a unique method has been developed. That is the granule polycrystalline Si synthesis by continuous recycling of chlorosilicate compounds using a Fluid Floor Reactor [1]. There are two methods of manufacturing single or semicrystalline Si substrate. One is the slice method in which wafers are cut from a lump of Si made by CZ or other methods, and the other is the sheet method in which Si wafers are directly formed to their cell thickness from molten material. The latter can simplify the substrate process but it brings much material loss. The former, slice method, holds a dominant position in many respects because of good mass productivity and good material performance. Especially, for the casting method, the representative slice method is being investigated as an effective way. The solar cells that are made from casting a semicrystalline wafer of SOG material, are developed to attain almost 13% conversion efficiency in production, and the cost of unit power is becoming the same as that for a single crystal wafer. These kinds of solar cell are expected to cost in the order of ¥500 per watt. Junction Formation Process The junction of solar cells is formed by the wet process method which uses chemicals analogous to conventional semiconductor devices, or by the dry process method which uses high vacuum technology. At the existing technical level, it is still hard to choose one method over the other in respect of costs, mass production and evaluated performance of solar cells. Packing In the terrestrial-use solar cell modules, the super-straight structures using glass boards are developed and commonly used instead of the boxed type structure used in the early days. In the near future will appear the ultrathin laminating structure, or lightweight mould type structure. Amorphous Silicon Solar Cells Amorphous Silicon (a-Si) has the physical characteristics of ‘very high solar absorption' differing from single crystal Si, and theoretically needs only 1 pm thickness to operate as a solar cell. In addition it has convenient properties of no grain growth, compared to other crystalline materials such as thin film. Nowadays, the efficiency of an a-Si solar cell comes up to 10% by improving deposition technique, and this is further increasing by 1% per year. On the other hand, a-Si solar cells tend to degrade by high-intensity irradiation such as direct sunlight, so that there is some restriction on outdoor use. But if these problems are settled, it is expected to be the leading technology of economic terrestrial-use solar cells. The a-Si solar cells have another characteristic of high spectral response at short wavelength. As indoor illumination is almost entirely by fluorescent lamp in Japan, a lot of a-Si solar cells are manufactured on a large scale for indoor personal microelectronics use, such as calculators, and the total production of a-Si solar cells is rather larger than that of crystalline-type ones. Table I shows the present state and future target of the terrestrial-use solar cell, and Tables II and III show the development of crystalline and amorphous solar cells.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==