Energy Environ. Sci. published a study in 2022. To enhance the efficiency of organic solar cells, the addition of solvent additives to the donor and acceptor solutions is considered to be a rather effective strategy. Since the current state-of-the-art photovoltaic materials have thiophene sequences on their conjugated backbones, the thiophene analogs 2,5-dibromothiophene (HBrT) and 2,5-dibromo-3,4-difluoro-thiophene (FBrT) are developed as solvent additives in this study.

　　It was found that the higher boiling point of FBrT and its ability to easily dissolve the donors and acceptors due to the principle of ” like dissolve like” (note: the closer the polarity and structure of the two molecules are, the easier they are to dissolve in each other), providing an effective tool for prolonging the crystallization and phase separation kinetic process of photovoltaic materials. Due to the simultaneous formation of higher crystallinity, favorable phase separation, and P-i-N-like heterojunction, the FBrT treated solar cells showed better exciton dissociation, charge transportation and extraction, and suppressed carrier recombination.

　　Therefore,

1. 1. The PM6:Y6-based solar cells with FBrT additive achieve efficiency of 17.9% and fill factor of 78.6%, which are one of the highest values achieved in PM6:Y6-based binary solar cells.
   2. More strikingly, the FBrT solvent additive has universal applicability in L8-BO, Y6-BO, and BTP-eC9 based solar cells, and achieves significantly efficiencies improvement of 18.6–18.7% in the devices.

　　These findings suggest that thiophene derivatives are effective solvent additives for further optimization of organic solar cells.