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Description
With renewable energy on the rise, researchers have turned their funding and their focus towards new solar cell technologies, and perovskites are a major source of interest. This class of materials is particularly interesting due to their quick, simple synthesis as well as their physical and electrical superiority when compared to current silicon-based solar cells. Through this thesis, we will explore the synthesis of various types of perovskites and their subsequent characterization, which includes optical microscopy, photoluminescence spectroscopy, Raman microscopy, and X-ray diffraction. Analyzing two different perovskites both before and after a two-week period of storage revealed that while synthesis is indeed experiment-friendly, these materials have a concerning lack of stability even in ideal conditions.
ContributorsBuzas, Benjamin Joseph (Author) / Tongay, Sefaattin (Thesis director) / Muhich, Christopher (Committee member) / Materials Science and Engineering Program (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2020-05
Description
Thin film solar cells are based on polycrystalline materials that contain a high concentration of intrinsic and extrinsic defects. Improving the device efficiency in such systems relies on understanding the nature of defects - whether they are positive, negative, or neutral in their influence - and their sources in order to engineer optimized absorbers. Oftentimes, these are studied individually, as characterization techniques are limited in their ability to directly relate material properties in individual layers to their impact on the actual device performance. Expanding the tools available for increased understanding of materials and devices has been critical for reducing the translation time of laboratory-scale research to changes in commercial module manufacturing lines. The use of synchrotron X-ray fluorescence (XRF) paired with X-ray beam induced current and voltage (XBIC, XBIV respectively) has proven to be an effective technique for understanding the impact of material composition and inhomogeneity on solar cell device functioning. The combination of large penetration depth, small spot size, and high flux allows for the measurement of entire solar cell stacks with high spatial resolution and chemical sensitivity. In this work, I combine correlative XRF/XBIC/XBIV with other characterization approaches across varying length scales, such as micro-Raman spectroscopy and photoluminescence, to understand how composition influences device performance in thin films. The work described here is broken into three sections. Firstly, understanding the influence of KF post-deposition treatment (PDT) and the use of Ag-alloying to reduce defect density in the Ga-free material system, CuInSe2 (CIS). Next, applying a similar characterization workflow to industrially relevant Ga-containing Cu(In1-xGax)Se2 (CIGS) modules with Ag and KF-PDT. The influence of light soaking and dark heat exposure on the modules are also studied in detail. Results show that Ag used with KF-PDT in CIS causes undesirable cation ordering at the CdS interface and affects the device through increased potential fluctuations. The results also demonstrate the importance of tuning the concentration of KF-PDT used when intended to be used in Ag-alloyed devices. Commercially-processed modules with optimized Ag and KF concentrations are shown to have the device performance instead be dominated by variations in the CIGS composition itself. In particular, changes in Cu and Se concentrations are found to be most influential on the device response to accelerated stressors such as dark heat exposure and light soaking. In the final chapter, simulations of nano-scale XBIC and XBIV are done to contribute to the understanding of these measurements.
ContributorsNietzold, Tara (Author) / Bertoni, Mariana I. (Thesis advisor) / Holt, Martin (Committee member) / Shafarman, William N. (Committee member) / Tongay, Sefaattin (Committee member) / Arizona State University (Publisher)
Created2021
Description
This paper begins with an introduction to the topics relevant to the research presented. Properties of diamond, diamond’s ability to be used in power electronics compared to other semiconducting materials, and a brief overview of field effect transistors are among the topics discussed. The remainder of the paper centers around research that has been conducted on seven diamond samples. Interface characterization was performed on two diamond samples, one with a high boron incorporation epitaxial layer and another with a low boron incorporation epitaxial layer. UPS He I analysis and UPS He II analysis were used to construct band alignments for the two samples, which revealed no significant differences between their measured properties. A Python program designed to optimize XPS loss peak and UPS He II graphical data analysis is also discussed in detail. Next, Hall effect measurements are examined. Hall effect measurements were carried out on seven diamond samples, two of which have high boron incorporation epitaxial layers, two of which have low boron incorporation epitaxial layers, one of which has a moderate boron incorporation epitaxial layer, and two of which have a phosphorus-doped epitaxial layer. Hall measurements of the boron-doped samples revealed no significant differences in measured parameters amongst the samples with varying boron incorporation epitaxial layers, with the exception of an expected difference in measured carrier concentration proportional to the amount of dopant incorporation in the layers. Some samples with boron-doped epitaxial layers produced measurements indicating n-type charge carriers, which is unexpected given the p-type charge carriers within these samples. The phosphorus-doped samples were unable to be measured due to overly high resistance following an oxygen termination step, and this effect was functionally reversed following hydrogen termination of the samples. It is hypothesized that Fermi pinning is responsible for this effect. The paper concludes with a summary of data discussed in previous sections and a suggested direction for future research on this topic.
ContributorsJacobs, Madeleine (Author) / Nemanich, Robert (Thesis director) / Botana, Antia (Committee member) / Barrett, The Honors College (Contributor) / College of Integrative Sciences and Arts (Contributor)
Created2022-05
Description
The proposed research mainly focuses on employing tunable materials to achieve dynamic control of radiative heat transfer in both far and near fields for thermal management. Vanadium dioxide (VO2), which undergoes a phase transition from insulator to metal at the temperature of 341 K, is one tunable material being applied. The other one is graphene, whose optical properties can be tuned by chemical potential through external bias or chemical doping.
