Four novel conjugated polymers (P1, P2, P3, and P4) based on coplanar thiophene-phenylene-thiophene (TPT) derivatives have been designed and synthesized for application in polymer solar cells (PSCs). The optical, electrochemical, field effect carrier mobility, and photovoltaic properties of P1-P4 are investigated and compared with those of poly(3-hexylthiophene) (P3HT). PSCs are fabricated based on the blend of the polymers and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) or 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-C-71 (PC71BM) with a weight ratio of 1:3. The maximum power conversion efficiency (PCE) of the PSCs based on P3/PC71BM system reaches 3.3% with a short circuit current density (J(sc)) of 7.6 mA/cm(2), an open circuit voltage (V-oc) of 0.8 V, and a fill factor (FF) of 0.54 under AM 1.5G (100 mW/cm(2)) illumination. The results indicate that the coplanar TPT conjugated derivatives are promising PSC materials.