Tailoring non-fullerene acceptors using selenium-incorporated heterocycles for organic solar cells with over 16% efficiency

Small molecular acceptors (SMAs) have gained extensive research attention as they offer many attractive features and enable highly efficient organic solar cells (OSCs) that cannot be achieved using fullerene acceptors. Recently, a new SMA named Y6 was reported, yielding high-performance OSCs with an efficiency of 15.7%. This report has inspired the OSC community to study the structure-property relationship and further modify this important class of materials. In this work, we used the selenium (Se) substitution strategy and developed two new Y6-type SMAs to study the effect of Se atoms on materials properties and device performances. It is found that the introduction of Se atoms can red-shift the absorption spectra and enhance the aggregation of the resulting SMAs. Interestingly, the variations in the substitution positions of Se atoms induce different intramolecular charge transfer within the SMAs. Se substitution at the benzothiadiazole ring is more effective than that at the thienothiophene rings, leading to the increased short-circuit current density (J(SC)) and higher efficiencies of over 16%. This contribution suggests that appropriate Se substitution is a promising method for optimizing the absorption and aggregation of Y6-type SMAs, thus enhancing their OSC performances.