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• NC 70 BA plays a dominant role in the photocurrent generating and charge transport. • The separation of exciton of NCBDT-4Cl mainly occurs on the NCBDT-4Cl/NC 70 BA interface. • The OSCs based on NC 70 BA exhibit a significant increase of 10% in PCE. • The shallower energy levels and better compatibility for double side chain fullerene derivative NC 70 BA than single side chain fullerene PC 71 BM. In this study, ternary organic solar cells (OSCs) are fabricated with the PBDB-T-2F as a polymer donor and NCBDT-4Cl as a fullerene-free acceptor, double side chain fullerene derivative NC 70 BA as a third component material and single side chain fullerene PC 71 BM as reference third component materials. The NC 70 BA-based ternary OSCs exhibit the highest PCE of 13.82%, which is 10% higher than that of PBDB-T-2F:NCBDT-4Cl binary OSCs and slightly higher than PC 71 BM-based ternary OSCs (13.24%). Detailed studies suggest that the shallow LUMO levels and double side chain for NC 70 BA is beneficial to broaden energy bandgap and improve compatibility, which is enhancing J SC and FF value. This work suggests that double side chain fullerene derivative NC 70 BA as third component materials is a promising way to finely tune the detailed photovoltaic parameters and further improve the photovoltaic performance of OSCs. [ABSTRACT FROM AUTHOR]