Design, Simulation, and Solution Processing of Spectrally-Selective Mirrors for Luminescent Solar Concentrators

Abstract

This thesis investigates the design, simulation, and solution processing of spectrally-selective mirrors for use in Luminescent Solar Concentrators (LSCs). Luminescent Solar Concentrators are transparent photovoltaic devices that can be applied to windows. Photons incident on the LSC are absorbed by luminophores within the device, which then emit photons at longer wavelengths (via photoluminescence). This light is then internally reflected across the LSC waveguide to its edges wherephotovoltaic cells are located, which convert the light to electricity. Some photons that are emitted by luminophores do not remain in the waveguide; if the photons are emitted at an angle less than the critical angle (determined by the refractive index surrounding mediums) they are lost to the environment. This reduces the efficiency of the LSC substantially. To improve this trapping efficiency, spectrally-selective mirrors can be placed above and below the waveguide in order to reflect escaped photons back into the device, so they potentially reach the photovoltaic cells. These spectrally-selective mirrors are composed of ultra-thin-film layers of alternating high and low refractive index materials, forming a 1D photonic crystal. The mirror design is dependent on the thickness and refractive index of each layer, and manipulating these parameters results in different reflectivity spectra. Using Monte Carlo and analytical models to simulate LSCs with spectrally-selective mirrors, designs are evaluated and optimized to best improve the optical efficiency of this particular LSC, with its particular dimensions and composition. Concurrently, thin-films of dielectric material are fabricated via sol-gel synthesis and solution-processing techniques such as spin-coating, doctor-blading, and bar coating. These films and their optical properties are then evaluated and characterized using spectroscopic ellipsometry. The work presented in this thesis weaves together fundamental aspects of thin-film design, simulation, and fabrication to develop a framework for creating efficient, aesthetically adequate, and readily producible Luminescent Solar Concentrators.