A donor–acceptor‐type conjugated alternating copolymer (PBDT–DFBSe) consisting of benzodithiophene (BDT) and a fluorinated 2,1,3‐benzoselenadiazole derivative (DFBSe) is synthesized using Stille cross‐coupling. The optical, electrochemical, and photovoltaic properties of PBDT–DFBSe are compared with those of its non‐fluorinated analog, PBDT–BSe, which is composed of BDT and 2,1,3‐benzoselenadiazole (BSe). The optical bandgap energies of PBDT–BSe and PBDT–DFBSe are determined from their absorption onsets to be 1.64 and 1.60 eV, respectively. Fluorine‐containing PBDT–DFBSe shows a deeper highest occupied molecular orbital (HOMO) energy level and higher hole mobility than PBDT–BSe. The device incorporating PBDT–DFBSe has a higher open‐circuit voltage (Voc), short‐circuit current density (Jsc), and power conversion efficiency (PCE) than the device incorporating PBDT–BSe.