Repository logo
 

Investigation of Group V doping and passivating oxides to reduce the voltage deficit in CdTe solar cells

Simple item page
dc.contributor.authorDanielson, Adam H., author
dc.contributor.authorSampath, W. S., advisor
dc.contributor.authorJames, Susan P., committee member
dc.contributor.authorPopat, Ketul C., committee member
dc.contributor.authorSites, James R., committee member
dc.date.accessioned2023-01-21T01:24:58Z
dc.date.available2023-01-21T01:24:58Z
dc.date.issued2022
dc.description.abstractThin film cadmium telluride is one of the most successful photovoltaic technologies on the market today. Second only to silicon in yearly output and accounting for 40% of U.S. utility-scale photovoltaic installation, CdTe is known for its ease of manufacture, ideal bandgap, and low levelized cost of energy. Despite its commercial success, CdTe underperforms compared to its theoretical potential. The current world record CdTe device is only 21.0% compared to a theoretical maximum of 33.1%. This significant discrepancy in efficiencies can mostly be attributed to the poor open-circuit voltage of CdTe devices. Compared to silicon technologies, CdTe has a large voltage deficiency, exceeding 250 mV. While copper doping has traditionally been used for CdTe devices, it has proven to be incapable of sufficiently doping CdTe. Copper typically dopes CdTe in the 1014 to 1015 holes/cm3 range where most models predict that 1016–1017 is needed. Additionally, interstitial copper is a fast diffuser in CdTe, and can lead to numerous stability issues. As an alternative to copper, this work explores arsenic as a dopant for CdTe. Using a novel arsenic doping technique, hole concentrations greater than 1015 cm-3, microsecond lifetimes, and increased radiative efficiency are achieved. These are important prerequisites to achieving higher voltages. Achieving high doping levels alone is not sufficient to achieve higher device performance. A well-passivated and carrier selective contact is needed to ensure that electron-hole pairs do not recombine and are extracted as useable energy. Aluminum oxide has been shown to passivate CdTe surfaces. This work illustrates the explorations of using Al2O¬3 as a passivation layer, pairing it with highly doped amorphous silicon as a hole contact, resulting in excess-carrier lifetimes up to 8 µs, the highest reported to date for polycrystalline Cd(Se)Te. Although the inclusion of arsenic doping and an aluminum oxide back contact are each explored separately, the combination of both methods result in massive improvements to the carrier lifetime, interface passivation and radiative efficiency. Through this combination, microsecond lifetime and External Radiative Efficiency of over 4% are achieved. The excellent ERE values measured here are indicative of large quasi-Fermi level splitting, leading to an implied voltage with multiple device structures of nearly 1 V and an implied voltage of 25%. Finally, while CdSeTe serves as a more promising photovoltaic absorber candidate compared to CdTe, certain difficulties remain which must be addressed. Careful selection of processing conditions is shown to create a dense and large-grained film while eliminating wurtzite-phase crystal growth, which has been shown to degrade device performance. Surprisingly, as-deposited CdSeTe is shown to be n-type or nearly intrinsic rather than the previously supposed p-type. This necessitates additional steps to account for very poor hole conductivity, which can produce zero-current devices if not addressed. Challenges notwithstanding, CdSeTe absorbers are shown to be a key component in devices capable of a photovoltaic conversion efficiency of greater than 25%.
dc.format.mediumborn digital
dc.format.mediumdoctoral dissertations
dc.identifierDanielson_colostate_0053A_17459.pdf
dc.identifier.urihttps://hdl.handle.net/10217/236018
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado State University. Libraries
dc.relation.ispartof2020-
dc.rightsCopyright 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.titleInvestigation of Group V doping and passivating oxides to reduce the voltage deficit in CdTe solar cells
dc.typeText
dcterms.rights.dplaThis 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.disciplineMechanical Engineering
thesis.degree.grantorColorado State University
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy (Ph.D.)

Files

Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
Name:
Danielson_colostate_0053A_17459.pdf
Size:
6.81 MB
Format:
Adobe Portable Document Format
Download

Collections

2020-
Theses and Dissertations