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822 Materiali in tehnologije / Materials and technology 51 (2017) 5, 813–822
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
J. P. BANTANG, D. CAMACHO: GELLING POLYSACCHARIDE AS THE ELECTROLYTE MATRIX ...
823–829
GELLING POLYSACCHARIDE AS THE ELECTROLYTE MATRIX
IN A DYE-SENSITIZED SOLAR CELL
@ELIRNI POLISAHARID KOT ELEKTROLITNA OSNOVA V
SOLARNIH CELICAH, OB^UTLJIVIH NA BARVILA
Jose Paolo Bantang1, Drexel Camacho1,2
1De La Salle University, Chemistry Department, 2401 Taft Avenue, 1004 Manila, Philippines
2De La Salle University, Organic Materials and Interfaces Unit, CENSER, 2401 Taft Avenue, 1004 Manila, Philippines
drexel.camacho@dlsu.edu.ph
Prejem rokopisa – received: 2016-09-30; sprejem za objavo – accepted for publication: 2017-03-16
doi:10.17222/mit.2016.294
Hydrophilic polysaccharide, -carrageenan, was utilized as the polymer matrix in gel-electrolyte systems for dye-sensitized
solar-cell (DSSC) applications. The influence of the solvent system was investigated to optimize the solubility of -carrageenan
and tetrabutylammonium-iodide (TBAI)/I2 electrolytes by minimizing the water content because of its unfavorable effect on
DSSCs. We report herein that two solvent systems, a water/acetonitrile mixed solvent and DMSO, were found to effectively
dissolve the components. The composite natures of the -carrageenan-electrolyte systems in these solvents were confirmed with
an FTIR analysis. The presence of -carrageenan did not impede the electrochemical properties of the electrolytes, as confirmed
with cyclic voltammetry, electrochemical impedance spectroscopy and linear sweep voltammetry. The incorporation of the gel
electrolytes in DSSCs showed that the DMSO system exhibited better solar-cell efficiency compared to the mixed-solvent
system.
Keywords: dye-sensitized solar cell, -carrageenan, gel electrolyte, electrochemical impedance spectroscopy, ionic conductivity
Hidrofilni polisaharid, -karagen, je bil uporabljen kot polimerna osnova v `elirno elektrolitskih sistemih za uporabo v barvno
ob~utljivih son~nih celicah (angl. DSSC). Da bi izbolj{ali topnost -karagena in elektrolitov tetrabutilamonijevega iodida
(TBAI)/I2 z zmanj{anjem vsebnosti vode, zaradi njenega ne`elenega u~inka na DSSC, je bila preiskovana ob~utljivost sistema
topil. ^lanek poro~a, da sta bila najdena dva nova sistema topil, me{anica topila voda/acetonitril in DMSO, ki u~inkovito
raztopita komponente. Lastnosti oz. obna{anje kompozitov elektrolitskega sistema -karagen v teh raztopinah, so bile potrjene z
FTIR-analizo. Prisotnost -karagenskega elektrolitnega sistem ni predstavljala ovire za imepdan~no spektroskopijo in lienarno
"sweep" voltametrijo. Vklju~itev gel-elektrolitov v DSSC je pokazala, da DMSO-sistem ka`e bolj{o solarno celi~no
u~inkovitost kot sistem me{anih topil.
Klju~ne besede: barvno ob~utljive son~ne celice, rastlinska `elatina -karagen, gel-elektrolit, elektrokemi~na impedan~na
spekroskopija, ionska prevodnost
1 INTRODUCTION
Gel-polymer electrolytes are promising materials for
a potential incorporation in electrochemical devices1
such as dye-sensitized solar cells (DSC). This is because
their mechanical behavior is that of solids, yet their inter-
nal structure is flexible and their conductivity behavior
resembles that of a liquid state allowing a good elec-
trode/electrolyte contact.2,3 Moreover, its ease of fabrica-
tion allows more tunability in designing systems for
specific applications.
Natural polysaccharide is a potential matrix for
polymer electrolytes owing to its hydrophilic and
gel-forming capacity that traps the solvent together with
the redox couple inside the polymer matrix. The high
water-retention property of polysaccharide-based poly-
mer-electrolyte systems was shown to promote good
ionic conductivities and thermal stability.4,5 Agarose,6,7
cellulose and its derivatives8,9 and -carrageenan10 are the
gel-forming natural polysaccharides that have been used
as polymer-electrolyte (PE) systems for dye-sensi-
tized-solar-cell (DSSC) applications. To maximize the
water-retention property of these polysaccharide-based
gel systems, an aqueous medium is necessary. However,
we can see that water disturbs the interfacial attachment
of dyes to TiO2. Thus, it is highly desirable to develop a
polysaccharide-based electrolyte system in a smaller
amount of water or in a non-aqueous medium.
-Carrageenan, which is composed mainly of
disaccharide units of -D-galactopyranose with either an
-D-galactopyranose or 3,6-anhydrogalactose is a pro-
mising polysaccharide matrix for electrolytes due to its
hydrophilic, linear and sulfated properties. The electro-
static interactions of ions with hydroxyl groups and
sulfate groups in the main chain are essential to the
conduction mechanism of a polysaccharide electrolyte
system.11,12 The promising features of -carrageenan as a
polymer-electrolyte system can be potentially applied to
DSSCs. Solid-state DSSCs using carrageenan-gel elec-
trolyte systems were fabricated by soaking the aqueous
polymer gel with the redox electrolytes11 and forming
thin polymer membranes13 leading to decent efficiencies.
To date, studies on the preparation and characterization
of carrageenan-electrolyte systems have been limited
Materiali in tehnologije / Materials and technology 51 (2017) 5, 823–829 823
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
UDK 67.017:621.3.035.22:544.623 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(5)823(2017)
only to pure aqueous systems. A significant amount of
water present in the electrolyte systems applied to
DSSCs causes a decrease in the photocurrent of the
device associated with dye desorption, iodate formation
and a decrease in the electron lifetime.14 Hence, the
amount of water must be controlled, if not eliminated. It
is the objective of this paper to investigate the influence
of the solvent system on carrageenan electrolyte and its
performance in a DSSC. This paper reports, for the first
time, on a novel carrageenan-based electrolyte system
with an iodide/tri-iodide redox couple prepared using a
mixed solvent system and a non-aqueous solvent.
2 MATERIALS AND METHODS
2.1 Optimization of the -carrageenan electrolyte sys-
tem
Different -carrageenan (Shemberg, Philippines)
biopolymer gel electrolytes were optimized by varying
the ratio of water/acetonitrile and the amount of polymer
with a constant amount of tetrabutylammonium iodide
(TBAI, Sigma Aldrich, a reagent grade of 98 %; 20 %
w/w of TBAI with respect to -carrageenan) and iodine
(I2, Aldrich, = 99.99 % metal basis). The molar ratio of
TBAI/I2 was 4:1. The ratio of water/ACN was optimized
by dissolving -carrageenan (0.2 g) with TBAI/I2 in
different solvent systems consisting of 100 % water, 3:1
water/ACN, 1:1 water/ACN, 1:3 water/ACN, and 100 %
ACN at 80 °C until a homogeneous solution was formed.
Thin films were formed by casting solutions on plastic
petri dishes and slowly drying in air. Different biopoly-
mer electrolytes were prepared using the same procedure
by varying the concentration of -carrageenan (0, 0.5,
1.0, 1.5 and 2 % w/v). Using the optimized parameters,
-carrageenan gel electrolytes containing 20 % w/w
(with respect to the amount of -carrageenan) of other
salts such as potassium iodide (Sigma Aldrich) and
trimethylsulfonium iodide (TMSI, Sigma Aldrich) were
also prepared.
A liquid-state polymer electrolyte and a gel-state
polymer electrolyte based on -carrageenan were pre-
pared by dissolving 1 % w/v or 2 % w/v of the poly-
saccharide in 2 mL of dimethylsulfoxide at 70 °C.
Tetrabutylammonium iodide (0.5 M), I2 (0.05 M) and LiI
(0.1 M) were added to the -carrageenan solution. As the
control, the same composition was used without adding
the biopolymer.
