Understanding the Impact of Fluorine Substitution on the Photovoltaic Performance of Block Copolymers

Abstract

Fluorine substitution was applied to the donor and acceptor segments of block copolymers to understand the impact of molecular structure on photovoltaic block copolymers and explore efficient materials for single-component organic solar cells (SCOSCs). Along this line, three fluorinated block copolymers, namely PBDB-T-b-PTYF6, PM6-b-PTY6, and PM6-b-PTYF6, derived from PBDB-T-b-PTY6 were designed and synthesized. The UV–Vis absorption, energy level, and thin-film morphology of these block copolymers were systematically characterized. All fluorinated block copolymers show narrow bandgap and improved crystallinity. An enhanced open-circuit voltage was observed in the SCOSC based on PM6-b-PTY6. However, SCOSCs based on all fluorinated block copolymers exhibited low short-circuit current due to energy level mismatch and therefore had low power conversion efficiency at around 4%. By contrast, the SCOSCs based on control block copolymer PBDB-T-b-PTY6 exhibited the highest power conversion efficiency approaching 10%, with a high short-circuit current of 18.57 mA/cm². Our study was the first to perform fluorination on photovoltaic block copolymers and provides insight into precisely controlling the polymer structure and understanding the structure–property relationship in SCOSCs based on block copolymers.

Keywords

Block copolymer / Fluorine substitution / Single-component organic solar cells / Morphology

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