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Operated for the U.S. Department of Energy 

Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337 

F.J. Pern and G.J. Jorgensen

Prepared for the 31st IEEE Photovoltaics Specialists 

Conference and Exhibition 

Lake Buena Vista, Florida 

January 3–7, 2005 

February 2005 • NREL/CP-520-37391 

Enhanced Adhesion of EVA 

Laminates to Primed Glass 

Substrates Subjected to 

Damp Heat Exposure 
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ENHANCED ADHESION OF EVA LAMINATES TO PRIMED GLASS SUBSTRATES 

SUBJECTED TO DAMP HEAT EXPOSURE

F. J. Pern and G. J. Jorgensen

National Center for Photovoltaics 

National Renewable Energy Laboratory 

1617 Cole Blvd., Golden, CO 80401 

ABSTRACT

We investigated the effectiveness of glass-surface

priming to promote enhanced adhesion of EVA laminates

during damp-heat exposure at 85o

C and 85% relative

humidity. The primary objective was to develop advanced

encapsulant formulations by incorporation of various 

primer formulations that exhibit improved adhesion during

damp-heat exposure. Several primer formulations were

identified that greatly enhanced the EVA adhesion

strength, including to the extent that peeling could not be

initiated, even for the laminates of the glass substrate/fastcure EVA15295P/TPE backsheet (a Tedlar/ polyester/EVA

tri-laminate) that were exposed in a damp-heat test 

chamber for more than 750 h. The results show that a

synergistic increase in the interfacial hydrophobicity,

siloxane density, and cross-linking density are the key 

attributes to the improvement in the EVA adhesion

strength. 

INTRODUCTION 

A critical issue in the long-term performance and

reliability of PV modules [1], especially polycrystalline thinfilm modules [2] without frames and edge seals, is their

resistance to moisture ingress. Passing the stringent 

damp-heat test at 85o

C and 85% relative humidity (RH) for

1000 h in the IEEE 1262 qualification test has proven 

difficult for many thin-film modules; delaminations of thinfilm solar cells, encapsulants, and/or backsheets have

occurred. Five workshops have been held in the last few

years to discuss and address the related moisture ingress

and thin-film reliability issues [3-7]. Moisture vapor is well

known to cause multiple problems on polymers as well as

adhesive joints. Upon absorption of water, a polymer may 

become swollen, plasticized, and/or hydrolyzed if its 

component bonding is susceptible to hydrolysis (such as

the ester linkage in polyester at high pH). Generally, water

can decrease the glass transition temperature, tensile

strength, and modulus of a polymer, but increase its

elongation at break. These properties can recover fully 

when the polymer is dried, unless irreversible hydrolysis

has occurred. The deterioration of a polymer is greater

and faster in higher relative humidity and temperature than

in liquid water, because permeation of the vapor is more

rapid [7]. The moisture ingress properties of a polymer can

be assessed by its permeability coefficient (P) and the

diffusion constant (D) of water [8,9]. For example, values

of P for more water-resistant polyisobutylene (PIB),

phenolic, and epoxy polymers at 25o

C are 7-22, 166, and

10-40 x 10-9 (cm3

 (STP) cm)/(cm2 s cm Hg), respectively. 

For less water-resistant polyvinyl acetate at 40o

C, P is 600 

x 10-9 (cm3

 (STP) cm)/(cm2 s cm Hg). The corresponding 

D values for the last three polymers (N/A for PIB) are 0.2-

10, 2-8, and 150 x 10-9 m2

/s, respectively [8]. For structural 

polymeric adhesives, moisture ingress is seldom the

dominant factor that affects durability. A more important 

issue is how the moisture influences the adhesive–

adherend interface region because of possible preferential

accumulation of moisture at the joint interface resulting in

loss of adhesion [9,10]. 

