(318a) Smaller Than the Bandgap: The Tale of Low-Energy Photons

Nagpal, P., University of Colorado Boulder
Sun, Q. C., University of Colorado Boulder
Lien, C. H., University of Colorado Boulder

Sun emits light in a broad spectrum of electromagnetic radiation. Conversion of this wide spectrum of incident radiation into more useful forms of energy, like electricity, using finite bandgap semiconductors leads to inefficiency. Since the photons with energy smaller than the semiconductor bandgap are simply transmitted through the photocell, more than 30% of incident radiation is not absorbed in the best photovoltaic cells available now. Utilizing this near-infrared, sub-bandgap radiation requires application of novel physical phenomena like upconversion, energy-transfer, and generation of low-energy hybrid photon-electron waves known as surface plasmon polaritons. I will summarize the efforts in my group towards utilization of sub-bandgap photons by a combination of single nanoparticle spectroscopy to optimize these novel physical phenomena, and translation of these concepts into device scale optoelectronics. These photonic devices can be combined with a wide-variety of semiconductor photocells for improving photovoltaic conversion efficiencies.  These results can have important implications for solar energy conversion, and for developing a new class of bio-nanomaterials for optics-based sensing in the region of optical transparency for biological tissues.