Computational Study of Halide Perovskite-Derived A₂BX₆ Inorganic Compounds: Chemical Trends in Electronic Structure and Structural Stability

Abstract

The electronic structure and energetic stability of A 2 BX 6 halide compounds with the cubic and tetragonal variants of the perovskite-derived K 2 PtCl 6 prototype structure are investigated computationally within the frameworks of density-functional-theory (DFT) and hybrid (HSE06) functionals. The HSE06 calculations are undertaken for 1 arXiv:1706.08674v1 [cond-mat.mtrl-sci] 27 Jun 2017 seven known A 2 BX 6 compounds with A = K, Rb and Cs, and B = Sn, Pd, Pt, Te, and X = I. Trends in band gaps and energetic stability are identified, which are explored further employing DFT calculations over a larger range of chemistries, characterized by A = K, Rb, Cs, B = Si, Ge, Sn, Pb, Ni, Pd, Pt, Se and Te and X = Cl, Br, I. For the systems investigated in this work, the band gap increases from iodide to bromide to chloride. Further, variations in the A site cation influences the band gap as well as the preferred degree of tetragonal distortion. Smaller A site cations such as K andRb favor tetragonal structural distortions, resulting in a slightly larger band gap. For variations in the B site in the (Ni, Pd, Pt) group and the (Se, Te) group, the band gap increases with increasing cation size. However, no observed chemical trend with respect to cation size for band gap was found for the (Si, Sn, Ge, Pb) group. The findings in this work provide guidelines for the design of halide A 2 BX 6 compounds for potential photovoltaic applications.

Computational prediction of structural, electronic, and optical properties and phase stability of double perovskites K2SnX6 (X = I, Br, Cl)

“…The calculated band gaps display a distinct variation tendency with respect to the choice of halogen atom, such that the band gaps decrease systematically as the ionic radius of halogen anion increases for all the phases. Such variation tendency agrees well with the previous calculations for the hybrid organic-inorganic, all-inorganic, and vacancy-ordered double perovskites [53,50,54,20,23], which can be understood through the analysis of total and atomic resolved DOS (see Figure 2). As can be seen in Figure 3, VBM is derived from the p orbitals of halide anion, while CBM is characterized by antibonding between the Sn s and the halide p orbitals.…”

“…This straightly indicates that changing from lower-to higher-symmetry phase as well as going from X = Cl to I, K 2 SnX 6 is expected to possess high mobility of charge carriers owing to the smaller effective masses of electron and hole. In addition, as confirmed in other types of double perovskite [53,50], the effective masses of holes were found to be larger than those of electrons for all the phases of K 2 SnX 6 (X = I, Br, Cl). Our calculated effective masses of m * e = 0.17m e and m * h = 0.46m e for the cubic K 2 SnI 6 are smaller than the previous calculations of m * e = 0.29m e and m * h = 1.34m e for the cubic Rb 2 SnI 6 , and m * e = 0.33m e and m * h = 1.50m e for the cubic Cs 2 SnI 6 [53], which agrees well with Cai's report [53] where they concluded that reducing the size of the A-site cation leads to a decrease in effective masses of both electron and hole for A 2 BX 6 .…”

Pressure‐Induced Structural Evolution and Bandgap Optimization of Lead‐Free Halide Double Perovskite (NH4)2SeBr6

“…Hence, VBM rises up greater that of the CBM, and consequently the bandgap is narrowed (as shown in the projected density of states of Figure 4b–c, and Figure S6, Supporting Information). Moreover, the X‐X bond distances may also play an important role in tuning the bandgap of the A 2 BX 6 perovskites . Our experimental results and findings are detailed as follows.…”

Influence of Sn/Ge Cation Exchange on Vacancy‐Ordered Double Perovskite Cs2Sn(1−x)GexI6: A First‐Principles Theoretical Study

“…In this paper, Kanatzidis's experimental data about the Cs 2 SnI 6 crystal structure was used to build the initial crystal structure. The GGA‐PBE method has been used to optimize the Cs 2 SnI 6 by Mark and coworkers . So we used PBE method to optimize pure Cs 2 SnI 6 crystal cell and Cs 2 SnI 6 crystal cells doped with Ge 4+ .…”

“…Spin‐orbit coupling effect (SOC) can significantly lower the calculated band gap of perovskite containing heavy element Pb . We compared the value of Cs 2 SnI 6 band gap (1.04 eV) calculated using HSE06 method by us with that (1.011 eV) calculated by Asta and coworkers using HSE06 including SOC, which shows that the effect of SOC is small for calculated band gap of Sn‐based perovskite. Ge is lighter than Sn, so the SOC effect is even smaller for calculated band gap of Ge‐containing perovskite.…”