Rational Design of Near‐Infrared Polymer Acceptors Using Steric Hindrance Strategy for High‐Performance Organic Solar Cells

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.