Gas-phase synthesis of nanoscale silicon as an economical route towards sustainable energy technology

In: KONA Powder and Particle Journal, Jg. 29 (2011), S. 191 - 207
ISSN: 0288-4534
Zeitschriftenaufsatz / Fach: Maschinenbau
Fakultät für Ingenieurwissenschaften » Maschinenbau und Verfahrenstechnik » Institut für Verbrennung und Gasdynamik
The silicon age that started in the 60s of the last century has changed the world profoundly, mainly
related to the invention and development of microprocessor technology. Meanwhile, the demand for
silicon is driven by the photovoltaics industry that consumes about 80% of the high-purity silicon
produced worldwide. Independent of the final product, all high-purity silicon has passed through a
couple of gas-phase reactions for purification. The most important gaseous species within this production
chain are chlorosilanes and monosilane. We will discuss the direct formation of crystalline
silicon by homogeneous gas-phase reactions as a direct and highly economical way to produce the required
high-purity raw material for silicon solar cells. The direct formation of solid silicon particles
from monosilane requires only a fraction of the energy compared to the established Siemens process
based on the chemical vapor deposition of silanes. We have developed a method to synthesize nanocrystalline
silicon powder using a hot-wall reactor, and the technology was scaled up to the pilot-plant
scale. While an economical production strategy is decisive for solar cell production, the structure of
the gas-phase product allows for additional, highly promising applications benefiting from the specific
properties of the nanoscale particulate material. Both, thermoelectric generators as well as lithiumion
batteries benefit from the nanocrystalline structure of the gas-phase product due to high phonon
scattering and short diffusion lengths, respectively. First successful examples with regard to these two
topics will be discussed. In these fields, silicon finds potential new markets for sustainable energy
technology because of its abundant availability and low-cost production.