A new, low band-gap donor-acceptor-type conjugated polymer, PDPP-PER, comprising 3,9-perylene (PER) and diketopyrrolo[3,4-c]pyrrole (DPP) was synthesized. The crystallinity of the synthesized polymer film significantly improved with thermal annealing to 150 °C. The PCE of the PDPP-PER device reached 6.35% with a high open-circuit voltage of 0.79 V.