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.

1. Compatibility of PV Ribbons and Fluxes with EVA
Laminating Films
Narahari S Pujari*, Mike Murphy and Anna Lifton
*:Narahari.Pujari@alphaassembly.com
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