We explored the impact of interfacial defects on the stability and optoelectronic properties of monolayer transition metal dichalcogenide lateral heterojunctions using a density functional theory ...approach. As a prototype, we focused on the MoS2–WSe2 system and found that even a random alloy-like interface with a width of less than 1 nm has only a minimal impact on the band gap and alignment compared to the defect-less interface. The largest impact is on the evolution of the electrostatic potential across the monolayer. Similar to defect-less interfaces, a small number of defects results in an electrostatic potential profile with a sharp change at the interface, which facilitates exciton dissociation. Differently, a large number of defects results in an electrostatic potential profile switching smoothly across the interface, which is expected to reduce the capability of the heterojunction to promote exciton dissociation. These results are generalizable to other transition metal dichalcogenide lateral heterojunctions.
A combination of experimental and computational methods was applied to investigate the crystal structure and optoelectronic properties of the non-stoichiometric pyrochlore Bi 2−x Ti 2 O 7−1.5x . The ...detailed experimental protocol for both powder and thin-film material synthesis revealed that a non-stoichiometric Bi 2−x Ti 2 O 7−1.5x structure with an x value of ∼0.25 is the primary product, consistent with the thermodynamic stability of the defect-containing structure computed using density functional theory (DFT). The approach of density functional perturbation theory (DFPT) was used along with the standard GGA PBE functional and the screened Coulomb hybrid HSE06 functional, including spin–orbit coupling, to investigate the electronic structure, the effective electron and hole masses, the dielectric constant, and the absorption coefficient. The calculated values for these properties are in excellent agreement with the measured values, corroborating the overall analysis. This study indicates potential applications of bismuth titanate as a wide-bandgap material, e.g. , as a substitute for TiO 2 in dye-sensitized solar cells and UV-light-driven photocatalysis.
The impact of the four predominant (010), (110), (001), and (121) exposed facets obtained experimentally for monoclinic BiVO4 on its photocatalytic performance for water splitting reactions is ...investigated on the basis of the hybrid density functional theory including the spin–orbit coupling. Although their electronic structure is similar, their transport and redox properties reveal anisotropic characters based on the crystal orientation and termination. The particular role of each facet in proton reduction was correlated with the surface Bi coordination number and their geometrical distribution. Our work predicts the (001) facet as the only good candidate for both HER and OER, while the (010) facet is a fitting candidate for OER only. The (110) and (121) surfaces are acceptable candidates only for OER but less potential than (001) and (010). These outcomes will efficiently conduct experimentalists for an attentive design of facet-oriented BiVO4 samples toward improving water oxidation and proton reduction.
The effects of intrinsic defects in monoclinic bismuth vanadate (BiVO4) on its stability and optoelectronic properties for photochemical water splitting application were examined using density ...functional theory. Among the most favorable structures, only that associated with V-antisites on Bi with additional Bivacancies (Bi(1–5x)V(1+3x)O4 with x = 0.0625) revealed narrower band gap energy by 0.5 eV compared to pristine material (calculated value is 2.8 eV) giving a value of 2.3 eV, which is very close to the experimentally reported ones (in the 2.4–2.5 eV range). The low electron mobility reported experimentally for this material was also confirmed by the relatively large electron effective masses obtained for the intrinsic defective Bi(1–5x)V(1+3x)O4 (x = 0.0625) structure along the three principal crystallographic directions. The strongly localized nature of the accommodated electrons on the d-orbitals of the newly substituted V at Bi sites was also predicted to be at the origin of the poor H2 evolution performance of this material.
The investigation of the BiCuOCh (Ch = S, Se and Te) semiconductor family for thermoelectric or photovoltaic materials is a topic of increasing research interest. These materials can also be ...considered for photochemical water splitting if one representative having a bandgap, Eg, at around 2 eV can be developed. With this aim, we simulated the solid solutions Bi1-xRExCuOS (RE = Y, La, Gd and Lu) from pure BiCuOS (Eg ∼ 1.1 eV) to pure RECuOS compositions (Eg ∼ 2.9 eV) by DFT calculations based on the HSE06 range-separated hybrid functional with the inclusion of spin-orbit coupling. Starting from the thermodynamic stability of the solid solution, several properties were computed for each system including bandgaps, dielectric constants, effective masses and exciton binding energies. We discussed the variation of these properties based on the relative organization of Bi and RE atoms in their common sublattice to offer a physical understanding of the influence of the RE doping of BiCuOS. Some compositions were found to give appropriate properties for water splitting applications. Furthermore, we found that at low RE fractions the transport properties of BiCuOS are improved that can find applications beyond water splitting.
