5101-284 DOE/JPL-1012-120

Flat-Plate Solar Distribution Category UC-63b

Array Project

Chemical Bonding Technology:

Direct Investigation of

Interfacial Bonds

J.L. Koenig

F.J. Boerio

E.P. Plueddemann

J. Miller

P.B. Willis

E.F. Cuddihy

(NASa-CK-176657) CHEMICA1 BONDING N86-21584

TECHNOLOGY: .'DIEECT INVESTIGATION Of -.

INTEBFACIftl BONDS (Jet Propulsion Lab.),

54 p HC A'04-/ttf J>01 CSCL 07C Unclas

v i G 3/2 3 03 8 6J

January 1986

Prepared for

U.S. Department of Energy

Through an Agreement with

National Aeronautics and Space Administration

by

Jet Propulsion Laboratory

California Institute of Technology

Pasadena, California

JPL Publication 86-6
5101-284 DOE/JPL-1012-120

Flat-Plate Solar Distribution Category UC-63b

Array Project

Chemical Bonding Technology:

Direct Investigation of

Interfacial Bonds

J.L. Koenig

F.J. Boerio

E.P. Plueddemann

J. Miller

P.B. Willis

E.F. Cuddihy

January 1986

Prepared for

U.S. Department of Energy

Through an Agreement with

National Aeronautics and Space Administration

by

Jet Propulsion Laboratory

California Institute of Technology

Pasadena, California

JPL Publication 86-6
Prepared by the Jet Propulsion Laboratory, California Institute of Technology,

for the U.S. Department of Energy through an agreement with the National

Aeronautics and Space Administration.

The JPL Flat-Plate Solar Array Project is sponsored by the U.S. Department of

Energy and is part of the National Photovoltaics Program to initiate a major

effort toward the development of cost-competitive solar arrays.

This report was prepared as an account of work sponsored by an agency of the

United States Government. Neither the United States Government nor any

agency thereof, nor any of their employees, makes any warranty, express or

implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process

disclosed, or represents that its use would not infringe privately owned rights.

Reference herein to any specific commercial product, process, or service by trade

name, trademark, manufacturer, or otherwise, does not necessarily constitute or

imply its endorsement, recommendation, or favoring by the United States

Government or any agency thereof. The views and opinions of authors expressed

herein do not necessarily state or reflect those of the United States Government

or any agency thereof.

This document reports on work done under NASA Task RE-152, Amendment

419, DOE/NASA IAA No. DE-A101-85CE89008.
ABSTRACT

This is the third Flat-Plate Solar Array (FSA) Project document reporting

on chemical bonding technology for terrestrial photovoltaic (PV) modules. The

impetus for this work originated in the late 1970s when PV modules employing

silicone encapsulation materials were undergoing delamination during outdoor

exposure. At that time, manufacturers were not employing adhesion promoters

and, hence, module interfaces in common with the silicone materials were only

in physical contact and therefore easily prone to separation if, for example,

water were to penetrate to the interfaces. Delamination with silicone

materials virtually vanished when adhesion promoters, recommended by silicone

manufacturers, were used.

With the decrease in use of silicone encapsulants, and the increase in use

of hydrocarbon encapsulants such as ethylene vinyl acetate (EVA), the need

developed for adhesion promoters specifically developed for these new materials.

The adhesion promoters being developed for EVA-type materials are based on

organosilanes, which generate primary chemical bonds at the interface, that is,

chemical bonding. These adhesion promoters are commonly referred to as

"primers."

The first report on this subject (Chemical Bonding Technology for

Terrestrial Solar Cell Modules, by E.P. Plueddeman, JPL 5101-132, dated

September 1, 1979) described the chemistry of primers based on organosilane

chemistry, and the second report (Chemical Bonding Technology for Terrestrial

Photovoltaic Modules, by D.R. Coulter, E.F. Cuddihy, and E.P. Plueddeman, JPL

Publication 83-86, dated November 15, 1983) described chemical bonding

theories, and also included a listing of candidate primer and adhesive systems

being investigated for all of the various module interfaces. This report

describes the activities related to the direct investigation of chemically

bonded interfaces.

111
ACKNOWLEDGMENT

The authors thank the following companies for courteously supplying solar

cells used for the adhesion studies discussed in this Project report: SOLEC

International, Hawthorne, California; Spectrolab, Inc., Sylmar, California; and

Tideland Signal, Houston, Texas.

IV
ABBREVIATIONS AND ACRONYMS

AES Auger electron spectroscopy

DRIFT diffuse reflectance infrared spectroscopy

EDAX energy dispersive x-ray analysis

EVA ethylene vinyl acetate

FSA Flat-Plate Solar Array

FTIR Fourier transform infrared spectroscopy

IPN Interpenetrating Polymer Network

OH organic alcohols

OR organic ethers

PV photovoltaic

RAIR reflection absorption infrared spectroscopy

XPS x-ray photoelectron spectra
CONTENTS

I. INTRODUCTION 1

II. CHEMICAL BONDING BETWEEN GLASS AND ETHYLENE

VINYL ACETATE (EVA) 3

A. FOURIER TRANSFORM INFRARED (FTIR) SPECTROSCOPY OF

SURFACES AND INTERFACES 6

1. Avantages of FTIR for Surface Studies 6

2. Sampling Techniques for FTIR Spectroscopy Studies . . 6

3. Data Processing Techniques 7

B. EXPERIMENTAL PROCEDURES (MATERIALS) '. 7

C. FTIR SPECTROSCOPY STUDIES OF UNAGED

EVA/GLASS INTERFACES 8

1. Glass 8

2. Coupling Agent on Glass Surface 11

3. Hydrothermal Stability of the Glass/Coupling

Agent Interface 13

4. EVA 14

5. EVA/Glass Interface 14

D. HYDROTHERMAL AGING OF EVA/GLASS INTERFACE 17

1. Mechanical Testing 17

2. Spectroscopic Testing 25

III. CHEMICAL BONDING BETWEEN SOLAR CELLS AND EVA 29

A. ALUMINUM MIRRORS ' 29

B. ALUMINUM MIRRORS WITH EVA COATINGS 31

C. ALUMINIZED SOLAR CELLS 33

D. REFLECTION ABSORPTION INFRARED SPECTROSCOPY STUDIES .... 39

IV. REFERENCES 43

vii

 PRECEDING PAGE BLANK NOT RLMED
Figures

1. Bonding of Silane Coupling Agents to Glass 5

2. Interdiffusion Model for a Silane-Primed

EVA/Glass Joint 5

3. Diffuse Reflectance Spectrum of Material Components

and Composites 10

4. Diffuse Reflectance FTIR Spectra of Y-MPS/Amine

Modified Particulate Glass, the Untreated Particulate

Glass, and the Difference Spectrum Showing the

Presence of the Y-MPS on the Surface of the Glass 11

5. DRIFT Spectrum of Y-MPS/Amine Modified Particulate

Glass Showing the Increase in the Intensities of the

Y-MPS with the Percent Loading of the Treating Solution . . 12

6. Plot of the Integrated Intensity of the Carbonyl

Band of Y-MPS on the Surface of the Particulate

Glass as a Function of Weight Percent Loading of

the Particulate Glass 12

7. Spectrum of Y-MPS on the Surface of the Glass in the

Carbonyl Stretching Region Showing the Vibrational

Band Assignments Including the C = 0 and C = C Modes .... 13

8. Plot of the Integrated Carbonyl Band as a Function of

Weight Percent Loading 14

9. Spectra of Y-MPS on Sunadex Glass Before and After

Hydrothermal Treatment Showing the Extensive Removal

of the Silane with Water Exposure 15

10. Spectra of Y-MPS on the Surface of Glass Spheres Which

Have Been Acid-Washed to Prepare the Surface Prior to

Treatment with the Silane 15

11. DRIFT Spectrum of Pure EVA 16

12. DRIFT Spectrum Showing the Silane at the EVA/Glass

Interface 16

13. DRIFT Spectrum of Silane at the Interface Between

Glass and EVA (Top Spectrum) and the Spectrum of the

Y-MPS Silane of the Glass 17

14. DRIFT Spectrum of the EVA/Y-MPS-Peroxide Before and

After Hydrothermal Cycling 26

15. FTIR Spectra of Primed EVA/Glass Bead Specimens,

Hydro thermally Aged at 60 °C 26

Vlll
Figures (Cont'd)

16. Infrared Spectra of Y-MPS Films with Three Different

Thicknesses Deposited on Aluminum Mirrors 30

L7. Infrared Spectra of: (A) Thick, and (B) Thin

(Monolayer) Films of Y-MPS on Aluminum Mirrors 30

18. Ellipsometry Parameter A Versus Immersion Time in

Water at 40°C for an Uncoated Aluminum Mirror 32

19. Ellipsometry Parameter A Versus Immersion Time in

Water at 40°C for EVA Cured with Lupersol 101

Laminated on Vapor-Deposited Aluminum 32

20. Ellipsometry Parameter A Versus Immersion Time in

Water at 40°C for EVA Cured with TBEC Laminated on

Vapor-Deposited Aluminum 33

21. Scanning Electron Micrograph of Back Side of

"Type 1" Silicon Cell (5000X) 34

22. EDAX: (A) Silicon and (B) Al Maps of Back Side of Same

Silicon Cell as in Figure 21 35

23. Auger Electron Spectra of Back Side of Same Silicon

Cell as in Figure 21 36

24. Scanning Electron Micrograph of Back Side of "Type 2"

Silicon Cell (2000X) 36

25. X-ray Photoelectron Spectrum of Back Side of

As-Received "Type 2" Silicon Cell 37

26. XPS Spectrum of Laminated "Type 2" Silicon Cell After

Peeling EVA Film 38

27. XPS Spectrum of Laminated "Type 2" Silicon Cell After

Boiling 1 h and Peeling EVA Film 38

28. Reflection Infrared Spectra Obtained from Aluminized

Back Side of "Type 1" Silicon Cell 40

29. Reflection Infrared Spectrum Obtained from Aluminized

Back Side of "Type 1" Silicon Cell, Boiled in Water

for 30 min, and Then Coated with a Thin Film of EVA .... 40

30. Reflection Infrared Spectra Obtained from Aluminized

Back Side of a "Type 1" Silicon Cell Coated with a Thin

Film of EVA 41

IX
Figures (Cont'd)

