Abstract Three simple structured DA copolymers, PBTBTz-1, PBTBTz-2, and PBTBTz-3, containing bithiophene (BT) donor unit and bithiazole (BTz) acceptor unit with different alkyl chain length were synthesized by the Pd-catalyzed Stille-coupling method. The copolymers were characterized by thermogravimetric analysis, UV–vis absorption, electrochemical cyclic voltammetry, and photovoltaic measurements. The results indicate that the introduction of ...