A theoretical study of the molecular passivation of p-/n-type defects on tin- and germanium-mixed perovskite surfaces using Lewis base/acid

), employing ethylenediamine and iodopentafluorobenzene as excellent passivation molecules. Our theoretical calculations show that the adsorption of these passivation molecules on the Pb-free perovskite surfaces could remove defect energy levels from the bandgap. Particularly, we discuss the effectiveness of a Lewis base to reduce deep defect levels for a Sn-Ge-mixed perovskite. Furthermore, we present a molecule-defect-level interaction model to understand the passivation mechanism, focusing on the chemical effects of Lewis bases/acids.