High‐Performance Polymer Donors Based on Dithienoquinoxaline Enabled by Electron‐Withdrawing Two‐Dimensional Conjugated Side Chains

In this work, two D‐A conjugated polymers, PBQx‐B and PBQx‐2FB, are designed and synthesized, featuring a benzodithiophene donor unit and a dithienoquinoxaline acceptor unit functionalized with either phenyl or difluorophenyl conjugated side chains. This molecular design extends the concept of two‐dimensional (2D) conjugated side chains to the acceptor unit in order to enhance intermolecular interactions and tune optoelectronic properties. Both polymers exhibit typical broadband absorption characteristics. Compared with PBQx‐B, PBQx‐2FB shows a deeper highest occupied molecular orbital level due to the electron‐withdrawing effect of fluorine, leading to an increased open‐circuit voltage in devices. Moreover, the fluorinated side chains enhance molecular aggregation, endowing PBQx‐2FB with pronounced temperature‐dependent aggregation behavior. When blended with the acceptor L8‐BO, PBQx‐2FB promotes a more favorable film formation process, which enables a well‐defined nanoscale phase separation with a fibrous morphology. Moreover, PBQx‐2FB:L8‐BO blend exhibits a nearly exclusive face‐on molecular packing with enhanced ordering. As a result, PBQx‐2FB:L8‐BO devices achieve a power conversion efficiency of 15.4%, significantly outperforming the non‐fluorinated counterpart (12.9%). This work demonstrates that incorporating electron‐withdrawing 2D conjugated side chains into acceptor units is an effective strategy for developing high‐performance polymer donors, providing a new avenue for molecular design in organic photovoltaics.