Recently, ternary solar cells have developed as a vital photovoltaic-technology since they combine the advantages of both single junction and tandem solar cells with their processing simplicity, mechanical flexibility, and lightweight. In this paper, we have investigated the role of domain size and the weight ratio of fullerene and non-fullerene acceptor on the performance of ternary blended PM6:Y6: PCBM organic solar cell. Using the effective medium approach and assuming the ternary blend of donor/acceptor1/acceptor2 nanocomposite as an effective integrated active layer, along with augmented Drift-diffusion formalism for the active layer of the organic solar cell, we have modeled the performance parameters of the device. The results show that the conversion efficiency of ternary solar cells depends on the distribution and size of both fullerene and non-fullerene acceptor domains. There are some optimal domain sizes where the optimum solar cell performance occurs. The obtained model results are in good agreement in comparison with experimental studies.