Solar Light Trapping and Harvesting with 3D Photonic Crystals

Photonic crystals are artificial periodic dielectric structures with the distinguishing characteristic of trapping and localizing light. While many important applications of photonic crystals are associated with the occurrence of a photonic band gap, light trapping for the purpose of solar energy harvesting is facilitated by spectral regions with a very high electromagnetic density of states. We describe designs of 3D photonic crystal silicon-based solar cells that enhance the overall absorption of sunlight using a three-section architecture consisting of less than 1 micron (equivalent bulk thickness) of silicon and no metallic mirrors. The three sections are (i) an antireflection (AR) layer consisting of a lattice of nanocones placed on top of simple cubic photonic crystal (ii) the 3D simple cubic photonic crystal (average rod diameter 170 nm and 350 nm lattice spacing) that traps light through a novel parallel-to-interface refraction (PIR) effect and (iii) a chirped photonic crystal back-reflector (BR) designed to absorb near-infrared light. Each rod contains a radial P-N junction and comprises an entire solar cell, with regions between the rods filled with silica (to mechanically protect the array) up to the tip of the nano-cones. These structures exhibit exceptionally good light absorption over a broad range of incident angles from 0 to 80 degrees. They can absorb roughly 75%-80% of all available sunlight above the electronic band gap of silicon. These nanostructured photonic crystals offer additional opportunities in combined photonic and electronic management to achieve and possibly surpass the Shockley-Queisser power efficiency limit of roughly 33%.

Biography:
Sajeev John is a "University Professor" at the University of Toronto and Government of Canada Research Chair. 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 originated the theory of classical wave localization and in particular the localization of light in three-dimensional strongly scattering dielectrics. From 1986-1989 he was an assistant professor of physics at Princeton University. While at Princeton, he co-invented (1987) the concept of photonic band gap materials, providing a systematic route to his original conception (1984) of the localization of light. In 1989 he joined the senior faculty at the University of Toronto.