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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.

Thin film solar cell techniques can effectively reduce the costs for photovoltaic solar power. However, most of these techniques still have the disadvantage of a comparatively low efficiency. One way to realize a thin film solar cell concept with high efficiency potential is the crystalline silicon thin-film (cSiTF) concept. Following the high-temperature approach, this concept is based on a silicon epitaxy process. This paper reports the current status of the development of a high throughput epitaxy tool at Fraunhofer ISE and presents first results. Also presented is the development of a simulation tool which is a virtual image of the real setup in order to forecast save deposition conditions. The presented epitaxy tool is the ConCVD (Continuous Chemical Vapour Deposition), in which an improved reactor setup has been installed, based on the experience gained so far. To provide insight into upcoming further advances, the industrial scale epitaxy tool ProConCVD is presented as well.

Two-phase flow and transport of reactants and products in the cathode of a transparent proton exchange membrane fuel cell (PEMFC) are studied experimentally. Images of water formed inside the cathode gas channels are presented to explain the phenomenon of water flooding. Effects of air stoichiometry, temperature, air humidity and different characteristics of diffusion layers are discussed. The influence of hydrophobic and hydrophilic diffusion layers compared to standard carbon papers on water transport is investigated. Mathematical verification of a threshold current density corresponding to first appearance of liquid water at the membrane/cathode interface confirms the experimental results.