Capturing excitonic effects in lead iodide perovskites from many-body perturbation theory

Lead iodide perovskites have attracted considerable interest as promising energy-materials. However, till date, several key electronic properties such as optical properties, effective mass, exciton binding energy, and the radiative exciton lifetime are largely unknown. Here, we employ an integrated approach with several state-of-the-art first-principles based methodologies viz. hybrid Density Functional Theory combined with spin-orbit coupling, many-body perturbation theory, model-BSE (mBSE), Wannier-Mott and Density Functional Perturbation Theory to address these properties by taking a prototypical model system viz. APbI₃ (A = Formamidinium (FA), methylammonium (MA), and Cs). We demonstrate that while the mBSE approach improves the excitonic feature in the optical spectra, the Wannier-Mott approach and ionic contribution to dielectric screening ameliorate the exciton binding energy. Moreover, the direct-indirect band gap transition (Rashba-Dresselhaus splitting) may be responsible for the reduced charge carrier recombination rate in MAPbI₃ and FAPbI₃. The role of cation “A” for procuring the long-lived exciton lifetime is well understood.