31. Reflection Infrared Spectra Obtained from the Back Side

of a "Type 1" Silicon Cell Coated with a Thin Film

of EVA, But No Primer 41

32. Reflection Infrared Spectra Obtained from the Back Side

of a "Type 1" Silicon Cell Coated with Thin Films

of A-11861 Primer and EVA 42

Tables

1. Adhesive Bonding Test Formulations 9

2. Hydrothermal Aging Conditions 9

3. Hydrothermal Aging of Glass Bead-Filled Polymer

Specimens at 40°C 19

4. Hydrothermal Aging of Glass Bead-Filled Polymer

Specimens at 60°C 20

5. Hydrothermal Aging of Glass Bead-Filled Polymer

Specimens at 80°C 21

6. Effect of Drying Out the Hydrothermally Aged

Specimens Reported in Table 3 22

7. Effect of Drying Out the Hydrothermally Aged

Specimens Reported in Table 4 23

8. Effect of Drying Out the Hydrothermally Aged

Specimens Reported in Table 5 24

x
SECTION I

INTRODUCTION

Adhesives and primers are necessary for the high reliability bonding of

photovoltaic (PV) module interfaces to ensure structural integrity and long

life. The adhesion between the pottant and other components (i.e., substrate,

superstrate, and outer cover) must have adequate bond strength to hold the

module components together, with a Flat-Plate Solar Array (FSA) Project goal

of 30 years of outdoor service life. Accordingly, the material components of

the module should be held together by strong chemical bonding, with the

interfacial bonding being resistant to delamination from the combined

weathering actions of moisture, temperature, and ultraviolet light.

Toward this end, Dow Corning (Dr. Edwin Plueddemann) is developing

chemical bonding agents based on organosilane chemistry called silane coupling

agents, which are chemically bifunctional. Using glass and ethylene vinyl

acetate (EVA) as an example, one of the chemical groups on a silane coupling

agent is designed to react with glass, while the other chemical group will

react with EVA. Thus, the interfacial bonding is accomplished by actual

primary chemical bonds bridging across the interface.

In general, the silanes employed for these coupling agents are typically

resistant to deterioration by ultraviolet light, and therefore the main

concern is from hydrothermal deterioration over a long exposure time

outdoors. Ordinarily the quality (strength) of bonded materials is monitored

by mechanical peel tests, where failure is defined as cohesive if it occurs in

either of the two bonded materials, or adhesive if failure occurs in the

interfacial region. Using silane coupling agents and, again, EVA and glass as

an example, failures of control and hydrothermally aged EVA/glass specimens

are normally cohesive within the EVA (References 1 and 2). That is, the bond

strength exceeds the tensile strength of EVA. Thus, accelerated hydrothermal

aging may be decreasing the bond strength, but if it continues to exceed the

EVA's tensile strength, it cannot be monitored by mechanical testing.

Dr. Koenig at Case Western Reserve University has been pioneering

techniques based on Fourier Transform Infrared (FTIR) spectroscopy to

investigate chemically bonded interfaces for information related to bond

population. The first part of this Project document is a report on

Dr. Koenig's FTIR activities at Case Western, in collaboration with

Dr. Miller. During this work, it was found necessary to disperse small

diameter glass beads in EVA in order to increase the surface-to-volume ratio

of test specimens for FTIR detection. Of technical significance, it was

recently found (Reference 2) that the equilibrium water absorption of these

composite specimens was a strong function of the level of chemical bonding.

For example, one series of unprimed EVA/glass specimens reported in

Reference 2 absorbed nearly 2000 wt % water at 60°C, whereas a primed

EVA/glass specimen absorbed only 35 wt % water at 60°C. For future work, this

finding offers a possibility for monitoring changes in the chemically bonded

interface from simple measurements of equilibrium-absorbed water contents of

aged specimens.
Dow Corning has successfully developed a silane coupling agent

formulation (called a "primer") for EVA and glass. This primer is designated

A-11861, and experimental quantities are available from Springborn

Laboratories. Separately, work continues at Dow Corning to develop primers

for bonding EVA to solar cells, and solar cell metallization materials, such

as aluminum. The reason for this activity is that silane coupling agents also

appear to passivate metal surfaces against corrosion (References 3, 4, 5,

and 6).

Dr. Boerio at the University of Cincinnati has been pioneering

techniques based on ellipsometry and reflection absorption infrared (RAIR)

spectroscopy to investigate chemically bonded interfaces between metals and

polymers. The second part of this Project document is a report on activities

at the University of Cincinnati. Of significance is the apparent finding that

the silane coupling agent employed in the A-11861 EVA/glass primer may be

effective for bonding EVA to the aluminized back surfaces of solar cells, and

may also be effective in stopping environmentally induced corrosion of this

aluminum. Thus, a self-priming EVA formulated with this silane coupling agent

would work with both glass and solar cells. Dr. Boerio's work indicates that

the silane coupling agent in A-11861 only works between EVA and the aluminum

on solar cells, and not between EVA and any other aluminum. Although

preliminary, new insights into the general area of bonding to aluminum may

result from this work.
SECTION II

CHEMICAL BONDING BETWEEN GLASS AND ETHYLENE VINYL ACETATE (EVA)

In order to meet the required specifications, encapsulated PV modules

must remain intact for 30 years, reliably resisting delamination and separation

of any of the component materials. For such long outdoor life, strong weatherstable interfacial bonds must be formed between the component materials. In

order to achieve such stability, adhesion promoters are used to enhance the

strength and durability of such bonds. The chemical bonding technology has

been described in two previous reports (References 7 and 8) and should be

reviewed prior to this report in order to ascertain the current status with

respect to materials, adhesion promoters, and process considerations.

Characterizing the chemical nature of the adhesion between different

materials is challenging and difficult. The first problem is the small

concentration of interfacial bonds relative to the bulk. The second problem

is that the interfacial bonds are generally quite similar to those of the

bulk, making the detection more difficult. Efforts have been made to

understand the mechanism of the coupling agent action. The earliest efforts

focused primarily on the role of the coupling agent in improving the

mechanical properties. Many potential coupling agents were tested and the

results generated a number of explanations ranging from improvements in

surface wettability, presence of acid-base reactions, and the formation of

chemical bonds. Each of these postulates describe some aspect of the response

of the mechanical properties to the different silanes and their processes, but

none of them are sufficient to explain all of the observations.

Over the past 40 years, many techniques have been used to evaluate the

interfacial chemistry of materials. Some of these techniques include

microscopy, contact angle measurements, gel permeation chromatography, zeta

potentials, heats of immersion, and radioactive labeling. Although these

techniques are precise in their analysis, the major limitation is that either

they do not yield molecular structural information or have sufficient

sensitivity to detect monolayers. Infrared spectroscopy has been widely used

as a technique to study surfaces (References 9 and 10) and with the advent of

FTIR, it has become an even more effective tool because of the high

sensitivity, excellent structural resolution, simple sampling techniques, and

computer processing of the spectra. The effectiveness of FTIR for the study

of the interfaces of glass fiber composites has been demonstrated

(References 11, 12, 13, and 14). On this basis, it was selected for use to

study the interfacial bonding of glass/EVA in terrestrial PV modules.

There are a number of factors that determine the chemical basis of the

adhesion. The nature of the surface functionality of the bonding materials

determines the potential for chemical modification of the adhesion. A

necessary prerequisite for molecular design of the adhesive interfacial bonds

is knowledge of the surface functionalities. Using FTIR spectral reflection

techniques, insights into the chemical nature of the surface can be obtained.
Adhesion is most often promoted using a coupling agent that is specific

for the materials to be bonded. A coupling agent, as the name implies, is a

molecule that couples together two different molecules. This molecular

fastening is made for the purposes of promoting adhesion between the two

molecules which are generally found at an interface between two surfaces. A

coupling agent is bifunctional so that each end of the molecule can connect

with the molecules of the surfaces that are being bonded. A especially useful

class of coupling agents is the organosilanes, where one end of the molecule

has organic functionality to react with organic surfaces, and the other end is

inorganic to react with inorganic surfaces.

Silane coupling agents have the general form X-(CH2)3-Si-(OR)3. The

functional group X can be varied to optimize the reactivity with the polymer

matrix to be connected to the glass (Figure 1). The organic ethers (OR)

groups are short chain ethers that are readily hydrolyzed in water that is

slightly acidic to alcohols leaving a silanetriol group which is very reactive

with itself (condensation/polymerization) and the glass surface. In

industrial practice, the silanes are dissolved in water or alcohol and the

glass is treated with a dilute (1% by weight) solution. This dilute solution

is commonly referred to as a "primer." The amount of silane on the surface of

the glass is very small and its molecular structure is a function of the

treating and drying conditions of the industrial process.

Beginning in the early 1960s, questions were being asked concerning the

nature of the coupling agent on the surfaces. Is the coupling agent bound to

the substrate material? If so, is the type of bonding important to the

adhesion? How much coupling agent is needed to yield maximum adhesion? Does

the coupling agent chemically react with the polymer matrix? Is the amount of

chemical reaction important to the adhesion? Could the performance of the

coupling agent be controlled by the treating conditions? These questions can

be answered using FTIR in the appropriate manner.

The questions of lifetime of the adhesive bond are also complex. Is the

coupling agent present on the substrate material after exposure to

water/humidity? Is the structure of the coupling agent modified by the

presence of water? Does the water preferentially attack the interfacial

bonds? Questions of this kind can be answered with accelerated exposure tests

combined with FTIR spectroscopic characterization.

The model of the adhesive joint for EVA/glass can be considered as a

sandwich structure (Figure 2) with a series of layers. These layers include:

(1) The bulk glass substrate.

