Competitive Ligand Modulation Reduces Buried Interfacial Voids and Defects Enabling 26.17% Efficient Perovskite Solar Cells

The buried interface between perovskite and SnO2 is plagued by defects and voids, limiting n-i-p solar cell performance. It is challenged for interfacial modification such as potassium salts to simultaneously passivate defects and modulate the buried PbI2·DMSO adduct. Here, we introduce a heterocyclic potassium salt, acesulfame potassium (Ace-K), with dual C═O and -SO2- groups for defect passivation and competitive ligand modulation. Ace-K anchors uncoordinated Sn4 + and oxygen vacancies on SnO2 via bidentate chelation. During PbI2 deposition, Ace-K competes with DMSO for PbI2, reducing PbI2·DMSO at the SnO2/perovskite interface. This reduction leads to a void-free perovskite bottom interface. Concurrently, it promotes DMSO escape to create a porous PbI2 structure, which facilitates organic salt penetration and yields high-quality perovskite films with released residual stress. Ace-K remaining at the interface enhances charge transfer kinetics. Consequently, the champion device (0.0729 cm2) achieves a lab-measured PCE of 26.17% with an open-circuit voltage of 1.19 V. The heterocyclic structure also imparts UV resistance, and the devices retain 92.4% of their initial efficiency after 1000 h of maximum power point tracking under continuous illumination. This work demonstrates a competitive ligand modulation strategy, offering a microstructural pathway toward efficient and stable perovskite photovoltaics.