Stability of Low-index Surfaces of Cs2SnI6 Studied by First-principles Calculations

doi:10.15541/jim20210491

Abstract

Abstract:

Cs₂SnI₆ is a stable and environmentally friendly halide perovskite material with great potential for photovoltaic and optoelectronic applications. While the surface properties are of paramount importance for device fabrications, there have been no such theoretical studies on this material. Using density functional theory calculations with the SCAN+rVV10 functional, the (001), (011) and (111) surfaces of Cs₂SnI₆were studied to reveal their thermodynamic stability. We constructed seven models for these surfaces, including two along the (001) orientation (CsI₂- and SnI₄-terminated surfaces), two along the (011) orientation (I₄- and Cs₂SnI₂-terminated surfaces) and three along the (111) orientation (non-stoichiometric CsI₃-, Sn- and stoichiometric CsI₃-terminated surfaces). Because most of the surfaces are non-stoichiometric, their relative stability depends on the experimental preparation condition, which is reflected by the chemical potentials of the constituent elements in the calculation. By determining the allowed chemical potential region, the thermodynamic stability of these Cs₂SnI₆ surfaces is analyzed. The results show that the surface energies of the (001) and (011) surfaces are affected by the chemical potentials, while the stoichiometric CsI₃-terminated (111) surface is unaffected by the chemical potentials and is energetically the most stable surface of Cs₂SnI₆. Thus, the observed exposure of (111) surface of Cs₂SnI₆ crystals in several recent experiments is determined to be driven by thermodynamics.

Key words: perovskite, surface energy, Cs₂SnI₆, photovoltaic material, luminescent material

CLC Number:

TQ174

LIN Aming, SUN Yiyang. Stability of Low-index Surfaces of Cs₂SnI₆ Studied by First-principles Calculations[J]. Journal of Inorganic Materials, 2022, 37(6): 691-696.

Figures/Tables 5

Fig. 1 (a) Atomic structure and (b) band structure and projected density of states (pDOS) of Cs2SnI6 Colorful figures are available on website

Fig. 2 Seven supercell models of Cs2SnI6 surfaces (a) For (001) surface: CsI2-terminated and SnI4-terminated slabs; (b) For (011) surface: I4-terminated and Cs2SnI2-terminated slabs; (c) For (111) surface: non-stoichiometric Sn-terminated, CsI3-terminated and stoichiometric CsI3-terminated slabs

Fig. 3 Calculated total cleavage, relaxation and surface energies of two complementary non-stoichiometric terminations in (001), (011) and (111) orientations, which are compared with the cleavage, relaxation and surface energies of the stoichiometric CsI3-terminated (111) surface

Fig. 4 Illustration of the accessible chemical potential region for Cs2SnI6 Constraints imposed by the formation of competing secondary phases resulting in the allowed region shaded in green

Fig. 5 Stability of low-index surfaces of Cs2SnI6 as a function of chemical potentials (a) Analysis of stability of the two terminations of Cs2SnI6 (001) surface with respect to the allowed region for maintaining equilibrium with the primary phase Cs2SnI6. The orange and blue regions indicate the stable region for CsI2- and SnI4-terminations, respectively; (b) Similar to (a) for the Cs2SnI6 (011) surface. The orange and blue regions are for the I4- and Cs2SnI2-terminations, respectively; (c) Similar to (a) for the Cs2SnI6 (111) surface. The orange and blue regions are for the Sn- and stoichiometric CsI3-terminations, respectively; (d) Surface energies of the seven surface models of Cs2SnI6 as a function of the chemical potentials colorful figures are available on website

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Stability of Low-index Surfaces of Cs₂SnI₆ Studied by First-principles Calculations

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