A new technique for producing silicon ribbons for solar-cell substrates is described. The process begins with inexpensive, 98% pure silicon that is crushed and acid leached to raise the purity to 99.9%. This powder is spread on a graphite plate and electron-beam annealed to form a flat, self-supporting "preribbon." After removal of the graphite and unmelted powder, the preribbon is given a second electron-beam scan that recrystallizes the silicon into a smooth polycrystalline ribbon. This zone melting further improves the purity to over 99.99%. Ribbons 0.4 mm thick and up to 16 mm wide were produced in this initial work. The ribbons are p-type, 0.07 R. cm, and have long crystals about 1 mm wide. Electron-diffusion lengths of 20-30 p m were measured. Calculations indicate that solar-cell efficiencies up to 13% should be possible. If the process can be scaled up and automated, the cost of volume production could be as low as 43 cents/W. It is concluded that the process has the potential for achieving low-cost "solar-grade" substrates and has advantages over other processes. Further work is planned.On dCcrit une technique nouvelle pour la production de rubans de sil~ce utilisCs comme couches de support dans les piles solaires. Le procCdt utilise au depart du silicium h 98%, peu dispendieux, qui est Ccrast et attaqut a I'acide pour porter le degrt de puretC ? i 99,9%. La poudre obtenue est Ctendue sur une plaque de graphite et recuite par un faisceau d'Clectrons pour former un "prC-ruban" plat et capable de se tenir sans support. Aprks enlevement du graphite et de la poudre non fondue, ce prC-ruban est de nouveau balayC par un faisceau d'Clectrons qui recristallise le silicium en un ruban polycristallin rkgulier. Cette fusion par zones amCliore encore la purett, au dela de 99,99%. Des rubans ayant 0,4 mm dlCpaisseur et jusqu'h 16 mm de largeur ont ttC produits dans ce travail init~al. Ces rubans sont de type p , ont une rtsistivite de 0,07 Re cm et contiennent des cristaux allonges larges de 1 mm environ. Des longueurs de diffusion dlClectrons de 20 h 30 p m ont CtC mesurees. Les calculs indiquent qu'on pourrait obtenir des rendements de piles solaires allant jusqu'h 13%. Si le procCdC peut Stre exCcutC h plus grande Cchelle et automatisk, le coDt de production en grande quantitk pourrait &be aussi bas que 43 cents/W. On conclut que le procCdC peut fournir a faible coDt des couches de support de qualit6 "solaire" et qu'il prtsente des avantages sur d'autres procCdCs. On se propose de pousser plus loin ce travail. [Traduit par le journal] Can. J Phys 63, 859 (1985)
Screen printable inks for Ta2O5 and TiO2 antireflection coatings have been applied to silicon wafers and characterized. On polished crystalline wafers, both coatings give near-zero minimum reflectance. The wavelength of the minimum can be easily tuned to match the solar spectrum by changing the screen mesh size. The average reflectance over the AM1 spectrum can be further reduced by texturizing the wafer surface prior to coating. Similar reflectance results are obtained for both crystalline and polycrystalline wafers, although the average reflectance is not quite as low in the latter case due to the difficulty of texturizing polycrystalline material.
The time evolution of the temperature profile during cw laser processing is calculated including the effects of melting using computer simulation. Results, presented for single-crystal silicon irradiated by an argon ion cw laser, show that high scanning speed can result in a non-steady-state situation for the temperature rise. In this case the maximum temperature and melt depth become functions of the dwell time and also less sensitive to the incident laser power, as a result of which scanning speed can be effectively used to control melting process induced by cw laser. Experimental results presented support the calculated dependence of the maximum melt depth on the laser power and scanning speed.
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