双钙钛矿卤化物Cs_(2)AgBCl_(6)(B=Cr,Mn,Fe)电子结构和光学性质的第一性原理研究

First-principles study on electronic structures and optical properties of double-peovskite halides Cs_(2)AgBCl_(6)(B=Cr,Mn,Fe)

无铅双钙钛矿卤化物因其无毒性、良好的化学稳定性和优异的光学特性,吸引了人们的注意,被广泛应用于太阳能电池、光电探测器、X射线探测器和发光二极管等器件。采用密度泛函理论的广义梯度近似加U方法,对双钙钛矿卤化物Cs_(2)AgBCl_(6)(B=Cr,Mn,Fe)电子结构和光学性质进行了研究,分析了二者的内在联系,讨论了B位元素的改变对材料电子结构和光学性质的影响。通过总能计算确定了晶体的磁基态,Cs_(2)AgCrCl_(6)和Cs_(2)AgFeCl_(6)为反铁磁态,Cs_(2)AgMnCl 6为铁磁态。在能带结构上,Cs_(2)AgCrCl_(6)和Cs_(2)AgFeCl_(6)为半导体,Cs_(2)AgMnCl_(6)为半金属。由于Ag_(4)d、B_(3)d以及Cl_(3)p价带的电子向B_(3)d导带跃迁,因此Cs_(2)AgBCl_(6)(B=Cr,Mn,Fe)在可见至红外波段都具有较宽的吸收光谱和较高的吸收系数。本研究可为Cs_(2)AgBCl_(6)在光电子器件领域的应用提供理论指导。

Lead-free double-perovskite halides have attracted people’s attention because of their non-toxicity,good chemical stability and excellent optical properties,and have been widely applied in the fields of solar cells,photodetectors,X-ray detectors,light emitting diodes,etc.The electronic structures and optical properties of double perovskite halides Cs_(2)AgBCl_(6)(B=Cr,Mn,Fe)were studied by using the generalized gradient approximation plus U method based on the density functional theory,and the internal relationship between them was analyzed.Also,the influences of the change of B-site elements on the electronic structures and optical properties were discussed.The magnetic ground states of the crystals were confirmed through calculating the total energy.Cs_(2)AgCrCl_(6) and Cs_(2)AgFeCl_(6) are antiferromagnetic states,and Cs_(2)AgMnCl_(6) is ferromagnetic state.From the energy band structures,Cs_(2)AgCrCl_(6) and Cs_(2)AgFeCl_(6) are semiconductors,and Cs_(2)AgMnCl_(6) is a half metal.Due to the transition processes from Ag_(4)d,B_(3)d and Cl_(3)p valence bands to B_(3)d conduction band,Cs_(2)AgBCl_(6)(B=Cr,Mn,Fe)have wide absorption spectra and high absorption coefficients in the visible to infrared regions.This study provides theoretical guidances for the application of Cs_(2)AgBCl_(6) in the field of optoelectronic devices.