Ternary blending is an effective strategy for broadening the absorption range of the active layer in bulk heterojunction polymer solar cells and for constructing an efficient cascade energy landscape at the donor/acceptor interface to achieve high efficiencies. In this study, we report efficient ternary blend solar cells containing an acceptor alloy consisting of the indacenodithiophene-based nonfullerene material, IDT2BR, and the fullerene material, phenyl-C-butyric acid methyl ester (PCBM). The IDT2BR materials mix fully with PCBM materials, and the energy state of this phase can be tuned by varying the blending ratio. We performed photoluminescence and external quantum efficiency studies and found that the ternary charge cascade structure efficiently transfers the photogenerated charges from the polymer to IDT2BR and finally to PCBM materials. Ternary blend devices containing the IDT2BR:PCBM acceptor blend and various types of donor polymers were found to exhibit power conversion efficiencies (PCEs) improved by more than 10% over the PCEs of the binary blend devices.