Thermophotovoltaics (TPV) allow one to harvest excess heat as electricity. While higher temperature heat allows TPV to operate more efficiently, the materials used in the emitter are often limited in their operating temperatures and atmospheres. In this study, we specifically focus on designing a multilayer system consisting of compatible oxides, capable of reaching high temperatures. We then provide materials characterization data to support this approach and predict the final performance of a TPV system using this approach.

Spectral control in thermophotovoltaic systems (TPV) is critical to achieving high thermal to electric conversion efficiency and power density. Closed thermal systems using a fixed heat source such as radio-isotope TPV, require the recuperation of below bandpass photons to maintain the temperature of the thermal source and maximize conversion efficiency. Open thermal systems designed to recover waste heat require a trade-off between high power density and minimal operating cost. Spectral control options are presented to meet the different end goals of the two systems.

The low-grade heat wasted globally contains an enormous amount of exergy that can be recovered for renewable energy generation. Current solid-state techniques for recovering low-grade waste heat, such as thermoelectric generators and thermophotovoltaics, are still limited by low conversion efficiencies or power densities. In this work, we propose a high-performance solid-state near-field thermophotonic system. We utilize the thermal radiation from nonequilibrium bodies by replacing the passive emitters in traditional thermophotovoltaic systems with electrically biased light-emitting-diodes (LEDs). we show that the proposed system can achieve a power density of 24.4 W/cm2 and a conversion efficiency of 15.5%, significantly outperforming the current record-setting thermoelectric generators. We also propose an electronic circuit design for the system by feeding part of the power produced by the PV cell back to the LED, to make the whole system self-sustaining.

We propose a wavelength-selective thermal emitter based on the resonator-pixel (RP) structure. This passive emitter is designed for thermophotovoltaic (TPV) power generation. It contains a thin SiC material etched into an array of micron-sized rings, and the etched surface is covered with a metal such as tantalum. The emissivity of the emitter is determined by equating it to the absorptivity, which is modeled by 3-dimensional electromagnetic modeling. The result shows that the RP emitter is able to increase the wavelength selectivity by 8 times relative to a bulk SiC emitter. Integrated with a resonant GaSb PV cell with enhanced absorption at the band edge, the power conversion efficiency (PCE) can be maintained constant at 80% between 600 and 1800°C while the power throughput increases by 1.72 times. We further modeled the far-field beam profile of the emitter and found the beamwidth to be less than 10° when the emitter area is larger than 10 × 10 μm². This highly collimated emission allows larger distance between the emitter and PV cell without reducing its PCE. The thermal management of the TPV system can thus be greatly improved. By modeling the emitter and PV cell together, we also found a near-field TPV effect, which increases the electrical power throughput by a factor of 2.

This work presents 3D printed polymer-based flexible electrode substrates exhibiting high surface area and flexibility in reverse electrowetting-on-dielectric energy harvesting for powering patchable human health monitoring sensors. Composite electrode substrates are printed using polydimethylsiloxane (PDMS) polymer and carbon black in 20:1 ratio by weight to provide some mechanical strength to the electrodes. Thin film layers of titanium for current collection and aluminum oxide as dielectric are deposited on the substrates to complete the electrode fabrication process. Without applying any bias voltage, the AC current due to periodic variance in capacitance resulting from mechanical modulation of an electrolyte droplet between two electrodes is measured for a low frequency range that falls within human motion activities. Mechanical integrity of the electrodes are characterized in terms of stress-strain analysis demonstrating robustness of their longevity.

High performance broadband Distributed Bragg Reflectors (DBRs) have become instrumental in the design of high efficiency Thermophotovoltaic devices, improving efficiency by redirecting parasitic photon loss during conversion towards the device for regenerating power. Broadband Bragg Reflectors designed to reflect in the 3-5 micron, 3-12 micron, and 1-12 micron infrared ranges are of crucial importance in such applications to maximize regeneration efficiency in TPV devices, as most parasitic photons fall in these ranges under typical operating temperatures. Additionally, omnidirectional capabilities further improve regeneration efficiency by absorbing parasitic photons at large angles of incidence. In this work, we present a novel inverse design transfer matrix optimization algorithm for designing variable layer thickness broadband DBRs for arbitrary wavelength ranges and angles of incidence, and we showcase the resulting ultra-high reflection DBRs designed with our algorithm, specifically for the 1-12μm IR range. We demonstrate that our DBRs provide very significant increases in average reflection over the IR ranges of interest as compared to state-of-the-art reflective coatings, even at large angles of incidence, and are also optimized to be considerably thinner than quarter wavelength and other state of the art DBRs with comparable reflection spectra. As such, the DBRs designed with our inverse design algorithm have significant applications in the design of very high efficiency TPV systems, while also being thin enough to embed onto devices or windows, and are also easy to fabricate due to their simple multilayer 1-D structure.