<p>Based on first principles, the electronic structure and optical properties of monolayer WSe₂ doped with alkaline earth metal (Be/Mg/Ca/Sr/Ba) are investigated. The results show that all doping systems exhibit excellent formation potential and structural stability. Compared with monolayer WSe₂, alkaline earth metal doping induces lattice distortion and generates impurity levels. Meanwhile, the relative effective mass of electrons and holes in all doping systems is more deviated from one. Therefore, the recombination of photogenerated electron–hole pairs is effectively inhibited after doping. In addition, doping monolayer WSe₂ with alkaline earth metals increases its static dielectric constant and enhances its polarizability. Notably, the Mg-WSe₂ system exhibits the highest static dielectric constant, indicating the strongest polarization capacity. The absorption spectra of the doped system show a redshift in the low-energy region, which expands the response range to sunlight after the introduction of impurities. From band alignment analysis, we can conclude that other doping systems, except the Ba-WSe₂ system, show superior visible light absorption and effectively inhibit photogenerated electron–hole pair recombination, indicating their potential as photocatalysts for water decomposition.</p> Graphical Abstract <p>Monolayer WSe₂ within the two-dimensional transition metal dichalcogenides (TMDCs) material family exhibits broad potential in optoelectronic devices and photocatalysis owing to their direct bandgap characteristics. In this work, upon doping alkaline earth metal into a monolayer WSe₂, denoted as X-WSe₂ (X = Be, Mg, Ca, Sr, Ba), intriguing alterations are observed in the electronic and optoelectronic properties. Furthermore, apart from the Ba-WSe₂ system, other doped systems exhibit suitable energy band edge positions, making them promising candidates for high-performance photocatalysts.</p> <p></p>