Molecular Design‐Driven Interface Engineering Enabling Simultaneous Defect Passivation and Enhanced Hole Extraction in Perovskite Solar Cells

Abstract Interface engineering has emerged as an effective strategy to address interface defects and energy level misalignment between the perovskite and hole transport layer (HTL). Herein, three novel multifunctional hole interface molecules with distinct substituents were designed to passivate defects at the perovskite/HTL interface. These molecules integrate hole‐transporting groups with passivating units, enabling effective defect passivation, improved energy level alignment, and facilitating efficient carrier extraction. Among the three hole transport interface molecules (HTIMs), the 3‐(3,6‐bis(4‐(bis(4‐(methylthio)phenyl)amino)phenyl)‐9H‐carbazol‐9‐yl)hexan‐1‐amine hydroiodide (MeS‐TPA‐Cbz‐HAI), comprising ‐MeS and HAI units, exhibited superior interface passivation capability and greater chemical compatibility with 2,2′,7,7′‐Tetrakis (N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (Spiro‐OMeTAD), leading to a reduction in defect density and enhanced hole transport. Consequently, the device based on MeS‐TPA‐Cbz‐HAI achieved a notable power conversion efficiency (PCE) of 25.83%. Moreover, the unencapsulated device maintained 94% of its initial efficiency after 1000 hours of continuous operation under ambient conditions (30%–65% relative humidity), demonstrating remarkable long‐term stability. This design strategy for hole interface molecules presents a promising avenue for achieving both high efficiency and operational stability in perovskite solar cells.