Narrow Bandgap Multi-Stage Structures for Thermophotovoltaics

University Of Oklahoma Norman Campus, Norman OK

Investigators

Abstract

Non-technical Description: About two-thirds of the energy generated to power the world's machinery is lost as waste heat. The recovery of even a fraction of these large losses would have a significant environmental impact. This project explores semiconductor multilayer structures for converting this otherwise wasted heat into useful electricity. The objectives of the project are to achieve extensive and systematic understanding of the fundamental aspects of the multilayer semiconductor structures, and to advance the knowledge of how underlying physical processes affect their electrical and optical properties. This enables development of novel concepts for effective conversion of radiant energy from a heat source into electricity. The project offers graduate and undergraduate students at the University of Oklahoma unique opportunities to pursue education, training and research in multidisciplinary topics, such as materials science, quantum engineering, photonics, and device fabrication. This project also enhances Oklahoma's infrastructure for science and technology development and opens new opportunities for students from under-represented groups. Technical Description: Narrow bandgap materials are desirable for making efficient thermophotovoltaic (TPV) cells that convert the otherwise-wasted radiant energy from a heat source into useful electrical energy. The TPV devices take advantage of the type-II band alignment of InAs/GaSb interfaces to form multi-stage cascade structures. These multi-stage structures have many potential advantages including: significantly improved collection efficiency for photo-generated carriers, a wide range of infrared spectral coverage, high open-circuit voltage due to the cascade architecture, as well as the benefits of current matching through adjustments of the number of cascade stages and the thickness of individual absorber layers. Consequently, these narrow bandgap materials enable TPV cells that effectively absorb infrared radiant photons from a heat source and efficiently convert them into electricity. The power conversion efficiency is expected to approach 20%, which would be remarkably high for a TPV system operating at long wavelengths and with a modest light intensity from a low temperature source. The approach and tasks involve: theory development and designs for multi-stage TPV structures, molecular beam epitaxial growth of the TPV structures, material characterization, and prototype device fabrication and characterization. The TPV cells enabled by multi-stage structures have important applications for waste-heat recovery, more efficient use of solar energy, space exploration, power beaming, as well as portable and quiet energy sources. This project not only advances the understanding of physical processes, it also generates new knowledge in the design of quantum-engineered structures and broadens their applications. The advancement of narrow bandgap multi-stage TPV structures in the mid-infrared wavelength region is a critical step toward harvesting energy from widely available heat sources.