Bandgap Narrowing in Non‐Fullerene Acceptors: Single Atom Substitution Leads to High Optoelectronic Response Beyond 1000 nm |
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Authors: | Jaewon Lee Seo‐Jin Ko Martin Seifrid Hansol Lee Benjamin R Luginbuhl Akchheta Karki Michael Ford Katie Rosenthal Kilwon Cho Thuc‐Quyen Nguyen Guillermo C Bazan |
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Institution: | 1. Center for Polymers and Organic Solids, Department of Chemistry and Department of Biochemistry, University of California at Santa Barbara, Santa Barbara, CA, USA;2. Center for Advanced Soft Electronics, Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, Korea |
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Abstract: | Two narrow bandgap non‐fullerene acceptors (NBG‐NFAs), namely, COTIC‐4F and SiOTIC‐4F, are designed and synthesized for the fabrication of efficient near‐infrared organic solar cells (OSCs). The chemical structures of the NBG‐NFAs contain a D′‐D‐D′ electron‐rich internal core based on a cyclopentadithiophene (or dithienosilole) (D) and alkoxythienyl (D′) core, end‐capped with the highly electron‐deficient unit 2‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene)malononitrile (A), ultimately providing a A‐D′‐D‐D′‐A molecular configuration that enhances the intramolecular charge transfer characteristics of the excited states. One can thereby reduce the optical bandgap (Egopt) to as low as ≈1.10 eV, one of the smallest values for NFAs reported to date. In bulk‐heterojunction (BHJ) OSCs, NBG‐NFA blends with the polymer donor PTB7‐Th yield power conversion efficiencies (PCE) of up to 9.0%, which is particularly high when compared against a range of NBG BHJ blends. Most significantly, it is found that, despite the small energy loss (Egopt ? eVOC) of 0.52 eV, the PTB7‐Th/NBG‐NFA bulk heterojunction blends can yield short‐circuit current densities of up to 22.8 mA cm?2, suggesting that the design and application of NBG‐NFA materials have substantial potential to further improve the PCE of OSCs. |
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Keywords: | near‐infrared optoelectronics non‐fullerene acceptors organic solar cells |
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