Exciton Binding Energy of Non‐Fullerene Electron Acceptors

Abstract

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.

Keywords

• exciton binding energy
• fused-ring electron acceptors
• non-fullerene acceptors
• organic photovoltaics
• organic solar cells