Molecular Lubricant Mitigates Self-Assembled Monolayer Aggregation in Perovskite Photovoltaics

Molecular aggregation in self-assembled monolayers (SAMs) remains a critical bottleneck for inverted perovskite solar cells (PSCs), particularly at buried interfaces where this phenomenon induces detrimental defects that severely compromise photovoltaic performance and operational stability. Addressing this challenge requires the development of novel functional materials capable of precisely regulating molecular packing in SAMs and suppressing their aggregation, which is a key research direction for enhancing device efficiency and durability. Herein, we introduce 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄), an ionic liquid employed as a molecular lubricant that effectively suppresses SAM aggregation through steric-electrostatic dual modulation. The steric hindrance exerted by BMIMBF₄ physically prevents close packing of adjacent SAM molecules, while its ionized moieties form electrostatic shielding that disrupts π-π stacking interactions and reduces micellar dimensions. Consequently, the fabricated PSCs deliver a champion power conversion efficiency (PCE) of 26.82% and retain 92.3% of their initial efficiency after 800 h of continuous operation at 85°C under AM 1.5G illumination. This work presents the novel concept of molecular lubricants that suppress SAM aggregation via synergistic steric and electrostatic modulation, enabling uniform and densely packed SAM anchoring for high-performance PSCs.