2.2 Fabrication of dye-sensitized solar cells (DSSCs)
The photoanode was prepared spreading a TiO2 paste
(Solaronix, Ti-Nanoxide T/SP) on a fluorine-doped
tin-oxide (FTO) conducting glass (TCO22-7) with the
doctor-blading method. The active area of the photo-
anode was fixed to 1 cm × 1 cm with adhesive tapes. The
deposited paste was sintered at 450 °C for 30 min and
cooled down slowly to room temperature. The deposited
TiO2 film was soaked in a dye solution containing a
ruthenium dye (Ruthenizer 535-bisTBA, Solaronix) in
ethanol for 24 h. The counter electrode was prepared by
sintering an FTO conducting glass coated with a pla-
tinum solution (Platisol 41121, Solaronix) at 450 °C for
30 mins. The photoanode and counter electrode were
sealed with a hot-melt thermoplastic material called
Surlyn (DuPont, thickness of 60 μm), also acting as a
spacer. A dye-sensitized solar cell was fabricated by
inserting a hot gel-electrolyte solution in a pre-drilled
hole on the counter electrode. Three different solar cells
were fabricated containing different iodide salts (KI,
TMSI, and TBAI) in a water/ACN -carrageenan matrix.
A control DSSC was prepared using an acetonitrile-
based liquid electrolyte (Iodolyte AN50, Solaronix). The
same process was used for the fabrication of a DSSC
incorporating gel electrolytes in DMSO.
2.3 Characterization
The surface morphology and thickness of the thin
films were characterized using scanning electron micro-
scopy (JEOL JSM-5310). The electrical conductivity
was measured using the 4-point probe Van der Pauw
method. In brief, four wires were attached to the corners
of a 1 cm × 1 cm thin film using a silver paste. The
voltage at a constant current was measured. The
resistivity and electrical conductivity were calculated
using the following equations:
Resistivity, s
d V
l
V
l
f
R
R
= +
⎛
⎝
⎜
⎞
⎠
⎟
⎛
⎝
⎜
⎞
⎠
⎟
π
ln 2
1
2
2
2
1
2
and Electrical
conductivity,  = 1/s, where d, V, I and f R /R( )1 2 refer to
the thickness, potential, current and van der Pauw
function, respectively.
The redox properties of the -carrageenan gel
electrolyte were characterized using 3-electrode cyclic
voltammetry (Powerlab/4SP potentiostat). The electrodes
composed of the Ag/AgCl reference electrode, plati-
num-wire counter electrode and glassy-carbon working
electrode were pierced through the gel. Electrochemical
impedance spectroscopy (Metrohm Autolab potentiostat
PGSTAT128N) was obtained by sandwiching the gel
electrolyte in between two platinum-coated FTO
conducting-glass electrodes. The active area was fixed to
1 × 1 cm2 and the thickness of the spacer was about
50 μm. The frequency was set from 106 Hz to 10–1 Hz
with an AC applied voltage of 10 mV. The ionic
conductivity () of the gel electrolyte was calculated
from the solution resistance (Rs) using Equation (3):
 =
L
ARs
(3)
The solution resistance (Rs) is determined as the
intercept of the Nyquist plot against the real part of the
impedance or the horizontal axis. The variables L and A
correspond to the thickness of the spacer and the active
area, respectively. The solar-cell parameters such as the
J. P. BANTANG, D. CAMACHO: GELLING POLYSACCHARIDE AS THE ELECTROLYTE MATRIX ...
824 Materiali in tehnologije / Materials and technology 51 (2017) 5, 823–829
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
open-circuit voltage, short-circuit current, fill factor and
efficiency of the fabricated dye-sensitized solar cells
with -carrageenan gel electrolyte were assessed using a
100 mW/cm2 AM 1.5 solar simulator (Abet Technolo-
gies) coupled with a potentiostat to obtain a current-
voltage (IV) curve.
3 RESULTS AND DISCUSSIONS
3.1 Carrageenan-electrolyte system in a mixed solvent
system
Acetonitrile (ACN), which is a common organic
solvent used for preparing liquid electrolytes for DSSC
applications, does not dissolve -carrageenan. Thus, to
form -carrageenan electrolytes containing a redox
couple I–/I3– (from TBAI and I2), the amount of water is
crucial to dissolve the hydrophilic polysaccharide.15
Using water only as the solvent, a black film was formed
with observable colorless crystals (Figure 1a) indicating
the unsuccessful dissolution of both TBAI salt and
iodine. Likewise, crystallization of the salt was formed
on the surface of the film prepared using a 3:1 v/v
water/ACN system (Figure 1b). The salt crystallization
is attributed to the relative insolubility of the salt in a
water-rich solvent. Moreover, the presence of the salt and
iodine crystals on the film surface indicates that it fails to
dissociate in the polymer matrix, leading to an un-
successful incorporation of the charge-carrier redox
couple I–/I3–. For a 1:1 v/v water/ACN mixed-solvent
system, a uniform orange polymer-electrolyte film with-
out visible crystals was formed (Figure 1c), indicating
good dissolution and incorporation of the I–/I3– redox
couple in the polymer matrix. No films were cast for the
1:3 v/v water/acetonitrile solvent systems and in 100 %
acetonitrile because of the relative insolubility of
carrageenan in an acetonitrile-rich solvent.
The concentration of carrageenan in the polymer
electrolyte containing 20 % w/w TBAI (w.r.t. -carra-
geenan) in the 1:1 H2O/acetonitrile mixed solvent affects
the property and the ionic conductivity of the electrolyte.
A liquid polymer electrolyte is formed when the con-
centrations of carrageenan are in a range of 0.1–0.5 %
w/v. Increasing the carrageenan concentration to  1.0 %
w/v gave a gel polymer electrolyte. Consequently, the
ionic conductivity of the polymer electrolytes changes in
response to its composite form. The ionic conductivity
(Figure 2) of -carrageenan-electrolyte systems in-
creases as the carrageenan concentration increases from
0.1 to 1.0 % w/v. The increase in the ionic conductivity at
low -carrageenan concentrations is attributed to high
free-ion concentrations due to their interaction with the
functional group present in -carrageenan.16. The ionic
conductivity decreases at carrageenan concentrations of
1.0–2.0 % w/v. The increase in the polymer concentra-
tion causes chain entanglements, impeding the move-
ment of the ions, thus, decreasing its ionic conductivity.16
Different iodide salts were incorporated in
-carrageenan to prepare the gel electrolytes. Films were
formed and the IR spectra of the electrolyte films con-
tained typical functional-group vibrations of -carra-
geenan.17 The bands at 1272 cm–1 were identified as an
O=S=O symmetric vibration that would respond in the
presence of a cation. A shift in the frequency was
observed in the O=S=O symmetric vibration compared
with the pure k-carrageenan reference (Table 1, entry 1).
This shift is attributed to the electrostatic interaction
between the negatively charged sulfate ions in the
carrageenan chains and the positively charged cations
from the iodide salt.4 The effect of the addition of iodide
salts generally increased the electrical conductivity
(Table 1, entry 2) of the films formed, as compared with
J. P. BANTANG, D. CAMACHO: GELLING POLYSACCHARIDE AS THE ELECTROLYTE MATRIX ...
Materiali in tehnologije / Materials and technology 51 (2017) 5, 823–829 825
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 2: Effect of -carrageenan concentration on ionic conductivity
of carrageenan/TBAI/I2 systems
Figure 1: Optical images of 1 % w/v -carrageenan films mixed with
40 % w/w TBAI (w.r.t. -carrageenan) in 4:1 mole ratio TBAI /I2
electrolyte in varying solvents a) in 100 % water, b) in 3:1
H2O/acetonitrile, c) in 1:1 H2O/acetonitrile, d) polymer gel
electrolytes containing -carrageenan and TBAI/LiI/I2 electrolyte:
left: 1 % w/v -carrageenan in DMSO (liquid state), right: 2 % w/v
-carrageenan in DMSO (gel-state)
only to pure aqueous systems. A significant amount of
water present in the electrolyte systems applied to
DSSCs causes a decrease in the photocurrent of the
device associated with dye desorption, iodate formation
and a decrease in the electron lifetime.14 Hence, the
amount of water must be controlled, if not eliminated. It
is the objective of this paper to investigate the influence
of the solvent system on carrageenan electrolyte and its
performance in a DSSC. This paper reports, for the first
time, on a novel carrageenan-based electrolyte system
with an iodide/tri-iodide redox couple prepared using a
mixed solvent system and a non-aqueous solvent.
