Organic A‐Site Cations Improve the Resilience of Inorganic Lead‐Halide Perovskite Nanocrystals to Surface Defect Formation

Abstract Lead halide perovskite nanocrystals (LHP NCs) are generally prone to surface defect formation during the purification process, resulting in a reduced photoluminescence (PL) quantum yield. The purification of LHP NCs using antisolvents leads to the detachment of surface atoms and ligandsin the form of alkylammonium‐halides or A‐carboxylates (A: Cs, methylammonium, MA, or formamidinium, FA. Currently, intense research is being carried out to improve the surface stability of LHP NCs using various long‐chain organic ligands that strongly bind to the surface of NCs. Herein, the findings on the higher surface stability of hybrid (MAPbBr 3 and FAPbBr 3 ) LHP NCs compared to that of inorganic CsPbBr 3 NCs against purification with polar antisolvents are reported. It is discovered that the CsPbBr 3 NC surface stability can be enhanced (reaching that of hybrid perovskite NCs) by the incorporation of a small amount of MA or FA A‐site organic cations into their lattice, corroborated by the evidence that the PL quantum yield of mixed A‐cation Cs x FA 1‐x PbBr 3 and Cs x MA 1‐x PbBr 3 NCs remains unaffected after several purification cycles. It is hypothesized that this is attributed to hydrogen bonding between the organic A‐site cations and the neighboring halides on the surface. These findings are not only fundamentally important but are also expected to have wide implications in the field of metal‐halide perovskite optoelectronics.