Synergy Between Dynamic Behavior of Hydrogen Defects and Non-Radiative Recombination in Metal-Halide Perovskites

In organic-inorganic hybrid perovskite solar cells (PSCs), hydrogen defects introduce deep-level trap states, significantly influencing non-radiative recombination processes. Those defects are primarily observed in MA-PSCs rather than FA-PSCs. As a result, MA-PSCs demonstrated a lower efficiency of 23.6% compared to 26.1% of FA-PSCs. In this work, both hydrogen vacancy (V_H ^-) and hydrogen interstitial (H_i ^-) defects in MAPbI₃ bulk and on surfaces, respectively are investigated. i) Bulk V_H ^- defects have dramatic impact on non-radiative recombination, with lifetime varying from 67 to 8 ns, depending on whether deprotonated MA⁰ are ion-bonded or not. ii) Surface H-defects exhibited an inherent self-healing mechanism through a chemical bond between MA⁰ and Pb²⁺, indicating a self-passivation effect. iii) Both V_H ^- and H_i ^- defects can be mitigated by alkali cation passivation; while large cations are preferable for V_H ^- passivation, given strong binding energy of cation/perovskite, as well as, weak band edge non-adiabatic couplings; and small cations are suited for H_i ^- passivation, considering the steric hindrance effect. The dual passivation strategy addressed diverse experimental outcomes, particularly in enhancing performance associated with cation selections. The dynamic connection between hydrogen defects and non-radiative recombination is elucidated, providing insights into hydrogen defect passivation essential for high-performance PSCs fabrication.