Enhancing the Buried Interfacial Interaction to Obtain Homogeneous Halogen-Phase Distribution for Efficient...

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 (-SCH₃) 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 Pb²⁺ 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 PbI₂ and PbBr₂, 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.