Matching Items (4)
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- All Subjects: solar
- Creators: Goodnick, Stephen
Description
In this thesis, a novel silica nanosphere (SNS) lithography technique has been developed to offer a fast, cost-effective, and large area applicable nano-lithography approach. The SNS can be easily deposited with a simple spin-coating process after introducing a N,N-dimethyl-formamide (DMF) solvent which can produce a highly close packed SNS monolayer over large silicon (Si) surface area, since DMF offers greatly improved wetting, capillary and convective forces in addition to slow solvent evaporation rate. Since the period and dimension of the surface pattern can be conveniently changed and controlled by introducing a desired size of SNS, and additional SNS size reduction with dry etching process, using SNS for lithography provides a highly effective nano-lithography approach for periodically arrayed nano-/micro-scale surface patterns with a desired dimension and period. Various Si nanostructures (i.e., nanopillar, nanotip, inverted pyramid, nanohole) are successfully fabricated with the SNS nano-lithography technique by using different etching technique like anisotropic alkaline solution (i.e., KOH) etching, reactive-ion etching (RIE), and metal-assisted chemical etching (MaCE).
In this research, computational optical modeling is also introduced to design the Si nanostructure, specifically nanopillars (NPs) with a desired period and dimension. The optical properties of Si NP are calculated with two different optical modeling techniques, which are the rigorous coupled wave analysis (RCWA) and finite-difference time-domain (FDTD) methods. By using these two different optical modeling techniques, the optical properties of Si NPs with different periods and dimensions have been investigated to design ideal Si NP which can be potentially used for thin c-Si solar cell applications. From the results of the computational and experimental work, it was observed that low aspect ratio Si NPs fabricated in a periodic hexagonal array can provide highly enhanced light absorption for the target spectral range (600 ~ 1100nm), which is attributed to (1) the effective confinement of resonant scattering within the Si NP and (2) increased high order diffraction of transmitted light providing an extended absorption length. From the research, therefore, it is successfully demonstrated that the nano-fabrication process with SNS lithography can offer enhanced lithographical accuracy to fabricate desired Si nanostructures which can realize enhanced light absorption for thin Si solar cell.
In this research, computational optical modeling is also introduced to design the Si nanostructure, specifically nanopillars (NPs) with a desired period and dimension. The optical properties of Si NP are calculated with two different optical modeling techniques, which are the rigorous coupled wave analysis (RCWA) and finite-difference time-domain (FDTD) methods. By using these two different optical modeling techniques, the optical properties of Si NPs with different periods and dimensions have been investigated to design ideal Si NP which can be potentially used for thin c-Si solar cell applications. From the results of the computational and experimental work, it was observed that low aspect ratio Si NPs fabricated in a periodic hexagonal array can provide highly enhanced light absorption for the target spectral range (600 ~ 1100nm), which is attributed to (1) the effective confinement of resonant scattering within the Si NP and (2) increased high order diffraction of transmitted light providing an extended absorption length. From the research, therefore, it is successfully demonstrated that the nano-fabrication process with SNS lithography can offer enhanced lithographical accuracy to fabricate desired Si nanostructures which can realize enhanced light absorption for thin Si solar cell.
ContributorsChoi, JeaYoung (Author) / Honsberg, Christiana (Thesis advisor) / Alford, Terry (Thesis advisor) / Goodnick, Stephen (Committee member) / Arizona State University (Publisher)
Created2015
Description
A primary motivation of research in photovoltaic technology is to obtain higher efficiency photovoltaic devices at reduced cost of production so that solar electricity can be cost competitive. The majority of photovoltaic technologies are based on p-n junction, with efficiency potential being much lower than the thermodynamic limits of individual technologies and thereby providing substantial scope for further improvements in efficiency. The thesis explores photovoltaic devices using new physical processes that rely on thin layers and are capable of attaining the thermodynamic limit of photovoltaic technology. Silicon heterostructure is one of the candidate technologies in which thin films induce a minority carrier collecting junction in silicon and the devices can achieve efficiency close to the thermodynamic limits of silicon technology. The thesis proposes and experimentally establishes a new theory explaining the operation of silicon heterostructure solar cells. The theory will assist in identifying the optimum properties of thin film materials for silicon heterostructure and help in design and characterization of the devices, along with aiding in developing new devices based on this technology. The efficiency potential of silicon heterostructure is constrained by the thermodynamic limit (31%) of single junction solar cell and is considerably lower than the limit of photovoltaic conversion (~ 80 %). A further improvement in photovoltaic conversion efficiency is possible by implementing a multiple quasi-fermi level system (MQFL). A MQFL allows the absorption of sub band gap photons with current being extracted at a higher band-gap, thereby allowing to overcome the efficiency limit of single junction devices. A MQFL can be realized either by thin epitaxial layers of alternating higher and lower band gap material with nearly lattice matched (quantum well) or highly lattice mismatched (quantum dot) structure. The thesis identifies the material combination for quantum well structure and calculates the absorption coefficient of a MQFl based on quantum well. GaAsSb (barrier)/InAs(dot) was identified as a candidate material for MQFL using quantum dot. The thesis explains the growth mechanism of GaAsSb and the optimization of GaAsSb and GaAs heterointerface.
