Highly Fluorescent and Stable Lead Halide Perovskite Nanocrystals Protected by an In Situ Formed Lead Halide–Amino Acid Matrix

Lead halide perovskite nanocrystals (PNCs) are a highly promising class of materials for optoelectronic applications, due to their exceptional optical properties. Nevertheless, their poor stability has remained a major obstacle to practical implementation. This work reports highly stable lead halide PNCs of the compositions MAPbBr 3 and FAPbBr 3 (MA = methylammonium, FA = formamidinium). The nanocrystals are prepared via a facile, single‐step precipitation procedure using the amino acid derivative N α ‐( tert ‐butoxycarbonyl)‐L‐lysine (boc‐Lys) and hexanoic acid as ligands. Films of the precipitated nanocrystals exhibit near‐unity photoluminescence quantum yields and outstanding stability, maintaining their optical properties for more than 150 days (MAPbBr 3 ) and 490 days (FAPbBr 3 ) under ambient conditions, and for over 20 h under continuous blue light excitation. The excellent stability of the nanocrystals is attributed to an in situ formed encapsulating matrix, which initially consists of a complex formed between PbBr 2 and boc‐Lys. Furthermore, it is demonstrated that the isolated PbBr 2 /boc‐Lys matrix material can be used as precursor for growing highly luminescent, stable MAPbBr 3 nanocrystals through exposure to methylammonium bromide vapors. The presented nanocrystals are excellent candidates for light‐emission applications and could provide a blueprint for designing precursor materials for the growth of high‐quality, stable PNCs via metal halide‐amino acid complexes.