Advanced methods for light trapping in optically thin silicon solar cells

The fi eld of light trapping is the study of how best to absorb light in a thin fi lm of material when most light either reflects away at the surface or transmits straight through to the other side. This has tremendous application to the fi eld of photovoltaics where thin silicon fi lms can be manufactured cheaply, but also fail to capture all of the available photons in the solar spectrum. Advancements in light trapping therefore bring us closer to the day when photovoltaic devices may reach grid parity with traditional fossil fuels on the electrical energy market. This dissertation advances our understanding of light trapping by fi rst modeling the eff ects of loss in planar dielectric waveguides. The mathematical framework developed here can be used to model any arbitrary three-layer structure with mixed gain or loss and then extract the total fi eld solution for the guided modes. It is found that lossy waveguides possess a greater number of eigenmodes than their lossless counterparts, and that these \loss guided" modes attenuate much more rapidly than conventional modes. Another contribution from this dissertation is the exploration of light trapping through the use of dielectric nanospheres embedded directly within the active layer of a thin silicon fi lm. The primary benefi t to this approach is that the device can utilize a surface nitride layer serving as an antireflective coating while still retaining the benefi ts of light trapping within the fi lm. The end result is that light trapping and light injection are eff ectively decoupled from each other and may be independently optimized within a single photovoltaic device. The fi nal contribution from this work is a direct numerical comparison between multiple light trapping schemes. This allows us to quantify the relative performances of various design techniques against one another and objectively determine which ideas tend to capture the most light. Using numerical simulation, this work directly compares the absorption gains due to embedded nanoparticles, surface text;ures, antireflective coatings, and plasmonic nanospheres. This work also introduces a new mathematical metric for dierentiating between index matching and angular scattering at a text;ured surface. Such information will prove useful in guiding future scientfi c eff orts in the fields of light trapping and light management in thin fi lm photovoltaics.