Strongly spatial-confined self-assembled monolayers for high-performance perovskite photovoltaics

Self-assembled monolayers (SAMs) as hole-selective contacts have driven the power conversion efficiencies (PCEs) of inverted perovskite solar cells (IPSCs) beyond 27%, yet their poor operational stability remains a major barrier to commercialization. We report that strengthening the spatial confinement of SAMs through robust out-of-plane anchoring and dense in-plane packing can effectively suppress molecular desorption and enhance thermal and solvent resistance. A custom-designed molecule, MeO-PABDCB, forms strong bonds with both the underlying indium tin oxide (ITO) and the overlying perovskite, while its rigid, planar backbone promotes tight π-π stacking (3.72 Å). This multi-dimensionally confined SAM structure not only resists solvent washing and thermal degradation but also mitigates interfacial strain in the perovskite layer, facilitating highly efficient and stable hole extraction. The resulting IPSCs achieve a champion PCE of 26.54% with a fill factor of 86.4% and retain 90% of their initial efficiency after 1000 h of maximum power point tracking (ISOS-L-1). Devices also withstand 250 harsh thermal cycles between -40 and 85 °C (IEC61215 and ISOS-T-3) while preserving over 90% of their initial performance. This work establishes spatial confinement as a general molecular design principle toward durable and high-performance perovskite optoelectronics.