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nanoengineered energy harvesting and storage devices
Title
nanoengineered energy harvesting and storage devices.
Creator
Li, Chao, Thomas, Jayan, Zhai, Lei, Yang, Yang, Gesquiere, Andre, Dong, Yajie, Sun, Wei, University of Central Florida
Abstract / Description
Organic and perovskite solar cells have recently attracted significant attention due to itsflexibility, ease of fabrication and excellent performance. In order to realize even betterperformance for organic and perovskite solar cells, rejuvenated effort towards developingnanostructured electrodes and high quality active layer is necessary.In this dissertation, several strategic directions of enhancing the performance of organicand perovskite solar cells are investigated. An introduction and...
Show moreOrganic and perovskite solar cells have recently attracted significant attention due to itsflexibility, ease of fabrication and excellent performance. In order to realize even betterperformance for organic and perovskite solar cells, rejuvenated effort towards developingnanostructured electrodes and high quality active layer is necessary.In this dissertation, several strategic directions of enhancing the performance of organicand perovskite solar cells are investigated. An introduction and background of organic andperovskite solar cells, which includes motivation, classification and working principles,nanostructured electrode materials and solvent effect on active materials, and devices fabrication,are presented. A facile method, called Spin-on Nanoprinting (SNAP), to fabricate highly orderedZnO-AgNW-ZnO electrode is introduced to enhance the performance of organic solar cell.Subsequently, a ternary solvent method is developed to fabricate high Voc thieno[3,4-b]thiophene/benzodithiophene (PTB7) and indene-C60 bisadduct (ICBA)solar cells. Theperformance of the devices improved about 20% compared to those made by binary solventmethod. In order to understand the fundamental properties of the materials ruling theperformance of the PSCs tested, AFM-based nanoscale characterization techniques includingPulsed-Force-Mode AFM (PFM-AFM) and Mode-Synthesizing AFM (MSAFM) are introduced.These methods are used to study the morphology and physical properties of the structuresconstitutive of the active layers of the PSCs. Conductive-AFM (cAFM) studies reveal localvariations in conductivity in the donor and acceptor phases as well as an increase in photocurrentmeasured in the PTB7:ICBA sample obtained with the ternary solvent processing technique.Moreover, efficient perovskite solar cells with good transparency in the visible wavelength rangehave been developed by a facile and low-temperature PCBM-assisted perovskite growth method.This method results in the formation of perovskite-PCBM hybrid material at the grain boundaries which is observed by EELS mapping and confirmed by steady-state photoluminescence (PL)spectra and transient photocurrent (TP) measurements. This method involves fewer steps andtherefore is less expensive and time consuming than other reported methods. In addition, wereport an all solid state, energy harvesting and storing (ENHANS) filament which integratesperovskite solar cell (PSC) on top of a symmetric supercapacitor (SSC) via a copper filamentwhich works as a shared electrode for direct charge transfer. Developing ENHANS on a copperfilament provides a low-cost solution for flexible self-sufficient energy systems for wearablesand other portable devices. Finally, a summary of this dissertation as well as some potentialfuture directions are presented.
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Date Issued
2016
Identifier
CFE0006693, ucf:51912
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006693
Complex-valued adaptive digital signal enhancement for applications in wireless communication systems
Title
Complex-valued adaptive digital signal enhancement for applications in wireless communication systems.
Creator
Liu, Ying, Mikhael, Wasfy, Batarseh, Issa, Yang, Thomas, Hunter, Matthew, Haralambous, Michael, Myers, Brent, University of Central Florida
Abstract / Description
In recent decades, the wireless communication industry has attracted a great deal of research efforts to satisfy rigorous performance requirements and preserve high spectral efficiency. Along with this trend, I/Q modulation is frequently applied in modern wireless communications to develop high performance and high data rate systems. This has necessitated the need for applying efficient complex-valued signal processing techniques to highly-integrated, multi-standard receiver devices.In this...
Show moreIn recent decades, the wireless communication industry has attracted a great deal of research efforts to satisfy rigorous performance requirements and preserve high spectral efficiency. Along with this trend, I/Q modulation is frequently applied in modern wireless communications to develop high performance and high data rate systems. This has necessitated the need for applying efficient complex-valued signal processing techniques to highly-integrated, multi-standard receiver devices.In this dissertation, novel techniques for complex-valued digital signal enhancement are presented and analyzed for various applications in wireless communications. The first technique is a unified block processing approach to generate the complex-valued conjugate gradient Least Mean Square (LMS) techniques with optimal adaptations. The proposed algorithms exploit the concept of the complex conjugate gradients to find the orthogonal directions for updating the adaptive filter coefficients at each iteration. Along each orthogonal direction, the presented algorithms employ the complex Taylor series expansion to calculate time-varying convergence factors tailored for the adaptive filter coefficients. The performance of the developed technique is tested in the applications of channel estimation, channel equalization, and adaptive array beamforming. Comparing with the state of the art methods, the proposed techniques demonstrate improved performance and exhibit desirable characteristics for practical use.The second complex-valued signal processing technique is a novel Optimal Block Adaptive algorithm based on Circularity, OBA-C. The proposed OBA-C method compensates for a complex imbalanced signal by restoring its circularity. In addition, by utilizing the complex Taylor series expansion, the OBA-C method optimally updates the adaptive filter coefficients at each iteration. This algorithm can be applied to mitigate the frequency-dependent I/Q mismatch effects in analog front-end. Simulation results indicate that comparing with the existing methods, OBA-C exhibits superior convergence speed while maintaining excellent accuracy. The third technique is regarding interference rejection in communication systems. The research on both LMS and Independent Component Analysis (ICA) based techniques continues to receive significant attention in the area of interference cancellation. The performance of the LMS and ICA based approaches is studied for signals with different probabilistic distributions. Our research indicates that the ICA-based approach works better for super-Gaussian signals, while the LMS-based method is preferable for sub-Gaussian signals. Therefore, an appropriate choice of interference suppression algorithms can be made to satisfy the ever-increasing demand for better performance in modern receiver design.
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Date Issued
2012
Identifier
CFE0004572, ucf:49192
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004572