Effect of alkoxy substitution position of phenyl side chains on the photovoltaic performance of nonfused acceptors

Abstract

Side chain configuration plays a significant role in intermolecular interaction and aggregation morphology of organic small molecules. In this work, by altering the position of the hexyloxy substitution on the phenyl side chains, three non-fused acceptors were designed and synthesized, e.g. o-2T2Se-F with 2,3-di(hexoxy)phenyl substituents, m-2T2Se-F with 2,4-di(hexoxy)phenyl substituents and p-2T2Se-F with 2,5-di(hexoxy)phenyl substituents. In comparison with its isomeric counterpart 2T2Se-F with 2,6-di(hexoxy)phenyl substituents, these three acceptors exhibit twisted backbones, which result in blue-shifted absorption and weak intermolecular interaction and molecular aggregation. When paired with donor PM6, all three blend films display weak crystallinity, leading to poor photovoltaic performance. The devices based on o-2T2Se-F, m-2T2Se-F and p-2T2Se-F obtained power conversion efficiencies (PCEs) of 4.43%, 1.77%, and 1.30%, respectively, which are significantly lower than that of 2T2Se-F-based devices (12.17%). The results reveal that manipulating the alkoxy-chain attaching point can significantly alter the molecular geometry, optoelectronic properties and molecular aggregation properties, thereby affecting the photovoltaic performance of OSCs.