Vinturaj, V.P.Yadav, A.K.Jasil, T.K.Kiran, G.Singh, R.Singh, A.K.Garg, V.Pandey, S.K.2026-02-042023Bulletin of Materials Science, 2023, 46, 3, pp. -2504707https://doi.org/10.1007/s12034-023-02963-xhttps://idr.nitk.ac.in/handle/123456789/21755In this work, we have investigated the various electronic and optical properties of undoped molybdenum diselenide (MoSe<inf>2</inf>) monolayer, such as band structure, density of states, electron density, dielectric function, refractive index, extinction coefficient, reflectivity and energy loss function using density functional theory. Additionally, substitutional doping using niobium (Nb) and manganese (Mn) atoms and introducing defects in undoped MoSe<inf>2</inf> lattice were investigated to know the detailed effect of the same on its properties. It is found that the undoped MoSe<inf>2</inf> monolayer demonstrates a direct energy bandgap of ~1.44 eV, which reduces after Mn, Nb doping and after introducing Mo, Se vacancy. The energy bandgap attains a very small value 0.2 eV after introducing Se vacancy defect in MoSe<inf>2</inf> lattice. The extinction coefficient of MoSe<inf>2</inf> monolayer demonstrates a significant increase from 1.79 to 2.66 a.u. after introducing the Mo vacancy in the undoped lattice. The variation of semiconductor to nearly semi-metallic character of MoSe<inf>2</inf> by introducing defects makes it very suitable for the application in high-performance solar cells, photo-electrochemical cells, sensors and biosensor applications. © 2023, Indian Academy of Sciences.DefectsEnergy dissipationEnergy gapManganese compoundsMolybdenum compoundsMonolayersPhotoelectrochemical cellsRefractive indexSeleniumSelenium compoundsSemiconductor dopingTransition metalsDensities of stateDensity-functional-theoryDichalcogenidesDielectric functionsElectronic and optical propertiesEnergy bandgapsEnergy loss functionExtinction coefficientsTheoretical investigationsTransition metal dichalcogenidesDensity functional theory