Spiro Linkage as an Alternative Strategy for Promising Nonfullerene Acceptors in Organic Solar Cells |
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Authors: | Xiao‐Feng Wu Wei‐Fei Fu Zheng Xu Minmin Shi Feng Liu Hong‐Zheng Chen Jun‐Hua Wan Thomas P. Russell |
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Affiliation: | 1. Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Hangzhou, P. R. China;2. State Key Laboratory of Silicon Materials, MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, P. R. China;3. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA;4. Polymer Science and Engineering Department, University of Massachusetts, Amherst, MA, USA |
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Abstract: | This work focuses on developing diketopyrrolopyrrole (DPP)‐based small molecular nonfullerene acceptors for bulk heterojunction (BHJ) organic solar cells. The materials, SF‐DPP s, have an X‐shaped geometry arising from four DPP units attached to a spirobifluorene (SF) center. The spiro‐dimer of DPP‐fluorene‐DPP is highly twisted, which suppresses strong intermolecular aggregation. Branched 2‐ethylhexyl (EH), linear n‐octyl (C8), and n‐dodecyl (C12) alkyl sides are chosen as substituents to functionalize the N,N‐positions of the DPP moiety to tune molecular interactions. SF‐DPPEH , the best candidate in SF‐DPP s family, when blended with poly(3‐hexylthiophene) (P3HT) showed a moderate crystallinity and gives a Jsc of 6.96 mA cm?2, Voc of 1.10 V, a fill factor of 47.5%, and a power conversion efficiency of 3.63%. However, SF‐DPPC8 and SF‐DPPC12 exhibit lower crystallinity in their BHJ blends, which is responsible for their reduced Jsc. Coupling DPP units with SF using an acetylene bridge yields SF‐A‐DPP molecules. Such a small modification leads to drastically different morphological features and far inferior device performance. These observations demonstrate a solid structure–property relationship by topology control and material design. This work offers a new molecular design approach to develop efficient small molecule nonfullerene acceptors. |
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Keywords: | diketopyrrolopyrrole nonfullerene acceptors nonplanarity organic solar cells spirobifluorenes |
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