Harry Atwater 2009-2010 Seminar Series
February 3, 2010
"Light-Matter Interactions for Terawatt-Scale Solar Energy Conversion: Sculpting the Flow of Light at the Nanoscale"
Photovoltaic (PV) technology is currently enjoying substantial growth and investment, owing to worldwide sensitivity to energy security and the importance of renewable energy as a means to mitigate carbon emissions. This talk will describe approaches to control of light-matter interactions leading to enhanced absorption in solar photovoltaic structures. Conventionally, it is thought that semiconductor photovoltaic absorbers should have a physical thickness comparable to the ‘optical thickness’ to enable nearly complete light absorption and photocarrier current collection. Solar cell design and material synthesis considerations are strongly dictated by this simple optical thickness requirement. Dramatically reducing the absorber layer thickness or volume confers several fundamental and practical benefits, including increased open circuit voltage and conversion efficiency, and also expansion of the scope and quality of absorber materials that are suitable for photovoltaic devices by, e.g., enabling efficient photocarrier collection across short distances in low dimensional structures.
Semiconductor wire array solar cells have a geometry that both facilitates photogenerated carrier collection and enhanced light absorption; results for enhanced optical absorption and carrier collection in Si wire array solar cells will be given, and limits to enhanced absorption will be explored.
To date, little systematic thought has been given to the question of how plasmonic and metamaterial structures might be exploited to advantage in photovoltaics. Atwater will describe design approaches using metallic nanostructures to excite localized and propagating surface plasmons which can dramatically increase the optical path length in thin active photovoltaic layers to enhance overall photoabsorption. Examples of plasmon-enhanced absorption in thin a-Si, GaAs and InGaN solar cells will be described. Future metamaterial optical design directions for dispersion of light and dramatic reduction of solar cell active volume will be outlined.