Exciton Binding Energy and the Nature of Emissive States in Organometal Halide Perovskites.
Exciton Binding Energy and the Nature of Emissive States in Organometal Halide Perovskites.
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DOI：
10.1021/acs.jpclett.5b01252
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发表时间：
2015-07
期刊：
影响因子：
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通讯作者：
Kaibo Zheng;Qiushi Zhu;M. Abdellah;M. Messing;Wei Zhang;A. Generalov;Y. Niu;L. Ribaud;S. Canton-S.-C
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文献类型：
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作者：
Kaibo Zheng;Qiushi Zhu;M. Abdellah;M. Messing;Wei Zhang;A. Generalov;Y. Niu;L. Ribaud;S. Canton-S.-C
纳米材料的特性往往不同于相应的体相性质，这为应用提供了新的、有时是意想不到的机会。在此我们研究了甲胺铅溴（MAPbBr3）钙钛矿8纳米胶体纳米粒子的性质，并将其与代表体相的大微晶的性质进行对比。X射线光谱学表明纳米粒子中的激子结合能为0.32±0.10电子伏特。这比体相晶体的值（0.084±0.010电子伏特）高5倍，这也很好地解释了纳米粒子中高的荧光量子产率。在体相中，在高激发浓度下，由于形成发射激子态的电荷的非成对复合，荧光强度遵循萨哈 - 朗缪尔模型呈二次方行为。在纳米粒子中，由于每个粒子的激发浓度显著小于1，观察到的是线性依赖关系。即使在体相中，在较低激发浓度下也显示出线性发射强度依赖关系。在这种情况下，平均激发间距变得大于载流子扩散长度，从而抑制了非成对复合。基于这些考虑，我们得出甲胺铅溴（MAPbBr3）中的载流子扩散长度为100纳米。
Characteristics of nanoscale materials are often different from the corresponding bulk properties providing new, sometimes unexpected, opportunities for applications. Here we investigate the properties of 8 nm colloidal nanoparticles of MAPbBr3 perovskites and contrast them to the ones of large microcrystallites representing a bulk. X-ray spectroscopies provide an exciton binding energy of 0.32 ± 0.10 eV in the nanoparticles. This is 5 times higher than the value of bulk crystals (0.084 ± 0.010 eV), and readily explains the high fluorescence quantum yield in nanoparticles. In the bulk, at high excitation concentrations, the fluorescence intensity has quadratic behavior following the Saha-Langmuir model due to the nongeminate recombination of charges forming the emissive exciton states. In the nanoparticles, a linear dependence is observed since the excitation concentration per particle is significantly less than one. Even the bulk shows linear emission intensity dependence at lower excitation concentrations. In this case, the average excitation spacing becomes larger than the carrier diffusion length suppressing the nongeminate recombination. From these considerations we obtain the charge carrier diffusion length in MAPbBr3 of 100 nm.