Capturing excitonic and polaronic effects in lead iodide perovskites using many-body perturbation theory

Lead iodide perovskites have attracted considerable interest in the upcoming photovoltaic technologies and optoelectronic devices. Therefore, an accurate theoretical description of electronic optical properties especially to understand excitonic effects this class materials is scientific practical interest. However, despite several research endeavours past, most analysis key parameters for solar cell performance, such as properties, effective mass, exciton binding energy (E$_B$) radiative lifetime are still largely unknown. Here, we employ state-of-the-art first-principles based methodologies viz. hybrid functional(HSE06) combined with spin-orbit coupling (SOC), many-body perturbation theory (GW, BSE), model-BSE (mBSE), Wannier-Mott (WM) Density Functional Perturbation Theory (DFPT). By taking a prototypical model system APbI$_3$ (A = Formamidinium (FA), methylammonium (MA), Cs), exhaustive presented on understanding optical, properties. We show that tuning exact exchange parameter ($\alpha$) HSE06 calculations incorporating SOC, followed by single shot GW, BSE play pivotal role obtaining reliable predictions experimental bandgap. demonstrate mBSE approach improves feature spectra w.r.t experiments. Furthermore, WM ionic contribution dielectric screening (below 16 meV) ameliorate E$_B$. Our results reveal direct-indirect band gap transition (Rashba splitting) may be factor responsible reduced charge carrier recombination rate MAPbI$_3$ FAPbI$_3$. The cation ''A'' procuring long-lived well understood. This proposed methodology allows design new tailored