A set of novel conjugated polyfluorene copolymers, poly[(9,9 0 -didecylfluorene-2,7-diyl)-co-(4,7 0 -di-2-thienyl-2 0 ,1 0 ,3 0 -benzothiadiazole-5,5-diyl)-co-(pyrene-1,6-diyl)], are synthesized via Pd(II)-mediated polymerization from 2,7-bis(4 0 ,4 0 ,5 0 , 5 0 -tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9 0 -di-n-decylfluorene, 4, 7-di(2-bromothien-5-yl)-2,1,3-benzothiadiazole, and 1,6-dibromopyrene with a variety of monomer molar ratios. The field-effect carrier mobilities and optical, electrochemical, and photovoltaic properties of the copolymers are systematically investigated. The hole mobilities of the copolymers are found to be in the range 7.0 Â 10 À5 À 8.0 Â 10 À4 cm 2 V À1 s À1 and the on/off ratios were 8 Â 10 3 À 7 Â 10 4 . Conventional polymer solar cells (PSCs) with the configuration ITO/PEDOT:PSS/polymer:PC 71 BM/ LiF/Al are fabricated. Under optimized conditions, the polymers display power conversion efficiencies (PCEs) for the PSCs in the range 1.99-3.37% under AM 1.5 illumination (100 mW cm À2 ). Among the four copolymers, P2, containing a 2.5 mol % pyrene component incorporated into poly[9,9 0 -didecylfluorenealt-5,5-(4 0 ,7 0 -di-2-thienyl-2 0 ,1 0 ,3 0 -benzothiadiazole)] (PFDTBT) displays a PCE of 3.37% with a short circuit current of 9.15 mA cm À2 , an open circuit voltage of 0.86 V, and a fill factor of 0.43, under AM 1.5 illumination (100 mW cm À2 ).