ContributorsGhosha, Kuṇāla (Author) / Bowden, Stuart (Thesis advisor) / Honsberg, Christiana (Thesis advisor) / Vasileska, Dragica (Committee member) / Goodnick, Stephen (Committee member) / Arizona State University (Publisher)
Created2011
Description
The project described here is a solar powered intrusion detection system consisting of three modules: a battery recharging circuit, a laser emitter and photodetector pair, and a Wi- Fi connectivity board. Over the preceding seven months, great care has been taken for the design and construction of this system. The first three months were spent researching and selecting suitable IC's and external components (e.g. solar panel, batteries, etc.). Then, the next couple of months were spent ordering specific materials and equipment for the construction of our prototype. Finally, the last two months were used to build a working prototype, with a substantial amount of time used for perfecting our system's packaging and operation. This report will consist of a detailed discussion of our team's research, design activities, prototype implementation, final budget, and final schedule. Technical discussion of the concepts behind our design will assist with understanding the design activities and prototype implementation sections that will follow. Due to the generous funding of the group from the Barrett Honors College, our overall budget available for the project was $1600. Of that amount, only $334.51 was spent on the actual system components, with $829.42 being spent on the equipment and materials needed for the testing and construction of the prototype. As far as the schedule goes, we are essentially done with the project. The only tasks left to finish are a successful defense of the project at the oral presentation on Friday, 29 March 2013, followed by a successful demo on 26 April 2013.
ContributorsTroyer, Nicole L. (Co-author) / Shtayer, Idan (Co-author) / Guise, Chris (Co-author) / Kozicki, Michael (Thesis director) / Roedel, Ronald (Committee member) / Goodnick, Stephen (Committee member) / Barrett, The Honors College (Contributor) / Electrical Engineering Program (Contributor)
Created2013-05
Description
This study focuses on the implications of a high reverse bias breakdown in silicon heterojunction cells (SHJ). In relevant literature, there is a lack of explicit investigation which
compares high breakdown voltage cells (commonly SHJ) to low breakdown voltage cells
(commonly silicon homojunctions) in an installation setting. In addition, their relationship with
shading and how they react with bypass diodes are also not very prevalent. Therefore, my project
dives into how shading impacts a string of high breakdown voltage cells and a string of low
breakdown voltage cells, as well as how those cells interact with a bypass diode.
In order to conduct this investigation, I used the simulation software LTSpice XVII to
create an accurate simulation model of a SHJ cell with a 21 V reverse breakdown voltage. With
this cell model, I strung 10 cells together, and varied the shading on a single cell while measuring
the string’s output current, voltage, and power. Next, I attached a bypass diode to the shaded
cell, and continued to increase the number of cells attached to the bypass diode while continuing
to examine the string’s output. Once I gathered this data, I modified the original cell model to
have a lower reverse breakdown voltage of 5 V. From here, I strung 10 cells together again, and
repeated the same measurements from the 21 V string.
Upon completing these measurements, I found that the SHJ cells were in fact harder to
force into reverse bias than the cells with the lower reverse breakdown voltage, suggesting that
solar installation owners should consider transitioning to SHJ-based modules. When bypass
diodes are being considered, my results demonstrated that heavy shading (about 65% and
higher) was required for the bypass diodes to have an observable impact on the string’s power
output. Therefore, owners should consider how severe the shading their installation may receive
before investing in bypass diodes. If owners do find the need for the bypass diodes, my findings
also show that the diodes should be used sparingly and in a compromise with output power and
cost.
ContributorsAvalos, Christian (Author) / Honsberg, Christiana (Thesis advisor) / Bowden, Stuart (Committee member) / Goodnick, Stephen (Committee member) / Arizona State University (Publisher)
Created2023