Comparative Study on Surface Passivation Effects of Organic Salts and Their Low-Dimensional Perovskites in Perovskite Solar Cells

Surface passivation strategies have been pivotal in advancing perovskite solar cells (PSCs) toward high power conversion efficiencies (PCEs). While organic ammonium salts (OS) and their low-dimensional (LD) perovskite derivatives are widely employed to suppress surface defects in three-dimensional (3D) absorber layers, a systematic understanding of their distinct passivation mechanisms remains elusive. In this work, we conduct a comprehensive comparison of OS and LD passivators, focusing on their impacts on film morphology, defect mitigation, and hole transport dynamics. Scanning probe microscopy (SPM) reveals that OS preferentially localizes at grain boundaries of 3D perovskite films, whereas LD forms a uniform passivation layer across both surfaces and grain boundaries. Both passivators induce a type-II energy-level alignment with the bulk 3D perovskite, as evidenced by surface potential mapping. However, films passivated with LD perovskite films exhibit superior hole extraction efficiency due to the formation of a conductive heterostructure between the LD layer and the 3D perovskite, which facilitates interfacial charge transfer. Consequently, LD-passivated n-i-p PSCs achieve a ∼10% enhancement in open-circuit voltage (VOC) and a ∼15% improvement in PCE compared to control devices. This study not only clarifies the mechanistic divergence between OS and LD passivation but also highlights the dual functionality of LD materials in simultaneously passivating defects and optimizing carrier extraction. These insights provide a design framework for next-generation surface modifiers in high-performance PSCs.