Journal
ENERGY & ENVIRONMENTAL SCIENCE
Volume 15, Issue 2, Pages 645-659Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/d1ee03225a
Keywords
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Funding
- U.S. Office of Naval Research [N00014-20-1-2116]
- U.S. Department of Commerce, National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design Award [70NANB10H005]
- Northwestern University Materials Research Science and Engineering Center Award [NSF DMR-1720139]
- DOE [DE-AC02-06CH11357]
- U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-FG02-99ER14999]
- Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource [NSFECCS-1542205, NSF NNCI-1542205]
- Northwestern University Materials Research Science and Engineering Center [NSF DMR-1720139]
- Northwestern U.S. National Science Foundation (NSF) [NSF CHE1048773]
- State of Illinois
- International Institute for Nanotechnology (IIN)
- Department of Energy [DE-AC02-05CH11231]
- DOE Office of Science [DE-AC02-06CH11357, DE-SC0012704]
- MRSEC Program of the Materials Research Center at Northwestern University [NSF DMR-1720139]
- Open Foundation of State Key Laboratory of Electronic Thin Films and Integrated Devices [KFJJ202001]
- Office of the Provost
- Office for Research
- Northwestern University Information Technology
- Institute for Sustainability and Energy at Northwestern
- Office of the Vice President for Research at Northwestern
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This study compares two types of end group fluorination patterns on Y6-based A-DAD-A cores, resulting in highly efficient NFAs: direct skeletal fluorination (BTF) and indirect trifluoromethyl fluorination (BTFM). The performance trends of BTF vs. BTFM OSCs can be correlated with diffraction-derived differences in molecular packing. DFT reveals low internal reorganization energies and high electronic coupling between NFA dimers, providing extended 3D charge transport networks in thin film crystalline domains.
The rational molecular design of non-fullerene acceptors (NFAs) in organic solar cells (OSCs) can profoundly influence the photovoltaic (OPV) performance. To date, NFA fluorination has proven beneficial to cell performance. However, there is a lack of comprehensive understanding of how various fluorination modalities influence film morphology, carrier mobility, molecular packing, other structural properties, electronic structure, exciton separation, and charge transport, that determine ultimate cell efficiency. Here, we compare two types of end group (EG) fluorination patterns on Y6-based A-DAD-A cores, resulting in highly efficient NFAs: direct skeletal fluorination (BTF) and indirect trifluoromethyl fluorination (BTFM). These two patterns induce distinctive behaviors in the active layer blends with a chlorinated donor polymer D18-Cl and the additive, 1-chloronaphthalene, affording high PCE values of 17.30% (BTF + additive) and 17.10% (BTFM, no-additive). The BTFvs.BTFM OSC performance trends can be correlated with diffraction-derived differences in molecular packing. Density functional theory (DFT) reveals remarkably low internal reorganization energies and high electronic coupling between NFA dimers, greater and more numerous than in other NFAs reported to date, thus providing extended 3D charge transport networks in the thin film crystalline domains. Transient absorption spectroscopy reveals that hole transfer from the acceptor to the donor occurs in BTF and BTFM cells is further clarified by recombination dynamics analysis using in situ photocurrent and impedance spectroscopy. Overall, this work provides guidance for developing new NFAs via direct and indirect fluorination strategies for high efficiency OSCs.
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