Developing Efficient Benzene Additives for 19.43% Efficiency of Organic Solar Cells by Crossbreeding Effect of Fluorination and Bromination

Employing volatile solid additives have emerged as a promising method to optimize the morphology and improve the performance of organic solar cells (OSCs). However, principles governing the efficient design of solid additives remain elusive. Herein, the programmed fluorination and/or bromination on benzene core to develop efficient additives for OSCs is reported. The programmed fluorination and/or bromination endow the five halogen benzene derivatives, 1,3,5-trifluorobenzene, hexafluorobenzene, 1,3,5-tribromo-2,4,6-trifluorobenzene (TFTB), 1,3,5-tribromobenzene, and hexabromobenzene, with different melting and boiling points, volatility, as well as interactions with the host blend. Studies indicate that the additives with extremely high and low volatility are almost powerless and even detrimental to the morphology evolution. Among them, the combination of fluorine and bromine atoms on TFTB not only enables the more appropriate m.p./b.p. and volatility, but also exerts stronger molecular interactions with the host blend, giving rise to higher ordered molecular packing and more favorable morphology. Importantly, TFTB exhibits good universality to optimize the performances of OSCs with high power conversion efficiencies (PCEs; over 18%) in a group of binary blend systems, and an impressive PCE of 19.43% in the ternary PBTz-F:PM6:L8-BO system. A series of volatile benzene additives is developed by crossbreeding effect of fluorination and bromination for improving blend morphology and charge extraction. A champion power conversion efficiency of 19.43% is realized finally in ternary blend organic solar cells.image

Automated summary

This study reports the programmed fluorination and/or bromination on the benzene core to develop efficient additives for organic solar cells (OSCs). The combination of fluoride and bromide atoms on the additives leads to more appropriate melting/boiling points, volatility, and stronger molecular interactions with the host blend, resulting in higher ordered molecular packing and improved morphology. The developed additive, 1,3,5-tribromo-2,4,6-trifluorobenzene (TFTB), shows good universality and high power conversion efficiency in various blend systems, achieving an impressive PCE of 19.43% in a ternary blend system.