(2) An interface between the glass and the coupling agent.

(3) A region of bulk polysiloxane (interphase).

(4) An interface between the coupling agent and the EVA.

(5) The bulk EVA region.

It is convenient to discuss the results of this report in terms of these

components as each plays a role in the ultimate properties of the adhesion.
ORIGINAL PAGE IS

OF POOR QUALITY

GENERAL STRUCTURE

X

TRIALKOXY Rn\n c j ^^ o,

i

 O — uRn

SILANE |

OR

PHYSICAL

ABSORPTION

X

1

HO— Si —OH

1

0

H

1

0

1

X

H20 I

— HO ^i

i

OH

OH

SOLVENT EVAPORATION

AND HYDROGEN

X

' s H *•

HO -Si— O

1 '•' H '

0

:^H

H

|

O

1

BONDING

X

1

' 0-Si— OH

1

o

.\H

*

H

1

0

1

X IS POLYMER REACTIVE GROUP

SUCH AS

• METHACRYLATE

• AMINE

• EPOXY

• STYRENE

SURFACE

POLYMERIZATION

X

* 1

Si — 0 -

1

0

1

X X

1 1

Si - O —Si — 0

1 1

0 0

I 1

/£ Si - 0 - Si - ///y/////////////- Si-O-Si-O-Si-O - - Si - O - Si - 0 - Si - 0 -

Figure 1. Bonding of Silane Coupling Agents to Glass

CHEMICALLY BONDED

INTERFACE

A

INTERPHASE

A.

OPEN CIRCLES INDICATE REGIONS OF COUPLING AGENT,

FILLED CIRCLES INDICATE REGIONS OF EVA

Figure 2. Interdiffusion Model for a Silane-Primed EVA/Glass Joint
A. FOURIER TRANSFORM INFRARED (FTIR) SPECTROSCOPY OF SURFACES AND INTERFACES

FTIR provides great potential for surface studies. Infrared spectroscopy

is one of the most versatile, widely used techniques for the determination of

molecular structure. Recent advances in infrared spectroscopy also offer new

sampling methods to characterize surfaces of materials and absorbed species on

the surfaces. These methods include reflection and emission techniques. These

new sampling techniques are further enhanced using FTIR, rather than the conventional dispersive-type spectrometer. Moreover, data processing techniques such

as spectral subtraction and computer-scale expansion allow improved selectivity.

In FTIR, a Michelson interferometer is used instead of the prisms and

slits used in conventional infrared spectroscopy. Obviously, a slitless

spectrometer has an advantage in energy throughput. However, a more pronounced

advantage comes from the so-called Fellget's advantage, or multiplex advantage,

which allows all resolution elements to be detected simultaneously throughout

the spectral range; a dispersive instrument receives a signal only from one

resolution element at a time. The signal-to-noise ratio is proportional to

the square root of the number of resolution elements (i.e., the spectral range

divided by the resolution). Each scan takes only 1 s, so the signal-to-noise

ratio can be further increased by consecutive accumulation of scans as the

scan rate is on the order of 1 s.

In FTIR, an interferogram is obtained that consists of many waves of

different frequencies. This interferogram is collected as a function of

retardation time of the moving mirror that separates the light frequencies

according to their time of travel which is a function of the wavelength. This

interferogram is the Fourier transform of the desired infrared spectrum. The

spectrum is digitized so that it can be stored on the dedicated minicomputer

for further data processing.

1. Advantages of FTIR for Surface Studies

Surface studies are always a challenge to the limitations of

instruments and methods. Surface studies require sufficient sensitivity, a

high signal-to-noise ratio, and selectivity. It is apparent that the amount

of material at the surface (four or five atomic layers) is negligible compared

to the bulk. In a transmission experiment with a pressed disc, the bulk

equivalent of 103 monolayers must be penetrated. Therefore, the suppression

of the signal of the bulk (i.e., selectivity) is an essential factor.

Furthermore, the dynamic range of the instruments and techniques need to be

large, as is the case for FTIR.

2. Sampling Techniques for FTIR Spectroscopy Studies

The various techniques for the study of surfaces using FTIR have

been reviewed recently (Reference 15). For this work, two techniques were

used: transmission and diffuse reflectance (DRIFT). A discussion of the

transmission technique is unnecessary, as the technique is routine. However,

the digital subtraction approach is important and will be described in the

next section.
Although diffuse reflection sampling has been used in the ultraviolet

and visible region for a long time, it was only with the increased sensitivity

of FTIR that diffuse reflectance was possible in the infrared region. The

basic principle behind diffuse reflectance spectroscopy is that light incident

upon a solid or powdered surface is diffusely scattered in all directions

(Reference 16). The scattered light is collected with the proper optical setup

and directed to the infrared detector for analysis. Thus, diffuse reflectance

permits the study of surfaces of particulate and rough samples to be studied.

The principal advantages of diffuse in the infrared are: (1) it is a surface

spectroscopy technique which is quantitative, and (2) it allows opaque and/or

strongly absorbing solids and other problem samples to be studied with

relative ease.

Diffuse reflectance rather than transmission methods were used in this

study for several reasons, the first and foremost being the increased

sensitivity of diffuse reflectance to the coupling agent on the glass surface.

This sensitivity made the observation of very small amounts of coupling agents

possible. These measurements would have been difficult with ordinary

transmission techniques. Also, it is not necessary to alter the sample in any

way to obtain the spectrum. For transmission studies, the sample must be

ground to a small particle size, dispersed in potassium bromide,

and pressed into a pellet. The grinding process may destroy those chemical

bonds of direct interest in adhesion. Normally, in diffuse reflectance, the

powdered sample is mixed with powdered KBr and placed in a sample chamber.

3. Data Processing Techniques

In spite of the development of the reflection methods indicated

above, the study of surfaces using transmission measurements.remains the most

widely used technique, particularly for inorganic and organic substrates which

can be prepared in the appropriate form. It was recognized that absorbance

subtraction could be used for the study of surfaces. If the infrared spectrum

of a bulk sample is obtained and the same bulk sample is given a surface

treatment, spectral subtraction can be used to remove the interference. The

bulk phase and the resultant difference spectrum would then reflect the

differences in the surfaces before and after treatment. If the untreated

sample is subtracted from the treated sample, positive absorbance bands would

rise from the higher concentration of surface species in the treated sample,

and negative bands from species would be preferentially found in the untreated

surfaces. After the isolation of the difference spectrum, the absorbance scale

can be expanded to one-third of the signal-to-noise ratio, as the strong

absorbing bands due to the bulk have been removed, giving a very high

sensitivity for the technique. In this manner, one can determine the nature

of the chemical reactions occurring with surface treatments.

B. EXPERIMENTAL PROCEDURES (MATERIALS)

Sunadex glass is preferred for the solar modules, but it was anticipated

and confirmed that the flat glass would not have sufficient surface area to

allow detection of the coupling agent by FTIR, so particulate glass was used

to increase the surface-to-volume ratio. The specimens were prepared by

dispersing high loadings of extremely fine, essentially spherical glass
powder^ in the EVA 'and curing as usual to "set" the bond chemistry. The test

specimens were prepared to determine the effects of hydrothermal aging (heat

and water) on glass/primer/EVA bonds. These specimens were designed for use

in a parallel program in which the decay of mechanical properties (bond

strength) could be measured with simultaneous spectroscopic investigation of

the interface to follow the chemistry.

The test specimens consisted of both primed and unprimed glass powders

and both EVA (Elvax 150) and polyethylene were used as the polymers. The glass

powders were first washed in dilute mineral acid to remove alkaline residues

on the surface,' then dried and treated with primer^ until a total of 2 wt %

of active primer was deposited on the surface. The treated glass was then

used to prepare the formulations described in Table 1.

Tensile bars were cut from cured molded plaques and then exposed to

hydrothermal aging conditions by immersion in water at the times and

temperatures described in Table 2. The test bars resulting from these

exposures were then tested for mechanical properties before and after drying,

and also for spectroscopic examination.

C. FTIR SPECTROSCOPY STUDIES OF UNAGED EVA/GLASS INTERFACES

The FTIR spectra of each of the components in the EVA/glass-coupling

agent has been isolated as indicated in Figure 3. Spectrum A is EVA. The

spectrum shown as B is obtained from the total system containing all of the

components. Spectra C are the spectra of the interfaces involving the silane

at the EVA/glass interface. Spectrum D is the Y-MPS coupling-agent

interphase, and Spectrum E is the particulate glass. The discussion that

follows will explain the nature of these spectra and the information they

contain.

1. Glass

The diffuse reflectance spectrum (DRIFT) of the untreated or

pristine glass is shown in Figure 4. The strong bands observed below

1320 cm~l are the symmetric and asymmetric Si-O-Si stretching modes. The

spectrum shows little absorption in the organic alcohols (OH) stretching

region indicating very few siloxyl groups on the surface.

1-Potter's Industries, Hasbrouck Heights, New Jersey, Product 5000. Spherical

A-glass powder, 400 mesh, mean particle diameter approximately 20u, mean

surface area, 0.269 m^/g.

^Springborn Laboratories, Primer A11861, consisting of 90% Dow Corning Z-6030,

9% of Benzyl dimethylamine catalyst, and 1% Lupersol TBEC peroxide. These

active ingredients are dissolved in methyl alcohol to give a 1% solution.

Equivalent to approximately 100 monolayers of silane. The Z-6030 coupling

agent is chemically Y-methacryloxypropyltrimethoxy silane, commonly referred

to as Y-MPS.
Table 1. Adhesive Bonding Test Formulations

18181-A 18181-B 18181-C 18181-D

Elvax 150 (EVA)

Chemplex 6230 polyethylene

Lupersol TBEC

Unprimed glass beads

Primed glass beads

Volume percent loading

Cure: 1508C/20 min

100 100

100 100

1.5 PHR 1.5 PHR 1.5 PHR 1.5 PHR

110.8 PHR — 110.8 PHR

110.8 PHR — 110.8 PHR

30% 30% 30% 30%

all

PHR = Parts per hundred parts EVA or polyethylene.

