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Thermophotovoltaics (TPVs) are solid-state devices that may enable scalable electricity generation from a variety of high-temperature heat sources in applications such as grid-scale electricity storage and distributed co-generation of heat and power. These systems consist of a thermal emitter and a photovoltaic (PV) cell in close proximity. Spectrally selective techniques, categorized as either emission control or absorption control, have led to improved performance in TPVs. In particular, suppression of sub-bandgap radiative transfer is essential for improving efficiency. However, the spectral-selectivity of absorption control strategies in conventional cells has been limited by parasitic absorption of sub-bandgap radiation due to a variety of possible mechanisms including absorption in the growth substrate, the thickest layer of the cell. Thin-film TPV cells have the potential to enable selective radiative transfer by reducing the optical path length through the cell and leveraging thin-film interference. Here, we demonstrate high spectral-selectivity in thin-film InGaAs-based TPV cells with back-surface-reflectors and optimized dielectric coatings. Selective absorption using thin semiconductor layers has been investigated for solar absorbers to minimize thermal re-radiation, but has not been demonstrated in the context of TPV cells. The fabricated TPV cells exhibit high absorption of radiation above the semiconductor bandgap and high reflectance below the bandgap, particularly when dielectric layers surrounding the InGaAs are optimized. Furthermore, thin-film devices have the potential for significant economic improvements over conventional TPVs that use expensive growth substrates in the operating device. Fabrication of thin-film group III-V semiconductor cells through non-destructive epitaxial lift-off has enabled wafer reuse. Considering the high cost of III-V wafers, reuse can be expected to significantly reduce the cost of TPV generators.
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