2 MATERIALS AND METHODS
2.1 Optimization of the -carrageenan electrolyte sys-
tem
Different -carrageenan (Shemberg, Philippines)
biopolymer gel electrolytes were optimized by varying
the ratio of water/acetonitrile and the amount of polymer
with a constant amount of tetrabutylammonium iodide
(TBAI, Sigma Aldrich, a reagent grade of 98 %; 20 %
w/w of TBAI with respect to -carrageenan) and iodine
(I2, Aldrich, = 99.99 % metal basis). The molar ratio of
TBAI/I2 was 4:1. The ratio of water/ACN was optimized
by dissolving -carrageenan (0.2 g) with TBAI/I2 in
different solvent systems consisting of 100 % water, 3:1
water/ACN, 1:1 water/ACN, 1:3 water/ACN, and 100 %
ACN at 80 °C until a homogeneous solution was formed.
Thin films were formed by casting solutions on plastic
petri dishes and slowly drying in air. Different biopoly-
mer electrolytes were prepared using the same procedure
by varying the concentration of -carrageenan (0, 0.5,
1.0, 1.5 and 2 % w/v). Using the optimized parameters,
-carrageenan gel electrolytes containing 20 % w/w
(with respect to the amount of -carrageenan) of other
salts such as potassium iodide (Sigma Aldrich) and
trimethylsulfonium iodide (TMSI, Sigma Aldrich) were
also prepared.
A liquid-state polymer electrolyte and a gel-state
polymer electrolyte based on -carrageenan were pre-
pared by dissolving 1 % w/v or 2 % w/v of the poly-
saccharide in 2 mL of dimethylsulfoxide at 70 °C.
Tetrabutylammonium iodide (0.5 M), I2 (0.05 M) and LiI
(0.1 M) were added to the -carrageenan solution. As the
control, the same composition was used without adding
the biopolymer.
2.2 Fabrication of dye-sensitized solar cells (DSSCs)
The photoanode was prepared spreading a TiO2 paste
(Solaronix, Ti-Nanoxide T/SP) on a fluorine-doped
tin-oxide (FTO) conducting glass (TCO22-7) with the
doctor-blading method. The active area of the photo-
anode was fixed to 1 cm × 1 cm with adhesive tapes. The
deposited paste was sintered at 450 °C for 30 min and
cooled down slowly to room temperature. The deposited
TiO2 film was soaked in a dye solution containing a
ruthenium dye (Ruthenizer 535-bisTBA, Solaronix) in
ethanol for 24 h. The counter electrode was prepared by
sintering an FTO conducting glass coated with a pla-
tinum solution (Platisol 41121, Solaronix) at 450 °C for
30 mins. The photoanode and counter electrode were
sealed with a hot-melt thermoplastic material called
Surlyn (DuPont, thickness of 60 μm), also acting as a
spacer. A dye-sensitized solar cell was fabricated by
inserting a hot gel-electrolyte solution in a pre-drilled
hole on the counter electrode. Three different solar cells
were fabricated containing different iodide salts (KI,
TMSI, and TBAI) in a water/ACN -carrageenan matrix.
A control DSSC was prepared using an acetonitrile-
based liquid electrolyte (Iodolyte AN50, Solaronix). The
same process was used for the fabrication of a DSSC
incorporating gel electrolytes in DMSO.
2.3 Characterization
The surface morphology and thickness of the thin
films were characterized using scanning electron micro-
scopy (JEOL JSM-5310). The electrical conductivity
was measured using the 4-point probe Van der Pauw
method. In brief, four wires were attached to the corners
of a 1 cm × 1 cm thin film using a silver paste. The
voltage at a constant current was measured. The
resistivity and electrical conductivity were calculated
using the following equations:
Resistivity, s
d V
l
V
l
f
R
R
= +
⎛
⎝
⎜
⎞
⎠
⎟
⎛
⎝
⎜
⎞
⎠
⎟
π
ln 2
1
2
2
2
1
2
and Electrical
conductivity,  = 1/s, where d, V, I and f R /R( )1 2 refer to
the thickness, potential, current and van der Pauw
function, respectively.
The redox properties of the -carrageenan gel
electrolyte were characterized using 3-electrode cyclic
voltammetry (Powerlab/4SP potentiostat). The electrodes
composed of the Ag/AgCl reference electrode, plati-
num-wire counter electrode and glassy-carbon working
electrode were pierced through the gel. Electrochemical
impedance spectroscopy (Metrohm Autolab potentiostat
PGSTAT128N) was obtained by sandwiching the gel
electrolyte in between two platinum-coated FTO
conducting-glass electrodes. The active area was fixed to
1 × 1 cm2 and the thickness of the spacer was about
50 μm. The frequency was set from 106 Hz to 10–1 Hz
with an AC applied voltage of 10 mV. The ionic
conductivity () of the gel electrolyte was calculated
from the solution resistance (Rs) using Equation (3):
 =
L
ARs
(3)
The solution resistance (Rs) is determined as the
intercept of the Nyquist plot against the real part of the
impedance or the horizontal axis. The variables L and A
correspond to the thickness of the spacer and the active
area, respectively. The solar-cell parameters such as the
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824 Materiali in tehnologije / Materials and technology 51 (2017) 5, 823–829
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
open-circuit voltage, short-circuit current, fill factor and
efficiency of the fabricated dye-sensitized solar cells
with -carrageenan gel electrolyte were assessed using a
100 mW/cm2 AM 1.5 solar simulator (Abet Technolo-
gies) coupled with a potentiostat to obtain a current-
voltage (IV) curve.
3 RESULTS AND DISCUSSIONS
3.1 Carrageenan-electrolyte system in a mixed solvent
system
Acetonitrile (ACN), which is a common organic
solvent used for preparing liquid electrolytes for DSSC
applications, does not dissolve -carrageenan. Thus, to
form -carrageenan electrolytes containing a redox
couple I–/I3– (from TBAI and I2), the amount of water is
crucial to dissolve the hydrophilic polysaccharide.15
Using water only as the solvent, a black film was formed
with observable colorless crystals (Figure 1a) indicating
the unsuccessful dissolution of both TBAI salt and
iodine. Likewise, crystallization of the salt was formed
on the surface of the film prepared using a 3:1 v/v
water/ACN system (Figure 1b). The salt crystallization
is attributed to the relative insolubility of the salt in a
water-rich solvent. Moreover, the presence of the salt and
iodine crystals on the film surface indicates that it fails to
dissociate in the polymer matrix, leading to an un-
successful incorporation of the charge-carrier redox
couple I–/I3–. For a 1:1 v/v water/ACN mixed-solvent
system, a uniform orange polymer-electrolyte film with-
out visible crystals was formed (Figure 1c), indicating
good dissolution and incorporation of the I–/I3– redox
couple in the polymer matrix. No films were cast for the
1:3 v/v water/acetonitrile solvent systems and in 100 %
acetonitrile because of the relative insolubility of
carrageenan in an acetonitrile-rich solvent.
The concentration of carrageenan in the polymer
electrolyte containing 20 % w/w TBAI (w.r.t. -carra-
geenan) in the 1:1 H2O/acetonitrile mixed solvent affects
the property and the ionic conductivity of the electrolyte.
A liquid polymer electrolyte is formed when the con-
centrations of carrageenan are in a range of 0.1–0.5 %
w/v. Increasing the carrageenan concentration to  1.0 %
w/v gave a gel polymer electrolyte. Consequently, the
ionic conductivity of the polymer electrolytes changes in
response to its composite form. The ionic conductivity
(Figure 2) of -carrageenan-electrolyte systems in-
creases as the carrageenan concentration increases from
0.1 to 1.0 % w/v. The increase in the ionic conductivity at
low -carrageenan concentrations is attributed to high
free-ion concentrations due to their interaction with the
functional group present in -carrageenan.16. The ionic
conductivity decreases at carrageenan concentrations of
1.0–2.0 % w/v. The increase in the polymer concentra-
tion causes chain entanglements, impeding the move-
ment of the ions, thus, decreasing its ionic conductivity.16
Different iodide salts were incorporated in
-carrageenan to prepare the gel electrolytes. Films were
formed and the IR spectra of the electrolyte films con-
tained typical functional-group vibrations of -carra-
geenan.17 The bands at 1272 cm–1 were identified as an
O=S=O symmetric vibration that would respond in the
presence of a cation. A shift in the frequency was
observed in the O=S=O symmetric vibration compared
with the pure k-carrageenan reference (Table 1, entry 1).
