Development in silicon sheet technologies

The status of techniques for the production of sheets, ribbons, and foils of silicon for solar cells is reviewed. Technical problems and economic constraints are analyzed. The horizontal support web technique relies on a wedge-shaped growth interface which decouples the pulling velocity and the growth velocity which are nearly perpendicular to each other. The growing ribbon floats on a silicon melt that is contained in a long silicon crucible and is withdrawn to one side. In the ramp assistant foil technique, the silicon melt is contained in a relatively flat crucible that is open on one side. A preheated substrate is moved across this opening, and some of the melt solidifies on the surface. The silicon-sheets-from-powder technique starts from Si powder or granular silicon (grain size: 50-500 mu m). Three steps are needed to obtain the final ribbon. It is concluded that although the basic ideas as well as the results of these three methods are very distinct, evaluation of their respective merits is difficult.