New amorphous semiconducting copolymers containing fluorene and thiophene moieties for organic thin-film transistors

Abstract

New amorphous semiconducting materials consisting of fluorene-based thiophene copolymers, poly(2-(5-(9,9-dibutyl-9 H-fluoren-2-yl)-3-hexylthiophen-2-yl)-5-(3-hexylthiophen-2-yl)thieno[3,2-b]thiophene) P1 and poly(2-(5-(9,9-dibutyl-9 H-fluoren-2-yl)-4-hexylthiophen-2-yl)-5-(4-hexylthiophen-2-yl)thieno[3,2-b]thiophene) P2, have been successfully synthesized via a palladium-catalyzed Suzuki coupling reaction. The number-average molecular weights (M_n) of P1 and P2 were found to be 18 300, and 15 800, respectively. These polymers dissolve in common organic solvents such as chloroform, chlorobenzene, and toluene. The UV-vis absorption maxima of P1 and P2 appeared at 436 and 427 nm in solution and 441 and 431 nm in the film state, respectively. X-Ray diffraction (XRD) analysis showed no reflection peaks indicating amorphous collections of randomly oriented polymer chains. Atomic force microscopy (AFM) images of P1 and P2 showed amorphous film morphologies. Field-effect transistor mobilities of stable amorphous OTFTs of P1 and P2 under ambient conditions have been achieved up to 5.4 × 10⁻⁴ cm²V⁻¹ s⁻¹ and 1.6 × 10⁻⁴ cm²V⁻¹ s⁻¹, respectively. The high stability and mobility of fluorene-based thiophene copolymers in the amorphous state make them a new family of promising candidates for organic thin-film transistors.