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Poster Session 2016 EU PVSEC: Compatibility of PV Ribbons and Fluxes with EVA Encapsulant Films

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Poster Session Presentation from 2016 EU PVSEC - Currently the reliability requirements for PV module service life are very high (for 25-30 years of service life) and packaging is the predominant cause of failure in modules. Polymer encapsulants, also known as ‘pottants’, play a key role in protecting the PV cell array modules from environmental effects such as UV radiation, moisture, extreme weather, electric leakage and wind damages. The most common polymer encapsulant in PV industry is ethylene vinyl acetate (EVA). Though EVAs are cheaper and versatile in its usage, they are sensitive to chemicals and other environmental factors. Ribbon and specially, flux manufacturers have to take utmost care in designing their products so that products won’t react with EVA and not suffer from reliability issues such as yellowing, thus affecting efficiency and reduced module life. Considering the flux and polymer encapsulant related compatibility concerns, a detailed study (DOE) was undertaken. The goal of the DOE was to achieve reliable solder joints with reduced yellowing of the PV module by optimizing the solder composition and flux chemistries.

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Poster Session 2016 EU PVSEC: Compatibility of PV Ribbons and Fluxes with EVA Encapsulant Films

  1. 1. Compatibility of PV Ribbons and Fluxes with EVA Laminating Films Narahari S Pujari*, Mike Murphy and Anna Lifton * The reliability requirements for module service life are very high (for 25-30 years of service life) Packaging is the predominant cause of failure in modules Industry often concerns for dis-coloration and subsequent loss of efficiency of the module due to the degradation in the encapsulant properties (yellowing, greening (corrosion), efficiency losses, etc. Introduction Experimental 1. Miller Dave, “The Critical Role of Materials in the Solar PV Industry”, GW Solar Institute Symposium, 2010. 2. S. Jiang et al., “Encapsulation of PV Modules Using Ethylene Vinyl Acetate Copolymer as the Encapsulant”, Macromolecular React. Eng. 9, 522, 2015. 3. E. Kaplani, “Degradation in Field -aged Crystalline Silicon Photovoltaic Modules and Diagnosis using Electroluminescence Imaging”, 8th International Workshop on Teaching in Photovoltaics IWTPV, 2016. 4. H. Raj, Polymer Encapsulants for Photovoltaic Applications’ Internal Cookson Electronics Report, 2009. Acknowledgements: We thank Dr. S. Sarkar for help and support DOE Factor 1 Ribbon type Ribbons from four sources Lead free, Ecosol Factor 2 Flux type Alpha’s PV fluxes Factor 3 EVA type Slow curing EVA Fast curing EVA Observation: a. PV ribbon analysis (Visual / Optical observations) b. Alloy composition and microstructure (surface contamination, thickness uniformity and edge exposure) c. EVA compatibility: Gel content, damp heat, optical observation Results & Discussion 75 80 85 90 95 100 EVA15295 EVA9918 %Gel Effect of fluxes on EVA gel content Control PV-32 PV50 PV21 PV61 Yellowing EVA protects the surface of the ribbons especially in presence of front glass would prevent whole PV assembly from discoloration/corrosion. As tinned PV ribbon surface morphology does not lay a significant role in resistance to yellowing (in case when the same alloy composition was used and surface cleanliness was acceptable), various types of EVA itself exhibit different resistance to discoloration Flux compatibility depends upon activity level in the formulation. Lead-free EcoSol alloy could be laminated at high temperatures. It shows good compatibility with EVA and excellent solder joints. This data further supports transitioning to lead free solar modules. Scant amount of information available on compatibility of lead free alloys with EVA Effect of Ribbons and Lamination Studies Tinning process has an effect on morphology and grain structure IMC layers formation is also a function of tinning process Solder thickness seems to be consistent expect on the edges As expected, PV ribbon coated with various fluxes but not laminated with EVA appears to be attacked/corroded while the fluxed material which was laminated did not show corrosion, just discoloration EVA A9918 EVA15295 Effect of Flux and EVA Compatibility Ecosol, lead free ribbon and microstructure Lead free alloy shows uniform microstructrure, has a similar appearance as alloys currently in use. Due to high liquidus temperature (179oC), Ecosol ribbon could withstand high laminating temperature (155oC). No colorization noted and solder joints were strong (>3 N/m2). Flux or EcoSol does not seem to have any adverse effect on EVA. Ecosol and EVA Compatibility PV-21 PV-38 PV-50 PV-61 EVA doped with different fluxes and cured ConclusionReferences Damp heat testing results 0 -5% Lowest allowable change Highest allowable change +5% Voc Isc Pmax FF 0.9 5 0.7 4 -0.56 -0.11 0.2 7 0.3 9 0.1 7 0.3 2 0.3 0 0.0 6 0.1 9 0.3 9 0.3 4 0.4 7 0.5 9 1.2 4 1.5 9 0.6 7 1.5 1 0.6 3 0.5 3 0.6 3 1.0 6 -0.34 %changeafterconditioning 60/40 Ecos ol SP2