Fluorescence Microscopy of Single Lead Bromide Nanocrystals Reveals Sharp Transitions during Their Transformation to Methylammonium Lead Bromide
Fluorescence Microscopy of Single Lead Bromide Nanocrystals Reveals Sharp Transitions during Their Transformation to Methylammonium Lead Bromide
复制标题
单溴化铅纳米晶体的荧光显微镜揭示了其转变为甲基溴化铅铵过程中的急剧转变
DOI：
10.1039/c8tc06470a
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发表时间：
2019
影响因子：
6.4
通讯作者：
Sadtler, Bryce
中科院分区：
文献类型：
--
作者：
Yin, Bo;Cavin, John;Wang, Dong;Khan, Daniel;Shen, Meikun;Laing, Craig;Mishra, Rohan;Sadtler, Bryce
控制卤化铅钙钛矿晶体的成核和生长对于在光电器件中获得高量子产率的半导体薄膜至关重要。在本报告中，我们利用荧光亮度的变化来成像单个溴化铅 (PbBr2) 纳米晶体通过插入 CH3NH3Br 向甲基溴化铅铵 (CH3NH3PbBr3) 的转变。一次分析一个纳米晶体的这种反应，揭示了当荧光强度在许多颗粒上平均时被掩盖的信息。单个纳米晶体强度的急剧上升表明它们的转变速度比整体平均转变所需的时间快得多。虽然整体反应速率随着 CH3NH3Br 浓度的增加而增加，但单个纳米晶体的强度增加对 CH3NH3Br 浓度不敏感。为了解释这些观察结果，我们提出了一个相变模型，其中将 PbBr2 纳米晶体转化为 CH3NH3PbBr3 所需的重构转变最初为离子嵌入创建了高能垒。当晶体采用钙钛矿相时，发生转变的临界点，此时进一步离子嵌入的活化能逐渐变小。蒙特卡罗模拟将激活势垒的变化纳入反应事件的可能性，再现了单个粒子强度轨迹的关键实验观察结果。从这项研究中获得的见解可用于进一步控制 CH3NH3PbBr3 和其他溶液加工半导体的结晶。
Control over the nucleation and growth of lead-halide perovskite crystals is critical to obtain semiconductor films with high quantum yields in optoelectronic devices. In this report, we use the change in fluorescence brightness to image the transformation of individual lead bromide (PbBr2) nanocrystals to methylammonium lead bromide (CH3NH3PbBr3) via intercalation of CH3NH3Br. Analyzing this reaction one nanocrystal at a time reveals information that is masked when the fluorescence intensity is averaged over many particles. Sharp rises in the intensity of single nanocrystals indicate they transform much faster than the time it takes for the ensemble average to transform. While the ensemble reaction rate increases with increasing CH3NH3Br concentration, the intensity rises for individual nanocrystals are insensitive to the CH3NH3Br concentration. To explain these observations, we propose a phase-transformation model in which the reconstructive transitions necessary to convert a PbBr2 nanocrystal into CH3NH3PbBr3 initially create a high energy barrier for ion intercalation. A critical point in the transformation occurs when the crystal adopts the perovskite phase, at which point the activation energy for further ion intercalation becomes progressively smaller. Monte Carlo simulations that incorporate this change in activation barrier into the likelihood of reaction events reproduce key experimental observations for the intensity trajectories of individual particles. The insights gained from this study may be used to further control the crystallization of CH3NH3PbBr3 and other solution-processed semiconductors.