High productivity Czochralski silicon ingot casting

Norwegian Crystals AS is a newly established producer of monocrystalline silicon wafers located in Glomfjord, Nordland. Wafer based solar cells is currently the dominant technology for photovoltaic energy generation, constituting about 90% of annual insta lled capacity. Following a steep learning curve over the past decade, the industry has managed to reduce production cost significantly and to increase the quality and performance of all products from wafer to module, leading crystalline solar cell technol ogy to grow from a niche product to being on the verge of competing with conventional energy sources in many markets. Norwegian Crystals AS main production process is seeded growth of monocrystalline silicon ingots from a silicon melt, a process known as the Czochralski process. High purity chunks of silicon are melted in a quartz crucible and a small seed crystal is dipped into the melt. The crystal is grown by pulling the seed from the melt with careful control of the pull speed and the thermal conditi ons. In this project, we will develop a process with larger batch size and increased crystal growth rates, both factors being major enablers to reduce production cost. The project will involve developing a new internal furnace design and introducing a ne w granular type silicon raw material to the material mix. The project will lead to annual cost savings of 25 MNOK. In addition, the energy savings during both raw material and crystal production will lead to shortened energy payback time and reduced car bon footprint.

Czochralski growth of silicon for solar cells is becoming more challenging. The price for wafers has reached an all time low level. At the same time, the quality demands are increasing, due to development of new and improved solar cell architectures were the potential only can be fully utilized with high wafer quality. In this project, the aim is to develop a process with increased charge weight and increased crystal growth rate that can meet current and future quality requirements. This will be achieved by the development of a new internal furnace design and the use of granular silicon raw material. The project will focus on achieving a robust process where productivity increase occurs without compromising ingot quality. The project will, therefore, comb ine numerical modelling, industrial experiments, statistics and advanced characterisation to reach the objectives.