Although single junction halide perovskite solar cells have demonstrated photoconversion efficiencies (PCEs) of up to 22 % (with efficiencies of 17 % routinely reported), there remains further room for improvement in the open circuit voltages (Voc) and short circuit current densities (Jsc) achievable. It has been shown that material quality no longer constrains performance in the best performing halide perovskite solar cells, rather it is inefficiencies in the management of photons that are the largest source of losses in Jsc and Voc due to poor harvesting of photons near the semiconductor band-edge, non-radiative carrier recombination losses limiting the match of the solar cell to a black body radiator at the same temperature, poorly optimized angular distribution of emission due to radiative recombination of carriers, and changes in the entropy of photons. In this talk, the use of active layer light management through the use of 1D metal oxide nanophotonic architectures to overcome these losses will be discussed. High performance photocatalysts need to make optimal use of incident light to drive chemical reactions. Photonic crystals are materials consisting of microscale- and submicron-scale periodicity in their refractive index wherein the propagation of light is prohibited in a certain frequency band (called the photonic stop-band). When pi-conjugated molecules or quantum dots are introduced into a photonic crystal whose absorption profile matches the photonic stop band, very strong absorption can result in such defect-doped photonic crystals, which is useful for photocatalysis. Likewise, nanoscale- and submicron-scale noble metal structures exhibit strong surface plasmon resonances (SPR) that result in an amplification of the local field and the generation of energetic carriers called "hot electrons". The exploitation of SPR in photocatalysis forms the basis for the rapidly expanding field of plasmonic photocatalysis. In this talk, our latest results on the use of 1D metal oxide nanophotonic architectures to achieve high rate CO2 photoreduction and photoelectrochemical water-splitting will be presented.
Karthik Shankar received his B.Tech degree in 2000 from the Indian Institute of Technology-Madras, India, where he was awarded the prestigious Governors Gold Medal for all-round excellence from his graduating class. Dr. Shankar was an Eastman Kodak Research Fellow in 2003. He received his M.S. (2002) and Ph.D. (2007) degrees in Electrical Engineering at Penn State University. In 2010, he received the PetroCanada Young Innovator Award. He joined the department of Electrical & Computer Engineering at the University of Alberta in Aug 2009 and is now a Professor. He was seconded to the NRC National Institute for Nanotechnology (NINT) from 2012-2017 and is currently a participant in the NRC-UofA NanoInitiative project on Organic and Hybrid Pohotovoltaics. He currently champions the solar energy theme and leads research into CO2 photoreduction at the CFREF-funded Future Energy Systems Resear ch Institute at the University of Alberta. He is the author of 100 refereed journal articles that have collectively been cited over 16,000 times. The Shankar Lab's research interests consist of organic and graphenic semiconductors, nanomaterials, plasmonics, solar cells and photocatalysts.