Understanding the role of Sn substitution and Pb vacancy in FAPbBr₃perovskites: A hybrid functional study

Hybrid inorganic-organic perovskites (HIOPs) solar cells have attracted intense attention because of its high carrier lifetime, long diffusion length and low manufacturing cost. Formamidinium Lead Bromide (FAPbBr₃), a HIOPs is immensely promising class of material for photovoltaic application. However, due to presence of hazardous Pb, its application to real life is hindered. Therefore, its our profound interest to understand if substitution of adatoms (e.g. Sn, Ge) or creation of Pb-vacancy [Vc] or doing the same simultaneously will be effective considering its efficiency in solar cell devices.
We address here the role of Sn substitution and Pb-Vc in regulating stability using state-of-the-art hybrid density functional theory. The explicit role of spin orbit coupling (SOC) and electron self interaction error are discussed. We find while SOC has significant role in regulating electronic bands, it doesn't affect the relative hierarchy of thermodynamic stability of different configurations of FAPb_(1-x-y)Sn_xVc_yBr₃. However inclusion of electron self interaction error is absolutely important to estimate formation energy of configurations correctly. The Spectroscopic Limited Maximum Efficiency (SLME) is compared of the most stable defected system with respect to the pristine FAPbBr₃.