A 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 Stile 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-pi-A-pi 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, V(oc), and efficiency to be developed and applied to the design of high-performance organic solar cells.