Z‑scheme Photocatalytic CO₂ Conversion on Three-Dimensional BiVO₄/Carbon-Coated Cu₂O Nanowire Arrays under Visible Light

Cuprous oxide (Cu₂O) is one of the most promising materials for photoreduction of CO₂ because of its high conduction band and small band gap, which enable the production of high-potential electrons under visible-light irradiation. However, it is difficult to reduce the CO₂ using a Cu₂O-based photocatalyst due to fast charge recombination and low photostability. In this work, we enhanced the photocatalytic CO₂ conversion activity of Cu₂O by hybridization of Cu₂O NWAs, carbon layers, and BiVO₄ nanoparticles. By construction of a Z-scheme charge flow on a 3-D NWA structure, the BiVO₄/carbon-coated Cu₂O (BVO/C/Cu₂O) NWAs show significantly enhanced charge separation and light harvesting property. As a result, CO formation rate of BVO/C/Cu₂O was 9.4 and 4.7 times those of Cu₂O mesh and Cu₂O NWAs, respectively, under visible light irradiation. In addition, the material retained 98% of its initial photocatalytic CO₂ conversion performance after five reaction cycles (20 h) because of the protective carbon layer and Z-schematic charge flow. We believe that this work provides a promising photocatalyst system that combines a 3-D NWA structure and a Z-scheme charge flow for efficient and stable CO₂ conversion

Improving Uniformity and Reproducibility of Hybrid Perovskite Solar Cells via a Low-Temperature Vacuum Deposition Process for NiO<i>_x</i> Hole Transport Layers

Recently, the trend in inverted hybrid perovskite solar cells (PVSCs) has been to utilize NiO<i>_x</i> as hole transport layers. However, the majority of reported solution-processed NiO<i>_x</i> films require a high-temperature thermal annealing process, which is unfavorable for large-scale manufacturing and suffers from lack of uniformity. We report, for the first time, e-beam evaporation as a low-temperature vacuum process for the deposition of NiO<i>_x</i> hole transport layers for PVSCs. Device characterization shows that efficiency is on par with solution-processed methods, the highest efficiency at 15.4% with no obvious hysteresis. Differences are found to be due to the presence of more Ni³⁺ in e-beam evaporated NiO<i>_x</i>, which are responsible for a lower transmittance but higher conductivity. Most importantly, e-beam-evaporated NiO<i>_x</i>-based PVSCs show greater uniformity and reproducibility compared to spin-coated NiO<i>_x</i>-based PVSCs. Finally, e-beam-evaporated NiO<i>_x</i> has the additional advantage of being produced by a low-temperature deposition process and applicable over large areas. This work, therefore, represents a significant step toward large-area PVSCs, where e-beam evaporation can be used for the low-temperature uniform deposition of charge-transport layers, such as NiO<i>_x</i>

Highly Transparent and UV-Resistant Superhydrophobic SiO₂‑Coated ZnO Nanorod Arrays

Highly transparent and UV-resistant superhydrophobic arrays of SiO₂-coated ZnO nanorods are prepared in a sequence of low-temperature (<150 °C) steps on both glass and thin sheets of PET (2 × 2 in.²), and the superhydrophobic nanocomposite is shown to have minimal impact on solar cell device performance under AM1.5G illumination. Flexible plastics can serve as front cell and backing materials in the manufacture of flexible displays and solar cells

Highly Efficient and Stable CO₂ Reduction Photocatalyst with a Hierarchical Structure of Mesoporous TiO₂ on 3D Graphene with Few-Layered MoS₂

The development of photocatalysts of CO₂ reduction based on stable and Earth-abundant materials is essential for utilizing solar energy and storing it in chemical forms. Here, we report the synthesis and characterization of a composite material consisting of a few layers of MoS₂ on a hierarchical porous structure of mesoporous TiO₂ and macroporous 3D graphene aerogel (TGM) as a high-performance, robust, noble-metal-free photocatalyst of CO₂ reduction. The hierarchical structure contributed to the high photocatalytic catalyst performance, which was investigated by controlling the morphologies of the mesopores and macropores. By optimizing the relative amounts of each component and the configuration of the composite, a TGM system was fabricated. The resulting TGM showed a lower extent of charge recombination and a higher photocurrent density, and hence a higher CO photoconversion rate (92.33 μmol CO/g·h) than those of other composite combinations, i.e., bare TiO₂, TiO₂-graphene, TiO₂-MoS₂, and TiO₂-graphene multiple-layered MoS₂. Also, the role of each component and the underlying mechanism in the catalysis of the reaction by TGM were investigated. The long-term stability of the TGM composite was tested and compared with that of a TiO₂-graphene-Ag composite. Over the course of 15 cycles, the TGM composite retained its original conversion rate, while the activity of the TiO₂-graphene-Ag composite decreased. The hierarchical porous structure with mesoporous TiO₂ and a few layers of MoS₂ on macroporous 3D graphene is expected to have great potential as an affordable, robust, high-efficiency CO-selective photocatalyst of CO₂ reduction

