Nature of Excitons in Bidimensional WSe2 by Hybrid Density Functional Theory Calculations

Abstract

2D tungsten diselenide (2D-WSe2) is one of the most successful bidimensional materials for optoelectronic and photonic applications, thanks to its strong photoluminescence properties and to a characteristic large exciton binding energy. Although these optical properties are widely recognized by the scientific community, there is no general understanding of the atomistic details of the excitonic species giving rise to them. In this work, we present a density functional theory investigation of excitons in 2D-WSe2, where we compare results obtained by standard generalized gradient approximation (GGA) methods (including spin-orbit coupling) with those by hybrid density functionals. Our study provides information on the size of the self-trapped exciton, the number and type of atoms involved, the structural reorganization, the self-trapping energy, and the photoluminescence energy, whose computed value is in good agreement with experimental measurements in the literature. Moreover, based on the comparative analysis of the self-trapping energy for the exciton with that for isolated charge carriers (unbound electrons and holes), we also suggest a simplified approach for the theoretical estimation of the excitonic binding energy, which can be compared with previous estimates from different approaches or from experimental data.

Study of Energetics of Polaron Dynamics in Monolayer and Bulk MoS2 Using Oxidation-State Constrained Density Functional Theory

“…This is sufficient as the conduction band minimum of MoS 2 is dominated by the Mo 4 d orbital. Furthermore, electron polarons formed using hybrid functionals on WSe 2 , a similar transition metal dichalcogenide, studied in the work of in Liu et al showed that such electron polaron mostly localizes on one of the W atoms. Hence, to localize an extra electron in an Mo ion, the target Mo ion is constrained to an oxidation state of +3.…”

Atomic-Scale Insights into Comparative Mechanisms and Kinetics of Na–S and Li–S Batteries

“…The pristine WSe 2 band gap is estimated to be 1.6 eV, consistent with previously reported results. 57,58 The electron transfer caused by the adsorption of M 2 S n species on the AMs results in a downshift of DOS, that is, a decrease in both the conduction band minima (CBM) and valence band maxima (VBM) relative to the Fermi level. The calculated band gaps of the M 2 S n absorbed structures, on the other hand, are comparable to those of the pristine WSe 2 , as shown in Figure S7.…”

“…Babu et al utilized the WS 2 electrode as a cathode material to stabilize the shuttle effect, which exhibited stable electrochemical performance through 350 discharge–charge cycles with a specific capacity of 590 mA h g –1 and an outstanding Coulombic efficiency of 99% . WSe 2 having the similar chemical structure to WS 2 , due to its extraordinary features (a narrower band gap of 1.6 eV and hydrophobic sticky surfaces), has gained substantial interest as a critical member of TMDs, which has been used in many fields as a functional material. − Till date, very few literature reported WSe 2 in Li–S battery applications. − For example, Wang et al utilized WSe 2 flakelets immobilized on N-doped graphene with abundant active sites as a dual-functional host for both the S cathode and Li anode chemistries …”

Pairing of Transition Metal Dichalcogenides and Doped Graphene for Catalytically Dual Active Interfaces for the Hydrogen Evolution Reaction

“…The TMDs have trigonal prismatic geometry with d z 2 , d x 2 − y 2 , d xy , d xz , and d yz orbitals, 22 as illustrated in Figure 3a. The Fermi energy of the semiconducting MoS 2 is located within the bandgap, whereas that of NbS 2 and TaS 2 is in the d z 2 state.…”