ThreeBond Technical News
Issued January 1, 2014

83

Dye-Sensitized Solar Cell SealantIntroduction
Renewable energy development is currently underway all across the world in an effort to ensuresufficient energy resources. Among such research, there are high expectations for the permanent andclean energy produced by solar cells, so a variety of solar power generation system specifications
are being constructed. While silicon solar cells are currently the most widely used, research on
alternative materials is aggressively pursued due to the high cost of silicon and supply issues
concerning silicon materials. One of these alternatives is the dye-sensitized solar cell (hereafter
abbreviated as DSSC).
As we mentioned in Technical News No. 65, ThreeBond has long been engaged in the developmentof DSSC sealant and we are pleased to announce the release of three dye-sensitized solar cellsealants, ThreeBond 3035B, ThreeBond 3035C and ThreeBond 3118.
In this article, we will explore their properties advantages and usage.
Hereafter, ThreeBond is abbreviated as TB.

Table of Contents

Introduction.................................................1
1. What are DSSC?.....................................2
2. DSSC Electricity Generation
Mechanism .............................................2
3. DSSC Composition.................................3
4. Properties Required of DSSC Sealant....3
5. DSSC Sealant and Application...............3
5-1 DSSC Sealant TB3035B .................4

5-2 DSSC Sealant TB3035C..................5
5-3 DSSC Sealant TB3118.....................5
6. Sealant Selection....................................7Closing........................................................81

1.

What are DSSC?

Solar cells are systems that convert energy from sunlightinto electrical energy. They are classified by materials
used as indicated in Figure 1. Dye-sensitized solar cells are
an organic type of solar cell where dyes absorbed within
titanium oxide nanostructures absorb light energy, convert
it into electrons via electrochemical properties then extract
it as electricity. Though inferior to the more widely usedsilicon solar cells in terms of power generation efficiency,
their materials are inexpensive, they are easy to construct
and their design is excellent. They can also generate powerwith weak indoor light, and such generation is not easilyinfluenced by the angle of incident light. Thus, development
continues to progress towards their practical application asa next-generation solar cell.

(4) These iodide ions are then oxidized into triiodide ions byredox reaction with the dye.
Electric energy is extracted through repetition of the processfrom (1) to (4).

Active electrodeee-

One of the issues getting in the way of this application is longterm durability. If the organic solvent electrolite solutionthat fills the cell should leak, performance dramatically.

2.

DSSC Electricity Generation
Mechanism

Electrolyticsolution

II-I3-I-ee-

DSSC generate electricity through the mechanism shown inFigure 2.

Counter electrode(1) Dye is excited by exposure to light, exciting the groundstate electrons.
(2) Excited electrons pass through the outer circuit, moving
toward a counter electrode.

TiO2
Dye

Conductive
film

Fig. 2 DSSC Electricity Generation Mechanism(3) Having reached the counter electrode, the electrons
reduce the triiodide ions contained in the electrolytic
solution into iodide ions.

Single crystal
CrystalPolycrystal

SiliconAmorphousSingle crystal (GaAs)
Solar cell

CompoundPolycrystal (CdS, CdTe, CuInGaSe2, etc.)

Dye sensitized (DSSC)
Organic
Organic thin film
Fig. 1 Solar Cell Classification

23.

DSSC Composition

Main seal

DSSC are structured as indicated in Figure 3 and mainly
made of the following materials.

End sealInterfaceleakage
Permeation
leakage• Substrate (glass or film with a transparent conductivefilm)

Interfaceleakage

Permeation
leakage• Electrolytic solution• Main sealant that encapsulates the electrolytic solution• End sealant that fills the electrolytic solution injection
holeCell diagram

Fig. 4 DSSC Electrolytic Solution Leakage
End sealant (seals the electrolytic
solution injection hole)
Substrate

Mixture with outside moisture causes the dye to detach aswell as interior cell damage, so moisture protection is alsonecessary.

5.
Electrolyticsolution
Main sealant(seals the electrolyticsolution)
Substrate

Fig. 3 DSSC Composition

4.

Properties Required for DSSC Sealant

DSSC generate electricity through the chemical reaction
between the dye and the electrolytic solution. Protection
against leakage of electrolyte solution is vital to the efficientelectricity generation and prolonged DSSC performance.
Main and end sealant interface and permeation leakage
are considered factors in electrolytic solution leakage fromDSSC as indicated in Figure 4. Strong adhesion is required
between the sealant and the substrate to prevent interface
leakage, and protection is needed to prevent permeation
leakage of the electrolyte solution.
The electrolytic solution used for DSSC consists of organic
solvent, iodine and additives. Organic solvents generally
used here are characterized by their high polarity and theease with which they dissolve organic compounds. Ordinary
polymer compounds cannot achieve sufficient chemical
resistance, which may cause the sealant to be affected by theelectrolytic solution. A resin with a chemical structure thatresists erosion due to polar solvents and iodine is required inorder prevent both the organic solvent and the iodine fromescaping the cell.

