ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
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- All Subjects: Alternative Energy
- Creators: Goodnick, Stephen
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
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