Improved Synthesis of Thienothiazole and Its Utility in Developing Polymers for Photovoltaics

In response to the structural and electronic limitations of the popular benzo[1,2-b:4,5-b′]dithiophene–thieno[3,4-b]thiophene (PBnDT–TT) polymer series, this study explores the design and synthesis of a thienothiazole (TTz) moiety. The synthesis of TTz was streamlined down to four high-yielding steps, resulting in the new polymer PBnDT–TTz for organic solar cells. By incorporating TTz, a nitrogen is directly introduced into the polymer backbone which tunes the HOMO level and eliminates the reliance on external substituents. Compared to its TT analogue, PBnDT–TTz exhibits the same HOMO level of −5.06 eV and the same Voc of 0.69 eV, yet a higher power conversion efficiency of 2.5%. These promising results demonstrate the benefits of backbone modification and the great potential of TTz in the design of new polymers for organic photovoltaics.