Study on the Ambient Temperature as an Important but Easily Neglected Factor in the Process of Preparing Photovoltaic All-Inorganic CsPbIBr₂ Perovskite Film by the Elegant Solvent-Controlled Growth Strategy

All-inorganic CsPbIBr2 perovskite has received extensive attention in the field of solar cells due to its good wet and thermal stability as well as a moderate band gap. In the preparation of CsPbIBr2 film by one-step spin-coating method, the amount of dimethyl sulfoxide solvent remaining in the precursor film has a great influence on the process of film growth. Therefore, it is necessary to ensure that an appropriate amount of solvent exists in the precursor film before annealing. Herein, we adopted the solvent-controlled growth (SCG) strategy, that is, standing by the precursor films in the nitrogen glovebox for a period of time before annealing, to make sure that excess solvent can be evaporated from the precursor film. In this work, we found that the ambient temperature is an important but easily neglected factor in the process of preparing CsPbIBr2 film by the SCG strategy. When the ambient temperature is 20 °C, SCG treatment is required to obtain a flat and dense CsPbIBr2 film. However, SCG treatment is not essential at 30 °C. The ambient temperature has an impact on the evaporation rate of the solvent in the precursor film, and thus affects the effect of the SCG strategy. This work highlights that, when preparing CsPbIBr2 film by a one-step spin-coating method, in order to obtain a high-quality CsPbIBr2 film, the influence of ambient temperature on solvent-controlled growth strategy should be considered

Probing the Performance Limitations in Thin-Film FeVO₄ Photoanodes for Solar Water Splitting

FeVO₄ is a potentially promising n-type multimetal oxide semiconductor for photoelectrochemical water splitting based on its favorable optical band gap of ca. 2.06 eV that allows for the absorption of visible light up to around 600 nm. However, the presently demonstrated photocurrent values on FeVO₄ photoanodes are yet considerably low when comparing with α-Fe₂O₃, although FeVO₄ can absorb comparable wavelengths of sunlight as α-Fe₂O₃. Donor-type doping and constructing nanoporous film morphology have afforded desirable (but far from satisfactory) improvements in FeVO₄ photoanodes, whereas the fundamental properties, such as absorption coefficients and the nature of optical transition, and a quantitative analysis of the efficiency losses for FeVO₄ photoanodes remain elusive. In the present study, we conduct a thorough experimental analysis of structural, optical, charge transport, and surface catalysis properties of FeVO₄ thin films to investigate and clarify how and where the efficiency losses occur. Based on the results, the charge recombination pathways and light-harvesting loss in FeVO₄ thin-film photoanodes are identified and quantitatively determined. Our study will deepen the understanding on the photoelectrochemical behaviors of FeVO₄ photoanodes and will also shed light on the optimization routes to engineer this material to approach its theoretical maximum

Band Structure Engineering of Carbon Nitride: In Search of a Polymer Photocatalyst with High Photooxidation Property

The electronic band structure of a semiconductor photocatalyst intrinsically controls its level of conduction band (CB) and valence band (VB) and, thus, influences its activity for different photocatalytic reactions. Here, we report a simple bottom-up strategy to rationally tune the band structure of graphitic carbon nitride (g-C₃N₄). By incorporating electron-deficient pyromellitic dianhydride (PMDA) monomer into the network of g-C₃N₄, the VB position can be largely decreased and, thus, gives a strong photooxidation capability. Consequently, the modified photocatalyst shows preferential activity for water oxidation over water reduction in comparison with g-C₃N₄. More strikingly, the active species involved in the photodegradation of methyl orange switches from photogenerated electrons to holes after band structure engineering. This work may provide guidance on designing efficient polymer photocatalysts with the desirable electronic structure for specific photoreactions

High-Crystallinity Urchin‑like VS₄ Anode for High-Performance Lithium-Ion Storage

VS₄ anode materials with controllable morphologies from hierarchical microflower, octopus-like structure, seagrass-like structure to urchin-like structure have been successfully synthesized by a facile solvothermal synthesis approach using different alcohols as solvents. Their structures and electrochemical properties with various morphologies are systematically investigated, and the structure–property relationship is established. Experimental results reveal that Li⁺ ion storage behavior in VS₄ significantly depends on physical features such as the morphology, crystallite size, and specific surface area. According to this study, electrochemical performance degrades on the order of urchin-like VS₄ > octopus-like VS₄ > seagrass-like VS₄ > flower-like VS₄. Among them, urchin-like VS₄ demonstrates the best electrochemical performance benefiting from its peculiar structure which possesses large surface area that accommodates the volume change to a certain extent, and single-crystal thorns that provide fast electron transportation. Kinetic parameters derived from EIS spectra and sweep-rate-dependent CV curves, such as charge-transfer resistances, Li⁺ ion apparent diffusion coefficients and stored charge ratio of capacitive and intercalation contributions, both support this claim well. In addition, the EIS measurement was conducted during the first discharge/charge process to study the solid electrolyte interface (SEI) formation on urchin-like VS₄ and kinetics behavior of Li⁺ ion diffusion. A better fundamental understanding on Li⁺ storage behavior in VS₄ is promoted, which is applicable to other vanadium-based materials as well. This study also provides invaluable guidance for morphology-controlled synthesis tailored for optimal electrochemical performance