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

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.