 

Among a number of encapsulant materials for

photovoltaic modules, ethylene-vinyl acetate (EVA)

copolymer has been the one most commonly used since

the mid-1980s. The commercial products of EVA have 

been found to fairly easily delaminate from glass

substrates upon prolonged immersion in an 85o

C water 

bath [11] or exposure to damp-heat, as observed in our

laboratories. To improve the adhesion strength of

adhesives against moisture-induced degradation, surface

priming and use of alternative non-EVA adhesives, along

with adequate substrate cleaning to reduce the surface

contamination, are among a number of approaches that 

can be taken [11,12]. For example, Tucker investigated

adhesion of two non-EVA polymers (CPVC and PMMA) on

glass and compared the effectiveness of two silanes in

enhancing EVA's long-term adhesion durability against 

damp-heat exposure, but with limited success [13]. The

key concepts in formulating the primer solutions in this

work were to use mixed silanes to introduce higher

degrees of (1) surface hydrophobicity to exclude water 

molecules from the interfacial regions, (2) siloxane

bonding density at the glass/EVA interface, and/or (3) 

cross-linking extent between the interfacial silanes and the

EVA. Custom-formulated EVA and non-EVA polymers

were also studied. 

EXPERIMENTAL

The primer formulations consisted of various 

combinations of silane-based coupling agents at a 2%

1 
total volumetric concentration in pH=5.0, 95:5 (v/v) 

ethanol/H2O mixture [14]. Table 1 shows the types of 

silane coupling agents and their interfacial functionality or 

purposes being studied. Table 2 lists the silane 

combinations of primer formulations used for the samples, 

but the exact concentration ratios of several were not 

indicated for proprietary reasons. Commercial low-iron, 

soda lime glass plates, AFG Krystal Klear®

, 3.2 mm (1/8") 

thick at a size of 10 cm x 10 cm (4" x 4"), were used. To 

ensure good silanization, the glass plates were thoroughly 

cleaned by first cleaning with diluted Liqui-Nox®

 for 15 min 

in a ultrasonicator, followed by soaking for about 30 min 

each in 1:1 (v/v) methanol/HCl and then in concentrated 

H2SO4; this was followed by rinsing with copious deionized 

H2O between and after acid soaking [15]. The cleaned 

glass surface gave an average contact angle of ~4.5o

 for 

water droplets (versus ~52.2o

 for the plates cleaned by the 

IPA-then-Billco 79A®

 scrubbing method used by some PV 

manufacturers). Priming was conducted by immersing the 

glass plates in the primer solutions for 2 min followed by 

brief rinsing with ethanol. The primed glass plates were 

then treated at ~93o

–97oC in a preheated oven for 10–12 

min. A commercial fast-cure EVA15295P/UF (0.46 mm 

thick), manufactured by Specialized Technology 

Resources (STR), was used for most sample laminations 

to the non-tinned glass surface side. Some customformulated, self-primed EVA and PMG formulations were 

also included in the test matrix. The PMG was an ethylene 

copolymer of methylacrylate containing glycidyl 

methacrylate. A total of 32 laminates were prepared with a 

common configuration of TPE/encapsulant/glass. The gel 

contents of the fast-cured EVA-15295, custom-formulated 

EVA, and PMG were analyzed using tetrahydrofuran 

extraction to be 90%-92%, 84%-86%, and 52%-64%, 

respectively. Damp-heat exposures were conducted in a 

Blue M, Model AC-7602HB chamber. The adhesion 

strength of the candidate encapsulants to the glass 

substrate was measured periodically using an Instron 

Model 5500 system with a 90-degree pull [16] and a crosshead speed of 10 mm/min. Typically, a 4-h dry-out was 

allowed before the peel tests were conducted. 

