The unprecedented development of all-polymer solar cells (all-PSCs) is hindered by their low short-circuit current density (Jsc), mainly due to the absence of near-infrared (NIR) polymer acceptor materials. To tackle this challenge, a molecular design principle is proposed, which involves the regulation of steric hindrance on the fused-ring backbone to obtain NIR polymer acceptors. Accordingly, three acceptors named PTz-Ph, PTz-Me, and PTz-H are synthesized by substituting the Phenyl, Methyl, and Hydrogen in the beta position of the thiophene unit based on fused-ring molecules. Different from the necessity of steric hindrance of small molecule acceptors in achieving an outstanding performance, polymer acceptor PTz-H without steric hindrance-substitution achieves a record-high efficiency for the benzotriazole-based all-PSCs. Then, introducing PTz-H into the binary PBDB-T:PTz-BO system, the ternary all-PSC exhibits a splendid efficiency of 18.16%, which has surpassed the efficiencies of most benzo[c][1,2,5]thiadiazole-based counterparts. In addition, an organic tandem solar cell is successfully fabricated, which exhibits a high efficiency of 17.49%. This work provides an effective and readily accessible design strategy for designing high-performance NIR polymer acceptors, showing the great potential for future organic photovoltaic applications.

Three polymer acceptors named PTz-Ph, PTz-Me, and PTz-H are synthesized by substituting the Phenyl, Methyl, and Hydrogen in the beta position of the thiophene unit based on small molecules. PTz-H-based device achieves a record-high efficiency of 18.16% and the highest photocurrent for all-polymer solar cells reported in the literature thus far.