Dante F. DeMeo

Stable high temperature metamaterial emitters for thermophotovoltaic applications

We report a metamaterial design for a thermophotovoltaic (TPV) emitter. TPVs are similar to photovoltaic solar cells, but they convert heat to electricity instead of sunlight. The focus of this paper is on the emitter stage of the TPV system, which converts the heat into a spectral band which is easily absorbable by the TPV photodiode. The proposed structure consists of a platinum metallic element, an alumina dielectric spacer, and platinum grounding plane on a sapphire substrate. This perfect absorber based metamaterial emitter is shown to robustly operate at 600 °C. This temperature is high enough to enable TPV use for many industrial applications.

GaSb Thermophotovoltaic Cells Grown on GaAs Substrate Using the Interfacial Misfit Array Method

We present gallium antimonide (GaSb) p–i–n photodiodes for use as thermophotovoltaic (TPV) cells grown on gallium arsenide (100) substrates using the interfacial misfit array method. Devices were grown using molecular beam epitaxy and fabricated using standard microfabrication processes. X-ray diffraction was used to measure the strain, and current–voltage (I–V) tests were performed to determine the photovoltaic properties of the TPV cells. Energy generation at low efficiencies was achieved, and device performance was critically analyzed.

Two dimensional metallic photonic crystals for light trapping and anti-reflective coatings in thermophotovoltaic applications

We report the development of a front-side contact design for thermophotovoltaics that utilizes metallic photonic crystals (PhCs). While this front-side grid replacement covers more surface area of the semiconductor, a higher percentage of photons is shown to be converted to usable power in the photodiode. This leads to a 30% increase in the short-circuit current of the gallium antimonide thermophotovoltaic cell.

Cryogenic thermal simulator for testing low temperature thermophotovoltaic cellsa)

Thermophotovoltaic (TPV) devices convert infrared electromagnetic radiation into electricity. The authors’ research involves the use of strained-layer superlattices to enable TPV devices to operate at longer wavelengths than the current state of the art designs. To determine the performance of these devices, a novel test apparatus was designed and constructed. Here, the authors present a custom-built, cryogenic vacuum chamber for the testing and characterization of TPV samples. As TPV cells become sensitive to longer wavelength photons (lower source temperatures) in the infrared, the need to control the sample’s ambient temperature becomes critical for accurate testing; thus, the tester includes two copper heat shields cooled via conduction with two liquid nitrogen reservoirs. A calibrated blackbody source is used to illuminate a temperature controlled sample in high vacuum (∼10−6 Torr). The chamber temperature is extensively monitored and is designed to generate current-voltage (I-V) curves for TPV sampl...

Heterogeneous metal-oxide nanowire micro-sensor array for gas sensing

Vanadium oxide, manganese oxide, tungsten oxide, and nickel oxide nanowires were investigated for their applicability as chemiresistive gas sensors. Nanowires have excellent surface-to-volume ratios which yield higher sensitivities than bulk materials. Sensing elements consisting of these materials were assembled in an array to create an electronic nose platform. Dielectrophoresis was used to position the nanomaterials onto a microfabricated array of electrodes, which was subsequently mounted onto a leadless chip carrier and printed circuit board for rapid testing. Samples were tested in an enclosed chamber with vapors of acetone, isopropanol, methanol, and aqueous ammonia. The change in resistance of each assembly was measured. Responses varied between nanowire compositions, each demonstrating unique and repeatable responses to different gases; this enabled direct detection of the gases from the ensemble response. Sensitivities were calculated based on the fractional resistance change in a saturated environment and ranged from 6 × 10−4 to 2 × 10−5%change ppm−1.

Simulations of indium arsenide antimonide (InAs 0.91 Sb 0.09 ) monovalent barrier-based thermophotovoltaic cells

Thermophotovoltaics (TPVs) have attracted interest due to their ability to harvest infrared radiation and produce usable energy. The focus of this research is the characterization of novel TPV cell designs which employ a barrier layer in the pn junction, creating a p-B-n (p-type, barrier, n-type) structure. First suggested for use with photodetectors, the monovalent barrier is designed to block only one carrier; it exists in either the valence band or conduction band but not both. This monovalent band is accomplished by careful selection of a wide bandgap material in place of, or in addition to, the intrinsic layer. The use of a barrier layer enables these p-B-n cells to operate at longer wavelengths, higher efficiencies, and higher operating temperatures. p-B-n designs utilizing InAs0.91Sb0.09 lattice matched to GaSb were examined. Barrier and absorber materials were researched and simulations were performed to determine optimal band alignments as well as to perform an initial optimization of the design.

