Since the great breakthrough made in 1991 by ORegan [1] and Grätzel [2] , dye-sensitized solar cells (DSSCs) have attracted tremendous interest and are becoming one of the most promising candidates for practical photovoltaic applications due to their low production cost and efficient photovoltaic performance. Up to now, more than 11 % power conversion efficiency has been reported for DSSCs based on TiO 2 nanocrystalline photoelectrodes.[3] It is well known that the composition and structure of the photoelectrode material play an important role in the photovoltaic performance and stability of DSSCs. As an efficient photoelectrode, the material should have a large surface area to adsorb larger amounts of dye and highly ordered nanoarrays or densely packed microstructure for fast electron transport and light scattering. [4][5][6] Among the photoelectrodes, one interesting structure is the double-layer electrode containing a dye adsorption layer (10-15 mm thick, consisting of % 20 nm particles) and a light-scattering layer (3-5 mm thick, consisting of a few hundreds of nanometer particles); this has been found to improve the photovoltaic performance. [7] Another novel photoelectrode is the hierarchically structured film consisting of submicron spheres that are made up of 10-20 nm particles. The photoelectrode consists of this kind of bifunctional material with both the dye adsorption layer (nanoparticles) and the light-scattering layer (submicron spheres), which results in a significant enhancement of power conversion efficiency. [5,6] However, most of the works have been only focused on the hierarchical TiO 2 or ZnO spheres. [5,6] Tin oxide, as an n-type semiconductor with a wide direct band gap of 3.6 eV at 300 K, [8] is one of the promising multifunctional materials in gas sensors, [9] dye-sensitized solar cells, [10] lithium ion batteries, and so on.[11] SnO 2 nanoparticles and hollow SnO 2 microspheres have been reported to exhibit about 5 % photovoltaic performance.[10] However, to the best of our knowledge, hierarchically structured octahedral (nonspherical) SnO 2 materials have not yet been reported for DSSCs applications; this might be an ideal structure because the eight faces at the submicron level can have a light-scattering effect.Herein, we report, for the first time, a rapid and facile sonochemical process to synthesize uniform octahedral Sn 6 O 4 (OH) 4 intermediates, resulting in hierarchical SnO 2 octahedra approximately 1.0 mm in size, consisting of SnO 2 nanoparticles about 30 nm in diameter by heat treatment of the as-made Sn 6 O 4 (OH) 4 at 800 8C for 3 h in air. The reaction solution containing SnCl 2 ·2 H 2 O (1.128 g), diethanolamine (5.0 mL), diethylene glycol (DEG, 40 mL), and deionized water (10 mL) is subjected to intense ultrasonic irradiation for 10 min; the resulting precipitates were collected by centrifugation at 5000 rpm for 5 min. The present sonochemical method has a few clear advantages over traditional hydrothermal processes, such as it is simple, fast, low energy cost, and does...
Following the previous report on the fabrication of three-dimensional hierarchical SnO 2 octahedra consisting of nanoparticles via a rapid sonochemical process (Wang et al., Chem.-Eur. J., 2010, 16, 8620-8625), the influences of ultrasonic time, amplitude, ratio of H 2 O-diethylene glycol (DEG), and different Sn salts on the morphology and size of SnO 2 have been further investigated in the present article. The hierarchical SnO 2 octahedra with average edge lengths of 0.5, 0.8, 1.0, 1.5 and 1.8 mm composed of 30-40 nm SnO 2 nanoparticles have been successfully obtained. The power conversion efficiencies of dye-sensitized solar cells (DSSCs) based on the hierarchical SnO 2 octahedra photoanodes varied from 5.57%, 5.82%, 6.40%, 6.45% to 6.80% with the corresponding octahedron sizes of 0.5, 0.8, 1.0, 1.5 and 1.8 mm, respectively. Intensity-modulated photocurrent spectroscopy (IMPS), intensitymodulated voltage spectroscopy (IMVS) and UV-vis diffuse spectroscopy were used to investigate the influences of the SnO 2 octahedron size on the photovoltaic performances of DSSCs.
Size is a defining characteristic of nanoparticles; it influences their optical and electronic properties as well as their interactions with molecules and macromolecules. Producing nanoparticles with narrow size distributions remains one of the main challenges to their utilization. At this time, the number of practical approaches to optimize the size distribution of nanoparticles in many interesting materials systems, including diamond nanocrystals, remains limited. Diamond nanocrystals synthesized by detonation protocols - so-called detonation nanodiamonds (DNDs) - are promising systems for drug delivery, photonics, and composites. DNDs are composed of primary particles with diameters mainly <10 nm and their aggregates (ca. 10-500 nm). Here, we introduce a large-scale approach to rate-zonal density gradient ultracentrifugation to obtain monodispersed fractions of nanoparticles in high yields. We use this method to fractionate a highly concentrated and stable aqueous solution of DNDs and to investigate the size distribution of various fractions by dynamic light scattering, analytical ultracentrifugation, transmission electron microscopy and powder X-ray diffraction. This fractionation method enabled us to separate gram-scale amounts of DNDs into several size ranges within a relatively short period of time. In addition, the high product yields obtained for each fraction allowed us to apply the fractionation method iteratively to a particular size range of particles and to collect various fractions of highly monodispersed primary particles. Our method paves the way for in-depth studies of the physical and optical properties, growth, and aggregation mechanism of DNDs. Applications requiring DNDs with specific particle or aggregate sizes are now within reach.
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