Difluorobenzoxadiazole-Based Polymer Semiconductors for High-Performance Organic Thin-Film Transistors with Tunable Charge Carrier Polarity

A series of difluorobenzoxadiazole-based copolymers are synthesized for applications in high-performance organic thin-film transistors. Four π-spacers with distinct electrical properties, bithiophene, difluorobithiophene, 2-thiophene-2′-thiazole, and bithiazole, are inserted between head-to-head linkage containing bithiophene to promote polymer chain packing. Among the series, polymer containing bithiophene exhibits a unipolar p-channel performance with a substantial hole mobility of 2.92 cm² V⁻¹ s⁻¹, and minor structural modification leads to polymer containing bithiazole showing a remarkable unipolar n-channel performance with an electron mobility of 0.83 cm² V⁻¹ s⁻¹. Through a simple structural modification, such a drastic charge carrier polarity change without sacrificing mobility is elusive in organic thin-film transistor field. Polymer containing hybrid 2-thiophene-2′-thiazole spacer exhibits ambipolarity with encouraging hole/electron mobility of 0.27/0.35 cm² V⁻¹ s⁻¹, and polymer containing difluorobithiophene shows an average hole mobility of 0.53 cm² V⁻¹ s⁻¹. Among the results, p-channel transistors exhibit encouraging device stability. The results demonstrate that difluorobenzoxadiazole is a versatile building block for enabling high-mobility semiconductors with variable charge carrier polarity. X-ray diffraction reveals that all difluorobenzoxadiazole-based polymers have substantial film crystallinity with close π-stacking and varied polymer chain orientation. The structure–property–device performance correlations from this study offer useful insights for materials innovation in organic thin-film transistors.