DFT/TDDFT study of electronic, structural and optical properties of RbPbBr₃ /RbSnBr₃ and RbXBr ₃/RbXBr ₂ Cl (X = Pb, Sn) heterostructures

The electronic and optical properties of RbPbBr₃ /RbPbBr₂Cl, RbPbBr₃ /RbSnBr₃ and RbSnBr₃ /RbSnBr₂Cl heterostructures were studied using first-principle approach. The calculations show that the energy gaps are equal to 1.54, 0.96 and 0.67 eV (the energies are in the infrared range), respectively. Also, unlike the strong metallic property of RbSnBr₃ /RbSnBr₂Cl, in the band structures of RbPbBr₃ /RbPbBr₂Cl and RbPbBr₃ /RbSnBr₃ , the minimum of conduction bands is tangential to the Fermi level. Also, the density of states (DOS) diagrams around the Fermi level have negligible amplitude, so, the density of charge carriers is low and thereby both heterostructures (similar to graphene) can be suitable for electronic applications. The effective mass calculations show; me & mh < 0.5 m e , therefore, in all three cases, charge carriers have significant mobilities and these structures are suitable for photovoltaic and optoelectronic applications. Also, partial density of states (PDOS) diagrams show that the charge carriers are concentrated in certain layers, therefore, in all three heterostructures, the two-dimensional electron gas is formed. By plotting the diagrams of changes in the length of the anion–cation–anion bond perpendicular to the junction, it can be seen that the ferroelectric-like property appears in these structures. The optical calculations show, for all cases, the refractive index in the range of (0.0–5.0 eV) has a value of about 1.6, with peaks as large as 1.87. In this range the reflectivity varies between 0.06 and 0.12. Finally, we found that the RbPbBr₃ /RbSnBr₃ structure has two visible absorption peaks at 1.96 and 3.09 eV, while the heterostructures of RbPbBr₃ /RbPbBr₂Cl and RbSnBr₃ /RbSnBr₂Cl, each have one visible peak that are located at 2.78 and 2.11 eV respectively. (author)