In this article, pendent thiophene (2-butyl-5-octylthiophene) side chain is used to modify the backbone of the polymers containing benzo[1,2-b:4,5-b]dithiophene (BDT) and thieno[3,4-c]pyrrole-4,6-dione (TPD). Compared with the dodecyloxy side-chained polymer (P1), pendent thiophene-based polymers (P2 and P3) show similar number-average molecular weight (M-n), polydispersity index, thermal stability (T-d approximate to 334-337 degrees C), and optical band gaps) (approximate to 1.8 eV). Polymer (P2)-based BDT with pendent thiophene and ethylhexyl-modified TPD shows relatively low-lying HOMO energy level (-5.52 eV) and nearly 1 V high open circuit voltage (V-OC). The polymer solar cell devices based on three copolymers show power conversion efficiencies from 2.01% to 4.13%. The hole mobility of these polymers tested by space charge limited current method range from 3.4 x 10(-4) to 9.2 x 10(-4) cm(2)V(-1)s(-1). (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1558-1566