Self-selective passivation of diversely charged SnO₂/CsPbI₃ heterointerfaces using binary ionic compounds

SnO2 is increasingly favored as an electron transport layer for perovskite solar cells due to its intrinsic advantages, but SnO2/CsPbI3 heterointerfaces exhibit considerable interfacial states causing severe recombination losses. The diverse atomic structures and charge states make targeted passivation of the interfaces with one dopant challenging. First-principles calculations identify that the negatively charged SnO2-SnO/CsPbI3-CsI and the positively charged SnO2-O(O & PRIME;)/CsPbI3-PbI heterointerfaces (SnO2-O and SnO2-O & PRIME; are the Tasker's type-II and type-III surfaces, respectively) are energetically favorable configurations, with deep-level states originating from the Sn-5s and Sn-5p orbitals, wrong bonds of Sn-5s/Pb-6p orbitals and the O-2p/I-5p anti-bonding orbitals, respectively. We find that Mg and Cl doping can selectively passivate these heterointerfaces by the effective formation of 3Mg(Sn), Cl-i and Cl-O defects, without introducing detrimental interfacial dipole moments. Moreover, nonadiabatic molecular dynamics simulations indicate improved carrier lifetimes, confirming the favorable passivation effect of the Mg and Cl doping. This study proposes that treating the SnO2 surface with soluble MgCl2 before depositing perovskites, combined with junction heat-treating, is expected to self-selectively heal the diversely charged defect states at the SnO2/CsPbI3 heterointerfaces, and the self-selective passivation strategy realized by the incorporation of binary ionic compounds is an alternative way to improve the diversely charged heterointerfaces of semiconductor devices.