Decoupling Bulk Homogenization and Interfacial Reconstruction via a Triple-Alkali-Cation Interlayer for...

Precise control over cation distribution is critical for high-performance perovskite solar cells (PSCs). Conventional bulk doping often leads to vertical segregation and lattice strain, while surface passivation dose not ensure bulk homogeneity. We introduce a triple-alkali interlayer (LiOH/KCl/CsI) deposited on the electron transport layer prior to crystallization of the perovskite film. This design spatially decouples crystallization regulation from compositional modulation, i.e., localized Li⁺ and K⁺ ions reconstruct the buried contact and passivate defects and interfacial Cs⁺ acts as a dynamic source for in situ upward diffusion. This bottom-up mechanism facilitates stress-free crystallization, resulting in a dense, preferentially oriented perovskite film with a void-free buried interface and superior compositional homogeneity. Consequently, the resulting champion n-i-p PSC achieves a remarkable power conversion efficiency of 26.13%, with a high open-circuit voltage of 1.184 V and a fill factor of 83.81%. Furthermore, the devices demonstrate robust durability maintaining 93.7% after 1440 h of continuous 1-sun irradiation at 65°C. This work provides a promising pathway for managing cation dynamics to realize efficient and stable perovskite photovoltaics.