Temperature-Dependent Optical Band Gap in CsPbBr3, MAPbBr3, and FAPbBr3 Single Crystals
Temperature-Dependent Optical Band Gap in CsPbBr3, MAPbBr3, and FAPbBr3 Single Crystals
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DOI：
10.1021/acs.jpclett.0c00295
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发表时间：
2020-04-02
影响因子：
5.7
通讯作者：
Cahen, David
中科院分区：
文献类型：
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作者：
Mannino, Giovanni;Deretzis, Ioannis;Cahen, David
单晶代表了了解卤化物钙钛矿体特性的基准。我们确实通过椭圆偏振光谱法在 1-5 eV 范围内研究了溴化铅钙钛矿单晶（MAPbBr(3)、CsPbBr3 和首次 FAPbBr(3)）的介电功能，同时将温度从 183 K 改变到 440 K。我们发现在子带隙区域具有极低的吸收系数，表明所有三种晶体都具有较高的光学质量。我们通过临界点分析提取了带隙值，表明基于 Tauc 的值被系统性地低估了。两种结构相变，即斜方-四方和四方-立方，表现出不同的光学行为，其中前者具有不连续的特征。光学数据与 DFT 计算的互相关证明了八面体倾斜在调整给定温度下带隙值中的作用，而热膨胀的差异会影响作为温度函数的带隙趋势的斜率。
Single crystals represent a benchmark for understanding the bulk properties of halide perovskites. We have indeed studied the dielectric function of lead bromide perovskite single crystals (MAPbBr(3), CsPbBr3 and for the first time FAPbBr(3)) by spectroscopic ellipsometry in the range of 1-5 eV while varying the temperature from 183 to 440 K. An extremely low absorption coefficient in the sub-band gap region was found, indicating the high optical quality of all three crystals. We extracted the band gap values through critical point analysis showing that Tauc-based values are systematically underestimated. The two structural phase transitions, i.e., orthorhombic-tetragonal and tetragonal-cubic, show distinct optical behaviors, with the former having a discontinuous character. The cross-correlation of optical data with DFT calculations evidences the role of octahedral tilting in tailoring the value of the band gap at a given temperature, whereas differences in the thermal expansion affect the slope of the band gap trend as a function of temperature.