Binghai Dong

Hierarchical ZnO microarchitectures assembled by ultrathin nanosheets: hydrothermal synthesis and enhanced photocatalytic activity

A simple and economical citrate-mediated hydrothermal route has been developed to fabricate three-dimensional hierarchical ZnO microarchitectures with high surface-to-volume ratio and large population of unconventional (0001) surface planes. This complex architecture with flowerlike morphology is assembled by many interleaving nanosheets which have ultrathin thickness of about 5 nm. According to the experimental results, a growth mechanism which involves the assembly of the nanosheets from nanoparticles into flowerlike morphology is proposed. Importantly, this type of hierarchically-structured ZnO displays a strong structure-induced enhancement of photocatalytic performance and exhibits a significantly improved photocatalytic activity in the photodegradation of methyl orange than that of other monomorphological ZnO, such as ZnO nanoparticles, nanorods, and nanosheets. In addition to the large specific surface areas due to ultrathin size of the nanosheet building blocks, the enhanced photocatalytic activity can mainly be ascribed to the special structural feature with good stability and high proportion of active (0001) planes. This work provides an efficient route for the structure-induced enhancement of photocatalytic performance by designing a desirable micro/nanoarchitecture, which could also be extended to synthesize other metal-oxide microarchitectures with superior photocatalytic performance.

A novel photoanode architecture of dye-sensitized solar cells based on TiO2 hollow sphere/nanorod array double-layer film.

A novel TiO(2) double-layer (DL) film consisting of TiO(2) hollow spheres (HSs) as overlayer and single-crystalline TiO(2) nanorod arrays (RAs) as underlayer was designed as the photoanode of dye-sensitized solar cells (DSSCs). This new-typed TiO(2) HS/RA DL film could significantly improve the efficiency of DSSCs owing to its synergic effects, i.e. the relatively large specific surface area of TiO(2) HSs for effective dye adsorption, enhanced light harvesting capability originated from TiO(2) RA film, and rapid interfacial electron transport in one-dimensional TiO(2) nanorod arrays. The overall energy-conversion efficiency of 4.57% was achieved by the formation of TiO(2) DL film, which is 16% higher than that formed by TiO(2) HS film and far larger than that formed by TiO(2) RA film (η=0.99%). The light absorption and interfacial electron transport, which play important roles in the efficiency of DSSCs, were investigated by UV-vis absorption spectra and electrochemical impedance spectra.

Surfactant-assisted hydrothermal synthesis of Bi2O3 nano/microstructures with tunable size

A novel and simple citrate-assisted solution approach has been developed for the shape-selective synthesis of Bi2O3 nanostructures with controllable bandgaps and morphologies at a relatively low temperature of 40 °C. Different distinctive morphologies, including nanorods, nanoplates, plate-built cylinders, nanoplates with holes, and nanorings, are created due to the selective adsorption of the citrate molecules on certain faces during crystal growth. The bandgaps and aspect ratios of the Bi2O3 nanostructures are easily tuned by modifying the product morphologies by adjusting the amount of trisodium citrate. More novel and complex Bi2O3 nanostructures with controllable morphologies and sizes can be manufactured with our method by optimizing the experimental parameters. The distinctive nanostructures presented here extend the family of Bi2O3 nanostructures, and they also provide new opportunities for exploring the potential applications of Bi2O3 in a number of fields including photocatalysis, gas sensors, and photoelectrochemistry.

Atomic Layer Deposition of TiO2 for a High-Efficiency Hole-Blocking Layer in Hole-Conductor-Free Perovskite Solar Cells Processed in Ambient Air

In this study we design and construct high-efficiency, low-cost, highly stable, hole-conductor-free, solid-state perovskite solar cells, with TiO2 as the electron transport layer (ETL) and carbon as the hole collection layer, in ambient air. First, uniform, pinhole-free TiO2 films of various thicknesses were deposited on fluorine-doped tin oxide (FTO) electrodes by atomic layer deposition (ALD) technology. Based on these TiO2 films, a series of hole-conductor-free perovskite solar cells (PSCs) with carbon as the counter electrode were fabricated in ambient air, and the effect of thickness of TiO2 compact film on the device performance was investigated in detail. It was found that the performance of PSCs depends on the thickness of the compact layer due to the difference in surface roughness, transmittance, charge transport resistance, electron-hole recombination rate, and the charge lifetime. The best-performance devices based on optimized TiO2 compact film (by 2000 cycles ALD) can achieve power conversion efficiencies (PCEs) of as high as 7.82%. Furthermore, they can maintain over 96% of their initial PCE after 651 h (about 1 month) storage in ambient air, thus exhibiting excellent long-term stability.

Low-toxic metal halide perovskites: opportunities and future challenges

Over the past few years, lead halide perovskites have emerged as a class of dominant semiconductor materials in the photovoltaic (PV) field with an unprecedented sharp enhancement of power conversion efficiencies (PCEs) up to 22.1%, as well as in other promising optoelectronic applications due to their extraordinary and unique properties. However, the lead toxicity and long-term stability of these lead-based perovskites have raised considerable concerns for their real applications. Exploration of potentially low-toxic metal halide perovskite materials becomes one of the significant pivotal challenges in this century for PV, optoelectronic, and other unexplored applications. In this review, we summarize the recent progress on the development of low-toxic metal halide perovskites with a particular focus on their structures and properties, and discuss their potential applications in PV and optoelectronic devices. Moreover, we suggest current challenges and future research directions with the goal of stimulating further research interest and potential applications.