This shift is attributed to the electrostatic interaction
between the negatively charged sulfate ions in the
carrageenan chains and the positively charged cations
from the iodide salt.4 The effect of the addition of iodide
salts generally increased the electrical conductivity
(Table 1, entry 2) of the films formed, as compared with
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Materiali in tehnologije / Materials and technology 51 (2017) 5, 823–829 825
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 2: Effect of -carrageenan concentration on ionic conductivity
of carrageenan/TBAI/I2 systems
Figure 1: Optical images of 1 % w/v -carrageenan films mixed with
40 % w/w TBAI (w.r.t. -carrageenan) in 4:1 mole ratio TBAI /I2
electrolyte in varying solvents a) in 100 % water, b) in 3:1
H2O/acetonitrile, c) in 1:1 H2O/acetonitrile, d) polymer gel
electrolytes containing -carrageenan and TBAI/LiI/I2 electrolyte:
left: 1 % w/v -carrageenan in DMSO (liquid state), right: 2 % w/v
-carrageenan in DMSO (gel-state)
the reference pure -carrageenan due to the addition and
incorporation of the redox species. The ionic conduc-
tivities (Table 1, entry 3) of the gel electrolytes are
generally higher than that of the acetonitrile-based liquid
electrolyte, indicating a facile transport of the redox
couple in the carrageenan matrix. Cyclic voltammetry of
the gel electrolytes with and without -carrageenan
(Figure 3) showed that the addition of the polymer does
not impede the electrochemical behavior of the I–/I3–
redox couple in the mixed water/acetonitrile system. Two
redox processes were observed, indicating the migration
of I–/I3– in the 3D matrix of -carrageenan.18
Solar cells were fabricated using the conventional
set-up composed of a TiO2/ruthenium dye as the photo-
anode and a platinum counter electrode sandwiching the
-carrageenan-gel electrolyte systems in water/ACN. I-V
characteristics of the DSSCs (Table 2 and Figure 4a)
containing the -carrageenan-gel electrolytes showed
poor efficiency (<0.10 %) as compared to the liquid
electrolyte (2.33 %), attributed to a much lower short-
circuit current, which can be associated with the pre-
sence of a significant amount of water in the electrolyte
system. The presence of water causes dye detachment
due to the weakening of the dye-TiO2 linkage, resulting
in a limited amount of electrons injected from the excited
state of the dye and consequently leading to the lowering
of the short-circuit current.16 The obtained efficiencies of
different -carrageenan-gel electrolytes with a mixture of
acetonitrile and water suggest that imparting a large
amount of water (50 %) in the electrolyte system for
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826 Materiali in tehnologije / Materials and technology 51 (2017) 5, 823–829
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 4: I-V curves of the DSSCs: a) containing different iodide salts
(KI, TMSI and TBAI) in the water/ACN -carrageenan matrix and
b) containing -carrageenan-based electrolytes in DMSO under a 100
mW/cm2 illumination
Table 2: Characteristics of the fabricated DSSCs under a 100
mW/cm2 illumination
Electrolyte Voc (V) Isc(mA/cm2) FF  ( %)
Iodolyte
(control) 0.695 6.444 0.521 2.333
KI:I2 0.746 0.100 0.819 0.061
TMSI:I2 0.776 0.0414 0.152 0.005
TBAI:I2 0.778 0.0817 0.765 0.049
Figure 3: Electrochemical-behavior (cyclic voltametry) analysis of
the -carrageenan-gel electrolytes containing different salts; control:
LiI/I2 in 1:1 v/v water/ACN without carrageenan
Table 1: FTIR and conductivity of the -carrageenan electrolytes containing different salts
Entry Pure - carrageenan(reference)
Iodolyte AN50
(control)
KI/I2 TMSI/I2 TBAI/I2
in -carrageenan
1 FTIR O=S=O vibration (cm–1) 1272 – 1261 1274 1263
2
Electrical conductivity of
polymer-electrolyte filmsa
(S cm–1)
0.127 – 0.281 0.189 0.326
3
Ionic conductivity of
polymer-electrolyte gelsb
(x10–4 S cm–1)
– 1.66 2.52 3.05 2.17
aMeasured with 4-point probe Van der Pauw technique
bMeasured with electrochemical impedance spectroscopy (EIS)
DSSCs is still detrimental to the performance of a solar-
cell device.
3.2 Carrageenan-electrolyte system in a non-aqueous
solvent
Carrageenan is not known to dissolve in purely non-
aqueous solvents. However, in the course of our
investigation of electrolyte systems, we observed that it
dissolves in dimethylsulfoxide (DMSO).19,20 We investi-
gated the solubility properties of -carrageenan in
DMSO, dissolving different amounts of the biopolymer
at 60 °C. A liquid solution is formed with 1 % w/v
-carrageenan (a solubility of 0.01 g/mL DMSO at room
temperature and at 60 °C). Increasing the -carrageenan
concentration from 1.5 to 3.5 % w/v allows the dissolu-
tion of the biopolymer in DMSO, forming a transparent
solution at 60 °C. However, upon cooling down at room
temperature, it forms into a stable gel (Figure 1d). A
further increase in the concentration of -carrageenan of
4–5 % w/v leads to the formation of a stable gel even at
60 °C. Other organic solvents such as ethanol, methanol,
acetonitrile, tetrahydrofuran, dimethylformamide and
methoxyethanol did not show good solubility. The
advantages of using DMSO are its relatively low vapor
pressure and relatively non-volatile nature, which are
useful for maintaining its gel state. Moreover, this orga-
nic solvent shows a relatively low toxicity and is con-
sidered environmentally benign.6 The addition of electro-
lyte systems TBAI and I2 turned the -carrageenan
DMSO solution into a dark-brown one indicating the
incorporation of the electrolytes. The IR spectrum of the
polymer-electrolyte system showed functional groups
typical of -carrageenan. A shift in the O=S=O symme-
tric vibration from typical 1272 for pure -carrageenan
to 1226 cm–1 for carrageenan gel electrolyte is attributed
J. P. BANTANG, D. CAMACHO: GELLING POLYSACCHARIDE AS THE ELECTROLYTE MATRIX ...
Materiali in tehnologije / Materials and technology 51 (2017) 5, 823–829 827
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 6: EIS spectrum of a DSSC containing -carrageenan-based
electrolytes in DMSO; inset: equivalent circuit model (R1 = series
resistance, R2 = TiO2/dye/electrolyte interface resistance, CPE =
constant phase element)
Figure 5: a) EIS spectra of electrolytes measured using a symme-
trical-cell set-up between two platinized FTO conducting glasses in a
frequency range of 1 MHz to 0.1 Hz, b) linear sweep voltammogram
of the electrolytes measured between two platinized FTO conducting
glasses swept between –1 V to 1 V. Scan rate: 10 mV/s
Table 3: I-V electrochemical properties of the carrageenan electrolyte in DMSO measured using two platinized FTO conducting glasses and I-V
characteristics of DSSCs under a 100 mW/cm2 illumination*
Electrochemical properties of electrolyte I-V characteristics of DSSC
Electrolytes in
DMSO Rb
** (Ù) RPt
(Ù)
Ionic con-
ductivity,
×10–4 (S/cm)
Diffusivity of
I3–, ×10–9
(cm2 s–1)
Short-circuit
current
(mA/cm2)
Open-circuit
voltage (V) Fill factor
Efficiency
(%)
Control (without
-carrageenan) 21.28 218.13 2.82 1.48 0.690 0.781 0.410 0.221
1% w/v
-carrageenan 25.33 296.41 2.37 1.41 0.960 0.763 0.483 0.354
2 % w/v
-carrageenan 25.25 338.46 2.38 1.11 0.983 0.751 0.488 0.360
*The electrolyte used was composed of tetrabutylammonium iodide (0.5 M), I2, (0.05 M) and LiI (0.1 M)
**Rb corresponds to the solution resistance, which corresponds to the intercept at the real part of the EIS spectrum
the reference pure -carrageenan due to the addition and
incorporation of the redox species. The ionic conduc-
tivities (Table 1, entry 3) of the gel electrolytes are
generally higher than that of the acetonitrile-based liquid
electrolyte, indicating a facile transport of the redox
couple in the carrageenan matrix. Cyclic voltammetry of
the gel electrolytes with and without -carrageenan
(Figure 3) showed that the addition of the polymer does
not impede the electrochemical behavior of the I–/I3–
redox couple in the mixed water/acetonitrile system. Two
redox processes were observed, indicating the migration
of I–/I3– in the 3D matrix of -carrageenan.18
Solar cells were fabricated using the conventional
set-up composed of a TiO2/ruthenium dye as the photo-
anode and a platinum counter electrode sandwiching the
-carrageenan-gel electrolyte systems in water/ACN. I-V
characteristics of the DSSCs (Table 2 and Figure 4a)
