| Description |
Thermophotovoltaic (TPV) energy conversion takes advantage of spectrally selective radiation that can be tailored to match the absorption characteristics of a photovoltaic (PV) cell. In the far field, where the gap spacing between the emitter and PV cell is much larger than the thermal wavelength, thermal radiation can be controlled by designing selective emitters to improve efficiency and power output of TPVs. Additionally, if the emitter and PV cell are separated by a subwavelength gap (near field), evanescent waves can be utilized to increase performance. The research objective of this work is to identify, quantify, and demonstrate potential radiative improvements to TPV energy conversion. This dissertation has three main contributions. First, optimization work is performed for an emitter at 2000 K that determines ideal radiation spectra for far-field TPVs when thermal impacts within a gallium antimonide (GaSb) PV cell are considered. It is shown that when designing emission spectra for maximizing power or conversion efficiency, thermal impacts in the PV cell must be accounted for. The second part of the dissertation discusses the importance of considering near-field impacts on external luminescence and photon recycling in a TPV device. Here, the PV cell is held constant at 300 K and again consists of GaSb. The emitter is fixed at 800 K and consists of either intrinsic silicon or a material supporting surface polaritons at a resonant frequency close to the GaSb bandgap. It is reported that external luminescence efficiency is a strong function of gap spacing in the near field and is not solely dependent on cell quality. Results show this near-field benefit is larger for realistic cells with significant nonradiative recombination compared to ideal cells operating in the radiative limit. The final part of the dissertation is focused on overcoming practical bottlenecks currently preventing the implementation of near-field TPVs into real world systems. Here, standalone devices consisting primarily of highly doped silicon capable of supporting near-field thermal radiation are designed, fabricated, and tested. Vacuum gap spacings as small as 110 nm between macroscale planar surfaces are achieved leading to an enhancement above the blackbody limit of 28.5 while maintaining parasitic thermal conduction below 2% of the total heat rate. |
