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- All Subjects: Nanostructures
Description
As existing solar cell technologies come closer to their theoretical efficiency, new concepts that overcome the Shockley-Queisser limit and exceed 50% efficiency need to be explored. New materials systems are often investigated to achieve this, but the use of existing solar cell materials in advanced concept approaches is compelling for multiple theoretical and practical reasons. In order to include advanced concept approaches into existing materials, nanostructures are used as they alter the physical properties of these materials. To explore advanced nanostructured concepts with existing materials such as III-V alloys, silicon and/or silicon/germanium and associated alloys, fundamental aspects of using these materials in advanced concept nanostructured solar cells must be understood. Chief among these is the determination and predication of optimum electronic band structures, including effects such as strain on the band structure, and the material's opto-electronic properties. Nanostructures have a large impact on band structure and electronic properties through quantum confinement. An additional large effect is the change in band structure due to elastic strain caused by lattice mismatch between the barrier and nanostructured (usually self-assembled QDs) materials. To develop a material model for advanced concept solar cells, the band structure is calculated for single as well as vertical array of quantum dots with the realistic effects such as strain, associated with the epitaxial growth of these materials. The results show significant effect of strain in band structure. More importantly, the band diagram of a vertical array of QDs with different spacer layer thickness show significant change in band offsets, especially for heavy and light hole valence bands when the spacer layer thickness is reduced. These results, ultimately, have significance to develop a material model for advance concept solar cells that use the QD nanostructures as absorbing medium. The band structure calculations serve as the basis for multiple other calculations. Chief among these is that the model allows the design of a practical QD advanced concept solar cell, which meets key design criteria such as a negligible valence band offset between the QD/barrier materials and close to optimum band gaps, resulting in the predication of optimum material combinations.
ContributorsDahal, Som Nath (Author) / Honsberg, Christiana (Thesis advisor) / Goodnick, Stephen (Committee member) / Roedel, Ronald (Committee member) / Ponce, Fernando (Committee member) / Arizona State University (Publisher)
Created2011
Description
A hybrid PV/T module was built, consisting of a thermal liquid heating system and a photovoltaic module system that combine in a hybrid format. This report will discuss the work on the project from Fall 2012 to Spring 2013 and the extended section on the economics for the Honors Thesis. Three stages of experiments were completed. Stage 1 showed our project was functional as we were able to verify our panel produced electricity and increased the temperature of water flowing in the system by 0.65°C. Stage 2 testing included “gluing” the flow system to the back of the panel resulting in an average increase of 4.76°C in the temperature of the water in the system. Stage 3 testing included adding insulating foam to the module which resulted in increasing the average temperature of the water in our flow system by 6.95°C. The economic calculations show the expected energy cost savings for Arizona residents.
ContributorsHaines, Brent Robert (Author) / Roedel, Ronald (Thesis director) / Aberle, James (Committee member) / Rauch, Dawson (Committee member) / Barrett, The Honors College (Contributor) / Electrical Engineering Program (Contributor)
Created2013-05
Description
Zinc telluride (ZnTe) is an attractive II-VI compound semiconductor with a direct
bandgap of 2.26 eV that is used in many applications in optoelectronic devices. Compared
to the two dimensional (2D) thin-film semiconductors, one-dimensional (1D)
nanowires can have different electronic properties for potential novel applications.
In this work, we present the study of ZnTe nanowires (NWs) that are synthesized
through a simple vapor-liquid-solid (VLS) method. By controlling the presence or
the absence of Au catalysts and controlling the growth parameters such as growth
temperature, various growth morphologies of ZnTe, such as thin films and nanowires
can be obtained. The characterization of the ZnTe nanostructures and films was
performed using scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy
(EDX), high- resolution transmission electron microscope (HRTEM), X-ray
diffraction (XRD), photoluminescence (PL), Raman spectroscopy and light scattering
measurement. After confirming the crystal purity of ZnTe, two-terminal diodes and
three-terminal transistors were fabricated with both nanowire and planar nano-sheet
configurations, in order to correlate the nanostructure geometry to device performance
including field effect mobility, Schottky barrier characteristics, and turn-on
characteristics. Additionally, optoelectronic properties such as photoconductive gain
and responsivity were compared against morphology. Finally, ZnTe was explored in
conjunction with ZnO in order to form type-II band alignment in a core-shell nanostructure.
Various characterization techniques including scanning electron microscopy,
energy-dispersive X-ray spectroscopy , x-ray diffraction, Raman spectroscopy, UV-vis
reflectance spectra and photoluminescence were used to investigate the modification
of ZnO/ZnTe core/shell structure properties. In PL spectra, the eliminated PL intensity
of ZnO wires is primarily attributed to the efficient charge transfer process
occurring between ZnO and ZnTe, due to the band alignment in the core/shell structure. Moreover, the result of UV-vis reflectance spectra corresponds to the band
gap energy of ZnO and ZnTe, respectively, which confirm that the sample consists of
ZnO/ZnTe core/shell structure of good quality.
bandgap of 2.26 eV that is used in many applications in optoelectronic devices. Compared
to the two dimensional (2D) thin-film semiconductors, one-dimensional (1D)
nanowires can have different electronic properties for potential novel applications.
In this work, we present the study of ZnTe nanowires (NWs) that are synthesized
through a simple vapor-liquid-solid (VLS) method. By controlling the presence or
the absence of Au catalysts and controlling the growth parameters such as growth
temperature, various growth morphologies of ZnTe, such as thin films and nanowires
can be obtained. The characterization of the ZnTe nanostructures and films was
performed using scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy
(EDX), high- resolution transmission electron microscope (HRTEM), X-ray
diffraction (XRD), photoluminescence (PL), Raman spectroscopy and light scattering
measurement. After confirming the crystal purity of ZnTe, two-terminal diodes and
three-terminal transistors were fabricated with both nanowire and planar nano-sheet
configurations, in order to correlate the nanostructure geometry to device performance
including field effect mobility, Schottky barrier characteristics, and turn-on
characteristics. Additionally, optoelectronic properties such as photoconductive gain
and responsivity were compared against morphology. Finally, ZnTe was explored in
conjunction with ZnO in order to form type-II band alignment in a core-shell nanostructure.
Various characterization techniques including scanning electron microscopy,
energy-dispersive X-ray spectroscopy , x-ray diffraction, Raman spectroscopy, UV-vis
reflectance spectra and photoluminescence were used to investigate the modification
of ZnO/ZnTe core/shell structure properties. In PL spectra, the eliminated PL intensity
of ZnO wires is primarily attributed to the efficient charge transfer process
occurring between ZnO and ZnTe, due to the band alignment in the core/shell structure. Moreover, the result of UV-vis reflectance spectra corresponds to the band
gap energy of ZnO and ZnTe, respectively, which confirm that the sample consists of
ZnO/ZnTe core/shell structure of good quality.
ContributorsPeng, Jhih-hong (Author) / Yu, Hongbin (Thesis advisor) / Roedel, Ronald (Committee member) / Goryll, Michael (Committee member) / Zhao, Yuji (Committee member) / Arizona State University (Publisher)
Created2017