High-performance dye-sensitized solar cell based on an electrospun poly(vinylidene fluoride-co-hexafluoropropylene)/cobalt sulfide nanocomposite membrane electrolyte

Article abstract of DOI:10.1039/c5ra04944j

Electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) nanocomposite membranes incorporated with different weight percentages (1, 2 and 3 wt%) of cobalt sulfide (CoS) were prepared by an electrospinning technique. The surface morphology, crystallinity, porosity and electrolyte uptake of the electrospun nanocomposite membranes were examined. The prepared electrospun PVdF-HFP/CoS nanocomposite membranes (esCPM) were activated by an ionic liquid electrolyte containing 0.5 M LiI, 0.05 M I₂, 0.5 M 4-tert-butylpyridine and 0.5 M 1-butyl-3-methylimidazolium iodide in acetonitrile to obtain electrospun PVdF-HFP/CoS nanocomposite membrane electrolytes (esCPMEs). The uniformly dispersed CoS nanoparticles increased charge transport and facilitated the diffusion of the redox couple in the electrolyte system. The electrochemical characteristics of the dye-sensitized solar cells depended on the amount of CoS incorporated into the esCPMEs. The photovoltaic performance of the dye-sensitized solar cell assembled using the esCPME incorporated with 1 wt% of CoS was measured and found to be 7.34%, which is higher than that of the dye-sensitized solar cell assembled using the esPME without CoS (6.42%).

Full text of DOI:10.1039/c5ra04944j

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Page 1 of 27
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High performance dye sensitized solar cell based on electrospun
poly(vinylidene fluoride-co-hexafluoropropylene)/Cobalt sulfide
nanocomposite membrane electrolyte
Vijayakumar. Ea, Subramania. Aa,*, Zhaofu Feib, Paul J. Dysonb
aElectrochemical Energy Research Lab, Centre for Nanoscience and Technology,
Pondicherry University, Puducherry - 605 014, India.
bInstitut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne
(EPFL) CH-1015, Lausanne, Switzerland.
(*Corresponding Author E-mail: a.subramania@gmail.com)
Fax: (+91) 413-2655 348 Phone: (+91) 413-2654612.
ABSTRACT
Different weight percentage (1, 2 and 3wt%) of cobalt sulfide incorporated (CoS)
incorporated electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP)
nanocomposite membranes were prepared by electrospinning technique. The surface
morphology, crystallinity, porosity and electrolyte uptake of the electrospun nanocomposite
membranes were examined. The prepared electrospun PVdF-HFP/CoS nanocomposite
membranes (esCPM) were activated by ionic liquid electrolyte containing 0.5M LiI, 0.05M I2
and 0.5M 4-tert butylpyridine, 0.5M 1-Butyl-3-methylimidazolium iodide in acetonitrile to
obtain electrospun PVdF-HFP/CoS nanocomposite membrane electrolytes (esCPMEs). The
uniformly dispersed CoS nanoparticles increase the charge transport and facilitate the
diffusion of redox couple in the electrolyte system. The electrochemical characteristics of
dye-sensitized solar cell (DSSC) depends on the amount of CoS incorporated in esCPME was
also studied in detail. The photovoltaic performance of DSSC assembled using 1wt% of CoS
incorporated esCPME was measured and it was found to be 7.34%, which is higher than that
assembled using esPME (6.42%).
KEYWORDS: Electrospinning, Dye-sensitized solar cell, Cobalt sulfide, Nanocomposite
membrane electrolyte.

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INTRODUCTION
Dye-sensitized solar cells (DSSCs) can serve as the promising mainstream renewable
energy resource because of their clean high energy efficiency and low cost. Since the first
report by Gratzel, the overall efficiency as high as 11% has been achieved with liquid
electrolytes through various works. However technical problems such as electrolyte leakage,
evaporation of solvent, high temperature instability and flammability limit their long term
performances. Among the alternatives such as inorganic or organic hole conductors1, ionic
2
liquids , polymer gel electrolytes
3,4
stand out because of their excellent properties such as
easy fabrication, low cost, and good stability. But, the gel network hinders the charge
transport in gel electrolytes to certain extent. Also, the gel electrolytes suffer from low
electrolyte loading per unit volume and consequently low ionic conductivity. In order to
rectify this negative influence of polymer gel electrolytes, electrospun polymer membrane
electrolytes have been investigated for DSSC applications. These polymer electrolytes have
several advantages over their liquid counter parts, such as no internal shorting, leakage of
electrolytes and non-combustible reaction products at the electrode surface than in liquid
electrolytes. Till date, polymer hosts such as poly(ethyleneoxide) (PEO), poly(propylene
oxide) (PPO), poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA), poly(vinyl
chloride) (PVC), poly(vinylidene fluoride) (PVdF), poly(vinylidene fluoride-hexafluoro
propylene) (PVdF-HFP), etc., have been used for DSSC applications 5. Recent advances have
proved that nanostructured metal chalcogenides (MCs) such as FeS2, CoS, NiS are great
potential materials for energy conversion and storage utilization because of their unique
physical and chemical properties 6–12. Following that, we have described the promising
applications of MCs in the field of DSSCs. The advantages of using MCs are higher electric
conductivity, and shorter path length for the transport of electrons.
In the present work, we have developed the cobalt sulfide (CoS) incorporated
esCPME due to the superior electrocatalytic activity of CoS. The electrospinning is the top-

