Erin E. Looney

Recombination activity of grain boundaries in high-performance multicrystalline Si during solar cell processing

In this work, we applied internal quantum efficiency mapping to study the recombination activity of grain boundaries in High Performance Multicrystalline Silicon under different processing conditio ...

Accelerating synchrotron-based characterization of solar materials: Development of flyscan capability

Synchrotron-based μ-XRF is a powerful tool to measure elemental distributions non-destructively with high spatial resolution and excellent sensitivity. Recently, we implemented on-the-fly data collection (flyscan) at Beamline 2-ID-D at the Advanced Photon Source at Argonne National Laboratory, making data acquisition faster than 300 ms per pixel practical. We show that flyscan mode at Beamline 2-ID-D enables (a) traditional elemental maps to be completed twenty times more quickly while maintaining reasonably high sensitivity, and (b) practical studies of materials with an order of magnitude lower total impurity concentration and sparser spatial density of impurities. We highlight opportunities for flyscan to enable qualitatively new forms of microscopy, leveraging the accelerated data-acquisition rate for multi-dimensional mapping.

Oxygen migration enthalpy likely limits oxide precipitate dissolution during tabula rasa

In industrial silicon solar cells, oxygen-related defects lower device efficiencies by up to 20% (rel.). In order to mitigate these defects, a high-temperature homogenization anneal called tabula rasa (TR) that has been used in the electronics industry is now proposed for use in solar-grade wafers. This work addresses the kinetics of tabula rasa by elucidating the activation energy governing oxide precipitate dissolution, which is found to be 2.6 ± 0.5 eV. This value is consistent within uncertainty to the migration enthalpy of oxygen interstitials in silicon, implying TR to be kinetically limited by oxygen point-defect diffusion. This large activation energy is observed to limit oxygen precipitate dissolution during standard TR conditions, suggesting that more aggressive annealing conditions than conventionally used are required for complete bulk microdefect mitigation.