Two donor/acceptor (D/A)-based benzo[1,2-b:4,5-b']dithiophene-alt-2,3-biphenyl quinoxaline copolymers of P1 and P2 were synthesized pending different functional groups (thiophene or triphenylamine) in the 4-positions of phenyl rings. Their thermal, photophysical, electrochemical, and photovoltaic properties, as well as morphology of their blending films were investigated. The poly(4,8-bis((2-ethyl-hexyl)oxy)benzo[1,2-b:4,5-b'] dithiophene)-alt-(2,3-bis(4'-bis(N,N-bis(4-(octyloxy) phenylamino)- 1,1'-biphen-4-yl)quinoxaline) (P2) exhibited better photovoltaic performance than poly(4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b'] dithiophene)-alt-(2,3-bis(4-(5-octylthiophen-2-yl)phenyl)quinoxaline) (P1) in the bulk-heterojunction polymer solar cells with a configuration of ITO/PEDOT:PSS/polymers: [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM)/LiF/Al. A power conversion efficiency of 3.43%, an open-circuit voltage of 0.80 V, and a short-circuit current of 9.20 mA cm-2 were achieved in the P2-based cell under the illumination of AM 1.5, 100 mW cm-2. Importantly, this power conversion efficiency level is 2.29 times higher than that in the P1-based cell. Our work indicated that incorporating triphenylamine pendant in the D/A-based polymers can greatly improved the photovoltaic properties for its resulting polymers.