Pratap Mahesh Rao
Department of Mechanical Engineering, Thermosciences Group
Metal Oxide Nanowire-Assisted Coal Direct Chemical Looping Combustion
One-dimensional metal oxide nanostructures are promising candidates for several energy applications including improved materials for photovoltaics and solar water-splitting photoanodes. An off-beat, energy-minded application for these 1-D metal oxide nanostructures is their use as a fixed-bed oxygen carrier in the Chemical Looping Combustion (CLC) of solid coal, achieving coal combustion with economical carbon dioxide sequestration. The nanostructures grow in situ and spontaneously form fixed, high-density arrays that can be cycled through air and coal to facilitate oxygen exchange while improving the kinetics of the reactions, offering fast, easy regeneration of the metal oxide, and avoiding coal-metal oxide separation problems. This project will focus on the development of methods to produce 1D metal oxide nanostructures in a rapid, simple, scalable fashion using various oxidative environments, including flames. Flame synthesis is used to produce metal oxide nanoparticles at an industrial scale, and its benefits, including high temperature capability, continuous production, scalability and economy, will be valuable for the synthesis of 1D metal oxide nanostructures, enabling their use in large-scale energy applications, such as direct coal CLC. The success of this research can lead to the quick realization of an economical, environmentally benign coal technology.
Timothy Paul Osedach
School of Engineering and Applied Sciences
Hybrid Organic/Quantum Dot Photovoltaics
Photovoltaic (PV) devices that incorporate heterojunctions of organic semiconductors and chemically synthesized nanocrystal quantum dots (QDs) may provide an inexpensive alternative to conventional PV technologies. These materials possess a number of advantages including high absorption coefficients and compatibility with low-cost deposition techniques that could enable inexpensive scaling of manufacturing. QDs, in particular, have a broad optical response that can be tuned from visible to infrared wavelengths by selection of the type and physical size of the nanocrystals. This tunability may enable multi-junction solar cells of high efficiency in which each layer is sensitized to a different part of the solar emission spectrum. I will be studying exciton dissociation, the mechanism that critically governs photogeneration in heterojunction PV’s, by fabricating and modeling devices that utilize a broad spectrum of nanostructured materials. A deeper physical understanding of device operation will support efforts to improve device performance, of which there are a number of promising directions. Of particular interest is the incorporation of infrared- absorbing QDs. Devices sensitized to infrared light would be able to harness the long- wavelength part of the solar emission spectrum that is inaccessible to most conventional solar cells, thus allowing for higher power conversion efficiencies.
Jonathan David Servaites Materials Science and Engineering Northwestern University Efficient and Cost Effective Solar Cells: New Materials for Improved Recombination and Charge Dissociation Losses in Organic Photovoltaics Research Advisors: Tobin Marks and Mark Ratner.
Jonathan David Servaites
Materials Science and Engineering
Efficient and Cost Effective Solar Cells: New Materials for Improved Recombination and Charge Dissociation Losses in Organic Photovoltaics
Research Advisors: Tobin Marks and Mark Ratner
My research focuses on new models and techniques for enhancing efficiencies in organic solar cells (also known as organic photovoltaics, or OPVs). While record OPV power conversion efficiencies recently have reached 7%, ultimately efficiencies well over 10% are regarded as necessary for widespread use. My project focus is therefore to articulate how losses are occurring and to propose materials and system designs for overcoming these losses.
Generally speaking, some loss mechanisms are understood. For example, the theoretical limit for “single active layer” solar cells is approximately 33% – this limit is largely due to the fact that only photons with frequencies beyond the active layer bandgap can be absorbed. Designing OPVs such that their efficiencies move closer to that 33% limit, however, remains a major challenge.
One key problem in OPVs is that electrons and positively charged “holes” are tightly bound together, and therefore, energy is typically spent in separating them (or else they will likely recombine, leading to lost current). I am developing models specifically to understand these dissociation and recombination processes and, ultimately, to propose new materials and experimental designs to help overcome current losses – with the aim of moving OPV efficiencies beyond the 10% threshold.