Role of Chalcogens in the Exciton Relaxation Dynamics of Chalcogenol-Functionalized CdSe QD: A Time-Domain Atomistic Simulation

Colloidal CdSe nanocrystals are often stabilized by organic ligands. The choice of such ligands has tremendous detrimental effects on interparticle charge transfer (CT) dynamics in nanocrystalline thin-film devices. It is evident from the recent experiment that photoexcited hole migrates from CdSe quantum dot (QD) to surface-passivating phenyl chalcogenol ligands (PhEH; E = S, Se, Te) at different time scales. But the backward electron–hole (e−h) recombination at the interface remained unexplored. A deep-level understanding of the mechanism of CT at the interface is therefore required to unravel the key role of chalcogen for the betterment of the device performance. Herein, we have performed time-domain density functional theory calculation along with nonadiabatic molecular dynamics (NAMD) simulation to investigate the photoinduced CT at the CdSe–PhEH interfaces. The simulated time scales for hole transfer (HT) are found to follow the trend PhSH > PhSeH > PhTeH that concur excellently with the experimental observations. We propose that lower electronegativity of the E atom that binds with the CdSe QD facilitates the hole migration. In addition, the delocalized nature of initial donor states, phonon modes, NA coupling, and quantum coherence are the major factors that control the faster HT. Meanwhile, for the first time, we study the linker atom-dependent e–h recombination at such interface. The recombination event is remarkably slower than the HT and occurs at the nanosecond regime. Due to the greater electronegativity of linker atom (E = S), a broad range of phonon vibration and longer-lived quantum coherence expedite the recombination at a higher rate. In contrast, for higher chalcogens with lower electronegativity (Se, Te), the exciton relaxes relatively at a lower rate. We believe our results of atomistic, time-domain methodology provide valuable insight into the exciton relaxation dynamics in CdSe–chalcogenol interface and may be useful for the enhancement of performance of future devices.