Importance of High‐Electron Mobility in Polymer Acceptors for Efficient All‐Polymer Solar Cells: Combined Engineering of Backbone Building Unit and Regioregularity

Abstract

AbstractThe charge transport ability of polymer acceptors (PAs) is crucial for achieving high power conversion efficiencies (PCEs) of all‐polymer solar cells (all‐PSCs). However, the electron mobilities (μes) of most PAs are inferior to those of their small molecule acceptor (SMA) counterparts. Herein, the authors design a new series of the polymerized SMA‐based PAs (Y5‐A‐B), where the donating moiety (A = selenophene (Se)/biselenophene (BiSe)) and the backbone regioregularity (B = In/Mix/Out) are 2D controlled, for enhancing both the μe and PCEs. Interestingly, the effects of regioisomers on the μe and all‐PSC performance are the opposite depending on the donating unit. For the Y5‐Se‐based PAs, the PCEs increase in order of Out (7.52%) < Mix (9.33%) < In (13.38%). In contrast, for the Y5‐BiSe‐based PAs, the PCEs decrease in order of Out (10.67%) > Mix (9.58%) > In (8.52%). These opposite trends in each series originate from the different planarity and intermolecular assembly of PAs depending on the regioregularity. Thus, the Y5‐Se‐In blend exhibits the highest μe and achieves the highest PCE (13.38%) among the all‐PSCs in this study. Therefore, the authors report the importance of simultaneous engineering of the backbone building unit and regioregularity to realize high‐mobility PA and highly efficient all‐PSCs.