The role of third component in coumarin-based all-small-molecule ternary organic solar cells with non-fullerene acceptor based on molecular stacking.

The power conversion efficiency (PCE) of ternary all-small-molecule organic solar cells (T-ASM-OSCs) differs significantly from that of the polymer systems (2 %), and the role of third component remains unclear. The electron donor of coumarin derivatives with simple structure and strong and broad light absorption has high PCE for T-ASM-OSCs composed of non-fullerene acceptors (Y6 and DBTBT-IC). Here, we calculated the electronic structure and interfacial properties of the binary C1-CN:Y6 and ternary C1-CN:Y6:DBTBT-IC systems using molecular dynamic (MD) simulations and density functional theory (DFT) to explore the role of the third component (DBTBT-IC). The addition of the third component mainly facilitates the different stacking patterns of the host system in ternary OSCs, optimizes the charge transfer properties, enhances the light absorption, generates more CT pathways and significantly promotes the charge separation for unfavorable stacking patterns. While the guest system composed of C1-CN:DBTBT-IC also leads to the ternary system with more stable stacking patterns and low exciton binding energy. This work elucidates the role of the third component and the importance of interfacial molecular stacking, providing theoretical guidance for the selection and design of organic photovoltaic materials.