Incorporating biphenyls as co-monomers in electron-deficient diketopyrrolopyrrole (DPP) conjugated polymers enables widening the optical band gap to 1.70 eV. Power conversion efficiencies of 3.7-5.7% and high open-circuit voltages of 0.80-0.93 V are obtained in solar cells based on these wide band gap DPP polymers.