This work presents a new strategy for the preparation of donor-acceptor conjugated copolymers, in which both donor and acceptor units derive from one mother structure. Benzo[1,2-b:4,5-b']dithiophene-4,8-dione (BQDT) is an electron-deficient unit. From BQDT, benzo[1,2-6:4,5-b']dithiophene (BDT) and benzo[1,2-b:4,5-b']dithiophene-4,8-dione dioxime (BXDT) can be easily derived and serve as electron-donating and another electron-accepting unit, respectively. Based on these three units, poly(BDT-alt-BQDT) (PBQ-C24, with 2-decyltetradecyl side chains) and poly(BDT-alt-BXDT) (PBX-C8, with 2-ethylhexyl side chains) have been designed and synthesized. Their thermal, optical and electrochemical properties have been investigated. PBQ-C24 has a broad absorption spectrum in the range of 300-700 nm, while PBX-C8 can only harvest the light from 300 to 600 nm. However, the bulk heterojunction cell based on the blend of PBX-C8 and [6,6]-phenyl-C-61-butyric acid methyl ester (PC61BM) displays a better performance with a power conversion efficiency of 0.51%. (C) 2013 Elsevier Ltd. All rights reserved.