A serial of polyfluorene copolymers have been developed by covalently attaching thiophene units to the side chain of polyfluorene with an alkyl spacer by means of Pd-catalyzed Suzuki coupling reactions. The electrochemical, photophysical and photovoltaic properties of the copolymers were studied. The absorption spectra of the copolymers measured in thin films display two absorption peaks. The power conversion efficiency achieved in the device configuration ITO/PEDT/ PFO-FT-DBT: PCBM (1:2)/Al is 0.83% with open-circuit voltage (Voc) 0.75V. Further investigation of more polyfluorene copolymers with narrow band gap aryl-hetero cycle units on the side chain is in progress.