Theoretical studies on the structural, electronic and optical properties of orthorhombic perovskites CH3NH3PbX3(X = I, Br, Cl)

In this study, we report advanced density functional theory (DFT) calculations on the structural, electronic, and optical properties of orthorhombic perovskite CH3NH3PbX3 (X = I, Br, Cl). We present basic parameters such as lattice constants, electronic structures, effective charge masses, optical absorption spectra, and excitonic binding energies to understand the fundamental properties of CH3NH3PbX3 (X = I, Br, Cl). We show that scalar relativistic (SR) DFT calculations yield good band gaps for three systems, and fully relativistic spin-orbital coupling (SOC) DFT calculations give excellent reduced excitonic effective charge masses, as compared to experiments. Moreover, our calculations show that the absorption onset of CH3NH3PbX3 moves to short wavelength region with the increase of band gap. Finally, we discussed the relationship between excitonic binding energies and dielectric constants.