Amine-Functionalized Graphene/CdS Composite for Photocatalytic Reduction of CO₂

This study provides a significant enhancement in CO₂ photoconversion efficiency by the functionalization of a reduced graphene oxide/cadmium sulfide composite (rGO/CdS) with amine. The amine-functionalized graphene/CdS composite (AG/CdS) was obtained in two steps. First, graphene oxide (GO) was selectively deposited via electrostatic interaction with CdS nanoparticles modified with 3-aminopropyltriethoxysilane. Subsequently, ethylenediamine (NH₂C₂H₄NH₂) was grafted by an <i>N</i>,<i>N</i>′-dicyclohexylcarbodiimide coupling reaction between the amine group of ethylenediamine and the carboxylic group of GO. As a result, a few layers of amine-functionalized graphene wrapped CdS uniformly, forming a large interfacial area. Under visible light, the photocurrent through the AG/CdS significantly increased because of enhanced charge separation in CdS. The CO₂ adsorption capacity on AG/CdS was 4 times greater than that on rGO/CdS at 1 bar. These effects resulted in a methane formation rate of 2.84 μmol/(g h) under visible light and CO₂ at 1 bar, corresponding to 3.5 times that observed for rGO/CdS. Interestingly, a high methane formation rate (1.62 μmol/(g h)) was observed for AG/CdS under CO₂ at low pressure (0.1 bar), corresponding to a value 20 times greater than that observed for the rGO/CdS. Thus, the enhanced performance for photocatalytic reduction of CO₂ on the AG/CdS is due to the improved CO₂ adsorption related to the amine groups on amine-functionalized graphene, which sustains the strong absorption of visible light and superior charge-transfer properties in comparison with those of graphene

Ultralong Radiative States in Hybrid Perovskite Crystals: Compositions for Submillimeter Diffusion Lengths

Organic–inorganic hybrid perovskite materials have recently evolved into the leading candidate solution-processed semiconductor for solar cells due to their combination of desirable optical and charge transport properties. Chief among these properties is the long carrier diffusion length, which is essential to optimizing the device architecture and performance. Herein, we used time-resolved photoluminescence (at low excitation fluence, 10.59 μJ·cm^–2 upon two-photon excitation), which is the most accurate and direct approach to measure the radiative charge carrier lifetime and diffusion lengths. Lifetimes of about 72 and 4.3 μs for FAPbBr₃ and FAPbI₃ perovskite single crystals have been recorded, presenting the longest radiative carrier lifetimes reported to date for perovskite materials. Subsequently, carrier diffusion lengths of 107.2 and 19.7 μm are obtained. In addition, we demonstrate the key role of the organic cation units in modulating the carrier lifetime and its diffusion lengths, in which the defect formation energies for FA cations are much higher than those with the MA ones

Inside Perovskites: Quantum Luminescence from Bulk Cs₄PbBr₆ Single Crystals

Zero-dimensional perovskite-related structures (0D-PRS) are a new frontier of perovskite-based materials. 0D-PRS, commonly synthesized in powder form, manifest distinctive optical properties such as strong photoluminescence (PL), narrow emission line width, and high exciton binding energy. These properties make 0D-PRS compelling for several types of optoelectronic applications, including phosphor screens and electroluminescent devices. However, it would not be possible to rationally design the chemistry and structure of these materials, without revealing the origins of their optical behavior, which is contradictory to the well-studied APbX₃ perovskites. In this work, we synthesize single crystals of Cs₄PbBr₆ 0D-PRS, and investigated the origins of their unique optical and electronic properties. The crystals exhibit a PL quantum yield higher than 40%, the highest reported for perovskite-based single crystals. Time-resolved and temperature dependent PL studies, supported by DFT calculations, and structural analysis, elucidate an emissive behavior reminiscent of a quantum confined structure rather than a typical bulk perovskite material