Table 2. Hydrothermal Aging Conditions

Water Temperature Hours

100 250 500 1000 2000 5000

40°C

60°C

80°C

X X X X

X X X X

X . X X X

X = Time and temperature conditions tested.
4000 2900 1800 700

(B) COMPOSITE

(EVA/TBEC/GLASS/MPS)

18152-B

I I I I I I I I I

3800 3400 3000 2600 2200 1800 1400 1000 600

(C) COMPOSITE INTERFACE

(SILANE AT EVA/GLASS INTERFACE) (SILANE AT GLASS/EVA INTERFACE)

X 20 X 20

3000 2860 2820 2680

I I I I I I I I I I

3020 2880 2840 2800 2660 18001780176017401720170016801660

(D) COUPLING AGENT INTERPHASE X 20

I J

4000 3500 3000 2500 2000

WAVENUMBERS

1500 1000

Figure 3. Diffuse Reflectance Spectrum of Material

Components and Composites

10
MPS/AMINE MODIFIED PARTICULATE GLASS

PARTICULATE GLASS

DIGITAL SUBTRACTION (x 10)

4000 3500 3000 2500

WAVENUMBERS

2000 1500 1000

Figure 4. Diffuse Reflectance FTIR Spectra of Y-MPS/Amine Modified Particulate

Glass, the Untreated Particulate Glass, and the Difference Spectrum

Showing the Presence of the Y-MPS on the Surface.of the Glass

2. Coupling Agent on Glass Surface

The spectrum of the treated glass is shown in Figure 3 (shown

as C). The bottom spectrum (shown as E) shows the scale expanded (X10)

difference obtained by subtracting the spectrum of the untreated glass from

the treated glass. This difference reflects the spectrum of the coupling

agent on the glass surface.

The amount of coupling agent on the surface is determined by the concentration of the coupling agent in the aqueous solution. The DRIFT spectra of

particulate glass that has been treated with different concentrations of the

Y-MPS/amine agent are shown in Figure 5. Below a weight percent of 0.03, no

coupling agent is detected on the surface. The amount on the surface increases

as the concentration of treating solution increases. Figure 6 shows the

relationship between the integrated intensity of the carbonyl band of the Y-MPS

and the weight percent loading in the treating solution. A nearly linear

correlation is found. Calculations indicate that at 1% loading, there are

approximately 50 monolayers of coupling agent on the surface. This result is in

agreement with previous measurements of this kind for glass fibers (Reference 17),

Figure 7 shows the band assignments in this region with the 1720 cm~l

band being assigned to the free carbonyl stretching mode and the 1700 cm~l

to the H-bonded carbonyl mode. This latter mode is probably associated with

11
0 14 I I I

MPS/AMINE MODIFIED PARTICULATE GLASS

000|_

1800 1750 1700 1650

WAVENUMBER, cm-1

1600 1550

Figure 5. DRIFT Spectrum of Y-MPS/Amine Modified Particulate Glass. Showing the

Increase in the Intensities of the Y-MPS with the Percent Loading of

the Treating Solution

1200

100 0

> 800

c/)

z

z

0 60 0

or

O

? 40 0

200

I 1 I

MPS/AMINE MODIFIED GLASS

00

^

1 1

2 3 4

WEIGHT PERCENT LOADING

Figure 6. Plot of the Integrated Intensity of the Carbonyl Band of Y-MPS on

the Surface of the Particulate Glass as a Function of Weight Percent

Loading of the Particulate Glass

12
Z

cc

3 5

30

2 5

2 0

1 5

1 0

0 5 I I

1800 1750 1700

WAVENUMBERS

1650 1600

Figure 7. Spectrum of Y-MPS on the Surface of the Glass in the Carbonyl

Stretching Region Showing the Vibrational Band Assignments Including

the C = 0 and C = C Modes. (The band at 1700 cnr1 is the carbonyl

stretching mode arising from hydrogen bonding of the initial layer of

Y-MPS to the silanols on the glass surface.)

the hydrogen bonding of the Y-MPS to the glass surface and arises primarily

from the first monolayer of Y-MPS on the surface of the glass. The weaker

band at 1640 cm~l is assigned to the C = 0 stretching mode of the Y-MPS. This

band (at 1640 cm""-'-) is especially useful for following the polymerization of

the Y-MPS to polymethacrylate.

3. Hydrothermal Stability of the Glass/Coupling Agent Interface

In an effort to determine the hydrothermal stability of the

coupling agent on the glass surface, the treated glass powder was exposed to

water at 80°C for 3 h, and the spectra measured afterward. The amount of

coupling agent remaining on the surface is indicative of the relative

hydrolytic stability of the coupling agent on the surface (Reference 18).

Figure 8 shows the results of these measurements by comparing the amount of

coupling agent on the surface before and after water exposure. The results

indicate that with the amine catalyst, very little of the coupling agent is

removed by the water exposure, although without the amine (except for the

initial monolayer on the surface), all of the coupling agent is removed. The

behavior observed for the coupling agent on glass fibers without amine

catalyst indicates that most of the coupling agent can be easily removed

(Reference 19). The amine catalyst is apparently effective in condensing and

crosslinking the coupling agent interphase on the surface making the

interphase hydrothermally stable.

13
Figure 8.

140.0

120 0

1000

1-

CA>

w 800

Q

tu

< 600

O

LU

1-

z

400

200

OOf

1 1 1 1 1

O BEFORE HYDROTHERMAL TREATMENT

— X AFTER HYDROTHERMAL TREATMENT X _

AFTER HYDROTHERMAL TREATMENT

WITHOUT THE AMINE IN THE „

TREATING SOLUTION

 U

X

X

o ~

o

— —

X

X

0

x o

rxx-CP °-t — , , .- .- yoo^-^ ^ 1 1 r 1

Plot of

Loading

1 2345 6

WEIGHT PERCENT LOADING

the Integrated Carbonyl Band as a Function of Weight Percent

However, it has been observed that the nature of the glass surface plays

an important role in the hydrothermal stability. Figure 9 shows the spectrum

before and after hydrothermal treatment of Sunadex Glass, and it is apparent

that nearly all of the coupling agent has been removed. This problem can be

alleviated by an acid pretreatment of the glass as shown in Figure 10. In the

latter case, the only effect of the water is to hydrolyze the residual methoxy

groups of the coupling agent.

A. EVA

The spectrum of EVA obtained by DRIFT is shown in Figure 11. The

bands near 2800 cm~l are the carbon-hydrogen stretching modes of the

polyethylene backbone. The sharp band near 1800 cm~l is associated with the

carbonyl group of the vinyl acetate copolymer, and the remaining bands are

hydrocarbon in nature.

5. EVA/Glass Interface

In Figure 12, the spectrum of an EVA/glass composite is shown as

well as the spectrum of the silane modified glass. The final spectrum is the

subtracted spectrum which isolates the spectrum of the silane at the EVA/glass

interface. It is apparent that the silane carbonyl mode can be observed, but

the overlap of the acetate carbonyl band is extensive, making quantitative

measurements difficult. In the carbon-hydrogen stretching region, it can be
0 35

HYDROTHERMAL TREATMENT

0 00

3200 3100 3000 2900

WAVENUMBER , cm-1

2800 2700

Figure 9. Spectra of Y-MPS on Sunadex Glass Before and After Hydrothermal

Treatment Showing the Extensive Removal of the Silane with Water

Exposure

040

0 30

> 0 20

m

111

H

£ 010

0 00

-0 10

50 LAYERS

HYDROTHERMAL TREATMENT

I I I I

3200 3100 3000 2900 2800 2700

WAVENUMBER, cm -1

Figure 10. Spectra of Y-MPS on the Surface of Glass Spheres Which Have Been

Acid-Washed to Prepare the Surface Prior to Treatment with the

Silane. (The spectra are shown before and after hydrothermal

treatment showing that the acid improves the stability.)

15
50000

40000

>- 30 000

- 20 000

10000

0 000 ±

3800 3300 2800 2300

WAVENUMBER, cm-1

1800 1300

Figure 11. DRIFT Spectrum of Pure EVA

1 4

1 2

1 0

0 8

0 6

0 4

0 2

00 —

-0 2

C = O STRETCHING

EVA/GLASS COMPOSITE

SILANE MODIFIED GLASS

SILANE AT EVA/GLASS INTERFACE

I I I I

1800 1780 1760 1740 1720 1700 1680 1660

WAVENUMBER,

Figure 12. DRIFT Spectrum Showing the Silane at the EVA/Glass Interface. (The

top spectrum is the EVA/glass spectrum, the middle spectrum is the

spectrum of the Y-MPS modified glass, and the bottom is the

difference spectrum obtained by subtracting the treated glass

spectrum from the composite. The bands observed are associated

with the interfacial silane structure.)

16
observed that structural changes occur as a result of the peroxide-induced

polymerization of the coupling agent. This polymerization is indicated by the

loss of the carbon-hydrogen stretching mode of the vinyl group as indicated in

Figure 13. Quantitative determinations of the amount of Y-MPS polymerization

can be made. The calculations indicate that nearly 80% of the Y-MPS has

polymerized with the peroxide, and only 2Q% of the Y-MPS has polymerized in

the absence of the peroxide. This polymerization of the Y-MPS produces an

interlocking interpenetrating network with the EVA (see Figure 2). This

interpenetrating network has nonhydrolyzable carbon-carbon bonds as well as the

hydrolyzable Si-O-Si bonds. The presence of the carbon-carbon bonds should

contribute to the hydrothermal stability of the EVA/glass interface.

D. HYDROTHERMAL AGING OF EVA/GLASS INTERFACE

Accelerated aging tests were performed by placing the model composites in

water at 40, 60, and 80°C for lengths of time up to 5000 h at present. Samples

were removed at specified times and tested mechanically according to specification

ASTM D-638, and also tested by FTIR spectroscopy.

1. Mechanical Testing

For mechanical testing, the following properties were measured:

(1) Modulus (1% strain).

