Proceedings of nanoGe Fall Meeting19 (NFM19)
Publication date: 18th July 2019
All inorganic cesium lead halide (CsPbX3, X is Cl, Br, or I) perovskite nanocrystals (NCs) prepared via colloidal synthesis have come into the spotlight since they are exceptionally bright without any post treatment. Widely tunable band gaps, extremely narrow emission linewidth, and highly dynamic surface-ligand interactions of CsPbX3 NCs also attract considerable attention from many researchers.[1,2] Unfortunately, however, serious instability of CsPbX3 NCs was reported in many studies, and the instability severely hinders wider utilization of CsPbX3 NCs in practical applications. For example, drastic drop of photoluminescence (PL) quantum yield (QY) was reported when CsPbX3 NCs were kept under ambient condition. Also, in particular for CsPbI3 NCs, unwanted transformation from cubic phase (perovskite) to orthorhombic phase (non-perovskite) was reported. The instability is attributed to metastable structures, dynamic surfaces, and imperfect surface passivation of CsPbX3 NCs, and stabilizing CsPbX3 NCs is must be the most urgent agenda in this field.[3]
In our previous study, we demonstrate in-situ stabilization of CsPbX3 NCs by introducing additional metal halides (e.g., ZnX2, InX3, etc.) during the synthesis. From the various investigations based on XPS, NMR, and TEM, inorganic passivating layer (e.g., lead halide) was proposed as the origin of significantly enhanced stability, but the role of additional metal halides in the synthesis was unrevealed. [3]
Herein, we show new surface atomic model for CsPbX3 NCs. In our new models, pristine CsPbX3 NCs have oleate (anion) ligand-rich surface, and we find transition to oleylammonium (cation) ligand-rich surface with presence of additional metal halides (e.g., ZnX2) during the synthesis. Oleate (anion)-rich or oleylammonium (cation)-rich surfaces are clearly demonstrated by selective ligand exchange study. Also, the role of additional metal halides was proposed by theoretical understanding based on DFT calculations. Finally, significantly enhanced stability is ascribed to suppressed growth of (110) surface in CsPbX3 NCs with oleylammonium (cation)-rich surface, which are synthesized by introducing additional metal halides.
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