3D epitaxial growth through holes for the fabrication of thin-film solar cells

Abstract

Some interesting effects of three-dimensional epitaxial growth have been observed and simulated during the development of a silicon deposition process for the fabrication of a new type of solar cell. The Epitaxy Wrap-Through (EpiWT) cell is a rear-contacted crystalline silicon epitaxial thin-film solar cell. This means that it consists of thin high-quality silicon layers that are grown on a substrate and wrapped through via holes from the front to the rear side of this substrate. The attempt to grow silicon layers epitaxially in this way three-dimensionally through small via holes, ∼200 μm diameter, is a completely new development. A process that provides a very suitable layer structure for the fabrication of the solar cells has been successfully developed. In order to gain a deeper theoretical understanding of this epitaxy-through-holes process, simulations were performed using computational fluid dynamics (CFD). The analysis focuses primarily on the gas flow through the via holes during the deposition. In this way, and by comparison of experimental samples with simulation results, it has been possible to explain some of the characteristics that were observed in the 3D epitaxial growth.