Enhancing UV Stability and Charge Extraction in Organic Solar Cells with Phenyl‐Linked Aromatic Self‐Assembled Monolayer

Abstract Carbazole‐derived self‐assembled monolayers (SAMs) are extensively employed as effective hole‐extracting layer (HEL) in organic photovoltaics (OPVs) for enhancing interfacial modification and carrier extraction. Despite their utility, the performance of these SAMs is significantly influenced by the length of the alkyl linker commonly used, and the electron‐rich carbazole moiety is susceptible to photo‐oxidation, which compromises the stability of the devices. In this study, a novel SAM is introduced, utilizing a rigid phenyl linker in place of the conventional flexible alkyl linker. This molecular design fosters a more dense and orderly SAM packing and facilitates electron delocalization in the electron‐rich carbazole unit, thereby enhancing both charge extraction and the photo/electrochemical stability of the SAM. The improvements at the molecular level have been effectively translated to the device level, realizing a power conversion efficiency (PCE) of 19.70% and notable operational stability (T₈₀ over 1100 h) in resultant OPV devices. Crucially, this includes enhanced resistance to ultraviolet irradiation. These results underscore the significance of molecular design in developing SAM‐based HELs to optimize both the efficiency and stability of OPVs.