Exciton Binding Energies in Organic Photovoltaic Materials: A Theoretical Perspective

Exciton binding energy (E-b) plays an essential role in organic electronics. For organic solar cells, the existence of E-b necessitates interfacial energy level offsets to drive exciton dissociation into free charge carriers at the donor/acceptor interfaces, which results in an extra energy loss with respect to inorganic and perovskite solar cells. Thus, it is highly desirable to reduce the E-b for improving the performance of organic photovoltaics. In this perspective, we summarize our recent advances on theoretical studies of the E-b in A-D-A small-molecule acceptors for organic photovoltaics. We highlight the importance of the polarization effect on decreasing the E-b by stabilizing charge carriers. Moreover, the polarization energies of charge carriers are found to be greatly influenced by different molecular packing structures. Remarkably, an extremely weak E-b is achieved in the state-of-the-art A-D-A acceptor of Y6 with a three-dimensional compact molecular packing, thus enabling direct photogeneration of free charge carriers even without the assistance of the donor/acceptor interfaces. We hope this perspective would be helpful to decrease the E-b and energy loss for high-efficiency organic solar cells.

Automated summary

Exciton binding energy (E-b) plays a crucial role in organic electronics, and reducing E-b is essential for improving efficiency. Recent studies have shown that the polarization effect and molecular packing structure can significantly decrease E-b, with the Y6 acceptor achieving an extremely weak E-b through its unique three-dimensional structure.