(2) Ultimate tensile strength.

8 0

7 0

6 0

5 0

4 0

3 0

2 0

1 0

00

SILANE AT

EVA/GLASS

INTERFACE

SILANE ON

SUBSTRATE

SURFACE

= CH2

3020 3000 2980 2960 2940 2920

WAVENUMBER, cm-1

2900 2880 2860

Figure 13. DRIFT Spectrum of Silane at the Interface Between Glass and EVA (Top

Spectrum) and the Spectrum of the Y-MPS Silane of the Glass. (The

top spectrum shows that the Y-MPS has polymerized during the

formation of the interface because of the initiation by the peroxide.)

17
(3) Ultimate elongation.

(4) Dimensional change (length).

(5) Weight change (water absorption).

These measurements are tabulated for each temperature in Tables 3 through

5, and Tables 6 through 8 give the results for the test specimens dried at 105°C

for a period of 72 h. The purpose for this was to determine the extent to which

the bond strength was reversible by simply removing the absorbed water.

At 40°C water immersion (see Table 3), little effect was noticed for all

the formulations except for 18181-A (EVA containing unprimed glass beads).

This specimen slowly increased in water absorption from +0.15% weight gain

after 100 h, to +51% weight gain after 2000 h. Apart from a minor decrease in

elongation, the properties of this compound remained unchanged.

The 60°C water immersions (see Table 4) were found to be more severe,

and then both the compounds with and without primer began to respond. The EVA

without primer gained an enormous +2000% increase in weight at the 2000-h test

point. The mechanical properties also shifted dramatically at this point and

the compound lost 90% of its modulus, 96% of its tensile strength, and about

90% of its elongation. The equivalent compound with primed glass gained only

+35% in weight; most of the other properties were only slightly affected. The

equivalent polyethylene specimens gained only 3 to 4% water and were

unaffected by the immersion. In the case of EVA, the difference between primed

and unprimed glass filler is noticeable and suggests that the properties at

the interface (adhesion bond) are responsible for the observed effects.

The next immersion temperature was 80°C (see Table 5) and resulted in

rapid deterioration of the EVA specimens containing unprimed glass. After

500 h, the specimen had increased 500% in weight, and lost 80% of its tensile

strength and elongation. Because of softening and tearing, this specimen did

not survive the 1000-h immersion test point and was removed from further

exposure. The EVA formulated with primer beads gained 61% by weight of water

at the 1000-h test point and retained most of its other properties reasonably

well. As with the previous experiments, the polyethylene compounds loaded

with primed and unprimed glass beads showed only small gains from water

absorption and were virtually unchanged.

It appears that the surface of the glass or the interface between the glass

and the polymer is extremely hygroscopic and is effective in trapping large

amounts of water in the polymer. The primer is of help in inhibiting this

phenomenon and seems to give at least a ten-fold reduction in the amount of water

absorbed. Water absorptions in the bulk polymer without fillers has been determined in a previous set of experiments (Reference 1). For EVA, the equilibrium

water content at 40 and 60°C is on the order of +0.3%. At 80°C, pure EVA (Elvax

150) equilibrates at approximately 1% by weight water. These water absorption

experiments indicate that the glass/polymer interface is the region affected.

A second set of test bars from the water immersion tests were dried to

determine the extent of property recovery and give an indication as to when

permanent and non-reversible damage had occurred. The results of these

experiments are given in Tables 6 through 8. For the 40°C immersions, all the

18
Table 3. Hydrothermal Aging of Glass Bead-Filled Polymer Specimens at 40°C

Specimen Property3

Control 100 h 500 h 2000 h

18181-A,

EVA, Without

Primer

18181-B,

EVA, With

Primer

18181-C,

Polyethylene,

Without

Primer

18181-D,

Polyethylene,

With Primer

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

2830

1380

600

—

—

2500

905

350

—

—

8 x 10*

2180

~0

—

—

1.6 x 105

4340

20

—

—

1.6 x 103

1295

600

+0.15%

0

1.6 x 103

1070

385

+0.19%

0

1.2 x 105

1995

10

+0.52%

0

1.7 x 105

4235

10

+0.31%

0

1.7 x 103

1230

570

+18.9%

+5.5%

1.8 x 103

900

190

+2%

0

1.2 x 105

-2200

0

+1.4%

0

1.6 x 105

-4380

0

0

0

8.3 x 102

1210

510

+51%

+15.3

2.4 x 103

1150

390

+3.5%

+1.3

1.2 x 105

2360

0

+2.5%

0

1.5 x 105

4490

0

+0.6%

0

aMechanical properties by ASTM D-638, 10 in./minimum rate of strain,

Awt % = percent weight gain; AL % = percent length gain-tensile bar.

19
Table 4. Hydrothermal Aging of Glass Bead-Filled Polymer Specimens at 60°C

Specimen

18181-A,

EVA, Without

Primer

18181-B,

EVA, With

Primer

18181-C,

Polyethylene,

Without

Primer

18181-D,

Polyethylene,

With Primer

Property3

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

Control

2830

1380

600

—

—

2500

905

350

—

—

8 x 104

2,180

~0

—

—

1.6 x 10'5

4340

20

—

—

100 h

1.8 x 103

1240

570

+0.92%

0

2 x 103

935

445

+0.36%

0

1.1 x 105

2230

5

+0.6%

0

1.6 x 105

4400

10

+0.33%

0

250 h

1.6 x 103

960

515

+29.3%

+10.8%

2.5 x 103

930

285

+4%

0

1.4 x 105

2510

~0

+1.4%

0

1.5 x 105

4450

~0

+0.7%

0

500 h

3.8 x 102

530

300

+410%

+78.4%

2 x 103

990

315

+6.3%

+6%

1.1 x 105

2070

~0

+2.5%

0

1.2 x 105

4270

~0

0

0

2000 h

3 x 101

50

60

+2015%

+179%

1.6 x 103

830

120

+34.7%

+12.5%

3 x 104

2710

~0

+4.8%

Ob

1.3 x 105

2980

~0

+3.08%

0

aMechanical properties by ASTM D-638, 10 in./minimum rate of strain,

Awt % = percent weight gain; AL % = percent length gain-tensile bar.

"Blistered appearance.

20
Table 5. Hydrothermal Aging of Glass Bead-Filled Polymer Specimens at 80°C

Specimen

18181-A,

EVA, Without

Primer

18181-B,

EVA, With

Primer

18181-C,

Polyethylene,

Without

Primer

18181-D,

Polyethylene,

With Primer

Property3

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

Control

2830

1380

600

—

—

2500

905

350

—

—

8 x 104

2180

~0

—

—

1.6 x 105

4340

20

—

—

100 h

1.7 x 103

460

365

+17.4%

+26.71

2.2 x 103

987

275

+1%

0

1.2 x 105

2145

10

+1.4%

0

1.8 x 105

4445

10

+0.43%

0

250 h

9.3 x 102

285

120

+568%

+109%

2.3 x 103

1010

245

+12.9%

+2.7%

1.3 x 105

2160

~0

+3 . 5%

+0.2%

1.7 x 105

3990

~0

+0.7%

0

500 h

1.1 x 103

310

100

+503%

+96 . 2%

3 x 103

910

220

+16.9%

+5.6%

1.3 x 105

2110

~0

+4.1%

+0.4%

1.4 x 105

3610

~0

+2.9%

+2.2%

1000 h

Removed*5

1.7 x 103

725

140

+61.7%

+21.5%

1.2 x 105

1930

~0

+4.3%

+0.6%

1.2 x 105

2910

~0

+4.5%

+0.2%

aMechanical properties by ASTM D-638, 10 in./minimum rate of strain,

Awt % = percent weight gain; AL % = percent length gain-tensile bar.

"Specimens too soft to be tested, break on handling.

21
Table 6. Effect of Drying Outa the Hydrothermally Aged Specimens

Reported in Table 3

Specimen

18181-A,

EVA, Without

Primer

18181-B,

EVA, With

Primer

18181-C,

Polyethylene,

Without

Primer

18181-D,

Polyethylene,

With Primer

Property^

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

Control

2.8 x 103

1380

600

—

—

2.5 x 103

905

350

—

—

8 x 104

2180

0

—

—

1.6 x 105

4340

20

—

—

100 h

2.4 x 103

1205

590

—

—

2.2 x 103

965

325

—

—

1.8 x 105

2790

-0

—

—

1.8 x 105

4720

~0

—

—

500 h

3.4 x 103

1280

565

—

—

3 x 103

990

315

—

—

1.6 x 105

1770,

~0

—

—

1.6 x 105

4571

~0

—

—

2000 h

2.2 x 103

1210

570

—

—

2.6 x 103

860

260

—

—

1.5 x 105

3710

~0

—

—

1.7 x 105

4380

~0

—

—

aDried in circulating air oven, 105°C, 72 h.

^Mechanical properties by ASTM D-638, 10 in./minimum rate of strain,

Awt % = percent weight gain; AL % = percent length gain-tensile bar.

22
Table 7. Effect of Drying Out3 the Hydrothermally Aged Specimens

Reported in Table 4

Specimen

18181-A,

EVA, Without

Primer

18181-B,

EVA, With

Primer

18181-C,

Polyethylene,

Without

Primer

18181-D,

Polyethylene,

With Primer

Property^

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

Control

2.8 x 103

1380

600

—

—

2.5 x 103

905

350

—

—

8 x 104

2180

0

—

—

1.6 x 105

4340

20

—

—

100 h

2.5 x 103

1270

590

—

—

2.6 x 103

955

290

—

—

1.6 x 105

2580

~0

—

—

1.9 x 105

4530

~0

—

—

250 h

3 x 103

1340

575

—

—

3.1 x 103

890

240

—

—

1.7 x 105

3680

~0

—

—

1.8 x 105

4890

~0

—

—

500 h

2.7 x 103

960

500

—

—

3.1 x 103

980

240

—

—

1.8 x 105

3050

~0

—

—

1.4 x 105

4510

~0

—

—

2000 h

1.1 x 103

480

280

—

—

2.8 x 103

850

240

—

—

1.8 x 105

2680

0

—

—

1.6 x 105

3590

0

—

—

aDried in circulating air oven, 105°C, 72 h.

