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Feng, Dudong
Zhang, Zhuomin
Yee, Shannon
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Radiative energy converters are semiconductor devices that realize energy conversions between thermal energy and electricity. These newly proposed solid-state heat engines/pumps are considered as promising technologies for energy harvesting and conversion applications on thermal energy storage, aerospace power generation, local thermal management, and thermal regulation for building and human thermal comfort. This dissertation is designated to develop a detailed and comprehensive modeling method to depict the photon-charge coupled transport for radiative energy converters, investigate the unique physical phenomena induced by the photon chemical potential inside the devices and explore the performance enhancement by using two-dimensional (2D) materials. A modification of the direct method is proposed using Boltzmann approximation to link the conventional and direct method for the modeling of near-field TPV cells. By contrasting different modeling approaches, the effect of evanescent waves on the dark current of a near-field TPV cell is quantitatively analyzed for different emitter and cell materials. To fully model a working near-field TPV cells, an iterative solver that combines fluctuational electrodynamics (FE) with the drift-diffusion (DD) model is developed to tackle the coupled photon and charge transport problem, enabling the determination of the spatial profile of photon chemical potential beyond the detailed balance approach. The difference between the results obtained by allowing the photon chemical potential to vary spatially and by assuming a constant value demonstrates the limitations of the conventional approaches. The performance improvement on a thin-film, near-field InAs TPV device with a back gapped reflector is investigated, comparing its performance to that with a conventional metal back surface reflector. Surface passivation conditions are also investigated to further improve the performance of TPV devices with back reflectors. The output power and efficiency are calculated using the newly proposed photon-charge coupled model. The absorption of the back reflectors and external luminescence loss are analyzed to explain the performance improvement. The external radiative recombination in thin-film, near-field radiative energy converters is investigated using FE. The spatial profile of the local external radiative recombination coefficient is calculated to investigate the thin-film effect, geometric effect, and doping effect on the external luminescence of a thin-film radiative energy converters under different configuration and working conditions. A novel photonic thermal diode is achieved in the near-field regime by coupling (or decoupling) the hyperbolic phonon polaritons (HPhPs) in hexagonal boron nitride (hBN) and temperature-dependent interband transition of indium antimonide (InSb). Taking the advantages of the forward bias operation condition, a near-field thermoradiative device with high performance can be realized. This thesis provides a comprehensive investigation of optical and electrical processes of radiative energy converters, which can benefit the design and optimization of solid-state energy converters with wide application scenarios. Fundamental understanding of the photon chemical potential may exploit a new pathway of control the radiative heat transfer for both far- and near-field regimes.
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