Using first principles Destiny Functional Theory methods to model the Seebeck coefficient of bulk silicon

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.Includes bibliographical references (leaves 27-28).Thermoelectrics are gaining significant amounts of attention considering their relevance today in the areas of sustainable energy generation and energy efficiency. In this thesis, the thermoelectric properties of bulk Silicon were modeled using ab initio density functional theory methods to determine the Si band structure. Specifically, three different models for determining the Seebeck coefficient - Parabolic Bands, Boltzmann's theory, and the 'Pudding Mold' approximation to Boltzmann's theory - were studied in depth and compared with experimental values. Here we show first principles calculations to yield Seebeck coefficients for n-type Silicon to be on the order of 300 gtV/K at -300 K, and -500 gtV/K at 300 K for the Parabolic Bands and Boltzmann approach, respectively. While the 'Pudding Mold' Theory failed in its approximations of the Seebeck coefficients, the calculations using the other two theories were found to agree closely with experimentally determined Seebeck coefficients.by Saahil Mehra.S.B

Efficiency Enhancement of Gallium Arsenide Photovoltaics Using Solution-Processed Zinc Oxide Nanoparticle Light Scattering Layers

We demonstrate a high-throughput, solution-based process for subwavelength surface texturing of a III-V compound solar cell. A zinc oxide (ZnO) nanoparticle ink is spray-coated directly on top of a gallium arsenide (GaAs) solar cell. The nanostructured ZnO films have demonstrated antireflection and light scattering properties over the visible/near-infrared (NIR) spectrum. The results show a broadband spectral enhancement of the solar cell external quantum efficiency (EQE), a 16% enhancement of short circuit current, and a 10% increase in photovoltaic efficiency

Low-Temperature Processed Ga-Doped ZnO Coatings from Colloidal Inks

We present a new colloidal synthesis of gallium-doped zinc oxide nanocrystals that are transparent in the visible and absorb in the near-infrared. Thermal decomposition of zinc stearate and gallium nitrate after hot injection of the precursors in a mixture of organic amines leads to nanocrystals with tunable properties according to gallium amount. Substitutional Ga3+ ions trigger a plasmonic resonance in the infrared region resulting from an increase in the free electrons concentration. These nanocrystals can be deposited by spin coating, drop casting, and spray coating resulting in homogeneous and high-quality thin films. The optical transmission of the Ga-ZnO nanoparticle assemblies in the visible is greater than 90%, and at the same time, the near-infrared absorption of the nanocrystals is maintained in the films as well. Several strategies to improve the films electrical and optical properties have been presented, such as UV treatments to remove the organic compounds responsible for the observed interparticle resistance and reducing atmosphere treatments on both colloidal solutions and thin films to increase the free carriers concentration, enhancing electrical conductivity and infrared absorption. The electrical resistance of the nanoparticle assemblies is about 30 k\u3a9/sq for the as-deposited, UV-exposed films, and it drops down to 300 \u3a9/sq after annealing in forming gas at 450 \ub0C, comparable with state of the art tin-doped indium oxide coatings deposited from nanocrystal inks