Table 1. Silanes and their Interfacial Application Purposes

Silane ID/Functional Group Interfacial Functionality or Purpose 

Z-6030®, Methacrylate- Cross-linking 

Z-6032®

, Vinylbenzyl- Cross-linking and hydrophobicity 

Vinyl-, Epoxy- Cross-linking and hydrophobicity 

Dipodal, Polysiloxane Cross-linking and siloxane-concentration enhancing 

Amino-, Diamino- Cross-linking and catalytic; but can be hydrophilic 

Fluoro-, Isobutyl, Phenyl- Hydrophobicity

Table 2. Ranking Order of Primer Formulations and Self-Primed Encapsulants based on Time-Averaged Peel 

Strength as a Function of Damp-Heat Exposure 

Sample Base Silane Silane Init. PS TAPS1 ∆PS2

 Rank 

 ID Silane #2 #3 (N/mm) (N/mm) (N/mm) Order 

PMG-K, D6-13 Z-6030 Epoxy- (Self-Primed4) 9.50 9.62 2.86 1 

Z6030-J3

 Z-6030 Fluoro- Dipodal 9.75 9.56 2.79 2 

Z6030-C Z-6030 Vinyl- N/A 10.25 9.32 2.56 3 

Z6032-B3

 Z-6032 Dipodal Amino- 9.00 9.27 2.51 4 

Z6032-A3

 Z-6032 Vinyl- Amino- 11.50 9.15 2.39 5 

Z6030-E Z-6030 Fluoro- N/A 9.50 8.83 2.07 7 

Z6030-L Z-6030 Phenyl- N/A 11.00 8.72 1.96 8 

Z6030-M Z-6030 Phenyl- Diamino- 11.00 8.69 1.93 9 

Z6030-G Z-6030 Fluoro- Amino- 10.50 8.66 1.90 10 

Z6030-I3

 Z-6030 Epoxy- Amino- 10.50 8.40 1.64 13 

Z6030-D Z-6030 Dipodal N/A 10.00 8.38 1.62 15 

Z6030-K Z-6030 Diamino- N/A 11.00 8.21 1.45 16 

Z6032-C Z-6032 Vinyl- Diamino- 10.00 7.83 1.07 18 

Z6030-S Z-6030 Phenyl- Dipodal 11.00 7.59 0.83 19 

Z6030-A Z-6030 N/A N/A 9.50 7.58 0.82 20 

Z6030-B Z-6030 Amino- N/A 11.50 6.93 0.17 24 

EVA-B, F/E-2 Z-6030 Polysiloxane (Self-Primed4

) 10.25 6.93 0.17 25 

Control Z-6030 (Self-Primed4

) 6.76 6.76 0.00 26 1

 Time-averaged peel strength after 500-h damp-heat test. 

2

 Difference in time-averaged peel strength from the control sample after 500-h damp-heat test. 

3

 Peeling could not be initiated because of TPE failure at T0 and subsequent damp-heat test intervals. 4

 The “self-primed” indicates the silane(s) was/were already blended in the extruded films. No glass priming for the sample. 

RESULTS AND DISCUSSION 

 In the commercial “self-primed” EVA formulations 

[13], a functional silane coupling agent such as Z6030®

(Dow Corning) is commonly used to enhance EVA 

adhesion strength to glass substrates by forming Si-O-Si 

siloxane bonds with the hydroxyl groups on the glass 

surface via a condensation reaction. Without the silane, 
the EVA adhesion strength would be about six to ten times

weaker [11,13]. However, in the presence of moisture and

elevated temperatures, the Si-O-Si bonding is reversible

by hydrolysis. A possible solution to the problem is to 

reduce the “free space” at the interfacial regions to 

exclude water molecules from accumulating at the

interfacial regions. This was achieved by using silanes

such as fluoro-, dipodal, phenyl-, and vinyl- (Table 1) for a

greater degree of hydrophobicity and density of siloxane

bonding between the silane and glass in formulating the

primer solutions. To increase the cross-linking between

the silane and EVA, functional silanes such as

methacrylate (Z-6030), vinylbenzyl (Z-6032), and vinyl

were used. Amino silanes were used primarily as

catalysts. Similar approaches of using mixed silanes for 

various polymer materials are reported in the literature

[17-20]. 

