Optoelectronic Structure and Photocatalytic Applications of Na(Bi,La)S₂ Solid Solutions with Tunable Band Gaps

Abstract

NaLa 1−x Bi x S 2 solid solutions with tunable band gaps were synthesized, and their optoelectronic structures and photocatalytic performance were investigated via experimental and theoretical approaches. The solid solution powders with various La/Bi ratios were synthesized with Na 2 CO 3 , La 2 O 3 , and Bi 2 O 3 as precursors and via sulfurization with flowing CS 2 at 800 °C for 2 h. The Vegard's law behavior of cell parameters showed a perfect Bi/La solid solution in the cubic NaLa 1−x Bi x S 2 with the associated linear variation of the lattice constants. On the contrary, the combination of diffuse reflectance ultraviolet−visible spectroscopy with density functional theory (DFT) calculations employing the HSE06 functional reveals a monotonic but nonlinear variation of the band gap of the solid solution. While consistent valence band maximum was obtained in NaLa 1−x Bi x S 2 consisting mainly of S 3p orbitalsthe conduction band minimum was contributed by discrete Bi orbitals present at more positive potential than La. As a result, the slight inclusion of Bi caused a drastic shift in the band gap, and 24% Bi substitution provided an absorption edge closer to that of pure NaBiS 2 . Systematic DFT calculations on NaLa 1−x Bi x S 2 determined the optoelectronic properties for improved photovoltaic and photocatalytic performance with a Bi-rich sample rather than a La-rich counterpart; that is, there were larger absorption coefficients, smaller effective masses, and larger dielectric constants for Bi-rich samples versus La-rich samples. The NaLa 1−x Bi x S 2 particles decorated with Pt nanoparticles show maximum hydrogen evolution performance with x = 0.02−0.06 of Bi samples consistent with the compensating effects between photon absorption capacity and loss of electromotive force with decreasing band gap.

Exploring the Relationship between Effective Mass, Transient Photoconductivity, and Photocatalytic Activity of SrxPb1–xBiO2Cl (x = 0–1) Oxyhalides

“…Recently, materials informatics, which enables efficient virtual screening of functional materials, has attracted great attention and has been deployed in various fields such as for the screening of materials for organic-light-emitting diodes, lithium ion batteries, and solar cells . Our work provides a foundation for exploring potential photocatalysts, in that the effective mass of the charge carrier calculated from DFT computations − or deduced from machine learning could serve as one of the good explanatory variables. It should be also noted that the combinatorial synthesis of polymer photocatalysts is highly compatible with these computations and transient spectroscopy like TRMC.…”

NaBiS2 as a Novel Indirect Bandgap Full Spectrum Photocatalyst: Synthesis and Application

“…The modified augmented plane wave method (WIEN2k program) and HSE06 single-point calculations were employed to study the electronic energy structure of NaBiS 2 . According to the difference of the theoretical model, the bandgap value varied between 1.12 eV and 1.37 eV [32,33]. The optical properties of NaBiS 2 were investigated first using diffuse-reflectance UV-Vis-NIR spectrophotometry.…”

Alternative Lone‐Pair ns2‐Cation‐Based Semiconductors beyond Lead Halide Perovskites for Optoelectronic Applications

“…Reproduced with permission. [ 163 ] Copyright 2019, American Chemical Society. d) I – V curves of the KBiS 2 nanoparticles photodetectors in the dark and under a 525 nm laser illumination with different power densities.…”

“…Consequently, a modulated bandgap can enhance the hydrogen evolution performance. [ 163 ] Yang et al. fabricated KBiS 2 nanoparticle‐based photodetectors, possessing a notable detectivity of 5.1 × 10 15 Jones and a high current on–off ratio of ≈40 (Figure 9d).…”

“…In addition, the alkali metal and lanthanide series were also reported to be conducive to the carrier concentration and emission, respectively. [ 35,104,163 ]…”