Solar Cell Silicon: Silicon Photovoltaics
Sponsored by: TMS Extraction and Processing Division, TMS: Recycling and Environmental Technologies Committee, TMS: Energy Committee
Program Organizers: Shadia Ikhmayies, Al Isra University; Neale Neelameggham, Ind LLC

Thursday 2:00 PM
March 2, 2017
Room: 19
Location: San Diego Convention Ctr

Session Chair: York Smith, University of Utah

2:00 PM  
Electrodynamic Eddy Current Separation of End-of-Life PV Materials: York Smith1; James Nagel1; Raj Rajamani1; 1University of Utah
    In this work, we discuss the efficacy of Electrodynamic Eddy Current Separation (EECS) techniques to recover valuable materials from end-of-life solar panels. Traditional rotary-based eddy current separators are capable of excitation frequencies of ~1 kHz or less and struggle to economically separate particles smaller than ~1 cm. A new design of eddy current separators has been developed at the University of Utah, which has no mechanically moving parts. This design is capable of excitation frequencies up to 50 kHz, enabiling sorting of particles as small as 1.0 mm. Recently, we have been successful in separating mixtures of Si/Al and CdTe/Al particles (1~3 mm) with recovery and grades greater than 85%, an energy demand of ~0.07 kWh/kg of sorted material, and throughput of roughly 10 kg/h. Current and future challenges utilizing this method for valuable material recovery from end-of-life solar panels are discussed.

2:20 PM  
Investigation on Quartz Crucibles for Monocrystalline Silicon Ingots for Solar Cells: Marisa Di Sabatino1; John Bones2; 1NTNU; 2SINTEF, Norway
    This study presents a new testing method to analyze the bubble content and distribution in quartz crucibles for monocrystalline silicon ingots. Two different types of silica (SiO2) crucibles have been investigated, before and after use during Czochralski (Cz) silicon ingot production for solar cells. Samples have been cut from three different positions along the crucible wall and then investigated by X-ray tomography, optical microscopy and scanning electron microscopy. The unused samples were heat-treated at 1400 C for 4 hours in Ar at 15 mbar. It is observed that the crucible bubbles grow in size and density during the Cz process. More bubbles are detected closer to the inner part of the crucible wall after use in the Cz-process. The results also indicate that there are some differences in quality between different crucible producers and that bubble formation and growth are significantly affected by the Cz process parameters, such as temperature and time.

2:40 PM  
Influence of Oxygen Content on the Wettability of Silicon on Graphite: Zineb Benouahmane1; Lifeng Zhang1; Yaqiong Li1; 1University of Science and Technology Beijing
    Graphite as refractory materials has been dried using a vacuum annealing treatment by varying the exposure time for (0, 6, 8, 12, 24 hours) at temperature of 1000 C. The oxygen to carbon atomic ratio (O/C ratio), assessed using X-ray photoelectron spectroscopy, decreased with increase of temperature and exposure time. Wetting angles between silicon and graphite were measured for silicon droplets. It was found with a low O/C ratio, the statistic contact angle may reach 82 . In contrast, a high O/C ratio leads in angles around 27. The infiltration of silicon into the graphite was occurred during the experiments. With increasing of O/C ratio, the infiltration depth of molten silicon increased.

3:00 PM  
Particle Separation in Silicon Ingot Casting Using AC Magnetic Field: Valdis Bojarevics1; Georgi Djambazov1; Koulis Pericleous1; 1University of Greenwich
    The AC electromagnetic (EM) field effects are investigated for the transport and possible extraction of particles (impurities, precipitates, oxides, bubbles, etc.) in molten silicon during the directional solidification of silicon ingot. The dynamics of particles are affected by the hydrodynamic drag, buoyancy, turbulent fluctuations and the EM force via the local pressure distribution. The EM force leads to high mixing rates, transitional flow structures and an intense turbulence of the melt, contributing to the particle dispersion, transport and possibly separation to a desired location. Application to silicon kerf loss recycling by remelting and solidifying in the presence of AC EM field is presented for a variety of cases using 3d models for general flow structure and axisymmetric models for moving solidification front long time tracking. This paper demonstrates the effects of flow on the time dependent particle ‘swarm’ like transport and the eventual modified distribution in the final ingot.