In the far field, a VO2-based metamaterial thermal emitter with switchable emittance in the mid-infrared has been theoretically studied. When VO2 is in the insulating phase, high emittance is observed at the resonance frequency of magnetic polaritons (MPs), while the structure becomes highly reflective when VO2 turns metallic. A VO2-based thermal emitter with tunable emittance is also demonstrated due to the excitation of MP at different resonance frequencies when VO2 changes phase. Moreover, an infrared thermal emitter made of graphene-covered SiC grating could achieve frequency-tunable emittance peak via the change of the graphene chemical potential.
In the near field, a radiation-based thermal rectifier is constructed by investigating radiative transfer between VO2 and SiO2 separated by nanometer vacuum gap distances. Compared to the case where VO2 is set as the emitter at 400 K as a metal, when VO2 is considered as the receiver at 300 K as an insulator, the energy transfer is greatly enhanced due to the strong surface phonon polariton (SPhP) coupling between insulating VO2 and SiO2. A radiation-based thermal switch is also explored by setting VO2 as both the emitter and the receiver. When both VO2 emitter and receiver are at the insulating phase, the switch is at the “on” mode with a much enhanced heat flux due to strong SPhP coupling, while the near-field radiative transfer is greatly suppressed when the emitting VO2 becomes metallic at temperatures higher than 341K during the “off” mode. In addition, an electrically-gated thermal modulator made of graphene covered SiC plates is theoretically studied with modulated radiative transport by varying graphene chemical potential. Moreover, the MP effect on near-field radiative transport has been investigated by spectrally enhancing radiative heat transfer between two metal gratings.
In the far field, a VO2-based metamaterial thermal emitter with switchable emittance in the mid-infrared has been theoretically studied. When VO2 is in the insulating phase, high emittance is observed at the resonance frequency of magnetic polaritons (MPs), while the structure becomes highly reflective when VO2 turns metallic. A VO2-based thermal emitter with tunable emittance is also demonstrated due to the excitation of MP at different resonance frequencies when VO2 changes phase. Moreover, an infrared thermal emitter made of graphene-covered SiC grating could achieve frequency-tunable emittance peak via the change of the graphene chemical potential.
In the near field, a radiation-based thermal rectifier is constructed by investigating radiative transfer between VO2 and SiO2 separated by nanometer vacuum gap distances. Compared to the case where VO2 is set as the emitter at 400 K as a metal, when VO2 is considered as the receiver at 300 K as an insulator, the energy transfer is greatly enhanced due to the strong surface phonon polariton (SPhP) coupling between insulating VO2 and SiO2. A radiation-based thermal switch is also explored by setting VO2 as both the emitter and the receiver. When both VO2 emitter and receiver are at the insulating phase, the switch is at the “on” mode with a much enhanced heat flux due to strong SPhP coupling, while the near-field radiative transfer is greatly suppressed when the emitting VO2 becomes metallic at temperatures higher than 341K during the “off” mode. In addition, an electrically-gated thermal modulator made of graphene covered SiC plates is theoretically studied with modulated radiative transport by varying graphene chemical potential. Moreover, the MP effect on near-field radiative transport has been investigated by spectrally enhancing radiative heat transfer between two metal gratings.
ContributorsYang, Yue (Author) / Wang, Liping (Thesis advisor) / Phelan, Patrick (Committee member) / Wang, Robert (Committee member) / Tongay, Sefaattin (Committee member) / Rykaczewski, Konrad (Committee member) / Arizona State University (Publisher)
Created2016
Description
A Fundamental study of bulk, layered, and monolayers bromide lead perovskites structural, optical, and electrical properties have been studied as thickness changes. X-Ray Diffraction (XRD) and Raman spectroscopy measures the structural parameter showing how the difference in the thicknesses changes the crystal structures through observing changes in average lattice constant, atomic spacing, and lattice vibrations.
Optical and electrical properties have also been studied mainly focusing on the thickness effect on different properties where the Photoluminescence (PL) and exciton binding energies show energy shift as thickness of the material changes. Temperature dependent PL has shown different characteristics when comparing methylammonium lead bromide (MAPbBr3) to butylammonium lead bromide (BA2PbBr4) and comparing the two layered n=1 materials butylammonium lead bromide (BA2PbBr4) to butylammonium lead iodide (BA2PbI4). Time-resolved spectroscopy displays different lifetimes as thickness of bromide-based perovskite changes. Finally, thickness dependence (starting from monolayers) Kelvin Probe Force Microscopy (KPFM) of the layered materials BA2PbBr4, Butylammonium(methylammonium)lead bromide (BA2MAPb2Br7), and molybdenum sulfide (MoS2) were studied showing an exponential relation between the thickness of the materials and their surface potentials.
Optical and electrical properties have also been studied mainly focusing on the thickness effect on different properties where the Photoluminescence (PL) and exciton binding energies show energy shift as thickness of the material changes. Temperature dependent PL has shown different characteristics when comparing methylammonium lead bromide (MAPbBr3) to butylammonium lead bromide (BA2PbBr4) and comparing the two layered n=1 materials butylammonium lead bromide (BA2PbBr4) to butylammonium lead iodide (BA2PbI4). Time-resolved spectroscopy displays different lifetimes as thickness of bromide-based perovskite changes. Finally, thickness dependence (starting from monolayers) Kelvin Probe Force Microscopy (KPFM) of the layered materials BA2PbBr4, Butylammonium(methylammonium)lead bromide (BA2MAPb2Br7), and molybdenum sulfide (MoS2) were studied showing an exponential relation between the thickness of the materials and their surface potentials.
ContributorsAlenezi, Omar (Author) / Tongay, Sefaattin (Thesis advisor) / King, Richard (Thesis advisor) / Yao, Yu (Committee member) / Arizona State University (Publisher)
Created2019