New lead-free double perovskites (Rb2GeCl/Br)6; a promising materials for renewable energy applications

• Published in: Materials chemistry and physics 2021-10, Vol.271, p.124876, Article 124876
• Main Authors: AlObaid, Abeer A., Rouf, Syed Awais, Al-Muhimeed, Tahani I., Aljameel, A.I., Bouzgarrou, S., Hegazy, H.H., Alshahrani, Thamraa, Nazir, Ghazanfar, Mera, Abeer, Mahmood, Q.
• Format: Article
• Language: English
• Subjects: Absorption spectra; Debye temperature; Density functional theory; Direct band gaps; Electrical resistivity; Electromagnetic absorption; Figure of merit; Lead free; Mechanical properties; Optical properties; Optoelectronics; Perovskites; Phonon dispersion; Refractivity; Room temperature; Seebeck effect; Structural stability; Thermal conductivity; Thermodynamic properties; Thermoelectric efficiency; Thermoelectricity; Transport properties
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2021.124876

The vacancy ordered double perovskites are emerging compounds for optoelectronics, and transport properties. In this article, optical, thermoelectric, mechanical, and thermodynamic properties of Rb2GeCl6 and Rb2GeBr6 are investigated comprehensively. The phonon band structures, and tolerance factor confirm their thermodynamic, and structural stabilities. The direct band gaps 2.60 eV and 1.78 eV are reported at Γ-symmetry point which ensure the absorption of light from visible to UV regions. The less dispersion of light, and refractive index range 1.5–2 along with broad absorption band in visible to UV regions make them outstanding materials for optoelectronics, Moreover, the transport characteristics are addressed by electrical conductivity, thermal conductivity and Seebeck coefficient, and Figure of merit. The room temperature ZT values 0.78, and 0.74 also ensure their importance for thermoelectric applications. The mechanical properties confirm their ductile, ionic, and anisotropic nature. The high Debye, and melting temperatures increases their heating resistant capacity and stability. •Double perovskites are more stable, cheap, and suitable materials for solar cells.•The maximum conversion efficiency of light energy into electrical energy.•The absorption of light falls in the visible to ultraviolet region.•The double perovskites have high figure of merit because of large Seebeck coefficient.