Achieving 19.2% High‐Efficiency Ternary Organic Solar Cells Through Novel Sequential Processing Technique With Hydrocarbon Solvent

ABSTRACT In organic solar cells (OSCs), typical methods for fabricating the ternary active layer are blend‐casting (BC) or two‐step sequential processing (SqP‐2T), where all three or at least two components are blended together, which affect the crystallization/aggregation behavior of each other during solid‐film formation. Herein, we introduce for the first time a novel three‐step sequential processing method, termed SqP‐3T, which utilizes hydrocarbon solvents to prepare high‐quality ternary active layers. Compared to the SqP‐2T and BC techniques, SqP‐3T yields an active layer with a higher acceptor ratio on its upper surface and exhibits a longer crystal coherence length in the out‐of‐plane direction (21.42 Å). These characteristics enhance charge transport and collection. Additionally, SqP‐3T devices demonstrate nearly a twofold increase in the transient photovoltage decay constant (up to 2.82 µs) that is related to carrier lifetime to a certain extent, leading to reduced recombination losses. Consequently, the SqP‐3T device achieves a high fill factor (75.67%) and a high short‐circuit current density (27.35 mA/cm²), contributing to a power conversion efficiency of 19.2%. These results highlight the potential of SqP‐3T or a multi‐step sequential deposition process in the production of ternary or multicomponent OSCs, which could be adopted by more material systems in the future.