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down, simple, versatile and cost effective approach allowing the fabrication of nanofibers
with high degree of reproducibility for various applications such as Dye sensitized solar cells,
supercapacitors, Li-ion batteries, nano-filters etc., 13–20. The electrospun polymer membranes
have their own unique properties such as high porosity, large surface area, fully
interconnected pore structure with sufficient mechanical strength and also have three-
dimensional network structure. They offer the advantage of cohesive properties of the gel
polymer electrolyte along with the diffusive nature of the liquid electrolyte due to its
interconnected pores that can easily entrap a large quantity of liquid electrolyte which
improve the interfacial contact of both electrodes with electrolyte21. The room temperature
ionic liquids are promising alternatives to volatile electrolyte due to their unique properties
such as negligible vapor pressure, excellent electrochemical and thermal stability as well as
the high ionic conductivity 22. The fluorinated polymers are known to be photochemically
stable even in the presence of TiO2 and Pt. The higher conductivity of PVdF-HFP films is
attributed to the higher amorphicity as there are two randomly mixed monomers providing
the mobile ions more free 23. Thus, to improve the interfacial and ionic conductivity of
electrospun polymer membrane electrolyte, CoS nanoparticles are introduced into the
electrospun membrane. The encapsulation of nanoparticles addresses a vast range of
problems such as low ionic conductivity, interfacial stability, mechanical strength
dimensional and thermal stabilities. The addition of CoS nanoparticles will increase further
the amorphous content, thereby increasing the electrolyte uptake. Also, the CoS nanoparticles
enhance the diffusion coefficient of
and also reduce the charge recombination at the
TiO2/electrolyte interface. The significance of this study lies in improving the kinetics of ion
transport and thereby the electrochemical activity of the electrospun membrane electrolyte.
By this approach, the electrospun polymer membrane electrolyte would increase the
photoconversion efficiency of DSSC.

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EXPERIMENTAL
Materials
Acetone and N,N’-dimethylacetamide were procured from Merck India Ltd. Lithium
iodide, iodide, 4-tert-butylpyridine and acetonitrile were procured from Sigma Aldrich and
PVdF-HFP from Arkema (Kynar flex 2801). All these chemicals are analytical grade and
used as received without any further purification. The cobalt sulfide nanoparticles were
prepared by a simple hydrothermal method. In this method, 3 mmol CoCl2.6H2O solution in
deionized water was added to the 3 mmol L-cysteine solution in deionized water with
constant and vigorous stirring. After 15 min, the resulting mixture was heated and maintained
at 190°C for 6 h in an autoclave. The resulting product was then washed and vacuum dried at
50°C for overnight24.
Preparation of electrospun PVDF-HFP/CoS composite membrane
The different weight percentage of CoS (1wt %, 2wt %, 3wt %) were added to 16
wt% solution of PVdF-HFP in a mixture of acetone/N,N’-dimethyl acetamide (7:3 wt%). The
electrospinning was carried out at 19 KV and the distance between the collector and tip of the
syringe was kept at 12cm. The polymer solution was supplied to the stainless steel needle (27
G) using a syringe pump at the flow rate of 0.5 ml/h. The thickness of the membrane was
controlled to 30 µm. Finally, the prepared nanofibrous composite membranes was vacuum
dried at 80°C for 12 h to remove residual solvent. The thickness of esCPMs was reduced
from ca. 30 to 20 µm by hot pressing21.
Characterization of esCPM
The surface morphology of esCPM was examined by field emission scanning electron
microscopy (FE-SEM; Model: JSM-7600F). The structural characterization of different wt%
of CoS incorporated esCPM was studied by X-ray diffraction technique (Rigaku, Ultima IV)
with nickel-filtered Cu-Kα radiation in a range from 20° to 80° with an increment of 0.05˚.
The fourier transform infrared (FT-IR) spectra were recorded for the esPM, CoS, esCPM

