Alkyl chain engineering on a dithieno[3,2-b:2 ',3 '-d]silole-alt-dithienylthiazolo[5,4-d]thiazole copolymer toward high performance bulk heterojunction solar cells

A new copolymer of dithienosilole and dithienylthiazolo[5,4-d]thiazole with a hexyl side chain on the 4-position of thiophene units was designed and synthesized. Polymer solar cells based on the polymer as a donor and PC70BM as an acceptor demonstrated a power conversion efficiency up to 5.88% with a high fill factor of 71.6%.