Fine-Tuned Morphology Based on Two Well-Miscible Polymer Donors Enables Higher Open-Circuit Voltage and Enhanced Stability for Highly Efficient Ternary All-Polymer Solar Cells.

Developing organic solar cells based on a ternary active layer is one of the most effective approaches to improve their photovoltaic performance. However, limited success has been achieved in all-polymer solar cells (all-PSCs). In this study, a ternary all-PSC with improved efficiency and stability is realized by using J71 as the third component to adjust the host system of PBDB-T:PG1. The deeper highest occupied molecular orbital (HOMO) energy level of J71 downshifts the mixed HOMO energy levels of donors. The two polymer donors (P D s) have good miscibility and present Förster resonance energy transfer. When blended with PG1, the optimized morphology is obtained, showing enhanced crystallinity but meanwhile slightly reduced phase separation with improved exciton dissociation and collection efficiency, suppressed charge recombination, and reduced energy loss (0.55 eV). Combining the benefits mentioned above, the ternary all-PSC exhibits an excellent efficiency of 12.8% with simultaneously elevated open-circuit voltage (0.96 V), short-circuit current density (18.4 mA cm -2 ), and fill factor (72.2%). Moreover, the optimized ternary all-PSC shows improved storage and thermal stability. This study demonstrates that the utilization of a ternary all-polymer system based on two well-miscible P D s is an effective strategy to enhance the photovoltaic performance and stability of all-PSCs.