Hiroshi Kuraseko

Inverted Aluminum-Induced Layer Exchange Method for Thin Film Polycrystalline Silicon Solar Cells on Insulating Substrates

In order to achieve high efficiency thin film polycrystalline silicon (poly-Si) solar cells on insulating substrate, we have developed a novel crystallization method of amorphous silicon (a-Si), an inverted aluminum-induced layer exchange (inverted-ALILE) method, where a metallic aluminum layer remains between the crystallized p+-layer and a glass substrate to function a back contact in contrast to the conventional ALILE method. Crystallization process of a-Si during inverted-ALILE was observed in-situ by optical microscope. The crystallized film was analyzed using Raman measurement, X-ray photoelectron spectroscopy (XPS) and electron back scatter diffraction (EBSD). Those analyses indicated poly-Si thin film with large grain size and preferential orientation of (100). The prepared poly-Si layer was applied to thin film solar cell and we confirmed a significant improvement in series resistance as compared to a conventional ALILE method.

Optical emission spectroscopy of atmospheric pressure microwave plasmas

The optical emission behaviors of Ar, He, and Ar+He plasmas generated in air using an atmospheric pressure microwave plasma source have been studied employing optical emission spectroscopy (OES). Emissions from various source gas species and air were observed. The variations in the intensities and intensity ratios of specific emissions as functions of the microwave power and gas flow rate were analyzed to investigate the relationship between the emission behavior and the plasma properties. We find that dependence of the emission behavior on the input microwave power is mainly determined by variations in electron density and electron temperature in the plasmas. On the other hand, under different gas flow rate conditions, changes in the density of the source gas atoms also significantly affect the emissions. Interestingly, when plasma is generated using an Ar+He mixture, emissions from excited He atoms disappear while a strong Hα signal appears. The physics behind these behaviors is discussed in detail.

Development of flexible fiber-type poly-Si solar cell

In order to obtain low-cost, high-performance and flexible silicon solar cell, a novel poly-Si solar cell using glass fiber substrate has been developed. Two ways for preparing poly-Si film on glass fiber for very high deposition rate were studied; one is atmospheric thermal CVD and the other is microwave PECVD. The film prepared by atmospheric thermal CVD showed good crystallinity and high hole mobility of 200cm 2/Vs at a carrier concentration of 6e15cm-3, despite its high deposition rate. The solar cell was examined on SiO2 substrate, and cell efficiency by atmospheric thermal CVD was 1.35%. Novel microwave PECVD system specialized for glass fiber substrate was also developed, and poly-Si film could be deposited on the glass fiber substrate at a deposition rate of 1 mum/s

Evolution of Film Crystalline Structure During the Ultrafast Deposition of Crystalline Si Films

By using a high density microwave plasma source, an ultrafast deposition rate over 1000 nm/s has been achieved for polycrystalline silicon (poly-Si) film deposition. We find that crystalline structure of the deposited film evolves along the film growth direction, i.e. large grains in surface region while small grains in the bottom region of the film. Systematic study of the deposition process has been performed as a function of the deposition duration. Based on the observed results, a possible mechanism, the annealing-assisted plasma-enhanced chemical vapor deposition, is proposed to describe the film growth process.