Elucidating fluorination effect on benzodithiophene-based donor material in organic solar cells

Side-chain engineering plays a crucial role in advancing the performance of organic solar cells (OSCs). Here, the symmetrical difluorophenyl molecule 1 (m1), the small molecule 2 (m2) and N3 were selected to systematically study the influences of fluorination on the photophysical properties. It was found that the planarity of the backbones of m1 and m2 facilitates charge transfer. Also, the investigated m1 or m2 and N3 show strong and broad light absorption in the visible region, demonstrating good short-circuit current density. Moreover, Compared to the m1/N3 system, the change in the number of fluorine atoms provides the m2/N3 system more favorable interfacial charge transfer mechanisms. In addition, the calculated electron separation rate and hole separation rate of the m2/N3 system are higher than those of the m1/N3 system, facilitating charge separation. We hope this work could provide theoretical guidance for further experimental work in molecular design, especially for fluorination.