Meeting the rising global energy need with clean and efficient energy systems is one of the greatest technological challenges of our time. Efficient conversion of heat and light to electricity is crucial in overcoming this challenge. Thermophotovoltaics is a promising technique for efficiently converting heat to electricity via light without any moving parts. The heat generated from industrial processes, nuclear fission reaction, automobile exhaust or absorption of sunlight results in thermal light radiating from hot surfaces. Photovoltaic conversion of this thermal light to electricity as in solar cells is called thermophotovoltaic conversion. The theoretical efficiency limit of thermophotovoltaic systems can be as high as 80%, though experimental demonstrations lie far below this number. The primary reason for low efficiency is the broadband nature of thermal light radiating from hot surfaces. Squeezing thermal light into a narrow band of frequencies is a challenging task especially when operating at high temperatures. This project aims to develop novel strategies to confine thermal light to a narrow band of frequencies and demonstrate efficient conversion of heat to light. Successful implementation of the project will result in discovering new tools to achieve extreme control on the flow of light and heat, educate and train next-generation scientists, and develop an efficient heat-to-electricity conversion technology for energy generation and storage applications. Given that the on-grid industrial waste heat alone is nearly 20% of the total industrial energy consumption, efficient thermophotovoltaic systems can make a huge impact in meeting the clean energy needs of the planet.

Technical Abstract

rmal radiation from hot surfaces is typically broadband in nature and limit the overall efficiency of thermophotovoltaic conversion. Confining thermal radiation to a narrow spectral band is the key to this problem. Previous attempts have investigated various nanophotonic principles to design narrowband thermal emitters or selective emitters, though their performance is still inadequate. All nanostructured optical materials degrade at high temperatures. Their optical losses significantly increase with temperature and limit the maximum possible spectral selectivity. Calculations show that a spectral contrast of at least 20 dB is required for efficient thermophotovoltaic conversion. Such high contrast over broad infrared wavelengths is not possible by conventional approach due to high optical losses in the constituent materials. Here in this project, an unorthodox approach using non-Hermitian physics or quantum optical description of resonant emitters is adopted to design thermal emitters. Unlike the conventional approach, non-Hermitian design exploits high optical losses in materials to simultaneously achieve high contrast and high emissivity. Further, a quantum optical description of the selective emitter allows its design as a system of coupled multiple nanoscale resonators. Such an approach is a paradigm shift in the design of selective emitters allowing novel many-body physical phenomena to be observed in thermal emission. As a result, new design tools such as symmetry, topology and internal phase of resonators present an unprecedented opportunity to extreme-engineer thermal emitters. This project aims to investigate the effect of these new design tools on the spatial and spectral properties of thermal radiation, build selective emitters with high contrast, directionality, and brightness, and demonstrate high-efficiency thermophotovoltaic conversion.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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Rice University
United States
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