Bis-adducted fullerene derivatives as third-component materials enabling efficient ternary all-small-molecule organic solar cells with over 16 % efficiency

All-small-molecule ternary organic photovoltaics (SMPVs) are composed of BTR-Cl as a donor, Y6 as an acceptor and NC₇₀BA as a third-component material. When the BTR-Cl:Y6:NC₇₀BA ratio was 1.6:1:0.15, the optimized ternary SMPVs achieved the highest PCE of 16.35 %, with a J_SC of 27.01 mA cm⁻², a V_OC of 0.850 V and an FF of 71.2 %. Owing to the hollow spherical structure of NC₇₀BA, better connections could be achieved between the donor and acceptor molecules. Moreover, the medium LUMO energy levels between BTR-Cl and Y6 are beneficial for forming a cascade of LUMO energy levels. In addition, NC₇₀BA adjusts the molecular arrangement and enhances the crystallinity of the photoactive layer. Thus, NC₇₀BA as a third-component material can support enhanced J_SC. Collectively, these findings highlight a promising pathway for improving SMPVs performance through the use of NC₇₀BA as a third-component material.