Interfacial Band Homogenization and Controlled Nucleation Synergistically Enable Vertical Monolithic Perovskite Films for High‐Efficiency Solar Cells

ABSTRACT Buried‐interface inhomogeneity remains a key limitation in inverted perovskite solar cells, where aggregated Al 2 O 3 nanoparticles can generate nonuniform interfacial potentials, local band inhomogeneity, charge accumulation, and nonradiative recombination losses. Here, we report a small‐molecule‐mediated Al 2 O 3 nanoparticle strategy that integrates interfacial band homogenization, gradient‐permeation defect passivation, and crystallization regulation. 1,3‐diamino‐2‐propanol (1,3‐DAP) anchors onto Al 2 O 3 nanoparticles, suppressing nanoparticle aggregation through surface electrostatic repulsion and homogenizing the buried interfacial potential distribution. Meanwhile, unanchored 1,3‐DAP molecules permeate from the buried interface into the shallow perovskite bulk, where they passivate defects and act as nucleation‐regulating sites. This dual regulation promotes vertically oriented grain growth along the (100) direction and forms vertically interconnected large‐grain perovskite films. Consequently, the modified devices achieve champion power conversion efficiencies of 26.00% under N 2 fabrication and 25.09% under ambient‐air fabrication, together with reduced voltage loss and enhanced stability. The unencapsulated modified devices further retain 90% of their initial maximum power output after 700 h of maximum power point tracking under continuous one‐sun illumination in N 2 . Comparative molecular studies further show that effective crystallization regulation requires cooperative amino‐hydroxyl functionalities and appropriate precursor compatibility, highlighting the broader applicability of the nanoparticle‐interface molecular regulation strategy represented by 1,3‐DAP.