A new soluble polythiophene copolymer with thiophene-vinylene conjugated side chain poly[3-(5'-octylthienylenevinyl) thiophene]-thiophene (POTVTh-Th) was successfully synthesized and characterized using NMR, UV-visible spectroscopy, etc. To study the photovoltaic property of the copolymer, photovoltaic device of ITO/PEDOT:PSS/POTVTh-Th:[6,6]-phenyl C61-butyric acid methyl ester (PC61BM) (weight ratio being 1 : 1)/LiF/Al was fabricated, in which POTVTh-Th acted as the electron donor in the active layer. Under 100 mW/cm(2) AM 1.5G simulated solar emission, the open-circuit voltage and the short-circuit current density of the device were 0.58 V and 2.50 mA/cm(2), respectively. The power conversion efficiency and the fill factor of the photovoltaic device were evaluated to be 0.42% and 0.30. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012