Vacancy-Regulated Charge Carrier Dynamics and Suppressed Nonradiative Recombination in Two-Dimensional ReX2 (X = S, Se)

Point defects in semiconductors usually act as nonradiative charge carrier recombination centers, which severely limit the performance of optoelectronic devices. In this work, by combining time-domain density functional theory with nonadiabatic molecular dynamics simulations, we demonstrate suppressed nonradiative charge carrier recombination and prolonged carrier lifetime in two-dimensional (2D) ReX2 (X = S, Se) with S/Se vacancies. In particular, a S vacancy introduces a shallow hole trap state in ReS2, while a Se vacancy introduces both hole and electron trap states in ReSe2. Photoexcited electrons and holes can be rapidly captured by these defect states, while the release process is slow, which contributes to an elongated photocarrier lifetime. The suppressed charge carrier recombination lies in the vacancy-induced low-frequency phonon modes that weaken electron-phonon coupling, as well as the reduced overlap between electron and hole wave functions that decreases nonadiabatic coupling. This work provides physical insights into the charge carrier dynamics of 2D ReX2, which may stimulate considerable interest in using defect engineering for future optoelectronic nanodevices.