Air-Bridge Si Thermophotovoltaic Cell with High Photon Utilization

Abstract

Thermophotovoltaic (TPV) cells convert photons emitted from hot surfaces into electrical power. Unlike solar cells, TPV cells can be placed in close proximity to the heat source, allowing below-bandgap (i.e., out-of-band, OOB) photons to be reflected and reabsorbed by the emitter. As the reflectance of OOB photons approaches unity, the spectral efficiency of the TPV becomes increasingly insensitive to the bandgap of the cell and the source temperature. Here, we employ air-bridge structures with a lateral junction Si TPV cell as a means of increasing OOB reflectivity, which allows for efficient operation at low thermal source temperatures that were long inaccessible to efficient Si TPV power generation. The devices exhibit an OOB reflectance of 98.0 ± 0.1% and an air-bridge scalability to at least 6 cm × 6 cm. Compared to devices with a Au back surface reflector (BSR), devices featuring an air-bridge BSR exhibit a 25% relative increase in power conversion efficiency at a thermal source temperature of 1988 K. Such performance improvements in TPV cells made with scalable and relatively low-cost Si can potentially expedite the widespread use of TPV systems in both energy storage and generation systems.

A Review on Thermophotovoltaic Energy Conversions and its Space Power Applications

“…However, sometimes at much lesser temperatures below 1,300°C, the observed efficiencies remain only as high as 32%, in comparison to expectations that TPV efficiencies can approach more than 32% [6,7]. The cells employ band-edge spectroscopic filtering to achieve maximum efficiency, rejecting radiation of extraneous sub bandgap material and return to the source with highly polished back surface reflectors [3,5,8]. In comparison with a photovoltaic cell or solar cell, a TPV device can store and ultimately transform the energy contained inside sub-bandgap photons.…”

“…Additionally, the TPV device produces a high-power energy density relative to other systems per unit area, making it appropriate for middle electrical systems. By combining nuclear fission sources with radioisotope TPV producers, the power output can be raised even more [5,8,9]. The usual heat limit for nuclear reactors starts at 10 kW to MWs.…”

Design of a High-Performance Titanium Nitride Metastructure-Based Solar Absorber Using Quantum Computing-Assisted Optimization

“…Solar energy is the most abundant, clean, and sustainable resource for addressing global energy and environmental challenges. − Therefore, solar energy harvesting has attracted great attention over the past few decades for converting solar energy into electricity for human use. − Among these applications, thermophotovoltaic (TPV) systems can be one of the most efficient technologies as the theoretical efficiency of TPVs (∼85.4%) is much higher than the Shockley–Queisser efficiency. − TPV systems generally include an absorber, an emitter, and a photovoltaic (PV) cell, where solar energy should be efficiently absorbed by the absorber (ideally 100%) in the solar spectrum range (300 < λ < 2500 nm). , Noble materials that show plasmonic effects in the solar spectrum, such as gold and silver, can be candidates for the absorber, but they cannot be used for TPV systems because of their weak chemical or thermal stabilities at elevated temperatures (>1300 K). − Despite their high absorption efficiency, carbon-based materials also cannot be used for the TPV absorber due to the usual high working temperature of TPV systems . Therefore, refractory materials that can withstand high working temperatures should be used ( e.g.…”

Enhanced Photon Utilization in Single Cavity Mode Air-Bridge Thermophotovoltaic Cells

“…The coupling of a reflector to a TPV cell facilitates effective recycling of unabsorbed below-bandgap or out-of-band (OOB) photons, thereby maximizing the TPV power conversion efficiency (PCE). − Recently, we have shown that nearly lossless Fresnel reflection can be achieved by introducing an air gap whose thickness is on the order of a wavelength, between the Au back surface reflector (BSR) and the cell active layer. , However, such thin-film membranes are vulnerable to strain, resulting in mechanical distortion and structural failures such as cracks . In this work, we analyze the multiple optical modes supported by a buckled, In 0.53 Ga 0.47 As thin-film air-bridge membrane, reducing R OOB by over 10%.…”