First-principles Study On ABX₃ Halide Perovskites And A₂B_ⅠB_ⅡX₆ Halide Double Perovskites

Perovskite has attracted much attention as the main material of the third-generation solar cells.ABX₃ perovskite has some problems in stability and environmental protection.The main solution currently is to find more environmentally and stable perovskite structures while improving its photoelectric conversion efficiency.This article studies ABX₃ halide perovskite and A₂B_ⅠB_ⅡX₆halide double perovskite using the first-principles method.These studies can help enrich and expand the application of perovskite materials.For ABX₃ perovskite,CH₃NH₃Pb I₃（MAPb I₃）with tetragonal phase was selected for research.The electronic properties,optical properties,and the energy of I^-migration along the<100>direction of MAPb I₃ were calculated using the first-nature principle approach.The calculated results indicate that the MAPb I₃ of the tetragonal phase is a direct bandgap semiconductor,the bandgap value is 1.71eV.The analysis of the density of states shows that Pb-s,Pb-p,and I-p orbital electrons have a significant impact on their electronic and optical properties.The static dielectric constants（?）₁（0）of MAPb I₃ in two polarization directions（parallel and perpendicular to the c-axis）are 5.75 and 6.43.It has high absorption coefficient,high refractive index,low reflectivity,and low energy loss in the visible light range.The migration energy of I^-in MAPb I₃along the<100>direction was calculated to be 0.41eV using the Climbing image nudged elastic band（CI-NEB）method and the supercell method.For A₂B_ⅠB_ⅡX₆ double perovskite,Cs₂RbSbX₆（X=Cl,Br,I）was selected for research.Calculate the electronic and optical properties of three materials using the first principles method.The calculation results indicate that all three materials are direct bandgap semiconductors,with bandgap values of 4.19eV,3.58eV,and 2.99eV,respectively.The results of partial wave density of states indicate that the conduction bands of the three materials are mainly contributed by Cs-d,Sb-p,and Cl-p（Br-p and I-p）orbital electrons;the valence band is mainly contributed by Cl-p（Br-p and I-p）orbital electrons,while the contribution of Sb-s orbital electrons is relatively small.By comparing the bandgap values,it can be found that replacing elements at the X position can modulate the bandgap value of Cs₂RbSbX₆.The static dielectric constants of Cs₂RbSbX₆（X=Cl,Br,I）materials are 2.48,2.74,and 3.20,respectively.The refractive indices n（0）of the three materials are 1.58,1.66,and 1.79,respectively.Cs₂RbSbX₆（X=Cl,Br,I）have superior properties such as high absorption coefficient,high refractive index,and low reflectivity in the ultraviolet region.The electronic properties of Cs₂RbSbX₆（X=Cl,Br,I）change with the order of Cl-Br-I,and the optical properties undergo a red shift with the change of X position elements.