Development of Cd1-xMgxTe thin films for application as an electron reflector in CdS/CdTe solar cells
| dc.contributor.author | Kobyakov, Pavel S., author | |
| dc.contributor.author | Sampath, W. S., advisor | |
| dc.contributor.author | Sites, James R., committee member | |
| dc.contributor.author | Olsson, N. Anders, committee member | |
| dc.contributor.author | Williams, John D., committee member | |
| dc.date.accessioned | 2007-01-03T06:31:46Z | |
| dc.date.available | 2007-01-03T06:31:46Z | |
| dc.date.issued | 2014 | |
| dc.description.abstract | Efficiencies of CdS/CdTe photovoltaic cells significantly lag behind their theoretical limit, primarily because open-circuit voltage (VOC) of record efficiency cells (872 mV) is well below what is expected for the CdTe band gap (1.5 eV). A substantial VOC improvement can be achieved through addition of an electron reflector (ER) layer to CdTe devices. The ER layer forms a conduction-band barrier that reflects minority-charge carriers (i.e. electrons in p-type CdTe) away from the back surface. Similar to back-surface fields in c-Si, III-V, and CIGS solar cells, the ER strategy is expected to reduce back-surface recombination and is estimated to increase CdTe VOC by about 200 mV based on numerical simulation. The presented research investigates the addition of a thin layer of wider band gap Cd1-xMgxTe (CMT) to achieve a CdTe ER structure. First, a novel co-sublimation process was developed for deposition of Cd1-xMgxTe thin films that demonstrates excellent experimental capabilities, commercial viability, and improved alloy control over other techniques. Next, the effects of processing on material properties of CMT deposition onto CdS/CdTe structures were investigated. It was discovered that substrate temperature during CMT deposition is a critical parameter for achieving uniform CMT film coverage on polycrystalline CdTe. Furthermore, CMT film growth was found to be epitaxial on CdTe where the CMT films retain the same microstructural features as the underlying CdTe grains. Despite film uniformity, significant Mg loss from the CMT film, oxide formation, and a reduction of the optical band gap was found after CdCl2-based passivation treatments. Preliminary process optimization found that band gap degradation can be minimized by utilizing MgCl2 in addition to CdCl2 as a treatment source material. Finally, development of CdS/CdTe/Cd1-xMgxTe electron reflector devices demonstrated a barrier behavior at high voltage bias and improved voltage when CdTe thickness is held below 1 μm. Additional electro-optical characterization and device modeling was used to understand the source of this device behavior. The results suggest the CdTe/Cd1-xMgxTe interface is likely free of detrimental electronic defects and the barrier behavior comes from a larger than expected valence band offset for the material system. Finally, future work to improve ER device performance is suggested. | |
| dc.format.medium | born digital | |
| dc.format.medium | doctoral dissertations | |
| dc.identifier | Kobyakov_colostate_0053A_12501.pdf | |
| dc.identifier.uri | http://hdl.handle.net/10217/83749 | |
| dc.language | English | |
| dc.language.iso | eng | |
| dc.publisher | Colorado State University. Libraries | |
| dc.relation.ispartof | 2000-2019 | |
| dc.rights | Copyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright. | |
| dc.subject | CdTe | |
| dc.subject | CdMgTe | |
| dc.subject | electron reflector | |
| dc.subject | photovoltaics | |
| dc.subject | solar cells | |
| dc.subject | solid-state physics | |
| dc.title | Development of Cd1-xMgxTe thin films for application as an electron reflector in CdS/CdTe solar cells | |
| dc.type | Text | |
| dcterms.rights.dpla | This Item is protected by copyright and/or related rights (https://rightsstatements.org/vocab/InC/1.0/). You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). | |
| thesis.degree.discipline | Mechanical Engineering | |
| thesis.degree.grantor | Colorado State University | |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Doctor of Philosophy (Ph.D.) |
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