Title :
Polymer encapsulants characterized by fluorescence analysis before and after degradation
Author_Institution :
Nat. Renewable Energy Lab., Golden, CO, USA
Abstract :
Structural changes of the luminescent chromophores in various polymer encapsulants for photovoltaic modules due to processing, weathering and artificial degradation are characterized by the nondestructive, noninvasive fluorescence analysis. Undegraded, simulation-degraded, and weathering-degraded EVA films have been studied. The results show that curing the EVA films can generate new chromophores of α,β-unsaturated carbonyls that can be excited by UV light up to ~400 nm. Their concentration in the EVA films made by a typical slow-curing process for EVA A9918 formulation is greater than those made by a fast-curing process for EVA 15295 formulation. Photothermal degradation of the EVA begins with an increase and lengthening of these chromophores. The UV-exposed EVA A9918 in solar cells turns brown and exhibits two types (one short and one long) of chromophores, and the thermally treated EVA shows yellow and only the short chromophores. The extent of discoloration from yellow to dark brown is a direct measure of the extent of degradation and an indication of an increase in the length of the polyconjugated carbon-carbon double bonds (polyenes). Similar results are observed for the weathering-degraded, yellow and brown PVB encapsulants in roof-top modules
Keywords :
environmental degradation; fluorescence; packaging; photothermal effects; polymers; solar cell arrays; solar cells; α,β-unsaturated carbonyls; EVA 15295 formulation; EVA A9918 formulation; UV light; artificial degradation; curing; fast-curing process; fluorescence analysis; luminescent chromophores; photothermal degradation; photovoltaic modules; polyconjugated carbon-carbon double bonds; polyenes; polymer encapsulants; roof-top modules; simulation-degraded films; slow-curing process; solar cells; undegraded films; weathering; weathering-degraded EVA films; Curing; Energy measurement; Fluorescence; Methanol; Photovoltaic cells; Photovoltaic systems; Polymers; Renewable energy resources; Solar power generation; Thermal degradation;
Conference_Titel :
Photovoltaic Specialists Conference, 1993., Conference Record of the Twenty Third IEEE
Conference_Location :
Louisville, KY
Print_ISBN :
0-7803-1220-1
DOI :
10.1109/PVSC.1993.346968