Device performances of BHJ solar cells based on poly[(4,4-didodecyldithieno[3,2-b:2', 3'-d] silole)-2,6-diyl-alt-(2,1,3-benzoxadiazole)-4,7-diyl] and PC(71)BM improve by capping the chain ends with thiophene fragments. This structural modification yields materials that are more thermally robust and that can be used in devices with thicker films important considerations for enabling the mass production of plastic solar cells.