Charge-transfer excitons are formed by photoexcited electrons and holes following charge transfer across a heterojunction. They are important quasiparticles for optoelectronic applications of semiconducting heterostructures. The newly developed two-dimensional heterostructures provide a new platform to study these excitons. We report spatially and temporally resolved transient absorption measurements on the dynamics of charge-transfer excitons in a MoS₂/WS₂/MoSe₂ trilayer heterostructure. We observed a non-classical lateral diffusion process of charge-transfer excitons with a decreasing diffusion coefficient. This feature suggests that hot charge-transfer excitons with large kinetic energies are formed and their cooling process persists for about 100 ps. The long energy relaxation time of excitons in the trilayer compared to its monolayer components is attributed to the reduced carrier and phonon scattering due to the dielectric screening effect in the trilayer. Our results help develop an in-depth understanding of the dynamics of charge-transfer excitons in two-dimensional heterostructures.

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过渡金属二硫杂化物异质结构中电荷转移激子的动力学

电荷转移激子是由光激发的电子和空穴在异质结上转移后形成的。对于半导体异质结构的光电应用，它们是重要的准粒子。新开发的二维异质结构为研究这些激子提供了新的平台。我们报告在MoS ₂ / WS ₂ / MoSe _2中的电荷转移激子动力学的时空分辨瞬态吸收测量三层异质结构。我们观察到电荷转移激子的非经典横向扩散过程，其扩散系数降低。该特征表明形成了具有大动能的热电荷转移激子，并且其冷却过程持续了约100 ps。与单层组分相比，三层中激子的能量弛豫时间长，是由于三层中的介电屏蔽效应导致了载流子和声子散射的降低。我们的结果有助于发展对二维异质结构中电荷转移激子动力学的深入理解。