Hideoki Fukushima

Fabrication of Thin-Film Polycrystalline Silicon Solar Cells by Silane-Gas-Free Process Using Aluminum-Induced Crystallization

The authors have proposed a silane-gas-free fabrication process for thin-film polycrystalline Si solar cells. The process includes formation of a polycrystalline Si seed layer by aluminum-induced crystallization (AIC), crystallization of a Si film formed by physical vapor deposition (PVD) techniques for a base layer, aluminum diffusion from the AIC-grown Si (AIC-Si) layer to the base layer and pn-junction formation by the spin-on-glass technique. The crystal grains grew to a size of ~20 µm in diameter through crystallization of the electron-beam-evaporated Si film on the AIC-Si layer, and the carrier lifetime was about 0.6 µs. In the solar cell fabricated by this process, the AIC-Si layer acts as a back-surface-field (BSF) layer, and the energy band is also inclined in its base layer so that the minority carriers can be pushed back to the depletion layer. These features indicate the possibility of fabricating low-cost and high-efficiency thin-film polycrystalline Si solar cells. The issues that must be pursued to realize high efficiency are reduction of oxygen atom inclusions during Si film deposition, passivation of the grain boundaries and development of a deposition technique for Si films having intermediate packing densities between those of electron-beam-evaporated films and sputter-deposited films, to prevent crack formation when the Si films are crystallized.

Microwave Heating of Ceramics and its Application to Joining

A new butt joining method for ceramics by microwave heating was developed. Ceramics were heated in a rectangular cavity. A klystron of maximum 3 kW at 6 GHz was used as the power amplifier. The heating system can control the iris, plunger and microwave power to keep a power efficiency up to 90% and a accuracy within ±10°C at 1800°C. Microwave ceramic-ceramic joining was tried by using this system. A bending strength of the joined alumina rod (92% purity) was 420 MPa without adhesive. This value was equal to the original strength. Silicon nitride ceramics were joined with adhesive, which was a sintered ceramic sheet having lower purity and larger dielectric loss factor than the base ceramics. The microwave energy was concentrated on the sheet, so that only the joining area was heated. The strengths of joined specimens were in excess of 70% of original strengths. The joined boundary line was not detected in microscopic observation, and there was little difference in microstructure between before and after joining. These results suggest that sintering aids in grain boundary phases were preferentially heated and melted or diffused, resulting in sound joining of ceramics.

Syntheses of Carbon Supported Pt-YOx and PtY Nanoparticles with High Catalytic Activity for Oxygen Reduction Reaction Using Microwave-Polyol Method

Carbon‐supported PtY alloy nanoparticles were prepared as oxygen reduction reaction (ORR) catalysts by reducing a mixture of cis‐[Pt(NH3)2(NO2)2] or Pt(C5H7O2)2 and Y(CH3COO)3⋅4 H2O in ethylene glycol (EG) with microwave (MW) heating. Microstructure and composition analyses of products by using TEM, TEM–energy‐dispersive X‐ray spectroscopy (EDS), XRD, X‐ray photoelectron spectroscopy (XPS), and inductively coupled plasma atomic emission spectroscopy (ICP‐AES) data showed that Pt–YOx/C (Y/Pt=0.11–0.75) catalysts involving amorphous yttrium oxide were formed as major products. When the YOx component in the catalysts was removed by using HNO3 treatment, Pt99.1–99.6Y0.4–0.9/C alloy catalysts with low Y contents remained. Higher ORR activity was shown by Pt–YOx/C and PtY/C catalysts than by Pt–Y(OH)3/C, Pt–YOx/C, or PtY/C catalysts prepared by using other conventional chemical reduction methods and thermal treatment methods under a H2/Ar or Ar atmosphere. The mass activity (MA) and surface specific activity (SA) of the best Pt99.5Y0.5/C catalyst, MA=245 A gPt−1 and SA=711 μA cmPt−2, were equal to or higher than those of the commercially used Pt86Co14/C catalyst, MA=245 A gPt−1 and SA=512 μA cmPt−2. The major reasons for the high ORR activity of these Pt–YOx/C and PtY catalysts are discussed. These Pt99.1–99.6Y0.4–0.9/C alloy catalysts prepared by using acid treatment are new and promising catalysts for use in proton exchange membrane fuel cells (PEMFCs).

RAPID HEATING BY SINGLE-MODE CAVITY CONTROLLED AT 6GHZ

The single-mode cavity is possible to concentrate the microwave energy, and so even the ceramics having extremely small loss factor e″ can be rapidly heated up to high temperature. But, it is difficult to control the resonant state of the cavity. Therefore, the control of the coupling window (iris) and the short circuit plate (plunger) becomes necessary to maintain the resonance of the cavity. In this paper, the fundamental concept of resonant control in the cavity at 6GHz band is described. Furthermore, the microwave heating of ceramics was done with the developed cavity and heating control system, and it is reported about various applications to rapid heating.

Microwave sintering of electronic ceramics

The feasibility of microwave sintering of ceramics was examined. ZnO varistor and PZT ceramics with high densities could be obtained by microwave sintering. They had higher electric properties compared with those sintered by a conventional process.