Highly crystalline acceptor materials based on benzodithiophene with different amount of fluorine substitution on alkoxyphenyl conjugated side chains for organic photovoltaics

Abstract

Organic solar cells based on narrow bandgap small-molecule acceptors (SMAs) with highly crystalline characteristics have attracted great attentions for their superiority in obtaining high photovoltaic efficiency. Employing highly crystalline SMAs to enhance power conversion efficiencies (PCEs) by regulating and controlling morphology and compatibility of donor and acceptor materials has turned out to be an effective approach. In this study, we synthesized three different crystalline SMAs by using fluorine substitution on alkoxyphenyl conjugated side chains to modulate the relationship of crystallinity and morphologies, namely ZY1 (zero F atoms), ZY2 (two F atoms), and ZY3 (four F atoms). The three SMAs show the broad absorption edges and similar frontier orbital energy levels, generating the analogical (over 0.9 ​V) open circuit voltage (VOC) of the polymer solar cells (PSCs). As a result, the PM6:ZY2-based PSCs yield a PCE of 10.81% with a VOC of 0.95 ​V, a short-circuit current density (JSC) of 16.154 ​mA ​cm−2, and a fill factor (FF) of 0.71, which is higher than that of 9.17% (PM6:ZY1) and 6.37% (PM6:ZY3). And the PCE (17.23%) of the PM6:Y6:ZY2 based ternary PSCs is also higher than that of 16.32% PM6:Y6 based binary device. Obviously, the results demonstrate that adding fluorine atoms on the conjugated side chains to construct high crystalline materials is a positive strategy to effectively increase the efficiencies of binary and ternary PSCs.