First-Principles Study of the Structural , Optical and Electronic Properties of the Lead-Halide-Based Organic Perovskites MAPbX3 , FAPbX3 , (X= I ,Br , Cl)

The electronic properties of MAPbX3(MA= CH3NH3+) units employing the experimental cell parameters (6.33,5.95 and5.66 Å for X = I,Br and Cl, respectively),FAPbX3(FA=( CH-(NH2)2+) units employing the experimental cell parameters (6.36 , 5.99 and5.60 Å for X = I ,Br and Cl, respectively) perovskite in the cubic phase are systematically studied using the first-principles calculations. We correlate our experimental results with first-principles theory and provide an insight into important parameters like; lattice constants, electronic structure , static and high-frequency dielectric constants, Reflection coefficient, Absorption coefficient , Optical conductivity , Refractive index,in these perovskite .Our calculations are performed using the Quantum-Espresso pakage in the framework of density functional theory (DFT). The projector augmented-wave (PAW) pseudopotentials are used within energy cutoff of 408 Ev for the plane-wave basis functions.For the exchange-correlationfunctional, the generalized gradient approximation(GGA) of Perdew-Burke-Ernzerhof(PBE) is used to relax the structural parameters. We substituted I- to Br- to Cl- in order to tune the bandgap from 1.6 eV to 2.4 ev to 3.2 eV of these materials. Electronic structure calculations reveal that electronic properties are mainly governed by Pb 6p and halide p orbitals. spin-orbit coupling (SOC) is included in all the calculations. All calculations reported in agreement with experimental data.