^Mechanical properties by ASTM D-638, 10 in./minimum rate of strain,

Awt % = percent weight gain; AL % = percent length gain-tensile bar.

23
Table 8. Effect of Drying Out3 the Hydrothermally Aged Specimens

Reported in Table 5

Specimen

18181-A,

EVA, Without

Primer

18181-B,

EVA, With

Primer

18181-C,

Polyethylene,

Without

Primer

18181-D,

Polyethylene,

With Primer

Property^*

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

MOD

UT

UF, %

Awt %

AL %

Control

2.8 x 103

1380

600

—

—

2.5 x 103

905

350

—

—

8 x 104

2180

0

—

—

1.6 x 105

4340

20

—

—

100 h

2.7 x 103

1175

545

—

—

2.6 x 103

905

240

—

—

1.4 x 105

3160

~0

—

—

1.6 x 105

4415

~0

—

—

250 h

1.8 x 103

560

290

—

—

2.6 x 103

920

310

—

—

1.8 x 105

3280

~0

—

—

1.5 x 105

4100

~0

—

—

500 h 2000 h

(see footnote c)

2.8 x 103

1020

405

—

—

1.7 x 105

2440

~0

—

—

1.6 x 105

3800

~0

—

—

2.6 x 103

880

260

—

—

1.8 x 105

3010

~0

—

—

1.8 x 105

3710

~0

—

—

aDried in circulating air oven, 105°C, 72 h.

^Mechanical properties by ASTM Dr638, 10 in./minimum rate of strain,

Awt % = percent weight gain; AL % = percent length gain-tensile bar.

cBroken, removed from further testing.

24
specimens recovered almost all their original properties. At 60°C, signs of

permanent damage now became apparent in the EVA specimen filled with unprimed

glass beads. At the 500-h point, the tensile strength decreased by 30%, and

at the 2000-h point, it had decreased to 65% of control. About a 50% reduction

of elongation at break was also found at this point. The other EVA compound

containing primed glass recovered most of its control properties upon drying.

The 80°C test specimens gave much the same performance except that now nonreversible effects seem to start at after about 250 h in the unprimed EVA/glass

specimen. Primed EVA/glass specimens survived 2000 h at this temperature

without damage.

2. Spectroscopic Testing

As reported in the previous section, the mechanical properties as

a function of hydrothermal aging of the EVA composites without primer had substantial declines, whereas when the glass surface is treated with the primer

solution, the composites show a remarkable resistance to loss of mechanical

properties, as a function of hydrothermal aging time and temperature.

An additional result of the accelerated hydrothermal aging is the

incorporation of water into the composite structure, generally absorbing water

to many times their original weight.

For chemical information using FTIR spectroscopy, a preliminary

experiment was carried out involving an accelerated hydrothermal aging of an

EVA/glass composite. The test consisted of an 85°C water treatment for

2 months with subsequent drying at 100°C in vacuum. The FTIR spectra of the

sample over the region 2200 to 3800 cm"1 before and after the hydrothermal

treatment are shown in Figure 14. No major chemical differences were observed

except for the apparent uptake of water which, was not removed in spite of the

rather substantial drying. This water is presumed to be on the surface of the

glass powder as it is well known that the interface is the preferred site of

the sorbed water. Examination of the spectra of the hydrothermally treated

sample in other spectral regions showed no observable chemical degradation

after 2 months. The primed EVA/glass interface has resisted hydrothermal

attack up to at least 2 months (1440 h) of accelerated testing. This

represents extraordinary stability.

The EVA/glass composites (which had undergone up to 2000 h of

hydrothermal aging in water at 60°C, and whose aging properties are shown in

Table 4) were also examined by FTIR spectroscopy. The FTIR spectra of these

samples after 100, 250, 500, and 2000 h are shown in Figure 15, over the

region 3500 to 4000 cm"1. Up to 500 h, FTIR spectroscopy of this sample

found no evidence for chemical changes and, as with the preliminary sample,

detected only water uptake.

However, at 2000 h of hydrothermal aging, a new infrared band occurred

at 3680 cm-1 [see Figure 15(D)]. With this finding, the FTIR spectra of the

unprimed EVA/glass composites which had been hydrothermally aged at 60°C were

taken to serve as comparative controls. Again, after 2000 h of aging, this new

band at 3680 cm"1 was observed, and it was tentatively concluded that this

was not related to the primer. Examination of the mechanical property data in

Table 4 for the primed EVA/glass specimen hints at changes (after 2000 h) that

25
EVA/MPS/PEROXIDE

BEFORE AND AFTER HYDROTHERMAL CYCLING

>-

t

z

200

15 0

10.0

5 0

00

3800 3600 3400 3200 3000 2800 2600 2400 2200

WAVENUMBER, cm-1

Figure 14. DRIFT Spectrum of the EVA/Y-MPS-Peroxide Before and After

Hydrothermal Cycling. (The uptake of water is shown by the

increase in the absorption between 3610 and 3200 cm^-.)

4000 3900 3800 3700

WAVENUMBER, cm~1

3600 3500

Figure 15. FTIR Spectra of Primed EVA/Glass Bead Specimens, Hydrothermally

Aged at 60°C

26
seem to be outside the data patterns observed for lower aging times. It is

tempting to interpret this band as spectroscopic evidence of some irreversible

interfacial event related to hydrothermal attack, although assignment of this

band to a given chemical reaction is not clear at this time.

27
SECTION III

CHEMICAL BONDING BETWEEN SOLAR CELLS AND EVA

Ethylene/vinyl acetate (EVA) has been developed for use as an

encapsulation material for photovoltaic devices. However, there are two

important problems associated with the use of EVA in such applications:

(1) the adhesion of EVA to the aluminized rear surface "of silicon cells is

poor, especially during exposure to moisture or high relative humidities at

elevated temperatures; and (2) most tests (such as the- peel test) that are

used to evaluate the adhesion are destructive in nature. Such tests provide

little information about the onset of delamination processes and about the

likely lifetime of a bonded assembly.

The initial phase of this research had two primary objectives: (1) to

investigate the use of silane coupling agents as primers to enhance the

hydrothermal stability of adhesive bonds between EVA and aluminum, and (2) to

develop non-destructive optical techniques for determining the stability of

polymer/metal interfaces during exposure to moisture at elevated temperatures.

Toward this end, qualitative tests were carried out investigating the adhesion

of EVA to several types of aluminum substrates, which included vapor-deposited

aluminum mirrors on glass, and the aluminized back surfaces of commercial solar

cells. The results obtained are described below.

A. ALUMINUM MIRRORS

Adhesive bonding between EVA and most aluminum surfaces without primers are

weak and are weakened even further by exposure to warm water.- The hydrothermal

stability of the EVA/aluminum interface is improved by the use of silane primers.

For studies with aluminum mirrors, reflection-absorption infrared (RAIR)

spectroscopy has been used to determine the nature of the interface between

Y-MPS and the oxidized surface of aluminum. RAIR is a technique for obtaining

infrared spectra of thin films on metal substrates by reflecting infrared

radiation polarized parallel to the plane of incidence off the metals at large,

almost grazing angles. RAIR spectra obtained- from Y-MPS films deposited on

aluminum mirrors from dilute methanol solutions were always characterized by

absorption bands near 1720 and 1100 cm~l that were assigned to carbonyl and

siloxane groups (Figure 16), regardless of the concentration of the solutions.

However, spectra obtained from Y-MPS films that were deposited from methanol

solutions, and then rinsed with methanol, were characterized by bands near 1700

and 930 cm~l (Figure 17). The band near 1700 cm~l was assigned to carbonyl

groups that were hydrogen bonded to surface hydroxyl groups. The band near 930

cm~l was assigned to silanol groups that were also hydrogen bonded to the

substrate. It seems that the first layer of Y-MPS molecules is absorbed onto

aluminum by hydrogen bonding through both the silanol and carbonyl groups. This

may help to explain the effectiveness of Y-MPS as a primer for enhancing the

hydrothermal stability of adhesive bonds between EVA and substrates such as

aluminum. If the first layer of Y-MPS is absorbed through two functional

groups, it may be more difficult to displace from the surface than if it was

absorbed only through, for instance, the silanol groups.

29

PRECEDING PAGE BLANK NOT FILMED
I 1'

05%

I 0 125%

I I I I

1800 1600 1400 1200 1000

WAVENUM8ER, cm-1

800

Figure 16. Infrared Spectra of Y-MPS Films with Three Different Thicknesses

Deposited on Aluminum Mirrors

0 025%

1800 1600 1400 1200 1000

WAVENUMBER, cm-1

800

Figure 17. Infrared Spectra of: (A) Thick, and (B) Thin (Monolayer) Films

of Y-MPS on Aluminum Mirrors

30
Another important result obtained during the first phase of this research

with aluminum mirrors was the development of ellipsometry as a non-destructive

probe for monitoring the polymer/metal interface during exposure to an

aggressive environment such as warm water. This technique involves the use of

an optical ellipsometer to measure the relative amplitude reduction (called Y),

and the relative phase shift (called A) for the parallel and perpendicular

components of linearly polarized light reflected from a polymer-coated metal

substrate that is immersed in warm water.

Results obtained for an uncoated aluminum mirror that was evaporated

onto a glass slide and then immersed in water at 40°C indicated that A

initially decreased by several degrees before increasing somewhat, and then

decreased again (Figure 18). The first decrease in A was interpreted as the

dissolution of the native oxide, and the second decrease indicated

reprecipitation of the hydroxide known as pseudoboehmite on the aluminum

surface.

