Koscher Brent A, Nett Zachary, Alivisatos A Paul
Department of Chemistry , University of California , Berkeley , California 94720 , United States.
Materials Science Division , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States.
ACS Nano. 2019 Oct 22;13(10):11825-11833. doi: 10.1021/acsnano.9b05782. Epub 2019 Oct 4.
Reliably accessing nanocrystal luminophores with near-unity efficiencies aids in the ability to understand the upper performance limits in optoelectronic applications that require minimal nonradiative losses. Constructing structure-function relationships at the atomic level, while accounting for inevitable defects, allows for the development of robust strategies to achieve near-unity quantum yield luminophores. For CsPbBr perovskite nanocrystals, bromine vacancies leave behind undercoordinated lead atoms that act as traps, limiting the achievable optical performance of the material. We show that selective etching represents a promising path for mitigating the consequences of optical defects in CsPbBr nanocrystals. A mechanistic understanding of the etching reaction is essential for developing strategies to finely control the reaction. We report a study of the selective etching mechanism of CsPbBr nanocrystal cubes by controlling the etchant chemical potential. We observe optical absorption and luminescence trajectories while varying the extent and rate of lead removal, removing in some cases up to 75% of the lead from the original nanocrystal ensemble. At modest etchant chemical potentials, the size and shape uniformity of the nanocrystal ensemble improves in addition to the quantum yield, proceeding through a layer-by-layer etching mechanism. Operating with excessively high etchant chemical potentials is detrimental to the overall optical performance as the etching transitions to nonselective, while too low of a chemical potential results in incomplete etching. Through this general approach, we show how to finely control selective etching to consistently access a steady state or chemical stability zone of near-unity quantum yield CsPbBr nanocrystals postsynthetically, suggesting a practical framework to extend this treatment to other perovskite compositions and sizes.
以接近单位效率可靠地获取纳米晶体发光体有助于理解在要求最小非辐射损耗的光电子应用中的最高性能极限。在考虑不可避免的缺陷的同时，构建原子水平的结构 - 功能关系，有助于开发实现接近单位量子产率发光体的稳健策略。对于CsPbBr钙钛矿纳米晶体，溴空位会留下配位不足的铅原子，这些铅原子充当陷阱，限制了材料可实现的光学性能。我们表明，选择性蚀刻是减轻CsPbBr纳米晶体中光学缺陷后果的一条有前途的途径。对蚀刻反应的机理理解对于制定精细控制反应的策略至关重要。我们报告了一项通过控制蚀刻剂化学势对CsPbBr纳米立方体选择性蚀刻机理的研究。我们观察了光吸收和发光轨迹，同时改变铅去除的程度和速率，在某些情况下从原始纳米晶体集合中去除高达75%的铅。在适度的蚀刻剂化学势下，除了量子产率提高外，纳米晶体集合的尺寸和形状均匀性也得到改善，这是通过逐层蚀刻机制进行的。使用过高的蚀刻剂化学势会损害整体光学性能，因为蚀刻会转变为非选择性的，而化学势过低则会导致蚀刻不完全。通过这种通用方法，我们展示了如何精细控制选择性蚀刻，以在合成后始终获得接近单位量子产率的CsPbBr纳米晶体的稳态或化学稳定区，这为将这种处理扩展到其他钙钛矿组成和尺寸提供了一个实用框架。
