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Dual Passivation of Point Defects at Perovskite Grain Boundaries with Ammonium Salts Greatly Inhibits Nonradiative Charge Recombination.

Experiments demonstrate that grain boundaries (GBs) exhibit detrimental effect on carrier lifetimes in MAPbI3 (MA= CH3NH3+). On the basis of the nonadiabatic (NA) molecular dynamics simulations, we demonstrated that NH4Cl can simultaneously passivate the common point defects that introduce recombination centers at GBs and accelerate electron-hole recombination but shows small effects in the bulk. The MA interstitial (MAi) and the substitutional MA to Pb (MAPb) in pristine MAPbI3 leave the band gap and charge recombination rates largely unchanged but create deep electron traps at GBs by separately either distorting inorganic octahedra or creating an I-dimer. Cl- and NH4+ remove the in-gap states by either restoring the distorted octahedra or destroying the I-dimer. Thus, the band gap recovers to the pristine system, NA coupling decreases, and decoherence accelerates, extending the carrier lifetime even twice longer than MAPbI3. This study shows that the negative role of GBs can be removed by dually passivating with NH4Cl.