Adding the third component with similar building blocks to regulate the miscibility of active layer enables high efficient ternary solar cells

The miscibility between active layer materials play a crucial role in fine tuning the film morphology and also have significant effect on device performance of organic solar cells (OSC). BTR-Cl is characterized as high crystallinity and high mobility, but suffers from excessive crystallization and inferior film morphology, which always lead to moderate fill factor (FF) in photovoltaic devices. Herein, the incorporating of the novel PBTz-F with similar building blocks as BTR-Cl can not only broaden the absorption spectrum range of ternary blends, but also relieve the excessive crystallization of BTR-Cl and regulate the miscibility of active layer by forming closer contact between BTR-Cl and PBTz-F, leading to the improved film morphology. Under the optimal condition, short-circuit current density (JSC) and FF were remarkably elevated because of more balanced efficient charge transport and suppressed trap-assisted recombination. As a result, the optimized device delivered an enhanced PCE of 15.22%. This study demonstrates that the strategy of relieving crystallization by adding the third component with similar building blocks as a guest material is a very promising strategy to improve the photovoltaic efficiency of ternary solar cells.