Collaborative Research: Photomechanical Behavior in Photovoltaic Semiconductors

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Photovoltaic semiconductors are capable of converting light into electricity. They are the principal components of solar cells that provide renewable energy from sunlight. These semiconductors tend to fail in a brittle manner, limiting their general use to small-scale applications. New evidence shows though that the mechanical behavior of photovoltaic semiconductors is sensitive to sunlight, exhibiting the potential of relative malleability under illumination. The mechanisms underlying such light-mechanical coupling effect remains elusive. This award supports fundamental research to elucidate how light-induced excitation controls the mechanical behavior of photovoltaic semiconductors. The new knowledge is expected to offer strategies to design highly stable and durable photovoltaic devices, such as solar cells, transistors, light-emitting diodes, and photodetectors, providing the basis for extensive engineering applications. This award will also offer education and training for graduate and undergraduate students in interdisciplinary areas of mechanics, materials science and engineering, and photophysics. The award will promote diversity by involving women and underrepresented minorities in research activities.The photomechanical behavior of photovoltaic semiconductors is determined by light-induced deformation mechanisms such as dislocation and twinning. In this project, a multiscale modeling and experimental framework will be used to accurately characterize the influence of photoinduced electron-hole excitation on the dislocation and twining mechanics in cadmium telluride, a prototype photovoltaic semiconductor. On the sub-atomic scale, advanced quantum mechanics simulations will be performed to determine the influence of electron-hole pair on the energy and force barriers of dislocation and twin nucleation, as well as dislocation mobility. On the atomic scale, the carrier concentration dependent mechanisms of the dislocation-dislocation and dislocation-twin interactions will be characterized using reactive force field based molecular dynamics simulations. On the mesoscale, the light-illumination effect on the stress-strain behavior will be quantified by developing an atomically-informed crystal plasticity model that incorporates dislocation slip and deformation twinning. Theoretical predictions will be validated through mechanical testing and materials characterizations using advanced experimental techniques, including nanoindentation, scanning probe microscopy, transmission electron microscopy, and electron backscatter diffraction. This work will result in a new physical picture of the deformation mechanism of photovoltaic semiconductors under light illumination, and provide a comprehensive understanding of light-mechanical coupling effects in general photovoltaic materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.