DSSC Sealant and Application

At ThreeBond, we have developed TB3035B, TB3035C andTB3118, UV-curing DSSC sealants. These sealants takeproductivity into account and enable application of sealantas called for by design width and height.
As indicated by usage shown in Fig. 5, the main sealantis either screen printed or dispense coated, and once thesubstrates are stacked, the main sealant is cured under therecommended curing conditions. After this, electrolytic
solution is injected through the hold, end sealant is applied
and then exposed to UV rays to completly seal the cell.
Injection method
Main sealant

ODF method
Main sealantElectrolyticsolution

UV exposure
Sealant curing
Electrolyticsolution

End sealant

UV exposure
Sealant curing

Fig. 5 Sealant Application3

5-1 DSSC Sealant TB3035B
TB3035B is an acrylic DSSC sealant that cures when
exposed to UV or visible light with a wavelength of 200 to420 nm. (Fig. 6).

9080

Mass change rate (%)

In the ODF (One Drop Fill) method, the main sealant is either
screen printed or dispense coated followed by injection ofelectrolytic solution. Once the substrates are stacked, they
are exposed to UV rays to cure the main sealant.

7060
50
4030
20
100

TB3035B

TB3118

Epoxy
resin

Siliconeresin

Urethane
resin

Acrylicresin

Fig. 7 Post-Curing Electrolyte Resistance per Resin

Electrolyticsolution injection

When viewed
from the side...

Fig. 6 TB3035B Product Specifications

Completely covered withthe same glass type

Enclosed in resinand glass

Fig. 8 Creating a Dummy Cell

Table 1 Sealant Properties
FeaturesUnit

TB3035B

TB3035C

TB3118

Testing method-

Milky white

Milky whiteWhite

3TS-2100-002-

30 kJ/m2

30 kJ/m2

30 kJ/m2 +80°C × 1 h--

200 to 420 nm

200 to 420 nm

200 to 350 nm-

Viscosity

Pa·s

51

47

86

3TS-2F00-007

Hardness

-

D48

D42

D83

3TS-2B00-004

MPa

4.8

4.1

6.0-°C26241013TS-4730-001

g/m2·24h

97

90

32JIS K 7129

85°C, 85%RH

g/m2·24h

258

275

13JIS Z 0208

85°C,
3-methoxypropionitrile

Appearance
Recommended
curing conditions
Absorption
wavelength

Cross-peelingstrength
Glass transition
temperature
Water-vapor
permeability
Solventpermeability

4Remark(s)2.5 rpm

Glass/GlassTB3035B characteristics are indicated in Table 1. Using
acrylic resin that erodes very little in electrolytic solution
further increases electrolytic solution resistance. Figure 7
compares the electrolytic solution resistance of conventional
reactive resin and TB3035B.

Figure 9 shows the results of the UV exposure test regarding
electrolytic solution leakage performance depending onsealant width and sealant height. This figure indicates thata wide seal width and a low seal height improve electrolytic
solution leakage performance strength.

This figure indicates that TB3035B has a lower affinity
to electrolytic solutions than silicone, epoxy, acrylic andurethane resins.

Next, we performed the same test with different types ofelectrolytic solution. These results are indicated in Figure
10. The results make clear that there are large variations inelectrolytic solution barrier performance depending on thetype of electrolytic solution.

Figure 8 shows how we used a dummy cell to test TB3035Bsealing performance, the results of which are indicated inFigure 9 and 10.

Electrolytic solution leakage ratio (%)

35In addition to use as a main and end sealant for glass
substrates, TB3035B also boasts use as a main and end
sealant for UV ray-cutting film DSSC due to flexibility
which enables it to cure in visible light as mentioned above.

Seal width 2 mm

30

From the results above, we were then able to adjustelectrolytic solution leakage performance strength via sealwidth, sealant height and electrolytic solution type.

Seal width 5 mm
2520TB3035B has been praised as an all-around main and end
sealant that deftly handles any configuration of firm orflexible substrate.

15105001020304050Sealant height (µm)

60

5-2 DSSC Sealant TB3035C
TB3035C is the same kind of acrylic DSSC sealant as
TB3035B but with a 30 μm spacer added (Fig. 11).

Test conditions:

102 min. sun, 18 min. rainfall;
Light source: Xenon lamp, 100 cycles
Resin used:
TB3035B
Electrolytic solution: Acetonitrile base (iodine 0.05 M, potassium
iodide 0.01 M)

Fig. 9 Connection Between TB3035B Seal Widthand Sealant Height

Electrolytic Solution Leakage Ratio (%)

100
γ-butyrolactone
80Acetonitrile
Propylene carbonate

Fig. 11 TB3035C Product Specifications

60TB3035C characteristics are indicated in Table 1.
40

A 30 μm spacer is added in advance, making it possible tomaintain a constant clearance of 30 between the upper andlower substrates when using the main sealant. This prevents
short circuit-causing contact between the substrates.

