Novel properties of vacancy-ordered perovskite-Cs2BCl6 induced by d-orbital electrons

The all-inorganic lead-free vacancy-ordered perovskite offers a promising avenue toward nontoxic and stable optoelectronic materials. Herein, we present a first-principles study of the structural stability, optical absorption, electronic structure, and mechanical behavior of Cs₂BCl₆ compounds with B-site substitutions (BGe, Sn, Pb, Cr, Mo, W, Ti, Zr, and Hf). The structural analysis shows that the Cs₂BCl₆ perovskite with face-centered cubes has a stable chemical environment, especially Cs₂HfCl₆, Cs₂WCl₆, and Cs₂PbCl₆. Hf⁴⁺ and W⁴⁺ with high-energy d-state external electron configurations can further lower the valence band maximum position of the Cs₂BCl₆ structures and thus increase the band gap, assisting in tuning the optical absorption and emission properties of these structures in the optoelectronic application. For the light absorption properties of Cs₂BCl₆ materials, the best light absorption properties have been concluded for Ti⁴⁺, Cr⁴⁺, and Pb⁴⁺-based perovskite in the visible range due to a suitable band gap. Therefore, the excellent optical absorption and electronic properties make these vacancy-ordered perovskites promising candidates for optoelectronic applications.