Introducing a Phenyl End Group in the Inner Side Chains of A-DA'D-A Acceptors Enables High-Efficiency Organic Solar Cells Processed with Nonhalogenated Solvent

Power conversion efficiency (PCE) of organic solar cells (OSCs) processed by nonhalogenated solvents is unsatisfactory due to the unfavorable morphology. Herein, two new small molecule acceptors (SMAs) Y6-Ph and L8-Ph are synthesized by introducing a phenyl end group in the inner side chains of the SMAs of Y6 and L8-BO, respectively, for overcoming the excessive aggregation of SMAs in the long-time film forming processed by nonhalogenated solvents. First, the effect of the film forming time on the aggregation property and photovoltaic performance of Y6, L8-BO, Y6-Ph, and L8-Ph is studied by using the commonly used solvents: chloroform (CF) (rapid film forming process) and chlorobenzene (CB) (slow film forming process). It is found that Y6- and L8-BO-based OSCs exhibit a dramatic drop in PCE from CF- to CB-processed devices owing to the large phase separation, while the Y6-Ph and L8-Ph based OSCs show obviously increased PCEs Furthermore, L8-Ph-based OSCs processed by nonhalogenated solvent o-xylene (o-XY) achieved a high PCE of 18.40% with an FF of 80.11%. The results indicate that introducing a phenyl end group in the inner side chains is an effective strategy to modulate the morphology and improve the photovoltaic performance of the OSCs processed by nonhalogenated solvents.