High-efficiency organic solar cells enabled by nonfullerene acceptors with varying alkyloxy substitution positions of the phenyl outer side chains

Abstract

Side-chain engineering has proven to be a highly effective approach in the manipulation of the molecular properties, morphology, and charge transfer/transport of non-fullerene acceptors. In addition to the alterations in branching locations and length of the alkyl side chain, a comprehensive exploration of the side chain configuration of nonfullerene acceptors (NFAs) is imperative to fully exploit their capabilities in organic solar cells (OSCs). Here, two isomeric NFAs (named m-BTP-OEH and p-BTP-OEH) with phenyl outer side chains attaching a 2-ethylhexyloxy substituent at the meta- or para-position were designed and synthesized. The effects of the alkyloxy substitution position of the phenyl outer side chains on the molecular properties, blend morphology and charge process using the polymer donor PM6 are investigated. In comparison to p-BTP-OEH with para-substitution, the meta-substituted side chains of m-BTP-OEH exhibited more favorable tilted orientations and thus better film-morphology, charge transfer/transport and reduced energy disorder when blending with PM6. As a result, the power conversion efficiency (PCE) of the devices based on m-BTP-OEH reached 18.02%, exhibiting a significantly enhanced fill factor (FF) of 78.41%, surpassing the photovoltaic performance of the devices based on p-BTP-OEH (17.63%). This study contributes to the comprehension of the significant influence of side chain configuration on the properties of molecules and its role in advancing the performance of photovoltaic systems.