Two new donor–acceptor (D–A) polymers composed of benzo[1,2-b:4,5-b′]dithiophene (BDT) as donor and thiadiazolo[3,4-c]pyridine (PyTZ) as acceptor were designed and synthesized. Compared to the polymer based on BDT and 4,7-dithien-2-yl-2,1,3-benzothiadiazole (DTBT), the planarity, energy levels, and band-gaps of the new polymers were fine adjusted by incorporating conjugated alkylthienyl side chains to BDT and substitute a stronger acceptor PyTZ for 2,1,3-benzothiadiazole. The new polymers exhibit broad absorption from 300 to 800nm in both solution and film state. The polymer band gaps and energy levels are close to the optimal values. As a result, power conversion efficiencies (PCEs) of 4.84% and 5.11% were obtained for inverted polymer solar cells based on these new polymers. The PCEs are significantly higher than those of the BDT–DTBT based polymers (2–4%).