Two-dimensional(2D)materials and their corresponding van der Waals(vdW)heterostructures are considered as promising candidates for highly efficient solar cell applications.A series of 2D HfX2(X = Cl,Br,I)monolayers are proposed,via first-principle calculations.The vibrational phonon spectra and molecular dynamics simulation results indicate that HfX2 monolayers possess dynamical and thermodynamical stability.Moreover,their electronic structure shows that their Heyd-Scuseria-Ernzerhof(HSE06)-based band values(1.033-1.475eV)are suitable as donor systems for excitonic solar cells(XSCs).The material's significant visible-light absorbing capability(～105 cm-1)and superior power conversion efficiency(～20％)are demonstrated by establishing a reasonable type Ⅱ vdW heterostructure.This suggests the significant potential of HfX2 monolayers as a candidate material for XSCs.