Thickness-Dependent Interlayer Charge Transfer in MoSe/MoS Heterostructures Studied by Femtosecond Transient Absorption Measurements.

We report observations of a strong thickness dependence for charge transfer (CT) from MoSe to MoS, as evidenced by transient absorption measurements. By time-resolving CT from MoSe monolayers (1Ls) to MoS flakes of varying thicknesses, including 1L, bilayer (2L), and trilayer (3L), we find that the CT time is several picoseconds in the 1L-MoSe/3L-MoS heterostructure, which is much longer than that of 1L-MoSe/1L-MoS and 1L-MoSe/2L-MoS heterostructures. In addition, the recombination lifetime of the interlayer excitons in the 1L/3L heterostructure is several times longer than that of 1L/1L and 1L/2L heterostructures, reaching 800 ps. Furthermore, we show that a prepulse can reduce the CT time and enhance the interlayer exciton recombination in the 1L/3L heterostructure. These findings illustrate that layer thickness can be an important parameter to control the CT property of van der Waals heterostructures. These experimental results also provide important information for further refining the understanding of the physical mechanisms of CT in van der Waals heterostructures.