Browsing by Subject "characterization"

Now showing 1 - 3 of 3
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    Device Modeling and Characterization for CIGS Solar Cells
    (2013-06) Song, Sang
    We studied the way to achieve high efficiency and low cost of CuIn1-xGaxSe2 (CIGS) solar cells. The Fowler-Nordheim (F-N) tunneling currents at low bias decreased the shunt resistances and degraded the fill factor and efficiency. The activation energies of majority traps were directly related with F-N tunneling currents by the energy barriers. Air anneals decreased the efficiency from 7.74% to 5.18% after a 150�C, 1000 hour anneal. The decrease of shunt resistance due to F-N tunneling and the increase of series resistance degrade the efficiencies of solar cells. Air anneal reduces the free carrier densities by the newly generated Cu interstitial defects (Cui). Mobile Cui defects induce the metastability in CIGS solar cell. Since oxygen atoms are preferred to passivate the Se vacancies thus Cu interstitial defects explains well metastability of CIGS solar cells. Lattice mismatch and misfit stress between layers in CIGS solar cells can explain the particular effects of CIGS solar cells. The misfits of 35.08o rotated (220/204) CIGS to r-plane (102) MoSe2 layers are 1% ~ -4% lower than other orientation and the lattice constants of two layers in short direction are matched at Ga composition x=0.35. This explains well the preferred orientation and the maximum efficiency of Ga composition effects. Misfit between CIGS and CdS generated the dislocations in CdS layer as the interface traps. Thermionic emission currents due to interface traps limit the open circuit voltage at high Ga composition. The trap densities were calculated by critical thickness and dislocation spacing and the numerical device simulation results were well matched with the experimental results. A metal oxide broken-gap p-n heterojunction is suggested for tunnel junction for multi-junction polycrystalline solar cells and we examined the characteristics of broken-gap tunnel junction by numerical simulation. Ballistic transport mechanism explains well I-V characteristics of broken-gap junction. P-type Cu2O and n-type In2O3 broken-gap heterojunction is effective with the CIGS tandem solar cells. The junction has linear I-V characteristics with moderate carrier concentration (2�1017 cm-3) and the resistance is lower than GaAs tunnel junction. The efficiency of a CGS/CIS tandem solar cells was 24.1% with buffer layers. And no significant degradations are expected due to broken gap junction.
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    Engineering Materials and Characterization Methods for Mass-produced Plasmonic Devices
    (2017-05) Otto, Lauren
    Over the last decade, plasmonic devices have seen considerable attention, and while there has been significant scientific advancement for plasmonic devices in the laboratory, there still are no industrially produced, high-tech devices which incorporate plasmonics on the market. Industry is in need of robust characterization methods for the development of near-field based devices en route to final product manufacturing lines as well as stable plasmonic materials that can easily be integrated into existing complex process flows. In this dissertation, original research that opens up doors for mass-produced plasmonic devices is presented. Engineered characterization methods include the development of a theoretical model for the prediction of scattering scanning near-field optical microscopy behavior of plasmonic devices, the use of this near-field characterization technique together with scanning electron microscopy cathodoluminescence to perform complete and convergent characterization of plasmonic excitation and coupled near-field emission. Engineered materials are centered on plasma-enhanced atomic layer deposited titanium nitride, discovering its chemistry and behavior under a variety of conditions, and demonstrating its fabricability as both two dimensional etched structures and three dimensional coatings of complex shapes.
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    Functionalization of Magnetic Nanoparticles with Deoxynucleotide Triphosphates for Utilization in DNA Sequencing
    (2023-02) Nazareth, Calvin
    Current methods for DNA sequencing leave a lot to be desired. There is immense research focused on developing methods to sequence longer and larger samples of DNA and to do so more rapidly. One possible new approach to DNA sequencing uses magnetically labeled deoxynucleotide triphosphates (dNTPs) as the complimentary bases for a sequencing-by-synthesis approach. The polymerase in this system would be immobilized on a sensor so that when the nucleotide is attached to the growing strand, the sensor can detect the signal. As the polymerase completes the strand for DNA extension, the signal from each magnetic nanoparticle (MNP) is recognized and generates a sequence.The contents of this thesis provide results for two critical initial steps in developing the proposed method. Firstly, we attached dNTPs to magnetic nanoparticles to create dNTP-MNP conjugates. We attempted two methods of conjugation with numerous characterization techniques to confirm the attachment. Secondly, we studied how the dNTP-MNP conjugation affected the dNTPs in quantitative polymerase chain reaction (qPCR) to model how they would interact with a polymerase in a hypothetical sequencer. The characterization results confirmed the conjugation of the dNTP to the MNP. qPCR was performed with various conditions and solvents which led to the conclusion that the MNP conjugation does not hinder polymerase interaction with the dNTP. This is a crucial result for the development of such a sequencer by providing the groundwork for the continuation of the project.