A polythiophene derivative with octyl diphenylamine-vinylene side chains: synthesis and its applications in field-effect transistors and solar cells

A new polythiophene derivative with octyl diphenylamine-vinylene conjugated side chains, DPAV-PT, was synthesized by the Stille coupling reaction, and characterized by ¹H NMR, GPC, TGA, UV-Vis absorption spectroscopy, and cyclic voltammetry. The copolymer is readily soluble in the common organic solvents and exhibits good thermal stability with 5% weight loss temperature of 267 °C. DPAV-PT possesses a broad absorption band at 300–650 nm (with an optical bandgap of 1.85 eV). Cyclic voltammetry displays a HOMO energy level of −5.01 eV. The weight average molecular weight (M_w) of DPAV-PT is 3.1 × 10⁴ with the polydispersity index of 1.3. A polymer solar cell with the configuration of ITO/PEDOT:PSS/DPAV-PT:PCBM (1 : 1 w/w)/Ca/Al has a power conversion efficiency of 0.7% under the illumination of AM1.5, 100 mW cm⁻². The field effect hole mobility of the polymer reached 6.1 × 10⁻⁴ cm² V⁻¹ s⁻¹ with an on/off ratio of 10³ and a threshold voltage of −7 V after 180 °C annealing.