# Predicting the thermodynamic stability of double-perovskite halides from density functional theory

## Abstract

Recently, a series of double-perovskite halide compounds such as Cs _{2}AgBiCl _{6} and Cs _{2}AgBiBr _{6} have attracted intensive interest as promising alternatives to the solar absorber material CH _{3}NH _{3}PbI _{3} because they are Pb-free and may exhibit enhanced stability. The thermodynamic stability of a number of double-perovskite halides has been predicted based on density functional theory (DFT) calculations of compound formation energies. In this paper, we found that the stability prediction can be dependent on the approximations used for the exchange-correlation functionals, e.g., the DFT calculations using the widely used Perdew, Burke, Ernzerhof (PBE) functional predict that Cs _{2}AgBiBr _{6} is thermodynamically unstable against phase-separation into the competing phases such as AgBr, Cs _{2}AgBr _{3}, Cs _{3}Bi _{2}Br _{9}, etc., obviously inconsistent with the good stability observed experimentally. The incorrect prediction by the PBE calculation results from its failure to predict the correct ground-state structures of AgBr, AgCl, and CsCl. By contrast, the DFT calculations based on local density approximation, optB86b-vdW, and optB88-vdW functionals predict the ground-state structures of these binary halides correctly. Furthermore, the optB88-vdW functional is found to give the most accurate description of the lattice constants of the double-perovskite halides and their competing phases. Givenmore »

- Authors:

- East China Normal Univ., Shanghai (China)
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- East China Normal Univ., Shanghai (China); Shanxi Univ., Shanxi (China)

- Publication Date:

- Research Org.:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

- Sponsoring Org.:
- USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)

- OSTI Identifier:
- 1440832

- Grant/Contract Number:
- AC05-00OR22725

- Resource Type:
- Journal Article: Accepted Manuscript

- Journal Name:
- APL Materials

- Additional Journal Information:
- Journal Volume: 6; Journal Issue: 8; Journal ID: ISSN 2166-532X

- Publisher:
- American Institute of Physics (AIP)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 36 MATERIALS SCIENCE

### Citation Formats

```
Han, Dan, Zhang, Tao, Huang, Menglin, Sun, Deyan, Du, Mao -Hua, and Chen, Shiyou.
```*Predicting the thermodynamic stability of double-perovskite halides from density functional theory*. United States: N. p., 2018.
Web. doi:10.1063/1.5027414.

```
Han, Dan, Zhang, Tao, Huang, Menglin, Sun, Deyan, Du, Mao -Hua, & Chen, Shiyou.
```*Predicting the thermodynamic stability of double-perovskite halides from density functional theory*. United States. doi:10.1063/1.5027414.

```
Han, Dan, Zhang, Tao, Huang, Menglin, Sun, Deyan, Du, Mao -Hua, and Chen, Shiyou. Thu .
"Predicting the thermodynamic stability of double-perovskite halides from density functional theory". United States.
doi:10.1063/1.5027414. https://www.osti.gov/servlets/purl/1440832.
```

```
@article{osti_1440832,
```

title = {Predicting the thermodynamic stability of double-perovskite halides from density functional theory},

author = {Han, Dan and Zhang, Tao and Huang, Menglin and Sun, Deyan and Du, Mao -Hua and Chen, Shiyou},

abstractNote = {Recently, a series of double-perovskite halide compounds such as Cs2AgBiCl6 and Cs2AgBiBr6 have attracted intensive interest as promising alternatives to the solar absorber material CH3NH3PbI3 because they are Pb-free and may exhibit enhanced stability. The thermodynamic stability of a number of double-perovskite halides has been predicted based on density functional theory (DFT) calculations of compound formation energies. In this paper, we found that the stability prediction can be dependent on the approximations used for the exchange-correlation functionals, e.g., the DFT calculations using the widely used Perdew, Burke, Ernzerhof (PBE) functional predict that Cs2AgBiBr6 is thermodynamically unstable against phase-separation into the competing phases such as AgBr, Cs2AgBr3, Cs3Bi2Br9, etc., obviously inconsistent with the good stability observed experimentally. The incorrect prediction by the PBE calculation results from its failure to predict the correct ground-state structures of AgBr, AgCl, and CsCl. By contrast, the DFT calculations based on local density approximation, optB86b-vdW, and optB88-vdW functionals predict the ground-state structures of these binary halides correctly. Furthermore, the optB88-vdW functional is found to give the most accurate description of the lattice constants of the double-perovskite halides and their competing phases. Given these two aspects, we suggest that the optB88-vdW functional should be used for predicting thermodynamic stability in the future high-throughput computational material design or the construction of the Materials Genome database for new double-perovskite halides. As a result, using different exchange-correlation functionals has little influence on the dispersion of the conduction and the valence bands near the electronic bandgap; however, the calculated bandgap can be affected indirectly by the optimized lattice constant, which varies for different functionals.},

doi = {10.1063/1.5027414},

journal = {APL Materials},

number = 8,

volume = 6,

place = {United States},

year = {Thu May 24 00:00:00 EDT 2018},

month = {Thu May 24 00:00:00 EDT 2018}

}

Works referenced in this record:

##
Air-Stable Molecular Semiconducting Iodosalts for Solar Cell Applications: Cs_{2}SnI_{6} as a Hole Conductor

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- Lee, Byunghong; Stoumpos, Constantinos C.; Zhou, Nanjia
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