Elastic, Optoelectronic and Thermoelectric Properties of the Lead-Free Halide Semiconductors Cs2AgBiX 6 (X = Cl, Br): Ab Initio Investigation

• Published in: Journal of electronic materials 2018-02, Vol.47 (2), p.1533-1545
• Main Authors: Guechi, N., Bouhemadou, A., Bin-Omran, S., Bourzami, A., Louail, L.
• Format: Article
• Language: English
• Subjects: Absorptivity; Band structure of solids; Chemical bonds; Coupling (molecular); Crystallography; Density distribution; Density of states; Elastic anisotropy; Elastic properties; Electron density; Energy consumption; Heavy elements; Investigations; Lead free; Magnetism; Materials research; Mathematical analysis; Modulus of elasticity; Optical properties; Optoelectronics; Perovskites; Response functions; Shear modulus; Single crystals; Strain; Thermoelectricity; Transport theory
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-017-5962-2

We report a detailed investigation of the elastic moduli, electronic band structure, density of states, chemical bonding, electron and hole effective masses, optical response functions and thermoelectric properties of the lead-free halide double perovskites Cs2AgBiCl6 and Cs2AgBiBr6 using the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA-PBEsol) and the Tran–Blaha modified Becke–Johnson (TB-mBJ) potential. Because of the presence of heavy elements in the studied compounds, we include the spin–orbit coupling (SOC) effect. Our calculated structural parameters agree very well with the available experimental and theoretical findings. Single-crystal and polycrystalline elastic constants are predicted using the total-energy versus strain approach. Three-dimensional representations of the crystallographic direction dependence on the shear modulus, Young’s modulus and Poisson’s ratio demonstrate a noticeable elastic anisotropy. The TB-mBJ potential with SOC yields an indirect band gap of 2.44 (1.93) eV for Cs2AgBiCl6 (Cs2AgBiBr6), in good agreement with the existing experimental data. The chemical bonding features are probed via density of states and valence electron density distribution calculations. Optical response functions were predicted from the calculated band structure. Both of the investigated compounds have a significant absorption coefficient (∼ 25×104cm-1) in the visible range of sunlight. The thermoelectric properties of the title compounds were investigated using the FP-LAPW approach in combination with the semi-classical Boltzmann transport theory. The Cs2AgBiCl6 and Cs2AgBiBr6 compounds have a large thermopower S, which makes them potential candidates for thermoelectric applications.