Enhancing Efficiency and Stability of Organic Solar Cells via Amide‐Functionalized UV Down‐Converters

ABSTRACT Organic solar cells (OSCs) have achieved power conversion efficiencies (PCEs) exceeding 20%, yet their long‐term operational stability, particularly under ultraviolet (UV) irradiation, remains a critical bottleneck for practical deployment. Herein, we report a molecular engineering strategy to enhance both the efficiency and photostability of OSCs using amide‐functionalized benzotriazole (BTA)‐based UV down‐converters. A novel down‐conversion (DC) material, BTA‐4, was designed by introducing polar amide groups to regulate intermolecular interactions and excited‐state planarity. Theoretical calculations and spectroscopic analyses reveal that BTA‐4 exhibits an exceptional intrinsic emission potential, achieving an exceptionally high solid‐state PLQY of 85.85%. The resulting red‐shifted emission aligns well with the high‐response spectral region of the active layer, enabling efficient UV–to–visible spectral conversion and thereby maximizing overall light utilization. When incorporated into PDMS encapsulation films at an optimized loading, BTA‐4/PDMS‐encapsulated devices achieved a superior PCE of 20.3%, outperforming those using commercial UV blockers. Furthermore, by effectively suppressing the photodegradation of both donor and acceptor components, BTA‐4 provides robust protection against UV‐induced decay, enabling devices to retain over 80% of their initial PCE after intensive UV exposure. This work provides an effective approach to advanced UV management in high‐performance OSCs, enabling the simultaneous enhancement of device efficiency and long‐term operational stability.