TiO2 Nanotube Arrays Composite Film as Photoanode for High-Efficiency Dye-Sensitized Solar Cell

A double-layered photoanode made of hierarchical TiO2 nanotube arrays (TNT-arrays) as the overlayer and commercial-grade TiO2 nanoparticles (P25) as the underlayer is designed for dye-sensitized solar cells (DSSCs). Crystallized free-standing TNT-arrays films are prepared by two-step anodization process. For photovoltaic applications, DSSCs based on double-layered photoanodes produce a remarkably enhanced power conversion efficiency (PCE) of up to 6.32% compared with the DSSCs solely composed of TNT-arrays (5.18%) or nanoparticles (3.65%) with a similar thickness (24 μm) at a constant irradiation of 100 mW cm−2. This is mainly attributed to the fast charge transport paths and superior light-scattering ability of TNT-arrays overlayer and good electronic contact with F-doped tin oxide (FTO) glass provided from P25 nanoparticles as a bonding layer.

One-Step Hydrothermal Formation of Bi2O3 Nanourchins with Radially Ultrathin Nanotubes

A novel Bi 2 O 3 urchin-like microarchitecture with high-density radially oriented Bi 2 O 3 nanotubes (NTs) was fabricated by a one-step hydrothermal approach without any template or surfactant at a relative low temperature of 90 °C. The radial Bi 2 O 3 NTs on the surface of nanourchins (NUs) were 4–7 nm in diameter and ∼1.7 µm in length. The mean wall thickness of the NTs was as thin as 1.5 nm. Based on the time-dependent evolutions of morphology examined by scanning electron microscope (SEM), a “rolling-up mechanism” was demonstrated to explain the formation of the ultrathin Bi 2 O 3 NTs. The ultrathin and long NTs bring on the high surface-to-volume ratios of the Bi 2 O 3 urchin-like microarchitectures, which makes them great potential applications in gas sensors, photocatalysis, environmental purification, and solar energy conversion.

New intelligent multifunctional SiO2/VO2 composite films with enhanced infrared light regulation performance, solar modulation capability, and superhydrophobicity

Abstract Highly transparent, energy-saving, and superhydrophobic nanostructured SiO2/VO2 composite films have been fabricated using a sol–gel method. These composite films are composed of an underlying infrared (IR)-regulating VO2 layer and a top protective layer that consists of SiO2 nanoparticles. Experimental results showed that the composite structure could enhance the IR light regulation performance, solar modulation capability, and hydrophobicity of the pristine VO2 layer. The transmittance of the composite films in visible region (Tlum) was higher than 60%, which was sufficient to meet the requirements of glass lighting. Compared with pristine VO2 films and tungsten-doped VO2 film, the near IR control capability of the composite films was enhanced by 13.9% and 22.1%, respectively, whereas their solar modulation capability was enhanced by 10.9% and 22.9%, respectively. The water contact angles of the SiO2/VO2 composite films were over 150°, indicating superhydrophobicity. The transparent superhydrophobic surface exhibited a high stability toward illumination as all the films retained their initial superhydrophobicity even after exposure to 365 nm light with an intensity of 160 mW.cm−2 for 10 h. In addition, the films possessed anti-oxidation and anti-acid properties. These characteristics are highly advantageous for intelligent windows or solar cell applications, given that they can provide surfaces with anti-fogging, rainproofing, and self-cleaning effects. Our technique offers a simple and low-cost solution to the development of stable and visible light transparent superhydrophobic surfaces for industrial applications.

Mechanically robust, thermally stable, highly transparent superhydrophobic coating with low-temperature sol–gel process

The wetting behavior of transparent superhydrophobic surfaces has attracted much attention in our daily life as well as in engineering applications. Optically transparent superhydrophobic silica films were synthesized by sol–gel method. The coating was formed by in a solution containing silica nanoparticles and silicic acid, in which the silica nanoparticles and silicic acid had different proportions to modulate the roughness of the coating. Comparing with the HMDZ modified films (140 ± 2°), the films modified by TMCS showed very high water contact angle (164 ± 2°), which indicating the excellent waterproof behavior of the films. When the TMCS modified films were heated at temperature above 350 °C and 400 °C, it became superhydrophilic. The transmittance of coated glasses were above 80% for wavelengths at 400–800 nm. Moreover, the properties of the film were almost unchanged after acid corrosion and immersion in salt solution, and still retained the superhydrophobicity. Even after the impact of water flow and sand impact abrasion, it can still maintain good performance of superhydrophobicity.

Nontoxic (CH3NH3)3Bi2I9 perovskite solar cells free of hole conductors with an alternative architectural design and a solution-processable approach

Methylammonium iodide bismuthate ((CH3NH3)3Bi2I9) (MBI) perovskite was introduced as a new lead-free and air-stable absorber for hole conductor-free perovskite solar cells. The two-step soaking-assisted sequential solution (2-S) method was adopted to fabricate MBI films for the first time. We compared the formation processes and final morphologies of the MBI films fabricated using the 1-S and 2-S methods on planar and mesoporous TiO2 layers, respectively. We also investigated the effects of the morphologies of MBI films and device architectural design on device performance. Results showed that the MBI films fabricated using the 2-S method achieved a superior coverage both on the compact TiO2 and mesoporous TiO2 layers. The mesoporous structure devices presented higher power conversion efficiencies than the planar structure devices. In addition, all devices exhibited excellent thermal and long-term stabilities. The presented architectural design and solution-processable approach could inspire further research and practical applications on lead-free organic–inorganic hybrid perovskite solar cells.