Light trapping designs for thin silicon solar cells

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University of Delaware
With the increasing scarcity of fossil fuels and a general concern for the environmental impacts of carbon emissions and hazardous radiation, the need for clean renewable energy sources has become not only a national priority but also an issue of national security. Renewed interest in the development of solar electricity has led to the development of new avenues that address the issues of cost and efficiency associated with photovoltaics. One of the prominent approaches being explored is thin film solar cell technology, which offers prospects of lower material costs and increases the adaptability of solar cell design. The goal of this work is to increase the efficiency and versatility of thin film solar cell devices through the development of improved light trapping schemes. Enhanced light trapping schemes increase the absorption of light within solar cell devices and thereby increase the efficiency and ultimately reduce the cost per watt of energy produced. This thesis introduces the fundamental ideas behind the science of light trapping in thin silicon solar cells. The specific approach involves enhancing the light trapping capabilities, of the thin solar cells, by incorporating photonic device engineering concepts which include photonic crystals, diffraction gratings and antireflective coatings. These concepts are then used to develop novel light trapping designs that are applied to stand alone and multiple junction thin silicon solar cells. The new designs, that are developed, incorporate one dimensional photonic crystals as band pass filters that reflect short light wavelengths (400 – 1100 nm) and transmit longer wavelengths(1100 -1800 nm) at the interface between two adjacent cells. In addition, nano structured diffraction gratings that cut into the photonic crystal layers are incorporated to redirect incoming waves and hence increase the optical path length of light within the solar cells.