Novel 3D photoactive direct bandgap perovskites CsBiPbX6: Ab initio structure and electronic properties

[Display omitted] •Novel 3D photoactive direct bandgap perovskites CsBiPbX6 are proposed.•Crystal structure and electronic properties of five solid phases are reported.•The perovskites feature low Pb content and bandgaps from 1.05 eV to 2.10 eV.•Bandgaps of the perovskites can be modulated via mixing of halide anions. We present DFT study on hypothetical 3D all-inorganic metal halide perovskites CsBiPbX6 (X = Cl, Br, I). According to the calculations, the perovskites form cubic, orthorhombic, monoclinic, and trigonal phases which are all direct bandgap semiconductors. Typical of metal halide perovskites, valence bands of the considered species are composed of halide anions’ occupied p-orbitals. Their conduction bands contain about equal contributions from vacant p-orbitals of both Bi3+ and Pb2+ cations. Electronic bandgaps of the studied perovskites range from 1.05 eV to 2.10 eV, whereas estimated optical bandgaps of their cubic F43m phase equal 1.50 eV (CsBiPbI6), 1.87 eV (CsBiPbBr6), and 2.40 eV (CsBiPbCl6). The perovskites’ electronic properties can be fine-tuned by mixing of halide anions. Mixed-halides CsBiPbBrnI(6-n), (n = 1–5) are considered here as an example. Majority of these compounds are direct bandgap semiconductor as well with electronic bandgaps falling in the range [1.08–1.72] eV. Their optical bandgaps are expected to exceed the corresponding electronic ones by a few tenths of an electronvolt. Owing to relatively low lead content, direct electronic transitions, and remarkable tunability of electronic properties the proposed materials may find applications in photovoltaics.