TiX2 (X=Cl, Br, I) monolayer and type II heterostructures as promising efficient solar cells

A series of two-dimensional TiX₂ (X=Cl, Br, I) monolayers and their corresponding van der Waals heterostructures were predicted by the first-principle calculations. The dynamic and thermodynamic stability of TiX₂ (X=Cl, Br, I) monolayers are confirmed by the phonon spectra and molecular dynamics simulations, respectively. The Heyd-Scuseria-Ernzerhof-based band values are 0.311-0.989 eV, showing the tunable transition probability between valence and conduction band. Additionally, the significant visible-light absorption coefficient (~ 10⁵ cm^-1) and high power conversion efficiency (~12%) of TiBr₂/TiCl₂ heterojunctions provide promising potentials for solar cells.