Two donor-acceptor (D-A) copolymers, PzNDTDTBT and PzNDTDTBO, using 4,9-bis(2-ethylhexyloxy)naphtho[1,2-b:5,6-b']dithiophene as an electron-rich unit and benzodiathiazole (BT) or benzoxadiazole(130) as an electron-deficient one, were designed and synthesized via a Pd-catalyzed Stifle-coupling method. The acceptor units were varied from BT to BO for adjusting the energy levels and optimizing the structures of polymers. Both copolymers possess good solubility, high thermal stability, broad absorption, and low bandgap and exhibit not only high field-effect mobilities but also high photovoltaic properties. The hole mobilities reach 0.43 and 0.34 cm(2) V-1 s(-1) for PzNDTDTBT and PzNDTDTBO film, respectively. Bulk heterojunction solar cells fabricated by using PzNDTDTBT or PzNDTDTBO as electron donor and PC71BM as acceptor show a power conversion efficiency of 3.22% and 5.07%, respectively, under illumination of AM1.5G, 100 mW cm(-2). Both the hole mobilities and PCEs are among the highest values in the current reports based on naphthodithiophene-based polymers, indicating that "zigzag" naphthodithiophene-based D-A copolymers are very promising for application as solution-processable organic semiconductors in optoelectronic devices.