SUMMARY

At the micro-/nano-scale regime, radiative energy converters made of semiconductor materials exhibit unusual phenomena due to photon tunneling effect. The coupled evanescent waves generated from total internal reflection and surface polaritons in certain materials greatly enhance the performance of radiative energy converters. The purpose of this proposal is to investigate the near-field effect on the device performance of radiative energy converters, especially for thermophotovoltaic cells. The effect of evanescent waves on dark current and reverse saturation current is demonstrated theoretically. Three modeling methods are compared for an ideal thermophotovoltaic cell. The applicability of particular modeling methods under different operation regimes is summarized to appropriately model TPV systems in a variety of conditions. The profile of photon chemical potential characterizes the luminescent effect of thermophotovoltaic cells, which is inappropriately assumed by conventional modeling methods. An iterative method is developed to solve the coupled photon and charge transport problem by combining the fluctuational electrodynamics with the drift-diffusion model. Detailed profile of photon chemical potential in the semiconductor devices is obtained with this iterative solver, enabling a more accurate performance prediction of near-field thermophotovoltaic cells than the conventional detailed balance analysis. The photogeneration profile of a thermophotovoltaic cell could be enhanced by optimizing systematic parameters related to geometric structure. An asymmetric Fabry-Perot cavity structure is designed to investigate the near-field coherent absorption, which could potentially increase the photon absorption by tuning the junction location and doping level of a pn junction. A silicon-based near-field thermophotovoltaic cell is proposed, and will be fabricated and characterized to illustrate the near-field effect on the performance of thermophotovoltaic cells.