Remodeling the Buried Interface via Polar Multisite Molecules for Efficient Low‐Dimensional Metal Halide‐Organic Interdigitated Heterojunction Solar Cells

ABSTRACT While ordered p–n interdigitated heterojunctions offer advanced architectures for photovoltaics, their application has been largely limited to three‐dimensional metal halides. Translating this structural advantage to low‐dimensional systems is fundamentally constrained by defective buried interfaces and imperfect crystallization of the low‐dimensional p‐type absorber. Here, we introduce a polar multisite molecular regulator, 2‐amino‐2‐cyanoacetamide (ACAA), into the MeO‐2PACz self‐assembled monolayer (SAM) to resolve this. ACAA mitigates MeO‐2PACz aggregation, enhances surface wettability, and aligns interfacial energetics to form a uniform hole‐selective contact. Concurrently, its cyano and amide groups interact with precursors via coordination and hydrogen bonding, regulating crystallization kinetics to yield high‐quality low‐dimensional metal halide films with enlarged grains, reduced trap densities, and homogeneous luminescence. By integrating this regulated buried interface into an ordered p–n interdigitated heterojunction featuring a ternary organic n‐layer, charge separation and extraction are synergistically accelerated across the enlarged interfacial area. Consequently, the champion device delivers an impressive efficiency of 24.11%, alongside minimized non‐radiative voltage loss. Furthermore, the unencapsulated device exhibits improved operational stability, retaining 85% of its initial efficiency after 800 h of maximum power point tracking. This work establishes polar multisite mixed‐SAM engineering as a highly effective strategy to unlock the full potential of advanced low‐dimensional photovoltaics.