Design of benzodithiophene-diketopyrrolopyrrole based donor–acceptor copolymers for efficient organic field effect transistors and polymer solar cells

Abstract

Three low-band-gap donor–acceptor (D–A) copolymers containing benzo(1,2-b:4,5-b′)dithiophene (BDT), 3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (TDP) or 3,6-di(furan-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (FDP) were designed and synthesized. Their thermal stability, optical and electrochemical properties, device performances for organic field effect transistors (OFETs) and polymer solar cells were systematically investigated. The device performances were significantly enhanced by the introduction of conjugated alkylthienyl side chains to the BDT core and the substitution of thiophene with furan moieties in polymer backbone. Compared to alkoxy side chains, conjugated alkylthienyl chains resulted in higher coplanarity, increased thermal stability (T_d increased from 364 °C to 417 °C) and a lower HOMO level (from −5.10 eV to −5.24 eV). The incorporation of furan evidently improved the polymer solubility, leading to a finer phase separation morphology as proved by atomic force microscopy and transmission electron microscopy. After optimization, the designed polymer showed excellent performance in both OFETs and PSCs with an optimal hole mobility of 0.16 cm² V⁻¹ s⁻¹ and a high power conversion efficiency of 5.54%.