Title: Systematic Merging of Nonfullerene Acceptor π-Extension and Tetrafluorination Strategies Affords Polymer Solar Cells with >16% Efficiency

Abstract

The end-capping group (EG) is the essential electron-withdrawing component of non-fullerene acceptors (NFAs) in bulk heterojunction (BHJ) organic solar cells (OSCs). The two frequent EG functionalization strategies to enhance OSC per-formance are π-extension and halogenation. To systematically probe their impact in A-DAD-A type NFAs, we designed, syn-thesized, and characterized four such NFAs, BT-BIC, BT-LIC, BT-L4F, and BT-BO-L4F. To assess the relative importance of these strategies, we compare/contrast these NFAs with the baseline A-DAD-A acceptors, Y5 (no π-extension or fluorination), and Y6 (fluorination only). Blending with donor polymers PBDB-T and PBDB-T-2F yields up to 16.6% power conversion efficiency (PCE) in binary inverted OSCs with BT-BO-L4F combining π-extension and halogenation. Multiple techniques, in-cluding UV-Vis-NIR absorption spectroscopy, cyclic voltammetry (CV), single crystal x-ray diffraction (XRD), density func-tional theory (DFT)-level computation, atomic force microscopy (AFM), transmission electron microscopy (TEM), grazing-incidence wide-angle x-ray scattering (GIWAXS), space-charge limited current (SCLC), femtosecond transient absorption (fsTA) spectroscopy, and integrated photocurrent device analysis (IPDA) are applied to assess the impact of these strategies. of all acceptors. When these two factors are combined, the impact on molecular energetics is minimal, whereas the effect on optical absorption is cumulative. Single-crystal diffraction π-π stacking distances indicate that combining π-extension (BT-LIC π-π ≈3.3more » Å) and fluorination (Y6 π-π ≈3.4 Å, Y5 π-π ≈3.6 Å) in BT-(BO)-L4F yields comparable distances (≈3.3 Å) but with multiple intermolecular stackings. Increasing the alkyl substituent length from BT-L4F to BT-BO-L4F significantly alters the packing motif and eliminates the EG·core interactions of BT-L4F. Electronic structure computations reveal some of the largest NFA π-π electronic couplings observed to date, 103.8 meV in BT-L4F and 47.5 meV in BT-BO-L4F. Computed elec-tronic reorganization energies, 132 and 133 meV for BT-L4F and BT-BO-L4F, respectively, are also lower than Y6 (150 meV). Morphological information from AFM and TEM indicates that blends fabricated from the π-extended acceptors have similar surface roughness, while GIWAXS shows preferential π-face-on orientation in the blends, regardless of the side chain. Both fluorination and π-extension increase NFA crystallinity, while overall film crystallinity is influenced by EG··EG stacking and alkyl chain length. fsTA and impedance based IPDA indicate that π-extension modifies the phase separation to enhance film ordering and carrier mobility, while fluorination suppresses unimolecular recombination. In conclusion, this systematic study highlights the synergistic effects of NFA π-extension and fluorination in affording efficient OSCs and provides insights into designing next-generation materials.« less

Authors:

Li, Guoping  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-8193-9639"

Zhang, Xiaohua ^[2]; Jones, Leighton O.  ^[1];

• Search DOE PAGES for author "Jones, Leighton O."
• Search DOE PAGES for ORCID "0000-0001-6657-2632"

Alzola, Joaquin M. ^[1]; Mukherjee, Subhrangsu  ^[3];

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• Search DOE PAGES for ORCID "0000-0002-5479-3750"

Feng, Liang-wen  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-0699-3747"

Zhu, Weigang  ^[4];

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• Search DOE PAGES for ORCID "0000-0002-5888-4481"

Stern, Charlotte L.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-9491-289X"

Huang, Wei  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-0973-8015"

Yu, Junsheng  ^[5];

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Sangwan, Vinod K.  ^[6];

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• Search DOE PAGES for ORCID "0000-0002-5623-5285"

DeLongchamp, Dean M. ^[3]; Kohlstedt, Kevin L.  ^[1];

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• Search DOE PAGES for ORCID "0000-0001-8045-0930"

Wasielewski, Michael R.  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-2920-5440"

Hersam, Mark C.  ^[7];

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• Search DOE PAGES for ORCID "0000-0003-4120-1426"

Schatz, George C.  ^[1];

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• Search DOE PAGES for ORCID "0000-0001-5837-4740"

Facchetti, Antonio  ^[8];

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• Search DOE PAGES for ORCID "0000-0002-8175-7958"

Marks, Tobin J.  ^[7]

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• Search DOE PAGES for ORCID "0000-0001-8771-0141"

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+ Show Author Affiliations

1. Department of Chemistry, the Center for Light Energy Activated Redox Processes (LEAP), and the Materials Research Center (MRC), Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
2. Department of Chemistry, the Center for Light Energy Activated Redox Processes (LEAP), and the Materials Research Center (MRC), Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States, State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China (UESTC), Chengdu, Sichuan 610054, P.R. China
3. Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
4. Department of Chemistry, the Center for Light Energy Activated Redox Processes (LEAP), and the Materials Research Center (MRC), Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States, Tianjin Key Laboratory of Molecular Optoelectronic Sciences (TJ-MOS), Department of Chemistry, School of Science, Tianjin University, Tianjin 300072, China
5. State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China (UESTC), Chengdu, Sichuan 610054, P.R. China
6. Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States
7. Department of Chemistry, the Center for Light Energy Activated Redox Processes (LEAP), and the Materials Research Center (MRC), Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States, Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States
8. Department of Chemistry, the Center for Light Energy Activated Redox Processes (LEAP), and the Materials Research Center (MRC), Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States, Flexterra Corporation, 8025 Lamon Avenue, Skokie, Illinois 60077, United States

Publication Date:

Tue Apr 13 00:00:00 EDT 2021

Research Org.:

Northwestern Univ., Evanston, IL (United States)

Sponsoring Org.:

U.S. Office of Naval Research; USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division

OSTI Identifier:

1859327

Alternate Identifier(s):

OSTI ID: 1798344

Grant/Contract Number:  

SC0001059; N00014-20-1-2116; AC02-05CH11231; AC02-06CH11357

Resource Type:

Published Article

Journal Name:

Journal of the American Chemical Society

Additional Journal Information:

Journal Name: Journal of the American Chemical Society Journal Volume: 143 Journal Issue: 16; Journal ID: ISSN 0002-7863

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Crystal structure; Molecules; Coupling reactions; Solar cells; Halogenation