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Title: Bulk lifetime limiting defects in Czochralski silicon and graphene oxide as a surface passivation material
Author: Vaqueiro Contreras, Michelle
ISNI:       0000 0004 8504 2305
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2019
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Crystalline silicon continues to be the backbone of solar cell technologies. Enormous efforts towards process optimisation, cell architecture and defect identification, amongst others, thus continue to be made in order to push the limits of achievable efficiencies. Consequently, this thesis aims to provide an improved understanding of a variety of defects related to light element impurities commonly found in silicon materials used for cell fabrication, and their effect on the minority carrier lifetime. This thesis begins with a chapter which includes the motivation and outline of the present document. There, a summary of the most important aspects of the presented investigations and the relevance of the carried out work is described. In the subsequent chapter, a review on diverse silicon materials used for solar cell fabrication and the characterization techniques applied by the author for the shown studies is conferred. The most important chapters then are those which follow Chapter 2, where all the contributions from this thesis are presented in the form of published, submitted or submission-pending papers. Lastly, a concluding chapter is presented with final remarks from the contributions from the thesis and further work. Amongst the most important contributions from this work stand out the following: 1. The identification of a lifetime-limiting complex which includes atomic H on its composition in phosphorous-doped Cz-Si crystals containing high levels of O and C. These findings thus include the rather controversial remark of having the ubiquitous H as a detrimental impurity for solar cell fabrication. 2. The identification of two previously unreported spectroscopic signals related to two thermal-donor species present in P-doped Cz-Si which have recently been suggested to limit the minority carrier of the material in literature. By means of various junction capacitance techniques evidence disproving the validity of such suggestion is provided. 3. The demonstration of a previously undetected spectroscopic signal attributed to a BO-complex in B-doped Cz-Si. Complex that appears to be related to the responsible defect of the decades-long problem of light-induced degradation occurring in solar cells made from this type of materials during the first few days of their operation. 4. The demonstration of graphene oxide as a potential cheap alternative for silicon surface passivation, and the identification of its primary passivation mechanism as a field-effect coming from the GO's negative surface charge.
Supervisor: Halsall, Matthew ; Vijayaraghavan, Aravind Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: deep level transient spectroscopy ; Minority carrier transient spectroscopy ; minority carrier lifetime ; recombination ; graphene oxide passivation ; light induced degradation ; hydrogen defects ; Silicon defects ; Czochralski silicon ; oxygen defects ; carbon defects ; solar cells