Figure 1 compares the peel strength (PS) data for six 

samples laminated with the glass substrates primed with

Z-6030-based primer solutions with a unprimed-glass

“control” as a function of damp heat exposure time to 500

h. Figure 2 shows the peel strength plot for three samples

laminated with the glass substrates primed with Z-6032-

based primer solutions, one custom-formulated EVA-B,

and two PMG-K samples. Upon longer exposures to 

~750–775 h, the TPE film was largely weakened or

degraded, with interlayer delamination of Tedlar/PET (TP)

from EVA (E). This delamination prevented reliable peel 

strength measurements from being made and shown in

both figures. As seen in Fig. 1, all the samples with Z6030-based primed glass substrates exhibit higher initial 

peel strength than that of the control with unprimed-glass

substrate. Their resistance to damp-heat exposure is also

generally better than the control, although two showed a

worse trend at 500 h. Similar results are observed in Fig.

2 for samples with Z-6032-base primed glass substrates.

For the EVA-B that was custom-formulated with Z-6030 

and a H-terminated polysiloxane (H-PDMS) and laminated

to the unprimed-glass substrate, a high initial peel strength

was followed by rapid deterioration of adhesion strength

after being exposed to damp heat. However, in a separate 

study, the H-PDMS catalytically primed on glass

substrates had shown very good resistance to hydrolytic

loss when soaked in an 85o

C water bath. The presence of

H-PDMS polysiloxane was observed to cause a great 

degree of difficulty for the EVA-B and PMG-B formulation

to be extruded into films. For PMG-K formulated with Z6030 and a second epoxy-type silane, film extrusion

problems were not observed, and the loss of adhesion

strength during damp-heat exposure was relatively small,

as seen in Fig. 2. 

Fig. 2. Peel strength measured for six TPE/EVA (or 

PMG)/glass laminates exposed to damp heat for 500 h

To evaluate and compare the effectiveness of the

various primer formulations on enhancing EVA adhesion 

during damp-heat exposures, a statistical analysis of

comparative time-averaged performance (i.e., “TAPS” in 

Table 2) was employed. A test criterion, w, was defined, 

which depends on the estimated standard deviation of the

acquired data and the percentiles of the studentized

range, q [21]. 

n

q w α ⋅σ = 1−

 

For a confidence interval of 99%, w was determined 

to be 0.94 N/mm for the set of 32 samples. If the 

difference in TAPS between two samples is greater than 

w, then we conclude with 99% confidence that a primer

produced a statistically significant improvement in peel 

strength between the two samples. The results of

calculated TAPS, their difference from the control (∆PS),

and the ranking order are given in Table 2 for 18 of the 32 

samples and their (unduplicated) primer silane

combinations. The six samples that performed poorer than 

the control are not shown. A comparison of the ∆PS

indicates that primer formulations Z-6030-A, B, S, and

EVA-B F/E-2, with ∆PS in the 0.17–0.83 range (< 1 w, 

rank order from 19 to 25), offer statistically insignificant

improvements versus the unprimed control. For the other

samples that show ∆PS in the 1.07–1.96 range (rank order

from 8 to 18), the largest spread, 2.80(Z6030-L) – 

1.62(Z6032-C) = 0.89, is less than w = 0.94, further

suggesting the adhesion strength improvements provided

by these primer solutions are statistically comparable. For

those primer formulations ranking from 2 to 7 in Table 2

with 2.07 < ∆PS < 2.79, the improvements on the

adhesion strength during damp-heat exposure are

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

0 100 200 300 400 500

Damp Heat Exposure Time (h)

Peel Strength (N/m

m)

Control Z6030-A Z6030-B

Z6030-C Z6030-G Z6030-H

Z6030-I Z6030-J

No data for >750h exposure due to

delamination of T/P layers from EVA

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

0 100 200 300 400 500

Damp Heat Exposure Time (h)

Peel Strength (N/m

m)

