To industrialize non-fullerene polymer solar cells (NFPSCs), the molecular design of the donor polymers must feature low-cost materials and a high overall yield. Two chlorinated thiophene-based polymers, P(F-Cl) and P(Cl-Cl), are synthesized by introducing halogen effects like fluorine (F) and chlorine (Cl) to the previously reported P(Cl), which exhibits low complexity. They show relatively low power conversion efficiencies (PCEs) of 11.8% and 10.3%, respectively, owing to insufficient molecular weights. To overcome these, two new terpolymers are designed and synthesized by introducing a small amount of 1,3-bis(5-bromothiophen-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (BDD) unit into each backbone, namely, P(F-Cl)(BDD=0.2) and P(Cl-Cl)(BDD=0.2). Finally, both polymers remain inexpensive and show a better molecular weight-solubility balance, achieving high PCEs of 12.7% and 13.9%, respectively, in NFPSCs processed using eco-friendly solvents.