containing the -carrageenan-gel electrolytes showed
poor efficiency (<0.10 %) as compared to the liquid
electrolyte (2.33 %), attributed to a much lower short-
circuit current, which can be associated with the pre-
sence of a significant amount of water in the electrolyte
system. The presence of water causes dye detachment
due to the weakening of the dye-TiO2 linkage, resulting
in a limited amount of electrons injected from the excited
state of the dye and consequently leading to the lowering
of the short-circuit current.16 The obtained efficiencies of
different -carrageenan-gel electrolytes with a mixture of
acetonitrile and water suggest that imparting a large
amount of water (50 %) in the electrolyte system for
J. P. BANTANG, D. CAMACHO: GELLING POLYSACCHARIDE AS THE ELECTROLYTE MATRIX ...
826 Materiali in tehnologije / Materials and technology 51 (2017) 5, 823–829
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 4: I-V curves of the DSSCs: a) containing different iodide salts
(KI, TMSI and TBAI) in the water/ACN -carrageenan matrix and
b) containing -carrageenan-based electrolytes in DMSO under a 100
mW/cm2 illumination
Table 2: Characteristics of the fabricated DSSCs under a 100
mW/cm2 illumination
Electrolyte Voc (V) Isc(mA/cm2) FF  ( %)
Iodolyte
(control) 0.695 6.444 0.521 2.333
KI:I2 0.746 0.100 0.819 0.061
TMSI:I2 0.776 0.0414 0.152 0.005
TBAI:I2 0.778 0.0817 0.765 0.049
Figure 3: Electrochemical-behavior (cyclic voltametry) analysis of
the -carrageenan-gel electrolytes containing different salts; control:
LiI/I2 in 1:1 v/v water/ACN without carrageenan
Table 1: FTIR and conductivity of the -carrageenan electrolytes containing different salts
Entry Pure - carrageenan(reference)
Iodolyte AN50
(control)
KI/I2 TMSI/I2 TBAI/I2
in -carrageenan
1 FTIR O=S=O vibration (cm–1) 1272 – 1261 1274 1263
2
Electrical conductivity of
polymer-electrolyte filmsa
(S cm–1)
0.127 – 0.281 0.189 0.326
3
Ionic conductivity of
polymer-electrolyte gelsb
(x10–4 S cm–1)
– 1.66 2.52 3.05 2.17
aMeasured with 4-point probe Van der Pauw technique
bMeasured with electrochemical impedance spectroscopy (EIS)
DSSCs is still detrimental to the performance of a solar-
cell device.
3.2 Carrageenan-electrolyte system in a non-aqueous
solvent
Carrageenan is not known to dissolve in purely non-
aqueous solvents. However, in the course of our
investigation of electrolyte systems, we observed that it
dissolves in dimethylsulfoxide (DMSO).19,20 We investi-
gated the solubility properties of -carrageenan in
DMSO, dissolving different amounts of the biopolymer
at 60 °C. A liquid solution is formed with 1 % w/v
-carrageenan (a solubility of 0.01 g/mL DMSO at room
temperature and at 60 °C). Increasing the -carrageenan
concentration from 1.5 to 3.5 % w/v allows the dissolu-
tion of the biopolymer in DMSO, forming a transparent
solution at 60 °C. However, upon cooling down at room
temperature, it forms into a stable gel (Figure 1d). A
further increase in the concentration of -carrageenan of
4–5 % w/v leads to the formation of a stable gel even at
60 °C. Other organic solvents such as ethanol, methanol,
acetonitrile, tetrahydrofuran, dimethylformamide and
methoxyethanol did not show good solubility. The
advantages of using DMSO are its relatively low vapor
pressure and relatively non-volatile nature, which are
useful for maintaining its gel state. Moreover, this orga-
nic solvent shows a relatively low toxicity and is con-
sidered environmentally benign.6 The addition of electro-
lyte systems TBAI and I2 turned the -carrageenan
DMSO solution into a dark-brown one indicating the
incorporation of the electrolytes. The IR spectrum of the
polymer-electrolyte system showed functional groups
typical of -carrageenan. A shift in the O=S=O symme-
tric vibration from typical 1272 for pure -carrageenan
to 1226 cm–1 for carrageenan gel electrolyte is attributed
J. P. BANTANG, D. CAMACHO: GELLING POLYSACCHARIDE AS THE ELECTROLYTE MATRIX ...
Materiali in tehnologije / Materials and technology 51 (2017) 5, 823–829 827
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 6: EIS spectrum of a DSSC containing -carrageenan-based
electrolytes in DMSO; inset: equivalent circuit model (R1 = series
resistance, R2 = TiO2/dye/electrolyte interface resistance, CPE =
constant phase element)
Figure 5: a) EIS spectra of electrolytes measured using a symme-
trical-cell set-up between two platinized FTO conducting glasses in a
frequency range of 1 MHz to 0.1 Hz, b) linear sweep voltammogram
of the electrolytes measured between two platinized FTO conducting
glasses swept between –1 V to 1 V. Scan rate: 10 mV/s
Table 3: I-V electrochemical properties of the carrageenan electrolyte in DMSO measured using two platinized FTO conducting glasses and I-V
characteristics of DSSCs under a 100 mW/cm2 illumination*
Electrochemical properties of electrolyte I-V characteristics of DSSC
Electrolytes in
DMSO Rb
** (Ù) RPt
(Ù)
Ionic con-
ductivity,
×10–4 (S/cm)
Diffusivity of
I3–, ×10–9
(cm2 s–1)
Short-circuit
current
(mA/cm2)
Open-circuit
voltage (V) Fill factor
Efficiency
(%)
Control (without
-carrageenan) 21.28 218.13 2.82 1.48 0.690 0.781 0.410 0.221
1% w/v
-carrageenan 25.33 296.41 2.37 1.41 0.960 0.763 0.483 0.354
2 % w/v
-carrageenan 25.25 338.46 2.38 1.11 0.983 0.751 0.488 0.360
*The electrolyte used was composed of tetrabutylammonium iodide (0.5 M), I2, (0.05 M) and LiI (0.1 M)
**Rb corresponds to the solution resistance, which corresponds to the intercept at the real part of the EIS spectrum
to the interaction of the cation with the sulfate functional
groups.5
The ionic conductivity and diffusivity of the
tri-iodide ion (Table 3) in DMSO showed that the
addition of -carrageenan decreases the ionic conduc-
tivity of the electrolyte system in comparison to the
DMSO-based liquid-electrolyte system. EIS spectra
(Figure 5a) of the electrolytes in DMSO show a broader
semi-circle arc upon the addition of -carrageenan,
which is associated with an increase in the
charge-transfer resistance at the platinum/electrolyte
interface (RPt). A higher RPt indicates a less efficient
electro-activity at the Pt/electrolyte interface attributed to
a slower ionic conductivity.21 The concentration of iodide
ions is in excess in comparison with the amount of
tri-iodide ions. Hence, the limiting current density of the
gel electrolytes is associated with the diffusion coeffi-
cient of the tri-iodide ions. The limiting current densities
of the electrolytes (Figure 5b) show negative and
positive values due to the transport of charge carriers
from one electrode to the other through the whole elec-
trolyte system.8 A slow diffusion of the tri-iodide ions is
consistent with the slow ionic conductivity of the
carrageenan-electrolyte system. The slow tri-iodide ion
diffusion in the -carrageenan electrolytes resulted in a
higher recombination.22 These results were consistent
with the decreasing trend in the open-circuit voltage of
the electrolytes with -carrageenan. The photovoltaic
performance of the -carrageenan-based dye-sensitized
solar cells (Figure 4b and Table 3) showed that the
addition of -carrageenan to the I–/I3– redox electrolyte
system in dimethylsulfoxide decreases the open-circuit
voltage and increases the short-circuit current of a solar
cell. The improvement in the short-circuit current of the
DSSCs with a -carrageenan/DMSO electrolyte system
is attributed to the ability of the hydroxyl functional
group and negatively charged sulfate ions of -carra-
