We recently reported that a donor-acceptor (D-A) type copolymer based on our developed tetrafluoro-substituted benzodioxocyclohexene-annelated thiophene (C 0 (F 4 )) as an acceptor unit and dithienosilole (DTS) as a donor unit shows low photovoltaic characteristics due to the strong electron-accepting nature of C 0 (F 4 ). Here we show that the incorporation of 3alkylthiophene spacer unit into DTS-C 0 (F 4 ) framework is an effective approach to tune frontier molecular orbital energy levels. Organic solar cells based on blend films of newly synthesized D-A copolymers and [6,6]-phenyl-C 71 -butyric acid methyl ester showed improved photovoltaic responses with a power conversion efficiency of up to 4.83%. This result indicates that the C 0 (F 4 ) unit can be an effective acceptor unit for D-A copolymers.