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

Abstract

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′)/CsPbI₃–PbI heterointerfaces (SnO₂–O and SnO₂–O′ 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.