Homogenizing Self-Assembled Monolayers via Covalent Organic Frameworks for Inverted Perovskite Solar Cells

Self-assembled monolayers (SAMs) have emerged as promising hole transport layers (HTLs) in inverted perovskite solar cells (PSCs) due to their unique capability to modulate energy level alignment and interfacial quality. However, the widely used SAM molecule [4-(3,6-dimethoxy-9H-carbazol-9-yl)butyl]phosphonic acid (MeO-4PACz) suffers from molecular aggregation, poor wettability with perovskite precursors, and limited electrical conductivity, which together hinder the formation of high-quality perovskite films and efficient charge extraction. Herein, we propose a rational SAM homogenization strategy by introducing two tailor-designed covalent organic frameworks (COFs)-PT-COF and Zn-PT-COF-into MeO-4PACz SAMs via co-assembly. These COFs are designed with rigid porphyrin cores to enhance charge transport and flexible hydrophilic side chains to improve substrate wettability. The incorporation of COFs effectively disrupts MeO-4PACz aggregation through π-π interaction and hydrogen bonding, resulting in uniform, conductive, and well-anchored SAMs. Consequently, the modified SAMs promote perovskite crystallization, reduce buried interface defects, and improve charge extraction. Devices employing Zn-PT-COF-modified SAMs exhibit a champion power conversion efficiency of 26.39% (certified as 26.12%) with negligible hysteresis and outstanding operational stability, retaining 95% of initial efficiency after 1000 h continuous operation. This study offers a comprehensive molecular-level strategy to overcome intrinsic limitations of MeO-4PACz, providing a pathway for highly efficient and stable PSCs.