Iodobismuthates Containing One-Dimensional BiI₄^– Anions as Prospective Light-Harvesting Materials: Synthesis, Crystal and Electronic Structure, and Optical Properties

Abstract

Four iodobismuthates, LiBiI4·5H2O (1), MgBi2I8·8H2O (2), MnBi2I8·8H2O (3), and KBiI4·H2O (4), were prepared by a facile solution route and revealed thermal stability in air up to 120 °C. Crystal structures of compounds 1-4 were solved by a single crystal X-ray diffraction method. 1: space group C2/c, a = 12.535(2), b = 16.0294(18), c = 7.6214(9) Å, β = 107.189(11)°, Z = 4, R = 0.029. 2: space group P21/c, a = 7.559(2), b = 13.1225(15), c = 13.927(4) Å, β = 97.14(3)°, Z = 2, R = 0.031. 3: space group P21/c, a = 7.606(3), b = 13.137(3), c = 14.026(5) Å, β = 97.14(3)°, Z = 2, R = 0.056. 4: space group P21/n, a = 7.9050(16), b = 7.7718(16), c = 18.233(4) Å, β = 97.45(3)°, Z = 4, R = 0.043. All solid state structures feature one-dimensional (BiI4)(-) anionic chains built of [BiI6] octahedra that share two opposite edges in such a fashion that two iodine atoms in cis-positions remain terminal. The calculated electronic structures and observed optical properties confirmed that compounds 1-4 are semiconductors with direct band gaps of 1.70-1.76 eV, which correspond to their intense red color. It was shown that the cations do not affect the optical properties, and the optical absorption is primarily associated with the charge transfer from the I 5p orbitals at the top of the valence band to the Bi 6p orbitals at the bottom of the conduction band. Based on their properties and facile synthesis, the title compounds are proposed as promising light-harvesting materials for all-solid solar cells.

Exciton-phonon interactions in the Cs3Bi2I9crystal structure revealed by Raman spectroscopic studies

“…Moreover, similar band structures and comparable absorption bands located at ∼ 2 eV of different inorganic bismuth iodides have been reported in the literature . The reason for the similar excitonic feature is associated with the band‐edge transitions that are assigned to the electronic states of the anionic Bi 2 I 9 3− cluster, where the cation seems to have no considerable effect on optical and electronic properties . Besides, considering the optical transition from the higher energy observed in PC and diffuse reflection spectra, one observes that there is no clearly detectable PL peak around the value of 2.6 eV.…”

“…The representation of orbitals is similar to the one disclosed by [PbI 6 ] −4 cluster and the coincidence is proved due to similar valence electronic configuration for both bismuth‐6s 2 6p 3 , and lead‐6s 2 6p 2 atoms. Additionally, the optical transition that is primarily associated with the charge transfer from the top of the valence band, mainly consisting of I(5p)–Bi(6s) orbitals to the bottom of the conduction band expressed by Bi(6p)–I(5p) are also highlighted by X‐ray photoelectron spectroscopy (XPS ) spectra . These experimental results are strengthened in Fig.…”

Progress on lead-free metal halide perovskites for photovoltaic applications: a review

“…LiBiI 4 ·5 H 2 O [186]) or (2) as bismuth halide chains of distorted BiX 6 octahedra in zigzag conformation, which are interconnected by dicationic alkyldiammonium species occupying the A-site positions (e.g. HDABiI 5 [54]).…”

“…The first motif can be found in LiBiI 4 ·5 H 2 O, MgBi 2 I 8 ·8 H 2 O, MnBi 2 I 8 ·8 H 2 O, and KBiI 4 ·H 2 O, which were studied by Yelovik et al [186]. The optical band gaps of the four compounds were determined to be between 1.70 and 1.76 eV, which is in good agreement with the electronic band structure calculations for the KBiI 4 model compound (1.78 eV).…”

“…The optical band gaps of the four compounds were determined to be between 1.70 and 1.76 eV, which is in good agreement with the electronic band structure calculations for the KBiI 4 model compound (1.78 eV). Due to these promising optical properties, one-dimensional perovskites might be prospective absorber materials for photovoltaic applications [186]. …”