Design of spectrally selective coatings for high efficiency power generation devices

Abstract

This thesis is aimed at designing and optimizing spectrally selective emitters/ filters for optical or thermal applications such as thermophotovoltaic (TPV) devices. Using spectrally selective emitters/filters in these devices is a crucial step to approach to an optimum system. Design of a spectrally selective filter based on one-dimensional Si/SiO2 layers is considered first for improved performance of TPV devices. Spec trally selective filters transmit only the convertible radiation from the emitter as non convertible radiation leads to a reduction in cell efficiency due to heating. The presented Si/SiO2 based filter concept reflects the major part of the unconvertible range back to the emitter to minimize energy required for the process and it is adaptable to differ ent types of cells and emitters with different temperatures since its cut-off wavelength can be tuned. While this study mainly focuses on InGaSb based TPV cell, Si, GaSb, and Ga0.78In0.22As0.19Sb0.81 based cells are also examined. The simulations show that significant enhancement in the overall system and device efficiency is possible by using such filters with TPV devices. In addition, graphene based spectrally selective nano structures are theoretically investigated to achieve absorption and transmission within narrow wavelength bands. Two concepts are identified to control the spectral ab sorptance and transmittance and the results showed that using these two-dimensional, multi-layered structures, with gratings and graphene layers narrow-band absorptance and transmittance can be achieved. The effect of the graphene layer is identified for the emitter structure using power dissipation profiles. The suggested filter structure is then optimized for a TPV system and it is shown that the overall TPV system efficiency can be improved by using the optimized filter. The methodology described in this thesis allows for an improved emitters/filters d