Conjugated polymers for bulk heterojunction polymer solar cells (BHJ PSCs) should be processed with nonhalogenated solvents because of environmental concerns. Here, we report novel regioregular copolymers for high-performance PSCs processed with nonhalogenated solvents. The regioregular copolymers (i.e., rr-PfBT2f4T-2OD and rr-PfBT2f4T-2DT) consist of 3 '',4 '-difluoro-2,2 ':5 ',2 '':5 '',2"'-quaterthiophene (2f4T) with different side chains (2-octadodecyl (OD) and 2-decyltetradecyl (DT)) and 5-fluorobenzo[c][1,2,5]thiadiazole (fBT). The regioregular copolymers with controlled fBT orientation show high solubility in nonhalogenated solvents. Both regioregular copolymers possess suitable energy levels, leading to sufficient energy offsets with a nonfullerene acceptor, BTP-eC11. An rr-PfBT2f4T-2DT:BTP-eC11-blended film exhibited predominant face-on orientation compared to the rr-PfBT2f4T-2OD:BTP-eC11-blended film. In addition, the rr-PfBT2f4T-2DT:BTP-eC11-blended film showed much more balanced hole/electron mobility (mu(h)/mu(e) similar to 4.73) than rr-PfBT2f4T-2OD:BTP-eC11-blended film (mu(h)/mu(e) similar to 45.86). Therefore, rr-PfBT2f4T-2DT:BTP-eC11-based PSCs, processed with 1,2,4-trimethylbenzene, showed a power conversion efficiency of 13.21% which is 60% higher than rr-PfBT2f4T-2OD:BTP-eC11-based PSCs.