Exciton Binding Energy of Non‐Fullerene Electron Acceptors

The past three years have witnessed the power conversion efficiency (PCE) of organic solar cells (OSCs) rocketing to over 18%, due to outstanding advantages of non‐fullerene acceptors (NFAs). However, large exciton binding energy ( E b ) caused by strong Coulombic force is still one of the main limiting factors for high‐performance OSCs. Thus, it is critical to reduce the E b for further enhancement of device performance. Many strategies have been developed to reduce the E b of organic materials previously. In this perspective, the calculation methods for E b and the relationship between E b and voltage loss ( V loss ) are discussed. Then, the effects of the properties of small‐molecule acceptors on E b from the perspectives of fused‐ring donor cores, end groups, side chains, and molecular packing are discussed. Finally, the potential directions for reducing E b and pointing out the trade‐off between E b and bandgaps/miscibility are put forward. It is hoped that this perspective could provide a new thinking of a molecular design for the breakthrough of OSCs.