A new donor-acceptor (D-A) conjugated copolymer based on benzo[1,2-b:4,5-b]dithiophene (BDT) and thieno[3,4-c]pyrrole-4,6-dione (TPD) was synthesized via a Stille cross-coupling reaction. A highly conjugated thiophene-based side group, tris(thienylenevinylene) (TTV), was incorporated into each BDT unit to generate the two-dimensional D-A copolymer (PBDT-TTV). An alkoxy-substituted BDT-based TPD copolymer (PBDT-OR) was synthesized using the same polymerization method for comparison. PBDT-TTV thin films produced two distinct absorption peaks. The shorter wavelength absorption (458 nm) was attributed to the BDT units containing the TTV group, and the longer wavelength band (567-616 nm) was attributed to intramolecular charge transfer between the BDT donor and the TPD acceptor. The highest occupied molecular orbital energy levels of PBDT-OR and PBDT-TTV were calculated to be -5.53 and -5.61 eV, respectively. PBDT-TTV thin films harvested a broad solar spectrum covering the range 300-700 nm. A comparison with the PBDT-OR films revealed stronger interchain - interactions in the PBDT-TTV films and, thus, a higher hole mobility. A polymer solar cell device prepared using PBDT-TTV as the active layer was found to exhibit a higher power conversion efficiency than a device prepared using PBDT-OR under AM 1.5 G (100 mW/cm(2)) conditions. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 653-660