Elsevier

Chemical Physics

Volume 533, 1 May 2020, 110704
Chemical Physics

First principles insight into the structural, electronic, optical and thermodynamic properties of CsPb2Br5 compound

https://doi.org/10.1016/j.chemphys.2020.110704Get rights and content

Abstract

The ternary CsPb2Br5 compound is a promising candidate for optoelectronic applications, however, its electronic properties are not well understood yet. In this work, the structural, electronic, optical and thermodynamic properties have been systematically examined using first-principles calculations. The exchange-correlation potentials are included in the calculations through the generalized gradient approximation (GGA-PBESol) and Tran-Blaha modified Becke-Johnson exchange (mBJ) potential. Obtained structural parameters match well with the experimental data. The CsPb2Br5 compound is an indirect semiconductor with a band gap of 3.589 eV predicted by mBJ potential. A wide absorption band in the ultraviolet region with very high absorption coefficient was observed for the ternary at hand. Finally, the thermodynamic behaviors of CsPb2Br5 are also computed using the Debye quasi-harmonic model. Properties are investigated as a function of pressure up to 25 GPa under different temperatures, and discussed in details.

Introduction

In recent years, solution process halide based materials have been extensively investigated due to their potential applicability in optoelectronic devices resulting from their extremely interesting physical and chemical properties such as tunable electronic properties, high absorption coefficient and long diffusion length of charge carriers [1], [2], [3], [4]. It shall be mention that the hybrid organic–inorganic CH3NH3PbX3 (X  = Cl, Br, and I) perovskites are of the most promising materials for applications in solar cells with a power conversion efficiency as high as up to 22.1% [5]. However, the low stability under working conditions has limited its practical applications. In this regard, Cesium Lead Halide based all-inorganic perovskites (CsPbX3, X = Cl, Br and I) have emerged as promising alternatives due to their higher chemical stability, intriguing electronic and photoluminescent properties [6], [7], [8].

Recently, other compound belonging to Cs-Pb-Br family, namely CsPb2Br5, has also attracted attention of the researcher. In general, this compound is formed during the synthesis of the perovskite CsPbBr3 as a secondary. The first CsPb2Br5 successful preparation was realized by I. Y. Kuznetsova et al. [9]. Such mentioned work has motivated a huge interest in synthesizing and characterizing the optical properties of this ternary. Experimental works have demonstrated that the CsPb2Br5 compound is a promising candidate for lasing and light-emiting applications [10], [4], [11], [12], [13]. Theoretically, electronic properties of the ternary CsPb2Br5 have been investigated by some research groups. For examples, Li et al. [10] determined a band gap value of 2.979 eV from DFT calculations. Later, Dursun et al. [12] also investigated the electronic band structure of the compound at hand using DFT calculations and obtained an indirect band gap of 3.1 eV. More recently, a band gap of 3.72 eV was determined by Jin et al. [14] using first-principles calculations in combination with hybrid HSE06 functional. Such mentioned results show a disagreement and an accurate calculation of the electronic band gap is still needed in order to understand deeply the optical properties of CsPb2Br5 compound. Therefore, we consider necessary to carry out a systematic investigation on the electronic and optical properties of the CsPb2Br5 compound.

Herein, we present results of the comprehensive study on the structural, electronic, optical and thermodynamic properties of the ternary CsPb2Br5 compound. Studies are done theoretically based on the density functional theory (DFT) and Debye quasi-harmonic model. Obtained results assert that the CsPb2Br5 compound is an indirect semiconductor with a band gap of 3.589 eV and it has a wide absorption band in the ultraviolet region with very high absorption coefficient up to 2.21 (×106/cm). Results suggest that the studied compound is very promising absorber to be used in optoelectronic devices. Calculations are performed using the full-potential linearized augmented plane-wave, the main used parameters are given in Section 2. The obtained results are presented in Section 3 and they are also discussed in details. Finally, in Section 4, we present a conclusion of the remarkable results of the work.

Section snippets

Computational details

Structural, electronic and optical properties of the CsPb2Br5 compound have been investigated using the WIEN2k package [15]. The full-potential linearized augmented plane-wave (FP-LAPW) method is applied to solve the self-consistent Kohn-Sham equations [16]. The exchange-correlation potentials were treated with the revised Perdew-Burke-Ernzerhof generalized gradient approximation for the densely packed solids and their surfaces (GGA-PBESol) [17]. Theoretical experiences have demonstrated that

Structural properties

The ternary CsPb2Br5 compound has been reported to crystallize in a tetragonal structure, space group I4/mcm (No. 140), where Cs, Pb, Br1 and Br2 atoms are positioned at (0.5; 0.5; 0.25), (xPb;yPb; 0), (0.5; 0.5; 0) and (xBr2;yBr2;zBr2), respectively. The crystal structure is displayed in Fig. 1. We start the structural optimization by freely relaxing all the atoms within the unit cell. Results are given in Table 1. According to our calculations, the energetically favorable positions of Cs, Pb,

Conclusions

In this paper, the full-potential linearized augmented plane wave approach and Debye quasi-harmonic model have been used to study systematically the structural, electronic, optical and thermodynamic properties of the ternary CsPb2Br5 compound. Remarkable results are summarized as follows:

  • CsPb2Br5 compound has an indirect band gap ΣΓ-Z, whose value is 2.964 and 3.589 eV obtained by PBESol and mBJ theories, respectively.

  • Valence band and conduction band are dominated mainly by the Br-4p and Pb-6p,

CRediT authorship contribution statement

D.M. Hoat: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Resources, Software, Supervision, Validation, Visualization, Writing - original draft, Writing - review & editing. Mosayeb Naseri: Formal analysis, Investigation, Methodology. R. Ponce-Pérez: Formal analysis, Investigation, Methodology. J.F. Rivas-Silva: Data curation, Formal analysis, Methodology, Software. Gregorio H. Cocoletzi: Data curation, Formal analysis, Methodology, Software, Validation, Writing -

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under Grant No. 103.01-2019.348.

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