Unveiling symmetry: a comparative analysis of asymmetric and symmetric non-fullerene acceptors in organic solar cells

This study investigates the design and analysis of symmetric and asymmetric non-fullerene acceptors (NFAs), focusing on the burgeoning interest in asymmetric NFAs due to their exceptional solar cell properties. Our approach involves modifying the core and introducing two distinct terminal end-groups to the π-core system. Through rigorous first-principle simulations, we systematically explore the solar cell parameters of the designed NFAs when combined with a PM6 polymer. Surprisingly, our results demonstrate that incorporating an A5 acceptor, alongside other end-group acceptors (A1-A5), leads to a significant increase in the difference between ground and excited dipole moments (Δμ), enhanced charge separation rates (k<inf>CS</inf>), and notably reduced energy losses (<0.35 eV) compared to other complexes. Furthermore, our findings challenge the conventional wisdom that asymmetric compounds consistently outperform symmetric ones. We identify specific symmetric configurations, particularly those paired with A5 acceptors that exhibit substantial improvements in solar cell properties. This study emphasizes the critical importance of thoughtful material design, providing valuable insights for researchers striving to develop next-generation small-molecule acceptors for organic solar cells.