Kensaku Kanomata

Room temperature atomic layer deposition of TiO2 on gold nanoparticles

The authors developed a room temperature atomic layer deposition (ALD) system that can deposit TiO2 on gold nanoparticles by using tetrakis(dimethylamino)titanium and plasma-excited humidified argon. The growth per cycle of TiO2 was measured to be 0.25 nm/cycle on a monitored Si sample. For applying the nanoparticle coating, the source material, i.e., gold particles, is electrostatically attached to the susceptor in the ALD system to avoid their gas transport. These particles are then mixed by a rotating scraper during the ALD process. This system allows a conformal deposition of TiO2 without the aggregation of nanoparticles. The thickness of TiO2 for shell coating is controlled by counting the number of ALD cycles. The deposition of TiO2 coating with a nanometer scale thickness on the gold nanoparticle is demonstrated in this paper.

Large difference between the magnetic properties of Ba and Ti co-doped BiFeO3 bulk materials and their corresponding nanoparticles prepared by ultrasonication

The ceramic pellets of the nominal compositions Bi0.7Ba0.3Fe1−x Ti x O3 (x = 0.00–0.20) were prepared initially by standard solid state reaction technique. The pellets were then ground into micrometer-sized powders and mixed with isopropanol in an ultrasonic bath to prepare nanoparticles. The x-ray diffraction patterns demonstrate the presence of a significant number of impurity phases in bulk powder materials. Interestingly, these secondary phases were completely removed due to the sonication of these bulk powder materials for 60 minutes. The field and temperature dependent magnetization measurements exhibited significant difference between the magnetic properties of the bulk materials and their corresponding nanoparticles. We anticipate that the large difference in the magnetic behavior may be associated with the presence and absence of secondary impurity phases in the bulk materials and their corresponding nanoparticles, respectively. The leakage current density of the bulk materials was also found to suppress in the ultrasonically prepared nanoparticles compared to that of bulk counterparts.

Optimized design of moth eye antireflection structure for organic photovoltaics

To improve the power conversion efficacy of organic photovoltaics (OPVs), it is required to design antireflection structures that could realize efficient and broadband light trapping. In this article, we perform global optimization of the textured pattern of moth eye antireflection surfaces to maximize the short-circuit current density (JSC) of OPVs with a poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)-based bulk heterojunction. We introduce an optimization algorithm consisting of two steps: in the first step, the simple grid search is conducted to roughly estimate a globally optimal solution, while in the second step, the Hooke and Jeeves pattern search is executed to refine the solution. By combining the optimization algorithm with the optical simulation based on the finite-difference time-domain method, we find the optimal period and height of moth eye array with which the level of JSC can be increased by 9.05% in the P3HT:PCBM-based organic solar cell. We also demonstrate that the optimized moth eye structure can significantly modify the light path at a long wavelength range to strengthen the electric field intensity and enhance energy absorption within the active layer.

Hybrid antireflection structure with moth eye and multilayer coating for organic photovoltaics

We propose a hybrid antireflection structure (ARS), which integrates moth eye texturing and multilayer interference coating, to improve efficiency of organic photovoltaic (OPV) solar cells. We perform nearly global optimization of the geometric parameters characterizing the hybrid ARS, by using optical simulations based on the finite-difference time-domain method. The proposed optimization algorithm consists of two steps: in the first step, only the moth eye structure is globally optimized and, in the second step, the whole hybrid structure is optimized efficiently based on the results of the first step. Thus, the optimal moth eye structure is additionally obtained as an intermediate result. By applying this optimization method to an organic thin film solar cell, we show that the short-circuit current density (JSC) is increased by 8.90% with the moth eye structure and by 9.89% with the hybrid ARS. We also study the sensitivity of photocurrent to the geometric parameters of hybrid ARS, and the change in the spatial distribution of electric field intensity by the ARS. The results show that the hybridization of the two types of light trapping techniques is effective to reduce the inhomogeneity in the electric field distribution and obtain higher electric intensity in almost the whole active layer. The design concept of the hybrid ARS is quite useful for improving light trapping in OPVs and allows for extending the options available for broadband antireflection.

Carrier mobility measurement across a single grain boundary in polycrystalline silicon using an organic gate thin-film transistor

In this study, we developed a measurement method for field-effect-carrier mobility across a single grain boundary in polycrystalline Si (poly Si) used for solar cell production by using an organic gate field-effect transistor (FET). To prevent precipitation and the diffusion of impurities affecting the electronic characteristics of the grain boundary, all the processing temperatures during FET fabrication were held below 150 °C. From the grain boundary, the field-effect mobility was measured at around 21.4 cm2/Vs at 297 K, and the temperature dependence of the field-effect mobility suggested the presence of a potential barrier of 0.22 eV at the boundary. The technique presented here is applicable for the monitoring of carrier conduction characteristics at the grain boundary in poly Si used for the production of solar cells.

Room-temperature plasma enhanced atomic layer deposition of aluminum silicate and its application in dye-sensitized solar cells

The authors present a plasma enhanced room-temperature atomic layer deposition (ALD) technique for depositing aluminum silicate on TiO2 photoanodes for dye-sensitized solar cells. In the ALD process, adsorption of the precursor is completed in a two-step process involving sequential application of a subsaturation quantity of tris(dimethylamino)silane (TDMAS) and an Al precursor trimethylaluminum to the target surface. The Al-to-Si atomic ratio is controlled by the initial coverage of TDMAS on the sample surface. Aluminum-silicate coatings with a balanced composition of Al and Si are applied to the TiO2 nanoparticle photoanodes in N719-based dye-sensitized solar cells. A one-cycle ALD coating improves the short circuit current density, suggesting the enhancement of N719 dye adsorption or charge separation at the interface of the dye and TiO2 photoanode. Electro-impedance analysis suggests that the improved power generation does not correlate with the charge recombination of electrons in TiO2 and I3− ions i...

An integrated antireflection design using nanotexture and high-refractive-index glass for organic photovoltaics

We propose a new antireflection (AR) design for organic photovoltaics (OPVs) to achieve broadband and omnidirectional enhancement of photocurrent. In the proposed design, a hybrid AR structure, which combines moth eye texturing and two-layer interference coating, is integrated with a glass substrate having a high refractive index (n). Using the optical simulation for OPV cells, we compare the performance of various AR configurations upon changing the refractive index of the glass substrate. We show that the short-circuit current density (

Fabrication and characterization of self-aligned ZnO and TiO 2 nanostructured films

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