FIRST-PRINCIPLE MODELING OF STRUCTURAL, ELECTRONIC, AND OPTICAL PROPERTIES OF CH3NH3PbBr3

Abstract

Organic-inorganic hybrid perovskites have recently attracted attention due to their potential applications in solar cells, light-emitting, and photovoltaic devices. In this work, we focused on the study within the density functional theory of the structural, electronic, and optical properties of three temperature-dependent phases of perovskite CH 3 NH 3 PbBr 3 . We present basic parameters such as lattice parameters, electronic structures, effective charge masses, and optical absorption spectra to understand the fundamental properties of the investigated perovskite. The change in the properties of the studied crystalline phases was analyzed using various approximations for the exchange-correlation functionals. For our theoretical calculations, exchange−correlation functional was chosen in the GGA-PBE and GGA-PBEsol parametrizations, also with Hubbard correction to GGA (GGA-PBEsol+U). The U parameter was selected at 5 eV and applied to Br p-states. The calculation of the electronic properties of the CH 3 NH 3 PbBr 3 perovskite shows the change in the electronic spectra was taken into account when the spin-orbit coupling (SOC) was included in the calculations. The results of band structure calculations showed that cubic, tetragonal, and orthorhombic perovskite crystal phases have semiconductor properties with direct band gaps. The use of the GGA-PBEsol and GGA-PBEsol+U methods gives the results closest to the experimental ones. We observed a radical change in the electronic spectrum when the SOC effect is included in the calculations, which leads to a reduction in the bandgap. Further explanation of the electronic bandgap nature of CH 3 NH 3 PbBr 3 crystals is performed through the total (DOS) and partial density of state (PDOS) analysis. For all crystalline phases, considered perovskites showed a similar DOS distributions, which may be divided by three regions. The first region is formed by the methylammonium ion p-states, which forms narrow bands located deep about at −8eV. The second region at −6.0 – 0 eV within the valence band complex, characterizes with the largest contribution being observed from hybrid Br p-orbitals and Pb s-orbitals. The third region is placed from 2.44 to 7.0 eV for cubic, from 2.24 to 6.9 eV for tetragonal, and from 2.35 to 6.3 eV for orthorhombic phases, respectively. The conduction band minimum is mainly formed by hybridized states of the Pb p-orbitals and a small contribution of Br p-orbitals. Calculations of the values of the effective masses in the three main directions for all crystalline phases were also carried out. The optical properties show that the CH 3 NH 3 PbBr 3 perovskite has a good ability for photon absorption and demonstrates the possibility of its use in a wide temperature range. Key words : density functional theory, band gap, perovskite, electronic structure, density of states, optical properties