Two random terpolymers bearing alkoxy-benzodithiophene as an electron-rich unit and N-octylthieno[3,4,c]pyrrole-4,6-dione (TPD) as an electron deficient group with thiophene and selenophene pi bridges, were synthesized and characterized. Electrochemical, optical properties of the polymers were analyzed to get an insight on the effect of different p bridges. Photovoltaic performances of the polymers were investigated with a conventional device architecture. PBTS, PBTSe based polymer solar cells (PSCs) exhibited power conversion efficiency of 3.32% and 3.19%. PCE of PBTS:PC71BM based PSCs were improved to 4.30% with the addition of 1% (vol/vol) 1,8-diiodooctane (DIO) as a solution processing additive. With the introduction of diphenyl ether (DPE) as the solvent additive, PBTSe based polymer solar cells attained 5.15% PCE value due to the formation of the interpenetrated network structure of domains. (C) 2019 The Electrochemical Society.