Benzothiadiazole Suppresses Hydrogen Bond‐Driven Aggregation to Enable Highly Uniform SAMs for 26.67%‐Efficient Perovskite Solar Cells

ABSTRACT Inverted perovskite solar cells (PSCs) employing self‐assembled monolayers (SAMs) as hole‐selective contacts have achieved remarkable power conversion efficiencies. However, the inherent amphiphilicity of SAM molecules and persistent intermolecular O─H···O hydrogen bonding interactions stimulate molecular clustering, compromising monolayer uniformity and device performance. Herein, we introduce 5‐fluorobenzo[2,1,3]thiadiazole (5FBT), a planar molecule devoid of oxyacid groups, as a co‐adsorbent to modulate the 4‐(7H‐dibenzo[c,g]carbazol‐7‐yl)butyl)phosphonic acid (4PADCB) self‐assembled monolayer. The electron‐withdrawing benzothiadiazole core of 5FBT promotes π‐π coupling with 4PADCB, while its planar geometry disrupts O─H···O hydrogen bonding networks, suppressing molecular aggregation. Additionally, rigid 5FBT molecules adopt a tilted vertical orientation on ITO, serving as structural pillars that template 4PADCB assembly. This co‐adsorbent‐modulated SAM strategy improves monolayer uniformity and energy level alignment, constructing a high‐quality perovskite/SAMs interface. Consequently, the resulting PSCs achieve a champion efficiency of 26.67% and demonstrate superior operational stability, retaining 94.6% of their initial performance after 1000 h. The strategy is also readily scalable, delivering efficiency of 22.78% for 12.87 cm 2 mini‐module. This work highlights mitigating hydrogen bond‐driven aggregation as a key design principle for efficient and stable SAM‐based PSCs.