In this work, we demonstrate the chemical optimization of benzo[1,2-b:4,5-b']dithiophene (BDT)-5,6-di-fluorobenzo-[2,1,3]thiadiazole (FBT) D-A alternating copolymer for obtaining the efficient polymeric donors for the environment-friendly solution processed polymer solar cells (PSCs). Three polymers PBTF, PBTTF-C-6 and PBTTF-H, in which one or two alky thiophene units are inserted into the backbone of BDT-FBT alternating copolymer, present much different performances either in the PSCs processed from halogenated solvent and additive or in the PSCs processed from non-halogenated solvent and additive. With an alky thiophene and a bare thiophene as the spacer, PBTTF-H performs best among the three. Especially when the devices processed from 1,2,4-trimethylbenzene and diphenyl ether, in which the highest PCE of 6.80% is achieved with a V-OC of 0.77 V, a J(SC) of 13.67 mA cm(-2) and a FF of 64.2%. We think these results will cast light on developing new polymeric donors of the green-solvent-processed PSCs.