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Defect Detection in Thin-film Photovoltaics; Towards Improved Efficiency and Longevity

Elrawemi, Mohamed, Blunt, Liam, Fleming, Leigh, Sweeney, Francis and Robbins, David (2014) Defect Detection in Thin-film Photovoltaics; Towards Improved Efficiency and Longevity. In: 5th International Renewable Energy Congress. IREC 2014 . IEEE, Hammamet, Tunisia, pp. 524-528. ISBN 978-1-4799-2196-6

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The photovoltaic (PV) industry is seeking to increase efficiency and functional lifetime of PV modules manufactured on polymer substrates. High resolution and high speed surface inspection for the quality control of the manufacture of large area flexible PV modules are necessary to guarantee maximum quality, longer lifetime and enhanced product yield. Flexible PV films are the newest development in the renewable energy field and the latest films have efficiencies at or beyond the level of Si-based rigid PV modules. These modules are fabricated on polymer film by the repeated deposition, and patterning, of thin layer materials using roll-to-roll technology. However, they are at present highly susceptible to long term environmental degradation as a result of water vapor transmission through the protective encapsulation to the active layer. To reduce the WVTR the PV encapsulation includes a barrier layer of amorphous Al2O3 on a planarised polymer substrate. This highly conformal barrier layer is produced by atomic layer deposition (ALD). Nevertheless water vapour transmission is still facilitated by the presence of micro and nano-scale defects in these barriers which results in decreased cell efficiency and reduced longevity.
Analytical techniques including: White Light Scanning Interferometry (WLSI), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) were used to characterise the water vapor barrier defects. Areal surface texture parameter analysis allows the efficient separation of small insignificant features from significant defects. This parametric analysis is then correlated with the water vapour transmission rate as measured on typical sets of films using standard MOCON test. The paper finishes by drawing conclusions based on analysis of WVTR and defect size, density and distribution, where it is postulated that small numbers of large features have more influence on the deterioration of water vapor transmission rates than large numbers of small features. This result provides the basis for developing roll-to-roll in process metrology devices for quality control.

Item Type: Book Chapter
Subjects: T Technology > TS Manufactures
Schools: School of Computing and Engineering
School of Computing and Engineering > Centre for Precision Technologies
School of Computing and Engineering > Electron Microscopy and Materials Analysis
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Depositing User: Sara Taylor
Date Deposited: 25 Jun 2014 10:01
Last Modified: 04 Nov 2015 23:30

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