GOALI: Polarized Infrared Imaging for the Mechanics of Photovoltaic Wafers

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The research objective of this Grant Opportunity for Academic Liaison with Industry (GOALI) award is to investigate the mechanics of stress, defects, and failure in thin silicon photovoltaic wafers using a combination of infrared photoelasticity and polarized photoluminescence inspection techniques. Silicon wafers are the most common base material in solar cells, but due to stress and defects that arise during the crystal growth process, material losses during manufacturing remain a significant problem. Under support from this award, the relationship between stress and defects in photovoltaic wafers will be studied directly using lock-in infrared photoelasticity. Also, a new class of inspection techniques based on a lock-in polarized photoluminescence method, in which both intensity and polarization of emitted light is measured, will be developed and used to study the interaction of stress and defects with light absorbed or emitted by the material. Finally, the relationship between stress and failure in these materials will be investigated using a series of imaging and fracture experiments.The award will support a collaborative effort between university and industry researchers. The research could have significant impact in the solar energy industry, as it will help to explain the role of stress and defects in photovoltaic wafer failure, and could enable a pathway to rapid inspection and sorting of silicon photovoltaic wafers based on the probability of mechanical failure. The results will also add to the fundamental understanding of the interaction of light with defects in crystalline materials. In addition to the research objectives, the award will support graduate and undergraduate education and training. The academic/industry partnership will be highlighted by the annual summer placement of a graduate research assistant in the industry facility to learn characterization and manufacturing methods. Undergraduate students will be involved through an engineering outreach event at the University of Illinois, and through research in the laboratory of the Principle Investigator.