2000

Test conditions:
Resin used:
Sealant Height:

24Seal width (mm)6102 min. sun, 18 min. rainfall;
Light source: Xenon lamp, 100 cycles
TB3035B
50 μm

85-3 DSSC Sealant TB3118
TB3118 is an epoxy DSSC sealant that cures under exposureof UV light with a wavelength of 200 to 350 nm (Fig. 12).

Fig. 10 TB3035B Sealing Performance byElectrolytic Solution

5

TB3118 characteristics are indicated in Table 1. TB3118
contains an epoxy resin that does not mix well withelectrolytic solution and has a high crosslink density,
making it excellent for water and electrolyte protection.
As shown in Figure 7, this results in electrolyte solutionresistance that is higher than that of conventional resins.
TB3118 sealing performance was tested using dummy cells,
the results of which are indicated in Figure 13 and 14.
The wider sealant width and lower sealant height of TB3118
also improve electrolyte solution leakage control.
Figure 15 shows electrolytic solution leakage in an 85°C
environment when TB3118 is cured as prescribed.

Fig. 12 TB3118B Product Specifications
Electrolytic solution leakage ratio (%)

35

TB3118 was applied to dummy cells, then cured at 30 kJ/m 2and 30 kJ/m2 + 80°C × 1 hr. These cells were then left in an
85°C environment for 6 weeks. Results of this test indicatethat 30 kJ/m2 + 30°C × 1 hr curing produces a lower rate ofelectrolytic solution leakage.

Seal width 2 mm

30Seal width 5 mm
2520While TB3118 cures to a practical level when exposed toUV rays at 200 to 350 nm, 30 kJ/m 2, adding heat is believed
to further accelerate the crosslinking reaction and improve
protection against electrolytic solution.

1510500102030405060

Center diameter or gap materials (µm)

Test conditions:

102 min. sun, 18 min. rainfall;
Light source: Xenon lamp, 100 cycles
Resin used:
TB3118
Electrolytic solution: Acetonitrile base (iodine 0.05 M, potassium
iodide 0.01 M)

Fig. 13 Connection Between TB3118 Seal Widthand the Seal Gap

Electrolytic solution leakage ratio (%)

Electrolytic solution leakage ratio (%)

When TB3118 is exposed to UV rays, the acid generated
acts as a catalyst to cause the curing reaction. This reaction
is neutralized if brought into contact with an electrolytic
solution containing a basic substance, preventing curing
through the acid/base reaction, which makes it unusable as
an ODF method end sealant.
5080
Acetonitrile

70

γ-butyrolactone

6050403020104530kJ/m 2

4030kJ/m 2+80˚C×1h35302520
151050001

Test conditions:
Resin used:
Sealant Height:

2345Seal width (mm)67102 min. sun, 18 min. rainfall;
Light source: Xenon lamp, 100 cycles
TB311850 μmFig. 14 TB3118 Seal Performance by Electrolytic
Solution6

Based on the above results, a combination of UV ray
exposure followed by heat application is recommended for
optimal curing of TB3118.

80123485°C curing time (weeks)

56Resin used:
TB3118
Seal width:
2 mm
Sealant height:
30 μm
Electrolytic solution: Acetonitrile base (iodine 0.05 M, potassium
iodide 0.01 M)

Fig. 15 TB3118 Electrolytic Solution Seal
Performance by Curing Conditions

Additionally, the film contains a UV ray absorber to prevent
deterioration, but this cuts UV ray wavelengths needed for
TB3118 to cure, making it impossible to use as a DSSC mainsealant. However, as indicated in Table 1, low moisture andsolvent permeability provide excellent protection, and crosspeeling bonding strength is high, giving it the durability
needed for use as a main sealant.

6.

Sealant Selection

There are certain main and end sealant combinations thatcannot be used depending on material composition.
This necessitates the selection of sealant that can handle
a variety of substrate materials, manufacturing methods
and other conditions. Figure 16 shows the process for mainsealant selection. Refer to Figure 16 to select the mostappropriate sealant.
Substrate material
Film

Glass

Cell manufacturing method
Injection method

No heat

TB311830µmTB3035C

Sealant curing method
Heat

Gap between substrates

ODF method

Other

TB3035B

Gap between substrates
30µm

Other

TB3035C

TB3035B

Gap between substrates
30µm

Other

TB3035C

TB3035B

Fig. 16 Main Sealant Selection

7

Closing

We are pleased to present our DSSC sealant.
Now that DSSC is commercially available, we expect that its utilization will only continue to expand. With this expansion, weare certain that what is required of sealants will also continue to grow.
At ThreeBond, we are dedicated to product and technology development centered on market trends that ensures our productdevelopment’s continued contribution to the manufacturing industry.
<References>
Technical News No. 65, Dye-Sensitized Solar Cell SealantThreeBond Fine Chemical Co., Ltd. R&D Headquarters
Development Division, Functional Materials Department
Masayuki Nagata
Hiroki Sakamoto
Kana Yasunaka

ThreeBond Co., Ltd.
84-3-3 Minamiosawa, Hachioji,
Tokyo 192-0398
Tel: +81-42-670-5333