Fluorine Substituted Bithiophene Imide-Based n-Type Polymer Semiconductor for High-Performance Organic Thin-Film Transistors and All-Polymer Solar Cells

Bithiophene imide (BTI) is a promising building block for constructing n-type organic semiconductors. The β-positions of thiophene in BTI offer an exceptional opportunity for further structural expansion and optimization. Herein, a novel fluorinated BTI, s-FBTI2, is designed and successfully synthesized, and its incorporation into a polymer backbone led to the resulting semiconductor s-FBTI2-FT with improved polymer backbone planarity enabled by the intramolecular non-covalent S···F interactions and optimized electronic structure attributed to the high electronegativity of F atoms. When applied in organic thin-film transistors (OTFTs), s-FBTI2-FT shows a unipolar n-type transport with a remarkable electron mobility approaching 3.0 cm² V⁻¹ s⁻¹, which is >3-fold higher than that of the polymer analogue without F. Moreover, all-polymer solar cells (all-PSCs) with s-FBTI2-FT as the electron acceptor polymer achieve a power conversion efficiency of 6.50% with a remarkably high open-circuit voltage of 1.04 V, which is substantially greater than that of solar cells based on the nonfluorinated analogue acceptor showing negligible photovoltaic performance. The results demonstrate that s-FBTI-FT is one of best-performing n-type polymer semiconductors reported till today in terms of both OTFT and all-PSC performances, and fluorination offers an effective approach for optimizing optoelectronic properties of BTI-based polymers for device performance improvement.