Trifluoromethylation Enables Compact 2D Linear Stacking and Improves the Efficiency and Stability of Q‐PHJ Organic Solar Cells

Abstract Compared to the bulk heterojunction (BHJ) devices, the quasiplanar heterojunction (Q‐PHJ) exhibits a more stable morphology and superior charge transfer performance. To achieve both high efficiency and long‐term stability, it is necessary to design new materials for Q‐PHJ devices. In this study, QxIC‐CF₃ and QxIC‐CH₃ are designed and synthesized for the first time. The trifluoromethylation of the central core exerts a modulatory effect on the molecular stacking pattern, leveraging the strong electrostatic potential and intermolecular interactions. Compared with QxIC‐CH₃, the single crystal structure reveals that QxIC‐CF₃ exhibits a more compact 2D linear stacking behavior. These benefits, combined with the separated electron and hole transport channels in Q‐PHJ device, lead to increased charge mobility and reduced energy loss. The devices based on D18/QxIC‐CF₃ exhibit an efficiency of 18.1%, which is the highest power conversion efficiency (PCE) for Q‐PHJ to date. Additionally, the thermodynamic stability of the active layer morphology enhances the lifespan of the aforementioned devices under illumination conditions. Specifically, the T₈₀ is 420 h, which is nearly twice that of the renowned Y6‐based BHJ device (T₈₀ = 220 h). By combining the advantages of the trifluoromethylation and Q‐PHJ device, efficient and stable organic solar cell devices can be constructed.