Optical Properties of Organometallic Perovskite: An ab initio Study using Relativistic GW Correction and Bethe-Salpeter Equation

TL;DR

This study uses advanced ab initio methods including relativistic GW correction and Bethe-Salpeter equations to accurately analyze the optical and vibrational properties of organometallic perovskite CH3NH3PbI3, highlighting the importance of many-body effects.

Contribution

It introduces a comprehensive first-principles approach combining GW and BSE calculations to better understand perovskite optical properties beyond conventional DFT methods.

Findings

Enhanced optical conductivity near the band gap due to many-body effects.

Good agreement between calculated and terahertz measured phonon frequencies.

Highlighting the role of low-energy vibrational modes in optical behavior.

Abstract

In the development of highly efficient photovoltaic cells, solid perovskite systems have demonstrated unprecedented promise, with the figure of merit exceeding nineteen percent of efficiency. In this paper, we investigate the optical and vibrational properties of organometallic cubic perovskite CH3NH3PbI3 using first-principles calculations. For accurate theoretical description, we go beyond conventional density functional theory (DFT), and calculated optical conductivity using relativist quasi-particle (GW) correction. Incorporating these many-body effects, we further solve Bethe-Salpeter equations (BSE) for excitons, and found enhanced optical conductivity near the gap edge. Due to the presence of organic methylammonium cations near the center of the perovskite cell, the system is sensitive to low energy vibrational modes. We estimate the phonon modes of CH3NH3PbI3 using small displacement approach, and further calculate the infrared absorption (IR) spectra. Qualitatively, our calculations of low-energy phonon frequencies are in good agreement with our terahertz measurements. Therefore, for both energy scales (around 2 eV and 0-20 meV), our calculations reveal the importance of many-body effects and their contributions to the desirable optical properties in the cubic organometallic perovskites system.