Cost-Effective High-Throughput Calculation Based on Hybrid Density Functional Theory: Application to Cubic, Double, and Vacancy-Ordered Halide Perovskites

Hybrid density functional theory calculations are commonly used to investigate the electronic structure of semiconductor materials but have not been ideal for high-throughput calculations due to heavy computation costs. We developed a computational approach to obtain the electronic band gap cost-effectively by employing not only non-self-consistent field calculation methods but also sparse k-point meshes for the Fock exchange potential. The benchmark calculation showed that our method is at least 30 times faster than the conventional hybrid density functional theory calculation to quickly screen materials. The band gaps of 290 materials in 5 different structures including cubic, double, and vacancy-ordered perovskites were obtained. The physical properties of Cs2WCl6 and Cs2NaInBr6, screened for optoelectronic applications, were in good agreement with the experiment

Carrier Transport in Dye-Sensitized Solar Cells Using Single Crystalline TiO₂ Nanorods Grown by a Microwave-Assisted Hydrothermal Reaction

Single crystalline rutile nanorod was grown directly on top of fluorine-doped tin oxide (FTO) substrate via a microwave assisted hydrothermal reaction which dramatically increased a growth rate over a conventional hydrothermal method. In addition, the introduction of thin TiO2 seed layer to FTO substrates promotes heterogeneous nucleation and increases the density. Dye-sensitized solar cells (DSSCs) were fabricated using the rutile nanorods that were differently treated with TiCl4 solution and the carrier transport mechanism in the nanorod-based DSSCs was systematically examined. When the nanorods were treated with TiCl4, more dye was adsorbed on the TiO2 films and the energy conversion efficiency increased to 3.7% for a 2.5 μm thick TiO2 film. Stepped light induced-transient measurement of photocurrent and voltage measurements showed that the role of the nanorods in DSSCs is to increase an electron diffusion coefficient in TiO2 mesoporous films. In contrast to the diffusion coefficient, the lifetime of electron is not dependent on the presence of the nanorods. To explain the experimental observations, we propose a surface diffusion model for electrons that are injected into the rutile nanorods from dye molecules. This surface diffusion may originate from the high crystallinity of nanorods and the homogeneous contact between nanorod and coated nanoparticle layer

Correlation between Photocatalytic Efficacy and Electronic Band Structure in Hydrothermally Grown TiO₂ Nanoparticles

The effects of electronic band structure, electron−hole recombination, and photocatalytic property of N- and/or Fe-doped TiO2 were systematically explored. Hydrothermal reaction was used to incorporate N and/or Fe into TiO2 nanoparticles. Structural analysis using Raman spectra, X-ray diffraction, and transmission electron microscope (TEM) indicates that hydrothermally grown TiO2 particles have anatase phase, and their average size is ∼10 nm. In addition, hydrothermal doping of N and/or Fe was found to significantly modify the electronic band structure. The photocatalytic performance of undoped and doped nanomaterials was examined under UV or visible light. N doping increased the photocatalytic efficacy of TiO2 under visible light by more than 2 times. In contrast, Fe-doped and N/Fe-codoped TiO2 show worse photocatalytic performance than pure TiO2 under both UV and visible light, in spite of their smaller band gaps. Fluorescence of terephthalic acid indicates that a change in the photocatalytic performance of doped TiO2 is closely related to the amount of photoinduced radical ions. X-ray photoelectron spectroscopy and low-temperature photoluminescence were employed to study the doping mechanism. While both N and Fe facilitate the absorption of the visible light, it is found that only Fe increases the electron−hole recombination rate, leading to the opposite effects of N and Fe doping on the photocatalytic performance of TiO2

Photophysical, Photoelectrochemical, and Photocatalytic Properties of Novel SnWO₄ Oxide Semiconductors with Narrow Band Gaps

