Enhancing the Buried Interfacial Interaction to Obtain Homogeneous Halogen‐Phase Distribution for Efficient Wide‐Bandgap Perovskite Solar Cells

ABSTRACT Wide‐bandgap (WBG) perovskite solar cells (PSCs) are promising for tandem photovoltaic applications, yet they often suffer from inhomogeneous halogen‐phase distribution and interfacial recombination losses. This work introduces a novel self‐assembled monolayer (SAM) hole‐transport material, MeS‐2PACz, engineered with a methylthio (‐SCH 3 ) group to strengthen the buried interfacial interaction in inverted p‐i‐n structured WBG PSCs (∼1.68 eV). Density functional theory (DFT) calculations reveal that the sulfur atom in MeS‐2PACz exhibits a stronger dipole moment and higher adsorption energy with the perovskite, facilitating robust S‐Pb coordination with undercoordinated Pb 2+ ions. This interaction effectively passivates interface defects, reducing the trap density from 1.07 × 10 16 to 8.25 × 10 15 cm −3 , which is lower than that of MeO‐2PACz. Crucially, MeS‐2PACz demonstrates nearly equal binding energies with PbI 2 and PbBr 2 , promoting synchronous crystallization and a homogeneous halogen‐phase distribution. Consequently, perovskite films on MeS‐2PACz show larger grain size, improved crystallinity, and enhanced charge extraction. The champion device based on MeS‐2PACz achieves a power conversion efficiency (PCE) of 22.83%. Furthermore, the unencapsulated devices retain over 90% of their initial PCE after 1500 h under dark‐state storage in a nitrogen atmosphere, demonstrating superior stability. This molecular engineering of the SAM provides a viable pathway toward high‐performance and stable WBG PSCs.