; Renewable and Green Energy; Solar cells; Steric hindrance; Thin films; Topology
• ISSN: 2058-7546; 2058-7546
• DOI: 10.1038/s41560-021-00820-x

Molecular design of non-fullerene acceptors is of vital importance for high-efficiency organic solar cells. The branched alkyl chain modification is often regarded as a counter-intuitive approach, as it may introduce an undesirable steric hindrance that reduces charge transport in non-fullerene acceptors. Here we show the design and synthesis of a highly efficient non-fullerene acceptor family by substituting the beta position of the thiophene unit on a Y6-based dithienothiophen[3,2-b]-pyrrolobenzothiadiazole core with branched alkyl chains. It was found that such a modification to a different alkyl chain length could completely change the molecular packing behaviour of non-fullerene acceptors, leading to improved structural order and charge transport in thin films. An unprecedented efficiency of 18.32% (certified value of 17.9%) with a fill factor of 81.5% is achieved for single-junction organic solar cells. This work reveals the importance of the branched alkyl chain topology in tuning the molecular packing and blend morphology, which leads to improved organic photovoltaic performance. Molecular design of acceptor and donor molecules has enabled major progress in organic photovoltaics. Li et al. show that branched alkyl chains in non-fullerene acceptors allow favourable morphology in the active layer, enabling a certified device efficiency of 17.9%.