2,2′-Bis(trifluoromethyl)biphenyl as a building block for highly ambient-stable, amorphous organic field-effect transistors with balanced ambipolarityElectronic supplementary information (ESI) available: Monomer synthesis, solubility, thermal properties, DFT-optimized molecular geometries, AFM, WAXS ring patterns, SAXS ring patterns and additional figures. See DOI: 10.1039/c5ra25884g

• Main Authors: Chaing, Chi-Jui, Chen, Jyh-Chien, Kuo, Yu-Ju, Tsao, Hsiang-Yen, Wu, Kuan-Yi, Wang, Chien-Lung
• Format: Journal Article
• Published: 21.01.2016
• ISSN: 2046-2069
• DOI: 10.1039/c5ra25884g

Novel conjugated polymers, PBPV-TPA, PBPV-CBZ, PBPV-MEH and PBPV-FLO, consisting of trifluoromethyl-substituted biphenyl (2,2′-bis(trifluoromethyl)biphenyl, CF 3 -BP) as the acceptor with various aromatic donors (triphenylamine TPA, carbazole CBZ, 2-(2-ethylhexyloxy)-5-methoxybenzene MEH and fluorene FLO, respectively) have been successfully synthesized. Their amorphous features, confirmed by wide-angle X-ray scattering, small-angle X-ray scattering and atomic force microscopy, are attributed to lateral side chains on the CBZ, MEH and FLO units, and the propeller geometry of the TPA unit. By integration of CF 3 -BPs into the polymer backbone, the ambipolarities and well-balanced charge mobilities of OFETs based on these polymers were successfully demonstrated. OFETs based on PBPV-FLO exhibit the highest hole mobility of 0.0152 cm 2 V −1 s −1 and electron mobility of 0.0120 cm 2 V −1 s −1 . In addition, these OFETs also exhibit annealing-free characteristics and ambient stability. The OFET performance without encapsulation remained nearly unchanged in ambient conditions for up to 90 days. This could be attributed to the enhanced oxidative stability from their relatively deep HOMO energy levels and better moisture resistance from the trifluoromethyl substitution. Considering the ambipolar, annealing-free and ambient-stable properties of these CF 3 -BP-based amorphous conjugated polymers, the electron-accepting CF 3 -BP unit can be considered as a promising building block in preparing the easily processable conjugated polymers used in high-stability optoelectronic applications. Ambipolar and annealing-free OFETs with high ambient-stability are achieved by introducing 2,2′-bis(trifluoromethyl)biphenyl as the acceptor.