Acetylacetone‐TiO2 Promoted Large Area Compatible Cascade Electron Transport Bilayer for Efficient Perovskite Solar Cells

In designing efficient perovskite solar cells (PSCs), the selection of suitable electron transport layers (ETLs) is critical to the final device performance as they determine the driving force for selective charge extraction. SnO 2 nanoparticles (NPs) based ETLs have been a popular choice for PSCs due to superior electron mobility, but their relatively deep‐lying conduction band energy levels ( E CB ) result in substantial potential loss. Meanwhile, TiO 2 NPs establish favorable band alignment owing to shallower E CB , but their low intrinsic mobility and abundant surface trap sites impede the final performance. For this reason, constructing a cascaded bilayer ETL is highly desirable for efficient PSCs, as it can rearrange energy levels and exploit on advantages of an individual ETL. In this study, we prepare SnO 2 NPs and acetylacetone‐modified TiO 2 (Acac‐TiO 2 ) NPs and implement them as bilayer SnO 2 /Acac‐TiO 2 (BST) ETL, to assemble cascaded energy band structure. SnO 2 contributes to rapid charge carrier transport from high electron mobility while Acac‐TiO 2 minimizes band‐offset and effectively suppresses interfacial recombination. Accordingly, the optimized BST ETL generates synergistic influence and delivers power conversion efficiency (PCE) as high as 23.14% with open‐circuit voltage ( V OC ) reaching 1.14 V. Furthermore, the BST ETL is transferred to a large scale and the corresponding mini module demonstrates peak performance of 18.39% PCE from 25 cm 2 aperture area. Finally, the BST‐based mini module exhibit excellent stability, maintaining 83.1% of its initial efficiency after 1000 h under simultaneous 1 Sun light‐soaking and damp heat (85 °C/RH 85%) environment.