Exploring the electronic and optical properties of vacancy-ordered double perovskites Cs2PtX6 (X = Cl, Br, I)

Highlights: • The stability and optoelectronic properties of Cs₂PtX₆ (X=Cl, Br, I) are studied. • Three compounds are direct bandgap semiconductors. • Cs₂PtI₆ shows good stability and a suitable band gap value. We have comprehensively investigated the structural stability, mechanical, electronic and optical properties of vacancy-ordered double perovskites Cs₂PtX₆ (X=Cl, Br, I) through the first-principles calculations in this article. The stability of three compounds are proved by calculating their elastic constants and phonon dispersion. The results suggest that three Pt-based double perovskites are direct bandgap semiconductors. The band gaps of Cs₂PtCl₆, Cs₂PtBr₆, and Cs₂PtI₆ are 3.45, 2.45, and 1.41eV, respectively. The optical properties of these compounds in the visible light region have been explored by the HSE06 method. The highest optical absorption coefficient of Cs₂PtBr₆ exceeds 5×10⁵cm⁻¹, and the strong optical absorption of Cs₂PtI₆ is in the range of 300–600nm. The excellent physical properties make lead-free Cs₂PtI₆ suitable for single-junction solar cells.