Z6032-A

Z6032-B

Z6032-C

EVA-B, F/E-2

PMG-K, D6-1

PMG-K, D6-2

No data for >750h exposure due to

delamination of T/P layers from EVA

or failure of TPE

Fig. 1. Peel strength measured for eight TPE/EVA/ 

glass laminates exposed to damp heat for ~500 h.
statistically more significant. Peeling could not be initiated 

for the four samples, Z-6030-I and J and Z-6032-A and B, 

before and after damp-heat exposure because of strong 

EVA adhesion. The peel strength results thus obtained are 

less accurate for these four samples. However, three of 

them, excluding Z6030-I, rank among the top five in TAPS 

values. For self-primed PMG-K D6-1, which ranks No. 1, 

peeling tests could not be ever truly performed even after 

750 h exposure. The enhanced adhesion is attributed to 

the presence of functional groups of methacrylate and 

glycidyl methacrylate in the PMG that provide greater 

bonding than EVA to the glass surface, in addition to the 

siloxane bonding from Z-6030 and epoxy silane in the 

formulation. As evaluated from the silane components of 

primer formulations for the six highest TAPS, the 

mechanisms responsible for enhanced EVA adhesion 

during damp-heat exposure are attributed to (1) an 

increase in the siloxane bonding density via the smaller 

silane molecules of cross-linking vinyl or dipodal silanes, 

(2) a presence of hydrophobic fluorosilane, (3) a dominant 

use of Z6032 vinylbenzyl silane (with vinyl and 

hydrophobic benzyl), and/or (4) a presence of lowconcentration aminosilane serving as a catalyst. These 

factors have worked synergistically as designed to 

increase the interfacial hydrophobicity and cross-linking 

density with the EVA. These results are consistent with 

those reported in the literature [17-19]. However, the 

presence of “additional” Z-6030 on the glass surface by 

priming with Z6030-A (see Table 2) provided only little 

improvement. A high concentration of amino silane alone 

(e.g., 25%) was found adverse to reduce adhesion 

strength by possibly causing the interfacial regions to 

become relatively more hydrophilic. 

CONCLUSIONS 

 Several primer formulations of mixed silanes are 

identified from peel tests to enhance the adhesion 

strength of EVA/glass laminates during prolonged dampheat exposure. A synergistic increase in the interfacial 

hydrophobicity, siloxane density, and cross-linking density 

by the use of carefully selected silane combinations are 

the key attributes to the improvement. Specifically, the 

carefully selected silane combinations that provided the 

most enhanced EVA adhesion consist of (1) an increase in 

the siloxane bonding density via the smaller silane 

molecules of cross-linking vinyl or dipodal silanes, (2) a 

presence of hydrophobic fluorosilane, (3) a dominant use 

of vinylbenzyl silane (with vinyl and hydrophobic benzyl), 

and/or (4) a presence of low-concentration aminosilane 

serving as a catalyst. Self-primed (non-EVA) PMG 

appears to be very promising for offering high waterresistant potential. For convenience in practical use, the 

best-performing primer formulations developed in this 

work have been formulated into EVA encapsulant films for 

damp-heat tests to further verify their performance. 

ACKNOWLEDGEMENT 

 This work was performed at NREL under U.S. 

Department of Energy Contract No. DE-AC36-99-

G010337. 

REFERENCES 

[1] E.L. Meyer and E.E. van Dyk, “Assessing the 

Reliability and Degradation of Photovoltaic Module 

Performance Parameters,” IEEE Trans. Reliability, 53, 

2004, pp. 83-92. 

[2] T.J. McMahon, “Accelerated Testing and Failure of 

Thin Film PV Modules,” Prog. Photovolt: Res. Appl.,

12, 2004, pp. 235-248. 

[3] Moisture Ingress and High Voltage Isolation 

Workshop, March 9-11, 2001, Golden, CO. 

[4] Proceedings of First Thin Film Module Reliability 

National Team Meeting, Sept. 4-5, 2002, Golden, CO. 

[5] Proceedings of Second Thin Film Module Reliability 

National Team Meeting, Feb. 27-28, 2003, Cocoa, FL. 

