Varadwaj Pradeep R
Department of Chemical System Engineering, School of Engineering, The University of Tokyo 7-3-1, Tokyo 113-8656, Japan.
Nanomaterials (Basel). 2020 May 18;10(5):973. doi: 10.3390/nano10050973.
With an interest to quest for transition metal-based halogenated double perovskites BBX as high performance semiconducting materials for optoelectronics, this study theoretically examined the electronic structures, stability, electronic (density of states and band structures), transport (effective masses of charge carriers), and optical properties (dielectric function and absorption coefficients, etc) of the series AgCrBr ( = K, Rb, Cs) using SCAN+10. Our results showed that AgCrBr ( = Rb, Cs), but not KAgCrBr, has a stable perovskite structure, which was revealed using various traditionally recommended geometry-based indices. Despite this reservation, all the three systems were shown to have similar band structures, density of states, and carrier effective masses of conducting holes and electrons, as well as the nature of the real and imaginary parts of their dielectric function, absorption coefficient, refractive index, and photoconductivity spectra. The small changes observed in any specific property of the series AgCrBr were due to the changes in the lattice properties driven by alkali substitution at the A site. A comparison with the corresponding properties of CsAgCrX (X = Cl, I) suggested that halogen substitution at the X-site can not only significantly shift the position of the onset of optical absorption found of the dielectric function, absorption coefficient and refractive spectra of CsAgCrCl and CsAgCrI toward the high- and low-energy infrared regions, respectively; but that it is also responsible in modifying their stability, electronic, transport, and optical absorption preferences. The large value of the high frequency dielectric constants-together with the appreciable magnitude of absorption coefficients and refractive indices, small values of effective masses of conducting electrons and holes, and the indirect nature of the bandgap transitions, among others-suggested that cubic AgCrBr ( = Rb, Cs) and CsAgCrCl may likely be a set of optoelectronic materials for subsequent experimental characterizations.
出于探索基于过渡金属的卤化双钙钛矿BBX作为光电子学高性能半导体材料的兴趣，本研究使用SCAN+10理论研究了AgCrBr（=K、Rb、Cs）系列的电子结构、稳定性、电子性质（态密度和能带结构）、输运性质（载流子有效质量）和光学性质（介电函数和吸收系数等）。我们的结果表明，AgCrBr（=Rb、Cs）而非KAgCrBr具有稳定的钙钛矿结构，这是通过各种传统推荐的基于几何结构的指标揭示的。尽管有此保留意见，但所有这三个体系都显示出具有相似的能带结构、态密度、传导空穴和电子的载流子有效质量，以及它们的介电函数、吸收系数、折射率和光电导光谱的实部和虚部性质。在AgCrBr系列的任何特定性质中观察到的微小变化是由于A位碱取代驱动的晶格性质变化所致。与CsAgCrX（X = Cl、I）的相应性质进行比较表明，X位的卤素取代不仅可以分别将CsAgCrCl和CsAgCrI的介电函数、吸收系数和折射光谱的光学吸收起始位置显著地向高能和低能红外区域移动；而且还负责改变它们的稳定性、电子性质、输运性质和光学吸收偏好。高频介电常数的大值——连同吸收系数和折射率的可观大小、传导电子和空穴的有效质量的小值以及带隙跃迁的间接性质等——表明立方AgCrBr（=Rb、Cs）和CsAgCrCl可能是一组用于后续实验表征的光电子材料。
