Precise Side Chain Engineering Enabling High‐Performance Wide‐Bandgap Polymer Donors

Abstract A series of wide bandgap (WBG) conjugated polymers PTFBDT‐C, PTFBDT‐O and PTFBDT‐S are designed and synthesized with alkyl, alkoxy and thioalkyl side chains. By selecting benzodithiophene derivatives as the donor units and benzothiadiazole derivatives as the acceptor units, PTFBDT‐C, PTFBDT‐O and PTFBDT‐S are all of wide optical bandgaps. Furthermore, low bandgap small molecule L8‐BO‐4F is used as the acceptor to fabricate organic solar cells (OSCs). According to the results, PTFBDT‐C:L8‐BO‐4F blend film displays appropriate phase separation, high hole and electron mobilities, etc. Thus, the power conversion efficiency (PCE) of PTFBDT‐C:L8‐BO‐4F based OSCs is 14.02%, which is much higher than those of PTFBDT‐O:L8‐BO‐4F based (9.06%) and PTFBDT‐S:L8‐BO‐4F based ones (10.45%). These results show that the side chain engineering is an effective strategy to improve photovoltaic performance of wide bandgap polymers.