Passivation of Hydrogen Interstitials in Metal Halide Perovskites: A Time-Domain Ab Initio Study

Hydrogen interstitials have been recognized recently as significant nonradiative recombination centers in hybrid lead halide perovskites. By utilizing time-domain density functional theory and nonadiabatic (NA) molecular dynamics, we investigate the nonradiative recombination mechanism and systematic passivation strategies for the H_i defect in FAPbI₃, where FA = CH(NH₂)₂. We show that H_i forms a Pb-H_i-I trimer that introduces shallow and deep-level traps within the bandgap, leading to severe nonradiative charge losses. We demonstrate that both iodine interstitial (I_i) and alkali metals can effectively passivate the H_i defect but by different mechanisms. I_i disrupts the Pb-H_i-I trimer interaction by breaking the H_i-Pb bond, accepting an electron from H_i and shifting the defect levels up into a conduction band. This results in mutual passivation of the nonmetal I_i and H_i defects. Alternatively, alkali metals disrupt the Pb-H_i-I trimer by breaking the H_i-I bond. They donate an electron to H_i and shift the defect states down to the valence band. The introduction of I_i and Na enhances structural disorder and shifts electron-vibrational interactions toward low-frequency modes. This, in turn, weakens the NA coupling and extends the charge carrier lifetime even relative to the pristine system. The study shows that disrupting interactions between nonmetal interstitial defects and the inorganic lattice is crucial for their passivation and that self-passivation of nonmetal interstitial defects exists in hybrid lead halide perovskites. The demonstrated systematic strategies of the H_i defect passivation advance understanding of the uncommon defect properties and provide guidelines for further improvement of optoelectronic performance of hybrid lead halide perovskites.