Yang Dongsheng, Cheng Xiangai, Liu Yu, Shen Chao, Xu Zhongjie, Zheng Xin, Jiang Tian
Appl Opt. 2017 Apr 1;56(10):2878-2885. doi: 10.1364/AO.56.002878.
In recent years, CsPbBr quantum dots (QDs) have attracted much attention due to their bright prospects in solar cell studies. Dielectric properties are important for the fabrication of optoelectronic devices. Here, the dielectric properties of a CsPbBr QD solution are investigated between 0.1 and 2.0 THz by terahertz time-domain spectroscopy. The measured frequency-dependent transmitted ratio is found to decrease from 0.96 to 0.80 in this range. By comparing different concentrations of the QD solution, the frequency-averaged absorption is linearly increased with the increase in QD concentration. After that, the frequency-dependent dielectric constant, including the complex refractive index, complex dielectric constant, and conductivity, is extracted by Fourier transform of the time-domain spectrum. An effective medium approach method is adopted to extract the complex dielectric constant of a CsPbBr QD inclusion, and a slight peak around 0.4 THz is found in the imaginary part of the dielectric constant. The result of Drude-Lorentz fitting shows that the phonon plays a dominant role in the dielectric properties of a CsPbBr QD solution. Moreover, the THz response of a CsPbBr QD is found to be unchanged when the test is conducted under illumination. We attribute this phenomenon to the discrete energy level of excitons in CsPbBr QDs due to quantum confinement, and design a comparative experiment to validate it. This study is significant for its deeper insight into the dielectric properties of CsPbBr QDs, and thus is helpful through its applications in optoelectronics.
近年来，CsPbBr量子点（QDs）因其在太阳能电池研究中的广阔前景而备受关注。介电性能对于光电器件的制造至关重要。在此，通过太赫兹时域光谱研究了CsPbBr量子点溶液在0.1至2.0太赫兹之间的介电性能。发现在该范围内测得的频率相关透射率从0.96降至0.80。通过比较不同浓度的量子点溶液，频率平均吸收率随量子点浓度的增加呈线性增加。之后，通过时域光谱的傅里叶变换提取频率相关的介电常数，包括复折射率、复介电常数和电导率。采用有效介质近似方法提取CsPbBr量子点夹杂物的复介电常数，并且在介电常数的虚部发现了一个约0.4太赫兹的小峰。德鲁德 - 洛伦兹拟合结果表明，声子在CsPbBr量子点溶液的介电性能中起主导作用。此外，当在光照下进行测试时，发现CsPbBr量子点的太赫兹响应不变。我们将此现象归因于由于量子限制导致的CsPbBr量子点中激子的离散能级，并设计了一个对比实验来验证它。这项研究对于更深入了解CsPbBr量子点的介电性能具有重要意义，因此通过其在光电子学中的应用而有所帮助。
