An original strategy to construct a new donor-acceptor (D-A)-integrated structure by directly imposing "pull'' unit on the "push'' moiety to form fused ring architecture has been developed, and poly{N-alkyl-carbazole[3,4-c:5,6-c]bis[1,2,5]-thiadiazole-alt-thiophene} (PCBTT) with D-A-integrated structure, in which two 1,2,5-thiadiazole rings are fixed on carbazole in 3-, 4- and 5-, 6-position symmetrically and thiophene is used as bridge, has been synthesized. The interaction between pull and push units has fine tuned the HOMO/LUMO energy levels, and the resulting copolymer covers the solar flux from 300 to 750 nm. The interaction between pull and push units is worth noting that due to the fused five rings inducing strong intermolecular interaction, an extremely short pi-pi stacking distance of 0.32 nm has been achieved for PCBTT both in powder and solid states. This is the shortest pi-pi stacking distance reported for conjugated polymers. Additionally, an obvious intramolecular charge transfer and energy transfer from donor units to acceptor units have been detected in this D-A integration. A moderate-to-high open-circuit voltage of similar to 0.7 V in PCBTT:[6,6]phenyl-C61 butyric acid methyl ester (PCBM) (w/w = 1/2) solar cells is achieved due to the low-lying HOMO energy level of PCBTT. (C) 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 565-574