geenan to allow dissociation of the ions in the polymer
matrix through the electrostatic interaction with the
cations. The enhancement in the short-circuit current of
the -carrageenan/DMSO electrolytes is the major
contribution to the improvement of the overall efficiency
of the dye-sensitized solar cells. Good dissociation of
ions in the polymer matrix increases the concentration of
I–, its counterion, and I3– leading to an increase in the
short-circuit current.23
A typical liquid-electrolyte-based DSSC show an EIS
spectrum consisting of three semi-circle arcs corres-
ponding to the interfacial resistances occurring during
the electrochemical reaction at the platinum/electrolyte
interface, during the charge-transfer process at the
TiO2/dye/electrolyte interface and Warburg diffusion of
I–/I3– in the electrolyte. A frequency-response-analyzer
(FRA) impedance analysis of the -carrageenan/DMSO
DSSC (Figure 6) showed a unique single semi-circle
arc, associated with the charge-recombination process
occurring at the TiO2/dye/electrolyte interface (R2). The
other parameters such as R1 and CPE corresponded to
the series resistance and constant phase element, respec-
tively. A decreasing trend in the semi-circle arc radius
was observed when the -carrageenan concentration was
increased. A quantitative approach of the recombination
resistance was done by fitting the Nyquist plot with its
corresponding equivalent circuit model. Chi-square
values for the fitted equivalent circuit model range from
0.02–0.07, indicating good value fitting. The charge-
recombination resistances (R2) of the DSSCs without
-carrageenan (control), with 1 % w/v -carrageenan
(liquid state) and 2 % w/v -carrageenan (gel state),
obtained from the plot are 515.19 , 317.88  and
292.86 , respectively. A higher R2 value signifies lower
charge recombination between the photoanode conduc-
tion-band electrons and I3– ions at the TiO2/dye/elec-
trolyte interface resulting in a higher Voc.24 The higher
charge recombination of the polymer electrolytes with
-carrageenan, compared to the electrolyte without the
polymer, is generally attributed to the slow ionic con-
ductivity of the ions in the gel matrix of carrageenan
(Table 3). Moreover, the -carrageenan electrolyte pene-
trates poorly into the TiO2 layer due to its polymeric
nature contributing to the less efficient charge-transfer
process.21 The results were consistent with the photo-
voltaic characteristics of the fabricated dye-sensitized
solar cells.
4 CONCLUSIONS
A hydrophilic polysaccharide, -carrageenan, was
successfully used as the polymer matrix for a gel-elec-
trolyte system in a mixed solvent of water and aceto-
nitrile for dye-sensitized solar cells. The solvent system
improved the dissolution of the components and the
electrolyte properties. Efficiencies of less than 0.1 % of
the fabricated DSSCs are attributed to the significant
amount of water. A novel gel-polymer electrolyte con-
sisting of -carrageenan electrolyte gel in DMSO was
developed for DSSCs. Removal of the water from the
polymer-electrolyte system improved the DSSC per-
formance from 0.049 to 0.36 %, a seven-fold increase in
the magnitude. The presence of -carrageenan in the
DMSO-based gel-electrolyte system helps improve the
solar-cell efficiency from 0.221 to 0.360 %.
Acknowledgments
The authors are grateful to Dr. Erwin Enriquez, Dr.
Arnel Salvador and Dr. Armando Somintac for the use of
the solar simulator and Ms. Anna San Esteban for
guidance in solar measurements. This work was
supported by research grants from DOST-PCIEERD of
the Republic of the Philippines; DOST-SEI-ASTHRDP
and DLSU-PhD Fellowship Grants to J. P. O Bantang;
DLSU Research Faculty Grant, DLSU Science
Foundation and DLSU-URCO to D. H. Camacho.
J. P. BANTANG, D. CAMACHO: GELLING POLYSACCHARIDE AS THE ELECTROLYTE MATRIX ...
828 Materiali in tehnologije / Materials and technology 51 (2017) 5, 823–829
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
5 REFERENCES
1 J. R. MacCallum, C. A. Vincent, Polymer Electrolytes Reviews-l,
Elsevier Applied Science, London, 1989
2 K. N. Kumar, T. Sreekanth, M. J. Reddy, U. V. S. Rao, Study of
transport and electrochemical cell characteristics of PVP:NaClO3
polymer electrolyte system, J. Power Sources, 101 (2001), 130–133
doi:10.1016/S0378-7753(01)00658-9
3 T. M. W. J. Bandara, P. Ekanayake, M. A. K. L. Dissanayake, I.
Albinsson, B. E. Mellander, A polymer electrolyte containing ionic
liquid for possible applications in photoelectrochemical solar cells, J.
Solid State Electrochem., 14 (2010), 1221–1226, doi:10.1007/
s10008-009-0951-x
4 X. Guo, P. Yi, Y. Yang, J. Cui, S. Xiao, W. Wang, Effects of
surfactants on agarose-based magnetic polymer electrolyte for
dye-sensitized solar cells, Electrochim. Acta, 90 (2013), 524–529,
doi:10.1016/j.electacta.2012.12.028
5 R. Singh, A. R. Polu, B. Bhattacharya, H.-W. Rhee, C. Varlikli, P. K.
Singh, Perspectives for solid biopolymer electrolytes in dye
sensitized solar cell and battery application, Renew. Sustainable
Energy Rev., 65 (2016), 1098–1117, doi:10.1016/j.rser.2016.06.026
6 W. Wang, X. Guo, Y. Yang, Lithium iodide effect on the
electrochemical behavior of agarose based polymer electrolyte for
dye-sensitized solar cell, Electrochim. Acta, 56 (2011), 7347–7351,
doi:10.1016/j.electacta.2011.06.032
7 H.-L. Hsu, W.-T. Hsu, J. Leu, Effects of environmentally benign
solvents in the agarose gel electrolytes on dye-sensitized solar cells,
Electrochim. Acta, 56 (2011), 5904–5909, doi:10.1016/j.electacta.
2011.04.117
8 P. Li, Y. Zhang, W. Fa, Y. Zhang, B. Huang, Synthesis of a grafted
cellulose gel electrolyte in an ionic liquid ([Bmim]I) for
dye-sensitized solar cells, Carbohydr. Polym., 86 (2011), 1216–1220,
doi:10.1016/j.carbpol.2011.06.017
9 X. Huang, Y. Liu, J. Deng, B. Yi, X. Yu, P. Shen, S. Tan, A novel
polymer gel electrolyte based on cyanoethylated cellulose for
dye-sensitized solar cells, Electrochim. Acta, 80 (2012), 219–226,
doi:10.1016/j.electacta.2012.07.014
10 M. Kaneko, T. Hoshi, Y, Kaburagi, H. Ueno, Solid type dye-sensi-
tized solar cell using polysaccharide containing the redox electrolyte
solution, J. Electroanal. Chem., 572 (2004), 21–27, doi:10.1016/
j.jelechem.2004.05.021
11 H. Ueno, M. Kaneko, Investigation of a nanostructured poly-
saccharide solid medium for electrochemistry, J. Electroanal. Chem.,
568 (2004), 87–92, doi:10.1016/j.jelechem.2003.12.044
12 N. N. Mobarak, N. Ramli, A. Ahmad, M. Y. A. Rahman, Chemical
interaction and conductivity of carboxymethyl -carrageenan based
green polymer electrolyte, Solid State Ionics, 224 (2012), 51–57,
doi:10.1016/j.ssi.2012.07.010
13 F. Bella, N. N. Mobarak, F. N. Jumaah, A. Ahmad, From seaweeds to
biopolymeric electrolytes for third generation solar cells: An
intriguing approach, Electrochim. Acta, 151 (2015), 306–311,
doi:10.1016/j.electacta.2014.11.058
14 C. Law, S. C. Pathirana, X. Li, A. Y. Anderson, P. R. F. Barnes, A.
Listorti, T. H. Ghaddar, B. C. O’Regan, Water-Based Electrolytes for
Dye-Sensitized Solar Cells, Adv. Mater., 22 (2010), 4505–4509,
doi:10.1002/adma.201001703
15 D. H. Camacho, S. J. M. Tambio, M. I. A. Oliveros, Carrageenan-
Ionic Liquid Composite: Development of Polysaccharide-Based
Solid Electrolyte System, The Manila J. of Science, 6 (2011), 8–15
16 H.-L. Lu, Y.-H. Lee, S.-T. Huang, C. Su, T. C.-K. Yang, Influences of
water in bis-benzimidazole-derivative electrolyte additives to the
degradation of the dye-sensitized solar cells, Sol. Energy Mater. Sol.
