A series of donor-acceptor copolymers based on a new silafluorene containing multifused heptacylic arenes have been designed and synthesized in order to further modulate and optimize their electronic and optical properties. Polymer solar cells based on a blend of these polymers and PC61BM exhibited high open circuit voltages of up to 0.86 V. Through simple and straightforward engineering of molecular structures, the devices based on the PSiFDCTBT:PC61BM (1:3.5 in wt %) blend provided, on average, a V-oc of 0.86 V, a J(sc) of 8.8 mA/cm(2), a FF of 56%, delivering a PCE of 4.2%.