Optoelectronic and hydrogen evolution study in transition metal dichalcogenides and their hetero structures

Abstract

2D Transition metal dichalcogenides (TMDs) generally denoted as MX2, where M is a Transition Metal (Mo, W, etc.) and X represents achalcogenatom (S,Se orTe), exhibit unique optical and electronic properties in comparison to their bulk counterpart. This thesis work primarily involves detailed analysis of MoSe2, WSe2, two most widely used TMDs. The bulk MoSe2has an indirect band gap(1.1eV) however the single-layer nano sheets MoSe2 possess a direct band gap of 1.6eV,which demonstrates a significant variation in the properties as a result of reducing the thickness from bulk to single monolayer. Theoretical calculations predict atype-IIband-alignment for van der Waals heterostructures (vdWHs) based on semiconducting TMDs with excitons (bound electrons and holes) localized in individual monolayers. These carriers form interlayer excitons which possess significantly extended lifetimes compared to their intralayer counterpart. Consequently, the TMD-based materials offer various promising wide range of applications including flexible electronics and optoelectronics, etc. However, the most significant challenge in realizing applications for these materials is the scalable synthesis of large-area and high-quality TMD heterostructures with atomically clean and sharp interfaces. it is essential to validate a fabrication technique to produce cost-effective, high yield and controllable stacking. Another important aspect is to understand how the properties of these materials modify upon fabricating the heterostructures formed from these weakly interacting stacked layers. newline