"Light Trapping and Solar Energy Harvesting in Thin Film Photonic Crystals"
Dept. of Physics
University of Toronto
Toronto, Ontario, Canada M5S 1A7
Date: March 13, 2013
Location: Energy Research Facility, Rm. 1207
Time: 11:00 am 12:00 pm
Photonic crystals are widely known for their light-trapping capabilities. This is often associated with the occurrence of a photonic band gap or other suppression in the electromagnetic density of states [1-3]. This enables guiding of light on an optical micro-chip and unprecedented forms of strong-coupling between light and matter. In the past, practical applications of these effects have focussed on information technology. More recently, an important opportunity has emerged in the area of energy technology. This arises from light-trapping in the higher bands of a photonic crystal, where the electromagnetic density of states is enhanced rather than suppressed. This enables unprecedented strong absorption of sunlight in a material with weak intrinsic absorption .
We describe designs of 3D photonic crystal silicon-based solar cells that enhance the overall absorption of sunlight using architectures consisting of just 1 micron (equivalent bulk thickness) of silicon. These crystals trap light through a parallel-to-interface negative refraction (PIR) effect and other optical resonances that occur over a broad angular and frequency range . These 3D photonic crystals exhibit an enhanced electromagnetic density of states, consisting of slow group velocity modes, in which the flow of energy is transverse to the depth of a thin film of material. In the case of a modulated nanowire photonic crystal solar cell, it is possible to absorb roughly 75% of all available sunlight in the wavelength range of 400-1100 nm, using one micron of silicon [5, 6]. In the case of conical nano-pore silicon photonic crystal, roughly 85% of all available sunlight is absorbed . The power conversion efficiencies of these one-micron photonic crystals rival those of present-day solar cells using up to 300 microns of silicon. Similar considerations apply to other materials such as GaAs where it is possible to absorb about 95% of sunlight above the bandgap with only 100 nm of material. These photonic crystals offer additional opportunities for solar spectral reshaping to rival and possibly surpass the famous Shockley-Queisser power conversion efficiency limit of 33%.
1. S. John, Physical Review Letters 58, 2486 (1987)
2. E. Yablonovitch, Physical Review Letters 58, 2059 (1987)
3. S. John, Physical Review Letters 53, 2169 (1984)
4. A. Chutinan and S. John, Physical Review A 78, 023825 (2008)
5. G. Demesy and S. John, J. Applied Physics 112, 074326 (2012)
6. A Deinega and S. John, J. Applied Physics 112, 074327 (2012)
7. S. Eiderman, S. John, A. Deinega (submitted for publication)
Sajeev John is a Professor of Physics at the University of Toronto and Canada Research Chair holder.
He received his bachelors degree in physics in 1979 from the Massachusetts Institute of Technology and his Ph.D. in physics at Harvard University in 1984. His Ph.D. work at Harvard introduced the theory of classical wave localization and in particular the localization of light in three-dimensional strongly scattering dielectrics. From 19841986 he was a Natural Sciences and Engineering Research Council of Canada postdoctoral fellow at the University of Pennsylvania, as well as a laboratory consultant to the Corporate Research Science Laboratories of Exxon Research and Engineering from 1985-1989.
From 1986-1989 he was an assistant professor of physics at Princeton University. In 1987, while at Princeton he co-invented, along with Eli Yablonovitch, the concept a new class of materials with a photonic band gap called photonic crystals. This provided a fuller explanation of his original conception (1984) of the localization of light. He was a laboratory consultant to Bell Communications Research (Red Bank, NJ) in 1989. In the fall of 1989 he joined the senior physics faculty at the University of Toronto. He has been a Principal Investigator for Photonics Research Ontario, and is a fellow of the Canadian Institute for Advanced Research.
Professor John is the winner of the 2001 King Faisal International Prize in Science, which he shared with C. N. Yang. He is also the first ever winner of Canadas Platinum Medal for Science and Medicine in 2002. Dr. John is the winner of the Institute of Electrical and Electronics Engineers (IEEE) LEOS International Quantum Electronics Award in 2007 for the invention and development of light-trapping crystals and elucidation of their properties and applications. He is the 2008 winner of the IEEE Pioneer Award in Nanotechnology. Dr. John also received the 1996 Herzberg Medal for Physics and the 2007 Brockhouse Medal for Condensed Matter and Materials Physics from the Canadian Association of Physicists. He received the first ever McLean Fellowship from the University of Toronto in 1996, the 1997 Steacie Prize in Science and Engineering from the National Research Council of Canada, and the 2004 Rutherford Medal from the Royal Society of Canada. He is the first ever winner of Brockhouse Canada Prize in 2004, which he shared with materials chemist Geoff Ozin for their groundbreaking interdisciplinary work on photonic band gap materials synthesis. Professor John has also received the Killam Fellowship of the Canada Council for the Arts, the Guggenheim Fellowship (USA), the Japan Society for the Promotion of Science Fellowship, and the Humboldt Senior Scientist Award (Germany). In 2007, Dr. John was awarded the C.V. Raman Chair Professorship of the Government of India. Prof. John is a Fellow of the American Physical Society, the Optical Society of America, the Royal Society of Canada, and a member of the Max Planck Society of Germany.