Facile Synthesis of Low-Band-Gap Donor-Acceptor Copolymers Based on Dithieno[3,2-b:2',3'-d]thiophene
A facile and scalable synthetic route to a soluble dithieno[3,2-b:2′,3′-d]thiophene (DTT) unit has been developed, which utilizes a Stille coupling reaction to efficiently synthesize the bisthienyl sulfide intermediate. This simplifies the overall DTT synthesis to only four steps with a 44% yield and facilitates its use as a donor unit in low-band-gap polymers. Solution processable alternating D-π–A-π polymers (DTTBTO and DTTDPP) have been synthesized with DTT as the donor unit and either a benzothiodiazole derivative (BTO) or fused ring 1,4-diketopyrrolo[3,4-c]pyrrole (DPP) serving as the acceptor unit. The ability to tailor the structure of these donor–acceptor systems permits a detailed understanding of structure/property relationships for band-gap engineering, absorbance, Voc, and efficiency to be developed and applied to the design of high-performance organic solar cells.