Strong Influence of the Anion Radius on the Passivation of Selenium Vacancy in Monolayer InSe: Insights from Time-Domain Ab Initio Analysis

Abstract

Using nonadiabatic molecular dynamics combined with the time-domain density functional theory, we have explored the influence of selenide vacancy and passivation of anions with different radii on the nonradiative charge trapping and recombination in monolayer InSe. Our results reveal that electron–hole recombination for pristine InSe occurs within several nanoseconds due to the weak nonadiabatic (NA) coupling. Selenide vacancy generates three trap states within the band gap, enhances the NA coupling, and provides new channels for charge carrier relaxation, resulting in the significantly decreased charge carrier recombination time. Passivating the selenide vacancy with anions (O2–, S2–, and Te2–) can eliminate the trap states within the band gap and extend the charge carrier lifetimes because of the decreased NA coupling. Meanwhile, the passivation effect of anions is dramatically dependent on the type of anions, and S2– is more suitable for repairing selenide vacancy than O2– and Te2– because S2– and Se2– have much closer radii. This study provides an atomistic mechanism of the effects of selenide vacancy and anion passivation on the performance of InSe thin-film solar cells and suggests that the choice of anions with a suitable radius is valuable for prolonging the excited-state lifetime.