[color_print] Micro-nano Seminar Series ________________________________ Wednesday, March 29, 2017 4:00 pm - Room 3-270 Dr. Jongseung Yoon Department of Chemical Engineering and Materials Science Department of Electrical Engineering University of Southern California New Approaches for Using III-V Compound Semiconductors in Photovoltaic and Photoelectrochemical Solar Energy Conversion Abstract Due to their highly favorable materials properties such as direct bandgap, appropriate bandgap energy against solar spectrum, and high electron mobilities, epitaxially grown III-V compound semiconductors have provided unmatched performance in solar energy harvesting. However, their large-scale deployment in terrestrial photovoltaics and solar fuel generation remains as a daunting challenge mainly due to the prohibitively high cost of growing device-quality epitaxial materials. In this regard, unconventional ways to exploit III-V compound semiconductors can create novel engineering designs, device functionalities, and cost structures, each with significant values in the next generation solar energy conversion technologies. In the first part of my talk, I will provide an overview of recent advances in materials design and fabrication concepts towards cost-efficient III-V photovoltaic systems based on multilayer-grown, ultrathin, nanostructured GaAs solar cells. Hexagonally periodic TiO2 nanoposts directly implemented on the window layer of GaAs solar cells served as a lossless diffractive coating for antireflection, diffraction, and light trapping in conjunction with a co-integrated back-surface reflectors, providing 20.8% one-sun efficiency with solar cells that have the thickness of active layer (emitter + base = 300 nm) more than 10 times thinner than conventional devices. In the second part, I will present a type of III-V photoelectrode systems for solar fuel generation based on heterogeneously integrated assemblies of epitaxially grown III-V materials. Specialized epitaxial design together with a bifacial electrode configuration decoupling optical and reactive interfaces enabled facile, independent control and optimization of light absorption, carrier transport, charge transfer, and materials stability in GaAs-based photoelectrodes, allowing for high efficiency (~13.1% STH), long lifetime (~ 8 days) operation of solar-driven water splitting for hydrogen generation. Biography [cid:image005.jpg@01D2A87B.283F5A50]Dr. Jongseung Yoon is an assistant Professor in the Mork Family Department of Chemical Engineering and Materials Science at the University of Southern California. He received a Ph.D. degree in Materials Science and Engineering from the Massachusetts Institute of Technology in 2006, and B.S. degree in Polymer Science from Seoul National University in 1996, respectively. Prior to joining USC, Prof. Yoon was a Beckman Institute Postdoctoral Fellow at the University of Illinois at Urbana-Champaign. His current research focuses on tailoring and understanding novel electrical, optical, electrochemical, and thermal properties of nanostructured inorganic single-crystalline semiconductor materials and exploiting them as synergistic materials building blocks into unusual format device implementation in areas ranging from photovoltaics, photoelectrochemical water splitting, to flexible/stretchable optoelectronics for skin-mountable/implantable sensing and therapeutic systems. Prof. Yoon is a recipient of DARPA Young Faculty Award in 2012 and Hanwha Non-Tenure Faculty Award in 2015. ________________________________ Host: Prof. Jeehwan Kim *Please email Prof. Kim at jeehwan@mit.edu<mailto:jeehwan@mit.edu> if you have any questions regarding this seminar. Refreshments provided. Thank you, Emilie Heilig Massachusetts Institute of Technology 77 Massachusetts Ave, 3-359 (32 Vassar St, 3-359 for packages) Cambridge, MA 02139 P: 617-253-2883