Crucial Role of Fluorine in Fully Alkylated Ladder-Type Carbazole-Based Nonfullerene Organic Solar Cells

Qiao He; Munazza Shahid; Xuechen Jiao; Eliot Gann; Flurin D Eisner; Tingmang Wu; Zhuping Fei; Thomas D Anthopoulos; Christopher R McNeill; Martin Heeney

doi:10.1021/acsami.0c00981

Crucial Role of Fluorine in Fully Alkylated Ladder-Type Carbazole-Based Nonfullerene Organic Solar Cells

ACS Appl Mater Interfaces. 2020 Feb 26;12(8):9555-9562. doi: 10.1021/acsami.0c00981. Epub 2020 Feb 12.

Authors

Affiliations

¹ Department of Chemistry and Centre for Plastic Electronics, White City Campus , Imperial College London , London W12 0BZ , U.K.
² Department of Chemistry, School of Science , University of Management and Technology , Lahore 54770 , Pakistan.
³ Department of Materials Science and Engineering , Monash University , Melbourne , Victoria 3800 , Australia.
⁴ Materials Measurement Science Division , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States.
⁵ Department of Physics and Centre for Plastic Electronics, South Kensington Campus , Imperial College London , London SW7 2AZ , U.K.
⁶ Institute of Molecular Plus, Tianjin Key Laboratory of Molecular Optoelectronic Science , Tianjin University , Tianjin 300072 , P. R. China.
⁷ KAUST Solar Centre , King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900 , Saudi Arabia.

PMID: 31999092
DOI: 10.1021/acsami.0c00981

Abstract

Two fused ladder-type nonfullerene acceptors, DTCCIC and DTCCIC-4F, based on an electron-donating alkylated dithienocyclopentacarbazole core flanked by electron-withdrawing nonfluorinated or fluorinated 1,1-dicyanomethylene-3-indanone (IC or IC-4F), are prepared and utilized in organic solar cells (OSCs). The two new molecules reveal planar structures and strong aggregation behavior, and fluorination is shown to red-shift the optical band gap and downshift energy levels. OSCs based on DTCCIC-4F exhibit a power conversion efficiency of 12.6%, much higher than that of DTCCIC-based devices (6.2%). Microstructural studies reveal that while both acceptors are highly crystalline, bulk heterojunction blends based on the nonfluorinated DTCCIC result in overly coarse domains, while blends based on the fluorinated DTCCIC-4F exhibit a more optimal nanoscale morphology. These results highlight the importance of end group fluorination in controlling molecular aggregation and miscibility.

Keywords: carbazole; fluorine effect; fully alkylated side chains; nonfullerene acceptors; organic solar cells.