Thermophotovoltaics: An Alternative to and Potential Partner with Rectenna Energy Harvesters

A technology that can be used in place of, or in addition to, rectennas is thermophotovoltaics (TPVs). The ultimate function of TPVs, like that of the rectenna, is the conversion of electromagnetic radiation to DC current. Rectennas use a rectifying diode coupled with an antenna to achieve this conversion. TPVs achieve this conversion through a single diode which both receive the radiation and converts it to a current. While rectennas are superior at longer wavelengths (greater than 5 μm), TPVs are more efficient at shorter wavelengths (less than 5 μm). Although rectennas and TPVs have been investigated independently, a hybrid technology may be possible which incorporates components from both technologies.

Metamaterial selective emitters for photodiodes

This work demonstrates metamaterial (MM) selective thermal emitters for potential use with energy harvesting photodiodes, such as thermophotovoltaic cells. Preliminary structures have been designed, simulated, and fabricated using CST Microwave Studio and microfabrication techniques including electron beam evaporation, atomic layer deposition, and electron beam lithography, respectively. Samples were tested to determine the effect of top layer metal thickness on the absorption of these devices. Preliminary simulation and testing was also performed to design a device for operation at 500°C.

Electrodeposited Copper Oxide and Zinc Oxide Core-Shell Nanowire Photovoltaic Cells

Uncertainty in energy capacity, limited fossil fuel resources, and changes in climate predicate a need for increased research and development into alternative and sustainable energy solutions. Solar energy is one solution to this problem and many variations of it exist; however, the majority of them are prohibitively expensive. We propose a low-cost solar energy generation method which is cost-effective both in materials and production. Our solution will utilize cheap, abundant materials as well as lower-cost fabrication methods to produce photovoltaic (PV) cells. Although it is unlikely that the efficiency of such cells will be record-breaking, its low cost should make its price-per-watt-produced competitive, which is one of the most important metrics for the commercialization of any solar technology. Our design consists of a radial heterojunction comprised of p-type copper oxide and n-type zinc oxide nanowires, which are oxides of earth-abundant materials. The nanowires have a core-shell design to minimize carrier travel distance and maximize junction area. Furthermore, we utilize a wet chemistry fabrication process, making the production of such cells inexpensive, easily scalable and non-demanding in terms of fabrication energy. The process involves growing copper nanowires, oxidizing, plating zinc oxide, and depositing a top contact.

Study of the effect of 2D metallic photonic crystals on GaSb TPV diode performance

Thermophotovoltaics (TPVs) are a potential technology for waste-heat recovery applications and utilize IR sensitive photovoltaic diodes to convert long wavelength photons (>800nm) into electrical energy. The most common conversion regions utilize Gallium Antimonide (GaSb) as the standard semiconductor system for TPV diodes due to its high internal quantum efficiencies (close to 90%) for infrared radiation (~1700nm). However, parasitic losses prevent high conversion efficiencies from being achieved in the final device. One possible avenue to improve the conversion efficiency of these devices is to incorporate metallic photonic crystals (MPhCs) onto the front surface of the diode. In this work, we study the effect of MPhCs on GaSb TPV diodes. Simulations are presented which characterize a specific MPhC design for use with GaSb. E-field intensity vs. wavelength and depth are investigated as well as the effect of the thickness of the PhC on the interaction time between the e-field and semiconductor. It is shown that the thickness of MPhC has little effect on width of the enhancement band, and the depth the ideal p-i-n junction is between 0.6μm and 2.1μm. Additionally, simulated results demonstrate an increase of E-field/semiconductor interaction time of approximately 40% and 46% for a MPhC thickness of 350nm and 450nm respectively.