Charge Transfer Mechanisms Regulated by the Third Component in Ternary Organic Solar Cells

For ternary organic solar cells (T-OSCs), introducing the third component (D₂) can significantly enhance the efficiency of cell while still maintaining easy fabrication. However, it brings difficulty in physical understanding of the fundamental mechanism because of the more complicated photophysical processes in T-OSCs. Accordingly, how the guest donor D₂ regulates the charge transfer mechanism was explored in theory using three T-OSCs containing two donors and an acceptor. The results point out that larger differences in molecular weight and/or backbone between D₂ and the host donor D₁ cause different charge transfer mechanisms, which hardly provide a coexisting charge transfer path. Besides, strong absorption capacity of D₂ with a high oscillator strength would produce favorable regulation of the charge transfer mechanism. Therefore, this work clarifies the influence of D₂ on the charge transfer mechanism in T-OSCs, which suggests that the method of improving the power conversion efficiency cannot be generalized but rather must be tailored to specific conditions.