Origin of the Size-Dependent Stokes Shift in CsPbBr3 Perovskite Nanocrystals
Origin of the Size-Dependent Stokes Shift in CsPbBr3 Perovskite Nanocrystals
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DOI：
10.1021/jacs.7b05683
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发表时间：
2017-09-06
影响因子：
15
通讯作者：
Kuno, Masaru
中科院分区：
文献类型：
--
作者：
Brennan, Michael C.;Herr, John E.;Kuno, Masaru
首次解释了CsPbBr3纳米晶体（NCs）中尺寸依赖的Stokes位移的起源。NCs的斯托克斯位移范围从82到20 meV，有效边缘长度从4到13 nm不等。我们表明，斯托克斯位移是NC电子结构固有的，而不是由外部效应引起的，如残余系综尺寸分布、杂质或溶剂相关效应。通过第一性原理计算阐明了斯托克斯位移的起源。相应的CsPbBr3 NC态密度和能带结构的理论建模表明，边缘长度为2 ~ 5 nm的NC在价带边缘态以上存在一个260 ~ 70 meV的本禀受限空穴态。因此，预测了大小相关的斯托克斯位移，并与实验数据在定量上一致。本体计算和NC计算的对比表明，限制孔态是NC所独有的。在更广泛的层面上，CsPbBr3的吸收和发射状态之间的区别可能是其他卤化物钙钛矿NC的一般特征，并且可以通过NC尺寸进行调整，以增强涉及这些材料的应用。
The origin of the size-dependent Stokes shift in CsPbBr3 nanocrystals (NCs) is explained for the first time. Stokes shifts range from 82 to 20 meV for NCs with effective edge lengths varying from similar to 4 to 13 nm. We show that the Stokes shift is intrinsic to the NC electronic structure and does not arise from extrinsic effects such as residual ensemble size distributions, impurities, or solvent-related effects. The origin of the Stokes shift is elucidated via first-principles calculations. Corresponding theoretical modeling of the CsPbBr3 NC density of states and band structure reveals the existence of an intrinsic confined hole state 260 to 70 meV above the valence band edge state for NCs with edge lengths from similar to 2 to 5 nm. A size-dependent Stokes shift is therefore predicted and is in quantitative agreement with the experimental data. Comparison between bulk and NC calculations shows that the confined hole state is exclusive to NCs. At a broader level, the distinction between absorbing and emitting states in CsPbBr3 is likely a general feature of other halide perovskite NCs and can be tuned via NC size to enhance applications involving these materials.