Novel SnWO4 visible-light active photocatalysts with two polymorphs (orthorhombic α and cubic β phases) were prepared by a conventional solid-state reaction method, and their optical properties, electronic band structure, and photocatalytic activities were investigated. It was found that the low-temperature phase, α-SnWO4 with corner-shared WO6 octahedra, exhibited a dark-red color and indirect band gap of 1.64 eV, whereas the high-temperature phase, β-SnWO4 with unshared WO4 tetrahedra, exhibited a light-yellow color and direct band gap of 2.68 eV. The Mott−Schottky plots obtained using a thick film electrode in 1 M NaCl electrolyte revealed the n-type semiconductive properties of the SnWO4 polymorphs; i.e., the flat-band potential values of α- and β-SnWO4 were −0.61 and −0.66 V (SCE), respectively. From the electronic band structure calculations performed using density functional theory, the Sn 5p and O 2p orbitals were hybridized to construct the valence band in both SnWO4 polymorphs. However, the constructions of the conduction band were quite different. β-SnWO4 with its shorter W−O bond lengths in the WO4 tetrahedra has a higher conduction-band potential than α-SnWO4 phase, which has larger W−O bond lengths in the WO6 octahedra and, thus, was able to produce H2 from an aqueous methanol solution under visible-light irradiation (>400 nm). Both SnWO4 polymorphs also exhibited good photocatalytic activity for the degradation of rhodamine B dye solution under visible-light irradiation (>420 nm). The photocatalytic activity of these SnWO4 polymorphs was higher than that of other visible-light active photocatalysts with much smaller particle sizes, such as nanosized WO3 (9.72 m2/g) and TiONx (112.13 m2/g). This higher photocatalytic activity of the SnWO4 polymorphs is mainly attributed to their smaller band gaps and unique band structures, resulting from their different bonding nature

Surfactant-Assisted Shape Evolution of Thermally Synthesized TiO₂ Nanocrystals and Their Applications to Efficient Photoelectrodes

TiO2 nanocrystals were synthesized via a two-phase thermal process, and the shape of the nanocrystals was controlled from nanospheres to nanorods by the ratio of two surfactants. The shape control of nanocrystals was ascribed to the selective adsorption of the two surfactants. The shape of TiO2 nanocrystals influenced the photocatalytic performances of the photoelectrodes through two compromising factors:  the relative surface area and the electron transport. The photoelectrode composed of nanorods showed a slower charge recombination rate, while it showed a smaller specific surface area, compared to nanospheres. As a result, the photoelectrodes showed the optimal photocatalytic performance when the nanospheres and the nanorods were mixed

Regulating Surface Heterogeneity Maximizes Photovoltage and Operational Stability in Tin–Lead Perovskite Solar Cells

We present a surface reconstruction strategy for tin–lead perovskites, effectively addressing the issue of oxidized Sn fragments on surfaces and interfaces. Our surface treatment involving postfabrication iodide supplementation effectively regulates undesired surface binding states and reconstructs the compositional gradient. Through surface-sensitive and depth-resolved analysis, we unveil a strong correlation among surface compositional disorder, photovoltage, and operational stability in tin–lead perovskites. Surface-reconstructed perovskite films demonstrate improved carrier lifetime, reduced defect density, and higher recombination resistance compared with untreated films. As a result, devices utilizing surface-reconstructed perovskites exhibit remarkable performance with high power conversion efficiency (up to 23%) and open-circuit voltage (0.88 V), alongside enhanced operational stability compared to untreated counterparts. These insights into the surface vulnerabilities of mixed tin–lead perovskites, coupled with the underlying chemistry of surface passivation, pave the way for significant advancements in narrow-band gap perovskite solar cells

Image_3_RpoS contributes in a host-dependent manner to Salmonella colonization of the leaf apoplast during plant disease.jpg

Contaminated fresh produce has been routinely linked to outbreaks of Salmonellosis. Multiple studies have identified Salmonella enterica factors associated with successful colonization of diverse plant niches and tissues. It has also been well documented that S. enterica can benefit from the conditions generated during plant disease by host-compatible plant pathogens. In this study, we compared the capacity of two common S. enterica research strains, 14028s and LT2 (strain DM10000) to opportunistically colonize the leaf apoplast of two model plant hosts Arabidopsis thaliana and Nicotiana benthamiana during disease. While S. enterica 14028s benefited from co-colonization with plant-pathogenic Pseudomonas syringae in both plant hosts, S. enterica LT2 was unable to benefit from Pto co-colonization in N. benthamiana. Counterintuitively, LT2 grew more rapidly in ex planta N. benthamiana apoplastic wash fluid with a distinctly pronounced biphasic growth curve in comparison with 14028s. Using allelic exchange, we demonstrated that both the N. benthamiana infection-depedent colonization and apoplastic wash fluid growth phenotypes of LT2 were associated with mutations in the S. enterica rpoS stress-response sigma factor gene. Mutations of S. enterica rpoS have been previously shown to decrease tolerance to oxidative stress and alter metabolic regulation. We identified rpoS-dependent alterations in the utilization of L-malic acid, an abundant carbon source in N. benthamiana apoplastic wash fluid. We also present data consistent with higher relative basal reactive oxygen species (ROS) in N. benthamiana leaves than in A. thaliana leaves. The differences in basal ROS may explain the host-dependent disease co-colonization defect of the rpoS-mutated LT2 strain. Our results indicate that the conducive environment generated by pathogen modulation of the apoplast niche can vary from hosts to host even with a common disease-compatible pathogen.</p