Cells, 95 (2011), 158–162, doi:10.1016/j.solmat.2010.02.018
17 C. Tranquilan-Aranilla, N. Nagasawa, A. Bayquen, A. Dela Rosa,
Synthesis and characterization of carboxymethyl derivatives of
kappa-carrageenan, Carbohydr. Polym., 87 (2012), 1810–1816,
doi:10.1016/j.carbpol.2011.10.009
18 S. Yuan, Q. Tang, B. He, P. Yang, Efficient quasi-solid-state dye-sen-
sitized solar cells employing polyaniline and polypyrrole
incorporated microporous conducting gel electrolytes, J. Power
Sources, 254 (2014), 98–105, doi:10.1016/j.jpowsour.2013.12.112
19 S. Chan, J. P. Bantang, D. Camacho, Influence of Nanomaterial
Fillers in Biopolymer Electrolyte System for Squaraine-Based
Dye-Sensitized Solar Cells, Int. J. Electrochem. Sci., 10 (2015),
7696–7706
20 J. P. Bantang, D. Camacho, A Novel Biopolymer Gel Electrolyte
System for DSSC Applications, Proceedings of the DLSU Research
Congress, 3, 2015
21 S. Venkatesan, N. Obadja, T.-W. Chang, L.-T. Chen, Y.-L. Lee,
Performance improvement of gel- and solid-state dye-sensitized solar
cells by utilization of the blending effect of poly (vinylidene
fluoride-cohexafluropropylene) and poly (acrylonitrile-co-vinyl
acetate) co-polymers, J. Power Sources, 268 (2014), 77–81,
doi:10.1016/j.jpowsour.2014.06.016
22 H.-L. Hsu, C.-F. Tien, Y.-T. Yang, J. Leu, Dye-sensitized solar cells
based on agarose gel electrolytes using allylimidazolium iodides and
environmentally benign solvents, Electrochim. Acta, 91 (2013),
208–213, doi:10.1016/j.electacta.2012.12.133
23 K. Hara, T. Horiguchi, T. Kinoshita, K. Sayama, H. Arakawa,
Influence of electrolytes on the photovoltaic performance of organic
dye-sensitizednanocrystalline TiO2 solar cells, Sol. Energy Mater.
Sol. Cells, 70 (2001), 151–161, doi:10.1016/S0927-0248(01)00019-8
24 Y. Yang, J. Cui, P. Yi, X. Zheng, X. Guo, W. Wang, Effects of
nanoparticle additives on the properties of agarose polymer
electrolytes, J. Power Sources, 248 (2014), 988–993, doi:10.1016/
j.jpowsour.2013.10.016
J. P. BANTANG, D. CAMACHO: GELLING POLYSACCHARIDE AS THE ELECTROLYTE MATRIX ...
Materiali in tehnologije / Materials and technology 51 (2017) 5, 823–829 829
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
to the interaction of the cation with the sulfate functional
groups.5
The ionic conductivity and diffusivity of the
tri-iodide ion (Table 3) in DMSO showed that the
addition of -carrageenan decreases the ionic conduc-
tivity of the electrolyte system in comparison to the
DMSO-based liquid-electrolyte system. EIS spectra
(Figure 5a) of the electrolytes in DMSO show a broader
semi-circle arc upon the addition of -carrageenan,
which is associated with an increase in the
charge-transfer resistance at the platinum/electrolyte
interface (RPt). A higher RPt indicates a less efficient
electro-activity at the Pt/electrolyte interface attributed to
a slower ionic conductivity.21 The concentration of iodide
ions is in excess in comparison with the amount of
tri-iodide ions. Hence, the limiting current density of the
gel electrolytes is associated with the diffusion coeffi-
cient of the tri-iodide ions. The limiting current densities
of the electrolytes (Figure 5b) show negative and
positive values due to the transport of charge carriers
from one electrode to the other through the whole elec-
trolyte system.8 A slow diffusion of the tri-iodide ions is
consistent with the slow ionic conductivity of the
carrageenan-electrolyte system. The slow tri-iodide ion
diffusion in the -carrageenan electrolytes resulted in a
higher recombination.22 These results were consistent
with the decreasing trend in the open-circuit voltage of
the electrolytes with -carrageenan. The photovoltaic
performance of the -carrageenan-based dye-sensitized
solar cells (Figure 4b and Table 3) showed that the
addition of -carrageenan to the I–/I3– redox electrolyte
system in dimethylsulfoxide decreases the open-circuit
voltage and increases the short-circuit current of a solar
cell. The improvement in the short-circuit current of the
DSSCs with a -carrageenan/DMSO electrolyte system
is attributed to the ability of the hydroxyl functional
group and negatively charged sulfate ions of -carra-
geenan to allow dissociation of the ions in the polymer
matrix through the electrostatic interaction with the
cations. The enhancement in the short-circuit current of
the -carrageenan/DMSO electrolytes is the major
contribution to the improvement of the overall efficiency
of the dye-sensitized solar cells. Good dissociation of
ions in the polymer matrix increases the concentration of
I–, its counterion, and I3– leading to an increase in the
short-circuit current.23
A typical liquid-electrolyte-based DSSC show an EIS
spectrum consisting of three semi-circle arcs corres-
ponding to the interfacial resistances occurring during
the electrochemical reaction at the platinum/electrolyte
interface, during the charge-transfer process at the
TiO2/dye/electrolyte interface and Warburg diffusion of
I–/I3– in the electrolyte. A frequency-response-analyzer
(FRA) impedance analysis of the -carrageenan/DMSO
DSSC (Figure 6) showed a unique single semi-circle
arc, associated with the charge-recombination process
occurring at the TiO2/dye/electrolyte interface (R2). The
other parameters such as R1 and CPE corresponded to
the series resistance and constant phase element, respec-
tively. A decreasing trend in the semi-circle arc radius
was observed when the -carrageenan concentration was
increased. A quantitative approach of the recombination
resistance was done by fitting the Nyquist plot with its
corresponding equivalent circuit model. Chi-square
values for the fitted equivalent circuit model range from
0.02–0.07, indicating good value fitting. The charge-
recombination resistances (R2) of the DSSCs without
-carrageenan (control), with 1 % w/v -carrageenan
(liquid state) and 2 % w/v -carrageenan (gel state),
obtained from the plot are 515.19 , 317.88  and
292.86 , respectively. A higher R2 value signifies lower
charge recombination between the photoanode conduc-
tion-band electrons and I3– ions at the TiO2/dye/elec-
trolyte interface resulting in a higher Voc.24 The higher
charge recombination of the polymer electrolytes with
-carrageenan, compared to the electrolyte without the
polymer, is generally attributed to the slow ionic con-
ductivity of the ions in the gel matrix of carrageenan
(Table 3). Moreover, the -carrageenan electrolyte pene-
trates poorly into the TiO2 layer due to its polymeric
nature contributing to the less efficient charge-transfer
process.21 The results were consistent with the photo-
voltaic characteristics of the fabricated dye-sensitized
solar cells.
4 CONCLUSIONS
A hydrophilic polysaccharide, -carrageenan, was
successfully used as the polymer matrix for a gel-elec-
trolyte system in a mixed solvent of water and aceto-
nitrile for dye-sensitized solar cells. The solvent system
improved the dissolution of the components and the
electrolyte properties. Efficiencies of less than 0.1 % of
the fabricated DSSCs are attributed to the significant
amount of water. A novel gel-polymer electrolyte con-
sisting of -carrageenan electrolyte gel in DMSO was
developed for DSSCs. Removal of the water from the
polymer-electrolyte system improved the DSSC per-
formance from 0.049 to 0.36 %, a seven-fold increase in
the magnitude. The presence of -carrageenan in the
DMSO-based gel-electrolyte system helps improve the
solar-cell efficiency from 0.221 to 0.360 %.
