Atomic structure, electronic structure and optical absorption of inorganic perovskite compounds Cs2SnI6-nXn (X=F, Cl, Br; n= 0~6): A first-principles study

TL;DR

This study uses first-principles calculations to analyze how substituting halogen ions in Cs2SnI6 affects its structure, electronic properties, and optical absorption, identifying potential solar cell materials.

Contribution

It provides a systematic first-principles investigation of Cs2SnI6 derivatives with various halogen substitutions, revealing their structural and electronic property changes.

Findings

Lattice constants and bond lengths decrease linearly with increased alloying.

Bandgap Eg increases nonlinearly with alloying level n.

Alloyed compounds maintain direct bandgaps suitable for solar absorption.

Abstract

As a possible alternative to organic-inorganic hybrid perovskite halide, inorganic Cs2SnI6 has drawn more and more research attention recently. In order to find more Cs2SnI6 derivatives as the potential solar cell absorber materials, I- ions in Cs2SnI6 are replaced by other halogen ions and forms the Cs2SnI6-nXn (X=F, Cl, Br; n=1~6) compounds, whose atomic structures, electronic structures and optical absorption are investigated by first principles calculation. When the alloying level n increases, the mean lattice constants, the weighted Sn-X and Cs-X bond lengths all decreases linearly; the bond length of each Sn-X diminishes slightly inside the octahedral structure; Eg of Cs2SnI6-nXn increases nonlinearly. Eleven Cs2SnI6-nXn compounds have an Eg between 1.0 eV and 2.0 eV and so can be potentially used as the light absorption layer of solar cells. Their partial DOS demonstrate that as the alloying level n increases, I 5p orbital in VBM and CBM is gradually substituted by Br 4p, or Cl 3p, or F 2p orbital. The eleven Cs2SnI6-nXn alloys all have a direct bandgap although the lattice distortion induced by the alloyed X- ion.