Ultrafast Charge Transfer in Lithium-Ion and Water-Intercalated\nMoS<sub>2</sub>/WS<sub>2</sub> Heterostructures

Heterostructures\nof monolayer transition metal dichalcogenides\nsuch as MoS<sub>2</sub> and WS<sub>2</sub> are promising for applications\nin optoelectronics and photocatalysis. However, the strong interlayer\ncoupling in MoS<sub>2</sub>/WS<sub>2</sub> heterostructures results\nin indirect bandgaps that significantly hinder their performance and\nefficiency in practical applications. Here, we use first-principles\ncalculations to demonstrate an effective method to weaken interlayer\ncoupling in MoS<sub>2</sub>/WS<sub>2</sub> heterostructures by intercalating\nlithium ions with water molecules. This approach results in a direct\nbandgap while maintaining the type-II band alignment. Interestingly,\nthe charge transfer process in the intercalated MoS<sub>2</sub>/WS<sub>2</sub> heterostructures is greatly accelerated, which is attributed\nto the enhanced nonadiabatic coupling between different energy states\nand the inversion of the effective electric field within the heterostructures.\nOur results provide a strategy for achieving ultrafast charge transfer\nin MoS<sub>2</sub>/WS<sub>2</sub> heterostructures via intercalation\nand offer insight into modulation of other van der Waals materials\nfor enhanced performance.