[6] Proceedings of Third Thin Film Reliability National 

Team Meeting, Sept. 18-19, 2003, Albuquerque, NM. 

[7] Proceedings of Fourth Thin Film Reliability National 

Team Meeting, June 23-24, 2004, Golden, CO. 

[8] “How Moisture Affects Adhesive and Sealant Joints – 

Part I,” Technical article of SpecialChem4Adhesives 

website, July 16, 2003. 

[9] “Polymer Permeability,” J. Comyn ed., Chaps. 1, 2, 

and 5, Elsevier Applied Science, New York, 1986. 

[10] “Improving the Moisture Resistance of Adhesives and 

Sealants – part II,” Technical article of SpecialChem4 

Adhesives website, July 23, 2003. 

[11] F.J. Pern, unpublished results. 

[12] “Cleaning Processes for Improving Adhesion,” 

Technical article of SpecialChem4Adhesives website, 

July 30, 2003. 

[13] R.T. Tucker, "Primers and Adhesion," presented in 

ref. 4. 

[14] "Silane Coupling Agents: Connecting Across 

Boundaries," Product brochure of Gelest Inc., 2003, 

"Applying Silanes," pp. 17. 

[15] J.J. Cras, C.A. Rowe-Taitt, D.A. Nivens, and F.S. 

Ligler, "Comparison of Chemical Cleaning Methods of 

Glass in Preparation for Silanization," Biosensors & 

Bioelectronics, 14, 1999, pp. 683-688. 

[16] F.J. Pern and S.H. Glick, "Adhesion Strength Study of 

EVA Encapsulants on Glass Substrates," 

Proceedings of NCPV and Solar Program Review 

Meeting, March 24-26, 2003, Denver, CO. 

[17] "Silane Coupling Agents," E. P. Plueddemann, 

Plenum Press, New York, 1982. 

[18] P.G. Page and E.P. Plueddemann, "Methods for 

Improving the Performance of Silane Coupling 

Agents," in "Silanes and Other Coupling Agents," K.L. 

Mittal ed., VSP, 1992, pp. 105-116. 

[19] R.G. Craig and E.R. Dootz, "Effect of Mixed Silanes 

on the Hydrolytic Stability of Composites," J. Oral 

Rehabilitation, 23, 1996, pp. 751-756. 

[20] N. Nishiyama, T. Ishizaki, K. Horie, M. Tomari, and M. 

Someya, "Novel Polyfunctional Silanes for Improved 

Hydrolytic Stability at the Polymer-Silica Interface," J. 

Biomed. Mat. Research, 25, 1991, pp. 213-221. 

[21] "Experimental Statistics," Handbook 91, U.S. 

Department of Commerce, NBS, 1963, pp. 3-40 - 3-

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4. TITLE AND SUBTITLE

Enhanced Adhesion of EVA Laminates to Primed Glass Substrates 

Subjected to Damp Heat Exposure 

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F.J. Pern and G.J. Jorgensen 

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14. ABSTRACT (Maximum 200 Words)

We investigated the effectiveness of glass-surface priming to promote enhanced adhesion of EVA laminates during 

damp-heat exposure at 85o

C and 85% relative humidity. The primary objective was to develop advanced encapsulant 

formulations by incorporation of various primer formulations that exhibit improved adhesion during damp-heat exposure. 

Several primer formulations were identified that greatly enhanced the EVA adhesion strength, including to the extent that 

peeling could not be initiated, even for the laminates of the glass substrate/fast-cure EVA15295P/TPE backsheet (a 

Tedlar/ polyester/EVA tri-laminate) that were exposed in a damp-heat test chamber for more than 750 h. The results 

show that a synergistic increase in the interfacial hydrophobicity, siloxane density, and cross-linking density are the key 

attributes to the improvement in the EVA adhesion strength. 

15. SUBJECT TERMS

PV; ethylene-vinyl acetate (EVA); glass surface priming; enhanced adhesion; damp-heat exposure; 

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