Poster: http://www.physics.uwo.ca/colloquia/Colloquia%20Notices/2012_2013/JOHN%20Colloquium.pdf
Western University
DEPARTMENT OF PHYSICS AND ASTRONOMY
PHYSICS & ASTRONOMY COLLOQUIUM
Date: Thursday, 1st November 2012
Time: 1:30 p.m.
Location: Physics & Astronomy Seminar Room 100
Dr. Sajeev John
Department of Physics
University of Toronto
“Light Trapping and Solar Energy Harvesting in Thin Film Photonic Crystals”
ABSTRACT
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. 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 focused 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. 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. 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%.
Coffee & snacks will be available.