Lead trihalide perovskite nanomaterials are widely studied due to their remarkable optoelectronic properties. Despite their outstanding and demonstrated potential, these materials have been kept from practical application due to their crippling instability in ambient conditions. From electron microscopy studies of this series of quantum dots (QDs) we demonstrate that the onset of degradation in optical properties coincides with the appearance of nano black spots (NBSs) on the QDs. Elemental mapping using electron microscopy revealed the NBSs to be areas with higher concentration of lead. We have looked at the possible mechanisms to explain NBSs and found that they may arise due to two very different pathways. The first one is due to crystal growth initiated by excess reactants and the second is due to chemical degradation of the QD surface. Further we have invoked the well known geometrical stability criterion for perovskites, Goldschmidt's tolerance factor to predict the appearance of NBSs and the onset of optical instability of CsPbBr_3−xI_x QDs. This correlation can be used as a criterion to aid the selection of more optically stable perovskite QDs for practical applications.

中文翻译：

---

混合卤化物钙钛矿量子点中的纳米黑点与光学稳定性的相关性†

三卤化铅钙钛矿纳米材料由于其卓越的光电性能而被广泛研究。尽管它们具有出色的潜力和已证明的潜力，但由于它们在环境条件下的致残性不稳定，因而无法实际应用。从对这一系列量子点（QDs）的电子显微镜研究中，我们证明了光学性能下降的开始与QDs上纳米黑点（NBS）的出现相吻合。使用电子显微镜的元素图谱显示NBS是铅浓度较高的区域。我们研究了解释NBS的可能机制，发现它们可能是由于两种截然不同的途径而产生的。第一个是由于过量反应物引发的晶体生长，第二个是由于QD表面的化学降解。_{3− x} I _x QD。该相关性可以用作标准，以帮助为实际应用选择光学上更稳定的钙钛矿QD。