Surface Engineering for Improved Stability of CH₃NH₃PbBr₃ Perovskite Nanocrystals

Organohalide perovskite nanocrystals (NCs) with a variety of nano-scale structure and morphology have shown a promising potential owing to their size- and composition-dependent optoelectronic properties. (e.g. solar energy harvesting, piezoelectric energy generator, lighting, sensor for gas and chemical substances, polarity chemosensor, photodetectors, etc.). Despite extensive studies on their size dependent optical properties, a lack of understanding on their morphological transformation and the relevant stability issues limits a wide range of applications. Herein we hypothesize a mechanism on the morphological transformation of perovskite NCs, which leads to dissolving NCs and forming microscale rectangular grains, resulting in a reduction of photoluminescence. We found that the morphological transformation from nanocrystal solids to microscale rectangular solids occurs via Ostwald ripening. A surface treatment with the identical surfactant suppresses the transformation, resulting in nearly monodisperse NCs with a square shape, and thus improves the stability of NC solution as well as their photoluminescence performance and quantum yield.