Hot-Injection-Driven Interfacial Stabilization of Lead-Free Halide Perovskites via Sulfur-Vacancy-Rich MoS₂ Toward...

Halide perovskites exhibit exceptional optoelectronic and catalytic properties but remain chemically fragile, rapidly degrading under moisture or alkaline conditions. Here, we introduce a synthesis-driven interfacial engineering strategy that stabilizes the intrinsically unstable lead-free ${\mathrm{CsSnBr}}_3$ perovskite by coupling nucleation and heterointerface formation within a single liquid-phase hot-injection process. During crystal growth, sulfur-vacancy-rich ${\mathrm{MoS}}_2$ nanosheets conformally encapsulate ${\mathrm{CsSnBr}}_3$ nanocrystals, forming coherent 2D-3D p-n heterojunctions that suppress ${\mathrm{Sn}}^{2+}$ oxidation, limit moisture penetration, and enable directional charge transport. The resulting heterostructure exhibits a built-in potential of 0.67 V, generating an internal electric field that promotes efficient charge separation and enhanced redox stability. Under alkaline conditions, the synthesis-driven heterointerface sustains bifunctional water splitting in both freshwater and seawater for over 24 h without chlorine evolution or structural degradation. More broadly, this approach provides a generalizable synthesis paradigm for stabilizing moisture- and oxidation-sensitive halide perovskites, enabling their integration into chemically robust and electronically coupled systems for aqueous electrocatalysis and other demanding environments.