Image_2_RpoS contributes in a host-dependent manner to Salmonella colonization of the leaf apoplast during plant disease.jpg

Contaminated fresh produce has been routinely linked to outbreaks of Salmonellosis. Multiple studies have identified Salmonella enterica factors associated with successful colonization of diverse plant niches and tissues. It has also been well documented that S. enterica can benefit from the conditions generated during plant disease by host-compatible plant pathogens. In this study, we compared the capacity of two common S. enterica research strains, 14028s and LT2 (strain DM10000) to opportunistically colonize the leaf apoplast of two model plant hosts Arabidopsis thaliana and Nicotiana benthamiana during disease. While S. enterica 14028s benefited from co-colonization with plant-pathogenic Pseudomonas syringae in both plant hosts, S. enterica LT2 was unable to benefit from Pto co-colonization in N. benthamiana. Counterintuitively, LT2 grew more rapidly in ex planta N. benthamiana apoplastic wash fluid with a distinctly pronounced biphasic growth curve in comparison with 14028s. Using allelic exchange, we demonstrated that both the N. benthamiana infection-depedent colonization and apoplastic wash fluid growth phenotypes of LT2 were associated with mutations in the S. enterica rpoS stress-response sigma factor gene. Mutations of S. enterica rpoS have been previously shown to decrease tolerance to oxidative stress and alter metabolic regulation. We identified rpoS-dependent alterations in the utilization of L-malic acid, an abundant carbon source in N. benthamiana apoplastic wash fluid. We also present data consistent with higher relative basal reactive oxygen species (ROS) in N. benthamiana leaves than in A. thaliana leaves. The differences in basal ROS may explain the host-dependent disease co-colonization defect of the rpoS-mutated LT2 strain. Our results indicate that the conducive environment generated by pathogen modulation of the apoplast niche can vary from hosts to host even with a common disease-compatible pathogen.</p

Preparation of a Nanoporous CaCO₃-Coated TiO₂ Electrode and Its Application to a Dye-Sensitized Solar Cell

A nanoporous CaCO3 overlayer-coated TiO2 thick film was prepared by the topotactic thermal decomposition of Ca(OH)2, and its performance as an electrode of a dye-sensitized solar cell was investigated. As compared to bare TiO2, nanoporous CaCO3-coated TiO2 provided higher specific surface area and, subsequently, a larger amount of dye adsorption; this in turn increased short-circuit current (Jsc). Furthermore, the CaCO3 coating demonstrated increased impedance at the TiO2/dye/electrolyte interface and increased the lifetime of the photoelectrons, indicating the improved retardation of the back electron transfer, which increases Jsc, open-circuit voltage (Voc), and fill factor (ff). Thereby, the energy conversion efficiency (η) of the solar cell improved from 7.8 to 9.7% (an improvement of 24.4%) as the nanoporous CaCO3 layer was coated onto TiO2 thick films

Image_4_RpoS contributes in a host-dependent manner to Salmonella colonization of the leaf apoplast during plant disease.jpg

Contaminated fresh produce has been routinely linked to outbreaks of Salmonellosis. Multiple studies have identified Salmonella enterica factors associated with successful colonization of diverse plant niches and tissues. It has also been well documented that S. enterica can benefit from the conditions generated during plant disease by host-compatible plant pathogens. In this study, we compared the capacity of two common S. enterica research strains, 14028s and LT2 (strain DM10000) to opportunistically colonize the leaf apoplast of two model plant hosts Arabidopsis thaliana and Nicotiana benthamiana during disease. While S. enterica 14028s benefited from co-colonization with plant-pathogenic Pseudomonas syringae in both plant hosts, S. enterica LT2 was unable to benefit from Pto co-colonization in N. benthamiana. Counterintuitively, LT2 grew more rapidly in ex planta N. benthamiana apoplastic wash fluid with a distinctly pronounced biphasic growth curve in comparison with 14028s. Using allelic exchange, we demonstrated that both the N. benthamiana infection-depedent colonization and apoplastic wash fluid growth phenotypes of LT2 were associated with mutations in the S. enterica rpoS stress-response sigma factor gene. Mutations of S. enterica rpoS have been previously shown to decrease tolerance to oxidative stress and alter metabolic regulation. We identified rpoS-dependent alterations in the utilization of L-malic acid, an abundant carbon source in N. benthamiana apoplastic wash fluid. We also present data consistent with higher relative basal reactive oxygen species (ROS) in N. benthamiana leaves than in A. thaliana leaves. The differences in basal ROS may explain the host-dependent disease co-colonization defect of the rpoS-mutated LT2 strain. Our results indicate that the conducive environment generated by pathogen modulation of the apoplast niche can vary from hosts to host even with a common disease-compatible pathogen.</p