The conversion of the native oxide on aluminum to the hydrated oxide

pseudoboehmite is generally considered to be the cause of debonding of

polymers from aluminum in the presence of warm water (Reference 20). In order

to obtain stable bonds between a rubbery polymer such as EVA and aluminum, it

is necessary to inhibit that corrosion. These preliminary tests with uncoated

aluminum mirrors demonstrated that the corrosion reaction could be followed by

RAIR and also by ellipsometry. The next series of experiments were intended

to learn if these same techniques could monitor the corrosion reaction through

a coating of EVA.

B. ALUMINUM MIRRORS WITH EVA COATINGS

When a thin film of EVA containing the cross-linking agent Lupersol 101

was laminated onto an unprimed, vapor-deposited aluminum mirror and then

immersed in warm water, ellipsometry results similar to those shown in

Figure 19 were obtained. An induction period lasting approximately 10 h was

observed during which A changed very little. Thereafter, A increased slowly,

but steadily. When a thin film of A-11861 primer was applied to the aluminum

substrate before the substrate was laminated with EVA, the ellipsometry results

were similar, but the rate of increase of A as a function of time after the

induction period was considerably lower.

When a thin film of EVA containing the cross-linking agent TBEC was

laminated onto an aluminum film that had been evaporated onto a glass slide and

then immersed in warm water, the ellipsometry results were quite different.

In that case, almost no induction period was observed. Instead, A began to rise

almost immediately (Figure 20).

These results were interpreted as follows:

(1) When EVA is cross-linked with Lupersol 101, the reaction proceeds

mostly through the vinyl acetate groups.

(2) The ethylene units are relatively unaffected and remain in rather

crystalline regions.

31
01

OJ

TJ

I_-l

L1J

Q

142

138

134

130

126

30 60 90 120

IMMERSION TIME, mm

150 180

Figure 18. Ellipsometry Parameter A Versus Immersion Time in Water at 40°C for

an Uncoated Aluminum Mirror

208

204

200

196

10 100

IMMERSION TIME, h

1000

Figure 19. Ellipsometry Parameter A Versus Immersion Time in Water at 40°C for

EVA Cured with Lupersol 101 Laminated on Vapor-Deposited Aluminum

32
—

<

265

255

245

235

O

I

10 100

IMMERSION TIME, h

1000

Figure 20. Ellipsometry Parameter A Versus Immersion Time in Water at 40°C

for EVA Cured with TBEC Laminated on Vapor-Deposited Aluminum

(3) Water does not diffuse through these crystalline regions very

quickly and a substantial induction period is observed before

water reaches the aluminum surface.

(4) Once water reaches the surface, dissolution of the native oxide

and reprecipitation of pseudoboehmite begin.

(5) The arrival of water at the interface and the precipitation of

pseudoboehmite both cause the parameter A to rise.

When EVA is cross-linked with TBEC, cross-linking occurs through both

the ethylene and vinyl acetate groups. In this case, there are no crystalline

ethylene regions and the diffusion of water to the interface is fast. The

ellipsometry parameter A rises quickly during exposure to water at elevated

temperatures.

Independent of the choice of cross-linking agent, these experiments

nevertheless demonstrated that the moisture-induced corrosion of the surfaces

of aluminum mirrors could be detected by ellipsometry through a coating of

cross-linked EVA. In addition, there was some evidence that Y-MPS slowed,

but did not stop the corrosion of these aluminum mirrors.

C. ALUMINIZED SOLAR CELLS

Two different kinds of aluminized back surfaces have been identified

using scanning electron microscopy. Both kinds are quite rough, but there are

significant differences in their morphologies. The first type of aluminized

33
back surface consists of ridges separated by channels (Figure 21). Analysis

of such surfaces by energy dispersive x-ray analysis (EDAX) showed that they

contained a great deal of silicon as well as aluminum. Generally speaking,

the ridges were rich in silicon and the channels were rich in aluminum

(Figure 22). These solar cells with a back surface mixture of aluminum and

silicon were designated "type 1" solar cells.

Auger electron spectroscopy (AES) was also used to characterize the back

surfaces of "type 1" cells. Auger spectroscopy is much more surface sensitive

than EDAX, but the results were similar. Silicon Auger bands were observed

near 78 and 92 eV (Figure 23). The band near 78 eV is characteristic of

silicon in an oxide and the band near 92 eV is indicative of elemental silicon.

The aluminum AES bands were observed near 53 and 64 eV. These bands are

characteristic of aluminum in the oxidized and elemental states, respectively.

The second type of aluminized back surface solar cells, designated as

"type 2," was characterized by large numbers of small, irregularly shaped

features (Figure 24). X-ray photoelectron spectra (XPS) of such surfaces were

characterized by bands near 74, 124, 285, and 531 eV (Figure 25). The XPS

bands near 74 and 124 eV were assigned to aluminum in an oxidized state, and

the XPS band near 531 eV was assigned to oxygen in an oxide, indicating that

the back surface of "type 2" cells was mostly composed of an aluminum oxide.

The XPS band near 531 eV was assigned to carbon in absorbed hydrocarbons.

There was essentially no silicon on the back surface of "type 2" cells.

Figure 21. Scanning Electron Micrograph of Back Side of

Cell (5000X)

'Type 1" Silicon

34
ORIGINAL PAGE IS

OF POOR QUALITY

(A)

Figure 22.

(B)

EDAX: (A) Silicon and (B) Al Maps of Back Side of Same Silicon

Cell as in Figure 21

35
t/5 3

LU

/A I

Figure 23.

10 20 30 40 50 60 70 80 90 100

KINETIC ENERGY, eV

Auger Electron Spectra of Back Side of Same Silicon Cell as in

Figure 21

Figure 24. Scanning Electron Micrograph of Back Side of "Type 2" Silicon Cell

(2000X)

36
Figure 25.

100009000 8000 7000 600.0 5000 4000 300.0 2000 1000 00

BINDING ENERGY, eV

X-ray Photoelectron Spectrum of Back Side of As-Received "Type 2"

Silicon Cell

Several different investigations were carried out to determine the

failure mechanisms for adhesive bonds between EVA and the aluminized back

surfaces of silicon cells. In one experiment, an EVA film was laminated onto

an unprimed "type 2" cell and then peeled off. The adhesion of the film to

the cell was very good and it was very difficult to peel the film. XPS

spectra, obtained from the cell after the EVA film had been peeled off, were

characterized by a strong band near 285 eV that was assigned to carbon

(Figure 26). However, there was very little evidence of aluminum, indicating

that the failure of the bond was cohesive within the EVA. In a repeat

experiment, EVA was laminated onto the backside of an unprimed "type 2" cell

and the cell was then boiled in water for 1 h. Once again, it was very

difficult to peel the EVA from the cell, indicating that the adhesion of the

film to the cell was still quite good. However, some evidence for aluminum

was observed in the XPS spectra obtained from the cells, showing that the

locus of failure between EVA and aluminum was closer to the interface after

boiling in water (Figure 27), presumably because of the formation of

pseudoboehmite.

The tests just described were destructive in nature and, as indicated

earlier, the program intent is to develop non-destructive tests. Therefore,

the application of optical techniques (such as ellipsometry and reflectionabsorption infrared spectroscopy) for the non-destructive characterization of

adhesive bonds between EVA, and the aluminized back surface of silicon cells

have been investigated.

It was determined, however, that ellipsometry was not suitable for use

on the back surfaces of the cells. These surfaces were much rougher than the

surfaces of aluminum mirrors and, therefore, accurate ellipsometry data could

not be obtained. As a result, we have concentrated on the use of infrared

37
l.O 9000 800.0 700.0 6000 500.0 4000 3000 2000 1000 00

BINDING ENERGY, eV

Figure 26. XPS Spectrum of Laminated "Type 2" Silicon Cell After

Peeling EVA Film

COo_

x

Figure 27.

i —

100009000 8000 7000 600.0 500.0400.0 3000 2000 1000 00

BINDING ENERGY, eV

XPS Spectrum of Laminated "Type 2" Silicon Cell After Boiling 1 h

and Peeling EVA Film

38
spectroscopy for the non-destructive characterization of the interface between

EVA and the backside of silicon cells. Trial experimentation indicated that

"type 1" solar cells were a better choice for RAIR examination because of much

higher specular infrared reflectivity.

D. REFLECTION ABSORPTION INFRARED SPECTROSCOPY STUDIES

As described earlier, the failure mechanism of adhesive bonds to

aluminum mirrors usually involves the conversion of the native oxide to the

hydrated oxide known as pseudoboehmite (Reference 20) and, initially, it was

desired to determine if exposure of solar cells to water at elevated

temperatures also resulted in the formation of pseudoboehmite on the back

surfaces of these cells. Infrared spectra was obtained from the backside of a

"type 1" cell before and after the cell was boiled in water for 1 h. The

results are shown in Figure 28. The spectrum obtained from the cell before

boiling was essentially flat and featureless, but the spectrum obtained after

boiling was characterized by a strong band near 1080 cm~l that was

indicative of pseudoboehmite.

Next, it was desired to determine if the formation of pseudoboehmite

beneath a film of EVA could be detected by RAIR. Accordingly, the infrared

spectrum was obtained of a "type 1" cell that was boiled in water for 30 min

and then coated with a thin film of uncrosslinked EVA that was several hundreds

of angstroms in thickness (Figure 29). Strong bands characteristic of EVA

were easily observed near 1740 and 1255 cm~^, but the band near 1080 cm~l

that is characteristic of pseudoboehmite was also observed. These results

showed that pseudoboehmite could be detected beneath EVA films on silicon

cells.

Next, a thin film of uncrosslinked EVA was applied to a "type 1" cell

and the cell was then boiled in water. Occasionally, the cell was removed

from the water and examined by infrared spectroscopy. The results obtained

are shown in Figure 30. Initially, only the bands characteristic of EVA were

observed near 1740 and 1255 cm"1-. However, after immersion of the cell in

boiling water for 20 min, some changes were observed in the infrared spectra

and, after 50 min, the band characteristic of pseudoboehmite was clearly

observed near 1080 cm"1-.

