Using the first principles calculation and Boltzmann transport theory,we study the thermoelectric properties of Si2BN adsorbing halogen atoms(Si2BN-4X,X = F,Cl,Br,and I).The results show that the adsorption of halogen atoms can significantly regulate the energy band structure and lattice thermal conductivity of Si2BN.Among them,Si2BN-4I has the best thermoelectric performance,the figure of merit can reach 0.50 K at 300 K,which is about 16 times greater than that of Si2BN.This is because the adsorption of iodine atoms not only significantly increases the Seebeck coefficient due to band degeneracy,but also rapidly reduces the phonon thermal conductivity by enhancing phonon scattering.Our work proves the application potential of Si2BN-based crystals in the field of thermoelectricity and the effective method for metal crystals to open bandgaps by adsorbing halogens.