SILASOL: New Silicon Materials for Solar Applications.

In today's solar systems, the material still accounts for a large part of the final cost of the system. The new Si material can be classified in two categories: 1. Ultra-thin silicon material. Two methods are developed in detail in SiLaSol. The first technology is the SLIM-Cut method. The principle is the following: a stress-inducing layer (e.g. metallic layer) is deposited on top of an ingot, then the layer is activated (e.g. with a temperature treatment). As a result of stress, a crack is initiated and propagated parallel to the surface, separating the top-most ~50 microns of Si from the rest of the ingot. SiLaSol targets screening of technological solutions to implement this concept and brings it up to industrial demonstration. SiLaSol targets also the solar cell fabrication process and aims at providing specifically-adapted solutions. The second crystalline thin-film technology is polycrystalline solar cells, based on the crystallization of amorphous Si. Focus will be on a two-step fabrication of this (~5 microns) microcrystalline Si material: first formation of a seed layer, then epitaxial thickening. Particular effort will thus be put on the understanding of the crystallization process. In addition, extremely-thin solar cells are very sensitive to light management. This solar cell process optimization will therefore also focus on light-trapping. The modeling will enable understanding of the fabrication process as well as to evaluate the potential of the device based on these new materials whereas the characterization platform will give insight on the quality of the interfaces or on the properties of these ultra-thin layers. 2. High-bandgap Si material. SiLaSol will also investigate silicon nanowires with a diameter as small as a few nanometers. Several methods of fabrication will be investigated, keeping at each step of the process in mind the specific problems of photovoltaics. Highly-controlled technologies (DUV lithography, dry etching,...) will be used to prove the concept and build the different elements of the high-bandgap silicon solar cell process, meanwhile cost-effective methods will be identified and developed to propose alternative industrial processes. Ab-initio calculations will be performed to predict the characteristics of the nanowires as a function of the diameter and as a function of the interfaces; the characterization platform will support continuously the development of the fabrication process. Once optimized, the material will be used as a proof-of-concept in a solar cell process.

Keywords:Ab-initio calculations, Si wafers, Silicon, Solar cells, Photovoltaic, Si nanowires, Device modeling, Polycrystalline Si

Disciplines:Other engineering and technology