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

Abstract

Abstract The charge transport ability of polymer acceptors ( P A s) is crucial for achieving high power conversion efficiencies (PCEs) of all‐polymer solar cells (all‐PSCs). However, the electron mobilities (μ e s) of most P A s are inferior to those of their small molecule acceptor (SMA) counterparts. Herein, the authors design a new series of the polymerized SMA‐based P A s (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 μ e and PCEs. Interestingly, the effects of regioisomers on the μ e and all‐PSC performance are the opposite depending on the donating unit. For the Y5‐Se‐based P A s, the PCEs increase in order of Out (7.52%) < Mix (9.33%) < In (13.38%). In contrast, for the Y5‐BiSe‐based P A s, 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 P A s depending on the regioregularity. Thus, the Y5‐Se‐In blend exhibits the highest μ e 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 P A and highly efficient all‐PSCs.