Interfacial Engineering of Moisture-Stable CsSnBr ₃ –MoS ₂ Heterostructures for High-Voltage Aqueous Energy Storage

Process-induced defect-state engineering and interfacial electrostatics provide powerful routes to stabilize lead-free halide perovskites for aqueous energy-storage applications. Here, we demonstrate that defect-rich MoS2 integrated with CsSnBr3 forms a moisture-stable type-II n–p heterostructure that enables stable, high-voltage aqueous energy storage. The interfacial band offsets (ΔEC ≈ −0.39 eV) generate a built-in potential of ∼0.35 V, promoting directional charge separation across the heterointerface. Vacancy-induced donor states elevate the Fermi level and reduce the activation energy by ∼0.11 eV, resulting in a 2-fold enhancement in charge-transfer rate and accelerated relaxation dynamics, as confirmed by Mott–Schottky and impedance analyses. The coupled influence of interfacial defects and the built-in electric field lowers the energy barrier for interfacial electron transfer, facilitating a defect-assisted transport pathway from CsSnBr3 to MoS2. Simultaneously, the hydrophobic MoS2 overlayer electrostatically suppresses Sn2+ oxidation, preserving the band structure and lattice integrity during aqueous operation, as verified by XPS and FTIR. As a result, the heterostructure delivers a wide 2.8 V operating window, a high energy density of 73.9 W h kg–1, and 90% capacitance retention after 10000 cycles. This work establishes a quantitative structure–defect–interface–performance relationship and highlights interfacially engineered perovskite heterostructures as a viable platform for moisture-stable, high-performance aqueous energy storage.