In another series of experiments, infrared spectroscopy was used to

determine the effects of a cross-linked coating of EVA with and without primer

A-11861 on the aluminized back surfaces of silicon cells. For the first test

without primer, a thin film of EVA was applied to a "type 1" cell by dipping

the cell in a 0.25% solution of EVA in chloroform. The film was then crosslinked using Lupersol 101 and the cell was immersed in boiling water. The cell

was removed from the water at intervals of 30 min and examined using infrared

spectroscopy. Initially, only bands characteristic of EVA were observed, but

after 30 min, the band characteristic of pseudoboehmite was clearly observed

near 1080 cm"1- (Figure 31). After 60 min, the band near 1080 cm~l was

quite strong, indicating that hydration of the aluminum oxide beneath the EVA

film was very rapid. Cross-linking of the EVA alone did not stop the

formation of the pseudoboehmite.

39
o

c/5

(/)

<

A

8

BEFORE IMMERSION IN BOILING WATER FOR 30 MIN

AFTER IMMERSION IN BOILING WATER FOR 30 MIN

2000 1800

I I I

1600 1400 1200

WAVENUMBER, cm-1

I

1000

Figure 28. Reflection Infrared Spectra Obtained from Aluminized Back Side of

"Type 1" Silicon Cell

05

oc

toc

\ \ I

2000 1800 1600 1400 1200

WAVENUMBER, cm~1

I

1000

Figure 29. Reflection Infrared Spectrum Obtained from Aluminized Back Side of

"Type 1" Silicon Cell, Boiled in Water for 30 min, and Then Coated

with a Thin Film of EVA
en

(T

IA = BEFORE IMMERSION IN BOILING WATER

AND AFTER IMMERSION FOR

B = 20 MIN

C = 50 MIN

I I I _L

2000 1800 1600 1400 1200

WAVENUMBER, cm-1

1000

Figure 30. Reflection Infrared Spectra Obtained from Aluminized Back Side of

a "Type 1" Silicon Cell Coated with a Thin Film of EVA

O

<

<r

A = BEFORE BOILING IN WATER FOR 30 MIN

B = AFTER BOILING IN WATER FOR 30 MIN

1800 1700 1600 1500 1400 1300 1200 1100 1000

WAVENUMBER, cm

-1

Figure 31. Reflection Infrared Spectra Obtained from the Back Side of a

"Type 1" Silicon Cell Coated with a Thin Film of EVA, But No Primer
Finally, the experiment just described was repeated, except that a thin

film of primer A-11861 was applied to the backside of the cell before the EVA

film was applied and cross-linked. The initial spectra of the cell were

similar to those of the unprimed cell, except that some bands characteristic

of the primer were observed between 1200 and 1000 cm~l [Figure 32(A)].

However, the band near 1080 cm~l was not observed even after the cell was

immersed in boiling water for times as long as 90 min [Figure 32(B)], and it

was concluded that the primer inhibited the formation of pseudoboehmite on the

aluminized back surfaces of "type 1" solar cells. This result is in dramatic

contrast to the behavior of aluminum mirrors, where EVA and the Y-MPS-based

primer was not effective to stop pseudoboehmite formation. Although

unexplained at this time, the possibilities of a self-priming EVA for both

glass and solar cells using a common primer is strongly indicated.

The results obtained thus far can be summarized as follows. The adhesion

of EVA to the oxidized surfaces of smooth metals is marginal, but is improved by

the use of primers containing silane coupling agents such as Y-MPS. Ellipsometry

is an excellent in-situ, non-destructive technique for monitoring the stability

of interfaces between EVA and smooth, reflecting metals. The aluminized back

surfaces of silicon cells are very rough and porous. The adhesion of EVA to such

surfaces is excellent, especially when primers containing Y-MPS are used.

Failure of adhesive bonds between EVA and the aluminized back surface of silicon

cells during exposure to moisture at elevated temperatures involves the transformation of the native oxide to the hydrated oxide known as pseudoboehmite.

Ellipsometry cannot be used to follow the formation of pseudoboehmite on the back

surfaces of such cells because of their poor reflectivity. However, infrared

spectroscopy can be used to determine the formation of pseudoboehmite under EVA

films on the back surfaces of silicon cells.

A = BEFORE BOILING IN WATER FOR 90 MIN

B = AFTER BOILING IN WATER FOR 90 MIN

o

(/5

5

C/J

<

Figure 32.

1800 1700 1600 1500 1400 1300 1200 1100 1000

WAVENUMBER, cm"1

Reflection Infrared Spectra Obtained from the Back Side of a

"Type 1" Silicon Cell Coated with Thin Films of A-11861 Primer

and EVA
SECTION IV

REFERENCES

1. Willis, P.B., Investigation of Test Methods, Material Properties, and

Processes for Solar Cell Encapsulants, Eighth Annual Report, DOE/JPL954527-84/27, Springborn Laboratories, Inc., Enfield, Connecticut,

July 1984.

2. Willis, P.B., Investigation of Test Methods, Material Properties, and

Processes for Solar Cell Encapsulants, Ninth Annual Report, DOE/JPL954527-85/28, Springborn Laboratories, Inc., Enfield, Connecticut,

July 1985.

3. White, M.L., "Encapsulation of Integrated Circuits," Proceedings of the

IEEE, Vol. 57, p. 1610, 1969.

4. Jaffe, D., "Encapsulation of Integrated Circuits Containing Beam Leaded

Devices with a Silicone RTV Dispersion," IEEE Transactions on Parts,

Hybrids, and Packaging, Vol. PHP 12, p. 182, 1976.

5. White, M.L., "Encapsulating Integrated Circuits," Bell Laboratories

Record, p. 80, March 1974.

6. Shar, N.L., and Feinstein, L.G., "Performance of New Copper-Based

Metallization Systems in an 85°C, 80% RH, Cl£ Contaminated

Environment," Proceedings of 1977 Electronic Components Conference,

pp. 84-95, 1977.

7. Plueddemann, E.P., Chemical Bonding Technology for Terrestrial Solar

Cell Modules, JPL 5101-132, Jet Propulsion Laboratory, Pasadena,

California, September 1, 1979.

8. Coulter, D.R., Cuddihy, E.F., and Plueddeman, E.P., Chemical Bonding

Technology for Terrestrial Photovoltaic Modules, JPL Publication 83-86,

Jet Propulsion Laboratory, Pasadena, California, November 15, 1983.

9. Hair, M.L., Infrared Spectroscopy in Surface Chemistry, Marcel Dekker,

Inc., New York, 1967.

10. Little, L.H., Infrared Spectra of Absorbed Species, Academic Press,

London, 1966.

11. Ishida, H., and Koenig, J.L., J. Coll. and Inter. Sci., Vol. 64, p. 555,

1978.

12. Chiang, C.H., and Koenig, J.L., J. Polym. Sci., Polym. Phys. Ed.,

Vol. 20, p. 2135, 1982.

13. Graf, R.T., Koenig, J.L., and Ishida, H., J. Adhesion. Vol. 16, p. 97,

1983.

43
14. Graf, R.T., Koenig, J.L., and Ishida, H., Anal. Chem., Vol. 56, p. 773,

1984.

15. Culler, S.R., Ishida, H., and Koenig, J.L., The Use of Infrared Methods

to Study Polymer Interfaces, Ann. Rev. Mater. Sci., Vol. 13, p. 363,

1983.

16. Kortum, G., Reflectance Spectroscopy, Springer-Verlag, New York, 1969.

17. Graf, R.T., Koenig, J.L., Ishida, H., Anal. Chem., Vol. 56, p. 773, 1984.

18. Ishida, H., and Koenig, J.L., J. Polym. Sci., Polym. Phys. Ed., Vol. 18,

p. 233, 1980.

19. Ishida, H., and Koenig, J.L., J. Polym. Sci., Polym. Phys. Ed., Vol. 18

p. 1931, 1980.

20. Boerio, F.J., Gosselin, C.A., Dillingham, R.G., and Liu, H.W., Analysis

of Thin Films on Metal Surfaces, J. Adhesion, Vol. 13, pp. 159-176, 1981.

44
TECHNICAL REPORT STANDARD TITLE PAGE

1. Report No. ^ 2. Government Accession No.

4. Title and Subtitle

Chemical Bonding Technology: Direct

Investigation of Interfacial Bonds

7. Authorfc)

J . Koenig

9. Performing Organization Name or

JET PROPULSION LAB<

California Institul

4800 Oak Grove Drii

Pasadena, Calif orn.

id Address

DRATORY

te of Technology

/e

La 91109 .

12. Sponsoring Agency Nome and Address

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

Washington, D.C. 20546

3. Recipient's Catalog No.

5. Report Dote

January 1986

6. Performing Organization Code

8. Performing Organization Report No.

10. Work Unit No.

11. Contract or Grant No.

NAS7-918

13. Type of Report and Period Covered

JPL Publication

14. Sponsoring Agency Code

15. Supplementary Notes Sponsored by the U.S. Department of Energy through Interagency

Agreement DE-AI01-85CE89008 with NASA; also identified as DOE/JPL 1012-120 and as

JPL Project No. 5101-284 (RTOP or Customer Code 776-52-61).

16. Abstract

This is the third Flat-Plate Solar Array (FSA) Project document reporting

on chemical bonding technology for terrestrial photovoltaic (PV) modules. The

impetus for this work originated in the late 1970s when PV modules employing

siliconne encapsulation materials were undergoing delamination during outdoor

exposure. At that time, manufacturers were not employing adhesion promoters

and, hence, module interfaces in common with the siliconne materials were only

in physical contact and therefore easily prone to separation if, for example,

water were to penetrate to the interfaces. Delamination with siliconne

materials virtually vanished when adhestion promoters, recommended by siliconne

manufacturers, were used. This report describes the activities related to the

direct investigation of chemically bonded interfaces.

17. Key Words (Selected by AutHor(j))

Organic Chemistry

18. Distribution Statement

Unclassified-unlimited

19. Security Clossif. (of this report)

Unclassified

20. Security Clossif. (of this poge)

Unclassified

21. No. of Poges

54

22. Price

JPL 01M N9IU