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
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.