In present article, the electronic, optical, mechanical, and thermoelectric characteristics of Cs2XAu(Br/I)6, where X = Y, Sc are addressed comprehensively. The Born stability criteria ensure the ...mechanical stability, whereas the structural, thermodynamic, and lattice stabilities are calculated from tolerance factor, formation energy, and phonons dispersion band structures. The ductility, hardness, lattice thermal conductivity, melting, and Debye temperatures are discussed in terms of elastic constants. The direct band gaps 1.90/1.35 eV Cs2ScAu(Br/I)6, and 2.23/1.74 eV for Cs2YAu(Br/I)6 fall the absorption of light energy in visible to near ultraviolet regions. The Cs2ScAuI6 has ideal band gap (1.35 eV) for solar cells because broad absorption band in visible region. Finally, thermoelectric behavior has been studied by Seebeck coefficient, electrical conductivity, power factor, and thermal conductivity in the temperature range 200 K–600 K. The highest figure of merit (1.0 at 300 K) for Cs2YAuBr6 increases demand for thermoelectric generators.
•Double perovskites are emergent materials for solar cells.•Thermodynamic, structural, and mechanical stability.•The absorption bands of light energy exist visible to infrared region.•The large figure of merit at room temperature and ultralow lattice thermal conductivity.
Widespread application of solar water splitting for energy conversion is largely dependent on the progress in developing not only efficient but also cheap and scalable photoelectrodes. Metal oxides, ...which can be deposited with scalable techniques and are relatively cheap, are particularly interesting, but high efficiency is still hindered by the poor carrier transport properties (i.e., carrier mobility and lifetime). Here, a mild hydrogen treatment is introduced to bismuth vanadate (BiVO4), which is one of the most promising metal oxide photoelectrodes, as a method to overcome the carrier transport limitations. Time‐resolved microwave and terahertz conductivity measurements reveal more than twofold enhancement of the carrier lifetime for the hydrogen‐treated BiVO4, without significantly affecting the carrier mobility. This is in contrast to the case of tungsten‐doped BiVO4, although hydrogen is also a donor type dopant in BiVO4. The enhancement in carrier lifetime is found to be caused by significant reduction of trap‐assisted recombination, either via passivation or reduction of deep trap states related to vanadium antisite on bismuth or vanadium interstitials according to density functional theory calculations. Overall, these findings provide further insights on the interplay between defect modulation and carrier transport in metal oxides, which benefit the development of low‐cost, highly‐efficient solar energy conversion devices.
Overcoming poor charge carrier transport represents one of the biggest challenges in the development of metal oxide photoelectrodes. Time‐resolved conductivity measurements and density functional theory calculations reveal that a simple postsynthesis hydrogen treatment at 300 °C reduces the number of deep trap states in metal oxides. As a result, the charge carrier lifetime and overall photoelectrochemical performance are significantly enhanced.
Recent progress on bismuth vanadate (BiVO4) has shown it to be among the highest performing metal oxide photoanode materials. However, further improvement, especially in the form of thin film ...photoelectrodes, is hampered by its poor charge carrier transport and its relatively wide bandgap. Here, sulfur incorporation is used to address these limitations. A maximum bandgap decrease of ∼0.3 eV is obtained, which increases the theoretical maximum solar-to-hydrogen efficiency from 9 to 12%. Hard X-ray photoelectron spectroscopy measurements as well as density functional theory calculations show that the main reason for the bandgap decrease is an upward shift of the valence band maximum. Time-resolved microwave conductivity measurements reveal a ∼3 times higher charge carrier mobility compared to unmodified BiVO4, resulting in a ∼70% increase in the carrier diffusion length. This work demonstrates that sulfur incorporation can be a promising and practical method to improve the performance of wide-bandgap metal oxide photoelectrodes.
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