Acknowledgments
The authors are grateful to Dr. Erwin Enriquez, Dr.
Arnel Salvador and Dr. Armando Somintac for the use of
the solar simulator and Ms. Anna San Esteban for
guidance in solar measurements. This work was
supported by research grants from DOST-PCIEERD of
the Republic of the Philippines; DOST-SEI-ASTHRDP
and DLSU-PhD Fellowship Grants to J. P. O Bantang;
DLSU Research Faculty Grant, DLSU Science
Foundation and DLSU-URCO to D. H. Camacho.
J. P. BANTANG, D. CAMACHO: GELLING POLYSACCHARIDE AS THE ELECTROLYTE MATRIX ...
828 Materiali in tehnologije / Materials and technology 51 (2017) 5, 823–829
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
5 REFERENCES
1 J. R. MacCallum, C. A. Vincent, Polymer Electrolytes Reviews-l,
Elsevier Applied Science, London, 1989
2 K. N. Kumar, T. Sreekanth, M. J. Reddy, U. V. S. Rao, Study of
transport and electrochemical cell characteristics of PVP:NaClO3
polymer electrolyte system, J. Power Sources, 101 (2001), 130–133
doi:10.1016/S0378-7753(01)00658-9
3 T. M. W. J. Bandara, P. Ekanayake, M. A. K. L. Dissanayake, I.
Albinsson, B. E. Mellander, A polymer electrolyte containing ionic
liquid for possible applications in photoelectrochemical solar cells, J.
Solid State Electrochem., 14 (2010), 1221–1226, doi:10.1007/
s10008-009-0951-x
4 X. Guo, P. Yi, Y. Yang, J. Cui, S. Xiao, W. Wang, Effects of
surfactants on agarose-based magnetic polymer electrolyte for
dye-sensitized solar cells, Electrochim. Acta, 90 (2013), 524–529,
doi:10.1016/j.electacta.2012.12.028
5 R. Singh, A. R. Polu, B. Bhattacharya, H.-W. Rhee, C. Varlikli, P. K.
Singh, Perspectives for solid biopolymer electrolytes in dye
sensitized solar cell and battery application, Renew. Sustainable
Energy Rev., 65 (2016), 1098–1117, doi:10.1016/j.rser.2016.06.026
6 W. Wang, X. Guo, Y. Yang, Lithium iodide effect on the
electrochemical behavior of agarose based polymer electrolyte for
dye-sensitized solar cell, Electrochim. Acta, 56 (2011), 7347–7351,
doi:10.1016/j.electacta.2011.06.032
7 H.-L. Hsu, W.-T. Hsu, J. Leu, Effects of environmentally benign
solvents in the agarose gel electrolytes on dye-sensitized solar cells,
Electrochim. Acta, 56 (2011), 5904–5909, doi:10.1016/j.electacta.
2011.04.117
8 P. Li, Y. Zhang, W. Fa, Y. Zhang, B. Huang, Synthesis of a grafted
cellulose gel electrolyte in an ionic liquid ([Bmim]I) for
dye-sensitized solar cells, Carbohydr. Polym., 86 (2011), 1216–1220,
doi:10.1016/j.carbpol.2011.06.017
9 X. Huang, Y. Liu, J. Deng, B. Yi, X. Yu, P. Shen, S. Tan, A novel
polymer gel electrolyte based on cyanoethylated cellulose for
dye-sensitized solar cells, Electrochim. Acta, 80 (2012), 219–226,
doi:10.1016/j.electacta.2012.07.014
10 M. Kaneko, T. Hoshi, Y, Kaburagi, H. Ueno, Solid type dye-sensi-
tized solar cell using polysaccharide containing the redox electrolyte
solution, J. Electroanal. Chem., 572 (2004), 21–27, doi:10.1016/
j.jelechem.2004.05.021
11 H. Ueno, M. Kaneko, Investigation of a nanostructured poly-
saccharide solid medium for electrochemistry, J. Electroanal. Chem.,
568 (2004), 87–92, doi:10.1016/j.jelechem.2003.12.044
12 N. N. Mobarak, N. Ramli, A. Ahmad, M. Y. A. Rahman, Chemical
interaction and conductivity of carboxymethyl -carrageenan based
green polymer electrolyte, Solid State Ionics, 224 (2012), 51–57,
doi:10.1016/j.ssi.2012.07.010
13 F. Bella, N. N. Mobarak, F. N. Jumaah, A. Ahmad, From seaweeds to
biopolymeric electrolytes for third generation solar cells: An
intriguing approach, Electrochim. Acta, 151 (2015), 306–311,
doi:10.1016/j.electacta.2014.11.058
14 C. Law, S. C. Pathirana, X. Li, A. Y. Anderson, P. R. F. Barnes, A.
Listorti, T. H. Ghaddar, B. C. O’Regan, Water-Based Electrolytes for
Dye-Sensitized Solar Cells, Adv. Mater., 22 (2010), 4505–4509,
doi:10.1002/adma.201001703
15 D. H. Camacho, S. J. M. Tambio, M. I. A. Oliveros, Carrageenan-
Ionic Liquid Composite: Development of Polysaccharide-Based
Solid Electrolyte System, The Manila J. of Science, 6 (2011), 8–15
16 H.-L. Lu, Y.-H. Lee, S.-T. Huang, C. Su, T. C.-K. Yang, Influences of
water in bis-benzimidazole-derivative electrolyte additives to the
degradation of the dye-sensitized solar cells, Sol. Energy Mater. Sol.
Cells, 95 (2011), 158–162, doi:10.1016/j.solmat.2010.02.018
17 C. Tranquilan-Aranilla, N. Nagasawa, A. Bayquen, A. Dela Rosa,
Synthesis and characterization of carboxymethyl derivatives of
kappa-carrageenan, Carbohydr. Polym., 87 (2012), 1810–1816,
doi:10.1016/j.carbpol.2011.10.009
18 S. Yuan, Q. Tang, B. He, P. Yang, Efficient quasi-solid-state dye-sen-
sitized solar cells employing polyaniline and polypyrrole
incorporated microporous conducting gel electrolytes, J. Power
Sources, 254 (2014), 98–105, doi:10.1016/j.jpowsour.2013.12.112
19 S. Chan, J. P. Bantang, D. Camacho, Influence of Nanomaterial
Fillers in Biopolymer Electrolyte System for Squaraine-Based
Dye-Sensitized Solar Cells, Int. J. Electrochem. Sci., 10 (2015),
7696–7706
20 J. P. Bantang, D. Camacho, A Novel Biopolymer Gel Electrolyte
System for DSSC Applications, Proceedings of the DLSU Research
Congress, 3, 2015
21 S. Venkatesan, N. Obadja, T.-W. Chang, L.-T. Chen, Y.-L. Lee,
Performance improvement of gel- and solid-state dye-sensitized solar
cells by utilization of the blending effect of poly (vinylidene
fluoride-cohexafluropropylene) and poly (acrylonitrile-co-vinyl
acetate) co-polymers, J. Power Sources, 268 (2014), 77–81,
doi:10.1016/j.jpowsour.2014.06.016
22 H.-L. Hsu, C.-F. Tien, Y.-T. Yang, J. Leu, Dye-sensitized solar cells
based on agarose gel electrolytes using allylimidazolium iodides and
environmentally benign solvents, Electrochim. Acta, 91 (2013),
208–213, doi:10.1016/j.electacta.2012.12.133
23 K. Hara, T. Horiguchi, T. Kinoshita, K. Sayama, H. Arakawa,
Influence of electrolytes on the photovoltaic performance of organic
dye-sensitizednanocrystalline TiO2 solar cells, Sol. Energy Mater.
Sol. Cells, 70 (2001), 151–161, doi:10.1016/S0927-0248(01)00019-8
24 Y. Yang, J. Cui, P. Yi, X. Zheng, X. Guo, W. Wang, Effects of
nanoparticle additives on the properties of agarose polymer
electrolytes, J. Power Sources, 248 (2014), 988–993, doi:10.1016/
j.jpowsour.2013.10.016
J. P. BANTANG, D. CAMACHO: GELLING POLYSACCHARIDE AS THE ELECTROLYTE MATRIX ...
Materiali in tehnologije / Materials and technology 51 (2017) 5, 823–829 829
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS