Tantalum Oxide as an Efficient Alternative Electron Transporting Layer for Perovskite Solar Cells

Electron transporting layers facilitating electron extraction and suppressing hole recombination at the cathode are crucial components in any thin-film solar cell geometry, including that of metal–halide perovskite solar cells. Amorphous tantalum oxide (Ta₂O₅) deposited by spin coating was explored as an electron transport material for perovskite solar cells, achieving power conversion efficiency (PCE) up to ~14%. Ultraviolet photoelectron spectroscopy (UPS) measurements revealed that the extraction of photogenerated electrons is facilitated due to proper alignment of bandgap energies. Steady-state photoluminescence spectroscopy (PL) verified efficient charge transport from perovskite absorber film to thin Ta₂O₅ layer. Our findings suggest that tantalum oxide as an n-type semiconductor with a calculated carrier density of ~7 × 10¹⁸/cm³ in amorphous Ta₂O₅ films, is a potentially competitive candidate for an electron transport material in perovskite solar cells.

Topotactic formation of poriferous (Al,C)-Ta2O5 mesocrystals for improved visible-light photocatalysis

Poriferous monocrystal-like nanostructures are contributing to fabricate long-distance charge transfer pathways and rapid diffusions of the degraded products, and attracts wide attentions. In this work, layered and poriferous (Al,C)-Ta₂O₅ mesocrystals were fabricated by topotactic transformation strategy with Ta₄AlC₃ MAX as starting materials for visible-light photocatalytic antibiotic degradation. The prepared sample exhibited enhanced visible-light absorption and visible-light photocatalytic performance, far superior to those of commercial Ta₂O₅ and Ta₄AlC₃ MAX, which was mainly because of the elemental doping in the samples. The experimental results also indicated that continuous attacks of the photo-generated holes and ·O₂^- species efficiently induced efficient visible-light photodegradation of tetracycline. Current work also indicates a new and potential tantalum-based semiconductors for high-performance environmental photocatalysis.

Monolayer Amorphous Carbon-Bridged Nanosheet Mesocrystal: Facile Preparation, Morphosynthetic Transformation, and Energy Storage Applications

Self-assembly of nanoscale building units into mesoscopically ordered superstructures opens the possibility for tailored applications. Nonetheless, the realization of precise controllability related specifically to the atomic scale has been challenging. Here, first, we explore the key role of a molecular surfactant in adjusting the growth kinetics of two-dimensional (2D) layered SnS₂. Experimentally, we show that high pressure both enhances the adsorption energy of the surfactant sodium dodecylbenzene sulfonate (SDBS) on the SnS₂(001) surface at the initial nucleation stage and induces the subsequent oriented attachment (OA) growth of 2D crystallites with monolayer thickness, leading to the formation of a monolayer amorphous carbon-bridged nanosheet mesocrystal. It is notable that such a nanosheet-coalesced mesocrystal is metastable with a flowerlike morphology and can be turned into a single crystal via crystallographic fusion. Subsequently, direct encapsulation of the mesocrystal via FeCl₃-induced pyrrole monomer self-polymerization generates conformal polypyrrole (PPy) coating, and carbonization of the resulting nanocomposites generates Fe-N-S-co-doped carbons that are embedded with well-dispersed SnS/FeCl₃ quantum sheets; this process skillfully integrated structural phase transformation, pyrolysis graphitization, and self-doping. Interestingly, such an integrated design not only guarantees the flowerlike morphology of the final nanohybrids but also, more importantly, allows the thickness of petalous carbon and the size of the nanoconfined particles to be controlled. Benefiting from the unique structural features, the resultant nanohybrids exhibited the brilliant electrochemical performance while simultaneously acting as a reliable platform for exploring the structure-performance correlation of a Li-ion battery (LIB).

Mesocrystalline Ta3N5 superstructures with long-lived charges for improved visible light photocatalytic hydrogen production

Highly ordered mesocrystalline semiconductors often indicate tremendous prospects in the clean energy production and environmental photocatalysis mainly because of their unique superstructure for efficient charge transport pathways and long-lived charges. Here, superstructure Ta₃N₅ mesocrystals with the high-energy surface {2 0 0} planes exposed were the first time to be successfully fabricated by topological transformation of Ta₂O₅ mesocrystals. The prepared Ta₃N₅ mesocrystals showed enhanced visible-light photocatalytic hydrogen production activity of 98.67 μmol g^-1 for 180 min irradiation, which was approximately 5.28 times that of comm-Ta₃N₅ prepared with commercial Ta₂O₅ as the starting material, mainly due to the formation of long-distance electron conduction pathways and long-lived charges. The detailed electronic band structures of the prepared Ta₃N₅ mesocrystals were also investigated by electrochemical method. Finally, possible visible-light photocatalytic mechanisms of Ta₃N₅ mesocrystals for enhanced hydrogen production was also proposed in detail. Current work also indicates that tantalum-based mesocrystals show great potential to enhance the charge separation for efficient photocatalytic water splitting.

Fabrication of Durable Ordered Ta2O5 Nanotube Arrays Decorated with Bi2S3 Quantum Dots

One of the most important challenges in the fabrication of ordered tantalum pentaoxide (Ta₂O₅) nanotube arrays (NTs) via the electrochemical method is the formation of nanotubes that adhere well to the Ta substrate. In this paper, we propose a new protocol that allows tight-fitting Ta₂O₅ nanotubes to be obtained through the anodic oxidation of tantalum foil. Moreover, to enhance their activity in the photocatalytic reaction, in this study, they have been decorated by nontoxic bismuth sulfide (Bi₂S₃) quantum dots (QDs) via a simple successive ionic layer adsorption and reaction (SILAR) method. Transmission electron microscopy (TEM) analysis revealed that quantum dots with a size in the range of 6-11 nm were located both inside and on the external surfaces of the Ta₂O₅ NTs. The effect of the anodization time and annealing conditions, as well as the effect of cycle numbers in the SILAR method, on the surface properties and photoactivity of Ta₂O₅ nanotubes and Bi₂S₃/Ta₂O₅ composites have been investigated. The Ta₂O₅ nanotubes decorated with Bi₂S₃ QDs exhibit high photocatalytic activity in the toluene degradation reaction, i.e., 99% of toluene (C₀ = 200 ppm) was degraded after 5 min of UV-Vis irradiation. Therefore, the proposed anodic oxidation of tantalum (Ta) foil followed by SILAR decorating allows a photocatalytic surface, ready to use for pollutant degradation in the gas phase, to be obtained.

Mesocrystals for photocatalysis: a comprehensive review on synthesis engineering and functional modifications

Mesocrystals are a new class of superstructures that are generally made of crystallographically highly ordered nanoparticles and could function as intermediates in a non-classical particle-mediated aggregation process. In the past decades, extensive research interest has been focused on the structural and morphogenetic aspects, as well as the growth mechanisms, of mesocrystals. Unique physicochemical properties including high surface area and ordered porosity provide new opportunities for potential applications. In particular, the oriented interfaces in mesocrystals are considered to be beneficial for effective photogenerated charge transfer, which is a promising photocatalytic candidate for promoting charge carrier separation. Only recently, remarkable advances have been reported with a special focus on TiO2 mesocrystal photocatalysts. However, there is still no comprehensive overview on various mesocrystal photocatalysts and their functional modifications. In this review, different kinds of mesocrystal photocatalysts, such as TiO2 (anatase), TiO2 (rutile), ZnO, CuO, Ta2O5, BiVO4, BaZrO3, SrTiO3, NaTaO3, Nb3O7(OH), In2O3-x (OH) y , and AgIn(WO4)2, are highlighted based on the synthesis engineering, functional modifications (including hybridization and doping), and typical structure-related photocatalytic mechanisms. Several current challenges and crucial issues of mesocrystal-based photocatalysts that need to be addressed in future studies are also given.

Regulating effect of heterojunctions on electrocatalytic oxidation of methanol for Pt/WO3-NaTaO3 catalysts

Pt/WO₃-NaTaO₃ composite catalysts for different W/Ta molar ratios were obtained via a facile hydrothermal method.