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