Using Two Compatible Donor Polymers Boosts the Efficiency of Ternary Organic Solar Cells to 17.7%

The use of ternary organic semiconducting blends is recognized as an effective strategy to boost the performance of polymer solar cells (PSCs) by increasing the photocurrent while minimizing voltage losses. Yet, the scarcity of suitable donors with a deep highest occupied molecular orbital (HOMO) level poses a challenge in extending this strategy to ternary systems based on two polymers. Here, we address this challenge by the synthesis of a new donor polymer (PM7-Si), which is akin to the well-known PM6 but has a deeper HOMO level. PM7-Si is utilized as the third component to enhance the performance of the best-in-class binary system of PM6:BTP-eC9, leading to simultaneous improvements in the efficiency (17.7%), open-circuit voltage (0.864 V), and fill factor (77.6%). These decisively enhanced features are attributed to the efficient carrier transport, improved stacking order, and morphology. Our results highlight the use of two polymer donors as a promising strategy toward high-performance ternary PSCs.