A new electron deficient monomer (PDBT) unit incorporating a weak electron accepting unit, pyrrolo[3,4-c]pyrrole-1,3-dione (DPPD), and a strong electron accepting unit, 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (BT), with a configuration of DPPD-BT-DPPD was prepared, and copolymerized with a benzodithiophene (BDTT) derivative to afford a new alternating ternary copolymer P(BDTT-PDBT). The estimated optical band gap (Eg) and highest occupied/lowest unoccupied (HOMO/LUMO) molecular orbital energy levels of P(BDTT-PDBT) were 1.72 eV and −5.45 eV/−3.62 eV, respectively. A field effect transistor made from P(BDTT-PDBT) exhibited a hole mobility of 3.2 × 10−3 cm2 V−1 s−1. Conventional single layer polymer solar cells (PSCs) prepared using P(BDTT-PDBT) with an additive offered a maximum power conversion efficiency (PCE) of 5.73% with an open-circuit voltage (Voc) of 0.90 V, a short-circuit current (Jsc) of 9.73 mA/cm2, and a fill factor (FF) of 0.66. Interestingly, the PSC device prepared without an additive also showed a similar PCE of 4.84% (Voc ∼ 0.92 V, Jsc ∼ 8.08 mA/cm2, and FF ∼ 0.65). This paper reports the preparation of an efficient ternary copolymer for polymer solar cells utilizing high energy sunlight, as well as the property modulation of an alternating binary copolymer, P(BDTT-DPPD), containing BDTT and DPPD derivatives via the insertion of a strong electron accepting BT unit on the P(BDTT-DPPD) backbone.