Advanced Co-Self-Assembled Monolayers for Stress Relief and Performance Optimization in Methylammonium-Free Perovskite Solar Cells

Abstract

Self-assembled monolayers (SAMs) have been widely used to improve interfacial energy alignment and surface passivation for efficient inverted perovskite solar cells (PSCs) in recent years. However, conventional single SAMs still leave key issues like interfacial defects and residual stress of the perovskite film. In this work, pyridine-based molecules isonicotinic acid (4-PA) and 3-(4-pyridine)acrylic acid (4-PAA) were introduced to improve the surface coverage of [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) and grain growth of perovskite films through hydrogen bonding. In particular, the co-self-assembled monolayer (Co-SAM) using 4-PAA effectively relieved residual stress in the perovskite film and suppressed trap-assisted recombination, yielding a champion power conversion efficiency (PCE) of 20.1% under AM 1.5G illumination. Furthermore, the unencapsulated device retained over 75% of its initial efficiency after 800 h storage, underscoring the effectiveness of Co-SAM engineering using 4-PAA for achieving efficient and stable PSCs.