Structural, electronic, and optical properties of Pt-based vacancy-ordered double perovskites A2PtX6 (A = K, Rb, Cs; X = Cl, Br, I) in tetragonal P4/mnc polymorph

Abstract

We study the structural, electronic, and optical properties of the Pt-based vacancy-ordered double perovskites A 2 Pt X 6 ( A = K, Rb, Cs; X = Cl, Br, I) in the tetragonal P 4/ mnc polymorph using the relativistic all-electron calculations based on the density functional theory. It is found that the rotation angles θ of the Pt X 6 octahedra are non-zero for all the compounds. For a given A -site cation, θ increases from Cl to Br to I while for a given halide anion, θ decreases from K to Rb to Cs. As a result, the largest θ is found for K 2 PtI 6 . Taking the three iodides, K 2 PtI 6 , Rb 2 PtI 6 and Cs 2 PtI 6 , as representatives, it is found that K 2 PtI 6 is a direct-band-gap semiconductor and that Rb 2 PtI 6 and Cs 2 PtI 6 are quasi-direct-band-gap semiconductors with the small differences between the indirect and direct band gaps. The band gap in the tetragonal P 4/ mnc polymorph is larger than the corresponding one in the cubic F m 3 ̄ m polymorph. Employing the spectroscopically limited maximum efficiency as a metric for quantifying the photovoltaic performance, K 2 PtI 6 , Rb 2 PtI 6 , and Cs 2 PtI 6 are found to be promising absorber materials for thin-film solar cells. • Pt-based vacancy-ordered double perovskites A 2 Pt X 6 in tetragonal P 4/ mnc polymorph were studied theoretically. • Non-zero rotation angles of Pt X 6 octahedra were found for all the compounds. • The electronic and optical properties of K 2 PtI 6 , Rb 2 PtI 6 , and Cs 2 PtI 6 were examined as representatives.