Photonic management is a key issue for the optimization of thermophotovoltaic (TPV) energy conversion systems. It is realized by selective emitters, front surface filters on TPV cells, and back surface reflectors (BSRs). Photonic management modifies photon energy transfer from the emitter to the TPV cell due to photon reuse and energy conversion processes in the TPV cell due to photon recycling and trapping in the cell. Our work has developed a comprehensive thermodynamic theory of photonic management in the TPV cell and in whole TPV systems to elucidate key optimization parameters. Our approach is based on the exact Lambert function solution of the generalized Shockley–Queisser model and the corresponding fundamental formulas of endoreversible thermodynamics for maximal electric power, emitted optical power, and dissipation losses. The model includes interrelated processes of photon recycling, photon trapping, nonradiative recombination, and parasitic absorption of the BSR. Optimization of a TPV system with photon reuse should take into account that the cell thickness that provides maximal output power does not correspond to the thickness, which gives the maximal conversion efficiency. The theory predicts the important limits for TPV efficiency and output power determined by the Auger recombination in low-bandgap semiconductor materials, various parasitic losses in the cell and conductive layers, and photon escape from the TPV system. For example, we consider the TPV system based on 0.6 eV InGaAs cells with a BSR and a front surface photon scattering layer, which provides Lambertian light trapping.
The quest for developing clean, quiet, and portable high energy density, and ultra-compact power sources continues. Although batteries offer a well known solution, limits on the chemistry developed to date constrain the energy density to 0.2 kWh/kg, whereas many hydrocarbon fuels have energy densities closer to 13 kWh/kg. The fundamental challenge remains: how efficiently and robustly can these widely available chemical fuels be converted into electricity in a millimeter to centimeter scale systems? Here we explore two promising technologies for high energy density power generators: thermophotovoltaics (TPV) and thermoelectrics (TE). These heat to electricity conversion processes are appealing because they are fully static leading to quiet and robust operation, allow for multifuel operation due to the ease of generating heat, and offer high power densities. We will present some previous work done in the TPV and TE fields. In addition we will outline the common technological barriers facing both approaches, as well as outline the main differences. Performance for state of the art research generators will be compared as well as projections for future practically achievable systems. A viable TPV or TE power source for a ten watt for one week mission can be built from a <10% efficient device which is achievable with current state of the art technology such as photonic crystals or advanced TE materials.
The advantages and applications of chalcogenide glass (ChG) thin film photoresists for grayscale lithography are demonstrated. It is shown that the ChG films can be used to make ultrathin (~600 nm), high-resolution grayscale patterns, which can find their application, for example, in IR optics. Unlike polymer photoresists, the IR transparent ChG patterns can be useful as such on the surface or can be used to transfer the etched pattern into silicon or other substrates. Even if the ChG is used as an etch mask for the silicon substrate, its greater hardness can achieve a greater etch selectivity than that obtained with organic photoresists. The suitability of ChG photoresists is demonstrated with inexpensive and reliable fabrication of ultrathin Fresnel lenses that are transparent in the visible as well as in the IR region. The optical functionality of the Fresnel lenses is confirmed. Application of silver photodissolution in grayscale lithography for microelectromechanical systems (MEMS) applications is also shown. A substrate to ChG/silver thickness etching ratio of ~10 is obtained for the transfer of patterns into silicon using reactive ion etching (RIE), more than a fivefold increase compared to traditional polymer photoresist.
The advantages and applications of chalcogenide glass (ChG) thin film photoresists for grayscale lithography are
demonstrated. It is shown that the ChG films can be used to make ultrathin (~600 nm), high-resolution grayscale
patterns, which can find their application, for example, in IR optics. Unlike polymer photoresists, the IR transparent
ChG patterns can be useful as such on the surface, or be used to transfer the etched pattern into silicon or other
substrates. Even if the ChG is used as an etch mask for the silicon substrate, its greater hardness can achieve a greater
transfer ratio than that obtained with organic photoresists. The suitability of ChG photoresists is demonstrated with
inexpensive and reliable fabrication of ultrathin Fresnel lenses that are transparent in the visible as well as in the IR
region. The optical functionality of the Fresnel lenses is confirmed. Application of silver photodissolution in grayscale
lithography for MEMS applications is also shown. The process consists of the following steps: ChG film deposition, Ag
film deposition, irradiation through a grayscale mask, removal of the excess Ag and the transfer of the pattern to Si by
dry etching. A substrate to ChG thickness etching ratio of ~ 10 is obtained for the transfer of patterns into silicon, more
than a five fold increase compared to traditional polymer photoresist.
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