Atom-Scale Control, Design and Transport Engineering in Two-Dimensional Transition-Metal Chalcogenides for Sustainable Energy Applications.

Two-dimensional transition metal chalcogenides (2D-TMCs) have emerged as a highly tunable class of layered materials with rich phase diversity, strong spin-orbit coupling, and exceptional electronic and optical properties. Their unique thickness-dependent behavior and defect-sensitive structure make them attractive for a range of applications in nanoelectronics, optoelectronics, and sustainable energy technologies. This review comprehensively discusses their crystallographic diversity and recent advances in understanding structural characteristics, electronic features, and optical responses, including the influence of dimensionality, defects, and heterostructuring. We examine various synthesis strategies, from exfoliation to vapor-phase and solution-based routes, highlighting their scalability and morphological control, with an emphasis on their roles in photovoltaics, photoelectrochemical water splitting, thermoelectrics, and supercapacitors. In addition, we highlight the role of density functional theory (DFT), many-body perturbation techniques, and other first-principles approaches in defining the stability, electronic structure, and optical responses of TMCs. Finally, future perspectives and key challenges for tailoring TMCs toward device-level integration are discussed.