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(Thermo Nicolet, Model:6700). Thermal behavior of esCPMs was studied by differential
scanning calorimetry (DSC) at a heating rate of 10°C/min under a nitrogen atmosphere over
the temperature range of 30 °C - 280 °C (TA Instruments; Model: Q600 SDT).
The crystallinity ( Xc ) of esCPMs was calculated as follows 25;
ꢀHmsample
ꢀHm∗
Xc
(
%
)
=
×100
(1)
where, ꢀHmsample is the heat of melting of the sample and ꢀHm∗ is the crystalline melting heat
of PVdF, 104.7 J/g.
The porosity (%) of esCPMs was measured by immersing the nanocomposite
membranes in 1-butanol for 2 hour. The porosity (P) was calculated using the following
equation26;
ma / ρa
ma / ρa + mp / ρp
(2)
P =
where, ‘ma ’ is the weight of esCPMs after impregnation with 1-butanol, ‘mp ’ is the weight
of esCPM before impregnation with 1-butanol, and ‘
and the dried esCPM, respectively.
ρ
a ’ and ‘ ρ p ’ are density of 1-butanol
To measure the electrolyte uptake of esCPMs, the nanocomposite membranes were
soaked in the ionic liquid electrolyte for 24 h. After activation, the electrolyte membranes
were taken out from the electrolyte solution and an excess of electrolyte on the electrospun
membrane was wiped off by whatman filter paper. Electrolyte uptake (U ) was estimated
using the formula 5;
U (%) = [(m − m° ) / m° ]×100
(3)
where, ‘m’ and ‘mo’ are the mass of wet and dry esCPMs, respectively.

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The leakage of the electrolyte was calculated using the equation 4;
MPE
R =
(4)
MPE,saturated
where, R is the relative absorption ratio of the liquid electrolyte, MPE,saturated is the mass of the
polymer electrolyte when the electrospun membrane is fully saturated with the liquid
electrolyte, and MPE is the mass of the electrospun membrane electrolyte after a time interval
when the saturated electrospun membrane electrolyte is squeezed by pressing it between two
filter papers.
The electrochemical impedance spectra and Tafel polarization measurements verify
the electrochemical activities. The different weight percentage of CoS incorporated esCPMs
were soaked in the ionic liquid electrolyte to form their corresponding esCPMEs. The ionic
conductivity of the resultant esCPMEs (
σ
) was measured by sandwiching the nanocomposite
membrane electrolyte in between two stainless steel blocking electrodes using AC-impedance
technique (Biologic, Model: VSP) at 25 ˚C. The ionic conductivity (σ) of the electrospun
PVDF-HFP nanocomposite membrane electrolytes was calculated using the equation 23;
σ = l / RA
(5)
where, l is the polymer membrane thickness, A is the area of the esCPME and R is the bulk
resistance. The bulk resistance could be obtained from the complex impedance plot. The
frequency limit was set between 1 mHz and 100 KHz with AC amplitude of 10 mV. The
thickness (l ) of the esCPM was determined using a digital micrometer and was found to be
20
ꢀ
m. The area (A) of the polymer membrane was 1 cm2.
The Tafel polarization measurement were carried out using symmetric cells consisting
of FTO/Pt/esCPMEs/Pt/FTO to reconfirm the electrocatalytic activity of esCPME 27.
Fabrication of dye-sensitized solar cells (DSSCs)
The DSSCs were assembled as per the earlier reports by sandwiching a slice of
esCPME in between a dye-sensitized TiO2 photoanode and Pt counter electrode 23. The dye

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adsorbed titania photoanode and Pt counter electrode were assembled using 60
ꢀm thick hot
melt thermoplastic sealer (Surlyn). A drop of the electrolyte solution containing 0.5 M LiI,
0.05 M I2 and 0.5 M 4-tertbutylpyridine and 0.5 M 1-butyl-3-methylimidazoliun iodide in
21
acetonitrile was introduced into the clamped electrodes through one of two small holes
drilled in the counter electrode. The DSSC based on esPME were also assembled following
the same procedure for comparison.
Photovoltaic Performance of DSSCs
The photovoltaic performance of DSSCs were measured using a calibrated AM 1.5
solar simulator (Newport, Oriel instruments, Model: 67005) with a light intensity of 100 mW
cm-2 and a computer controlled digital source meter (Keithley, Model: 2420). I-V
measurements were carried out on the DSSCs after an aging period of 24 h. The assembled
DSSCs were stored in a desiccator and the electrochemical measurements were conducted for
every 48 h to study their long term stability. The photoelectrochemical parameters, i.e., the
fill factor (FF) and light-to-electricity conversion efficiency (η) were calculated with the
following equations 28:
Vmax Jmax
Voc Jsc FF
η
(%) =
×100 =
×100
(6)
P
P
in
in
Vmax Jmax
FF =
(7)
Voc Jsc
where, Jsc is the short-circuit current density (mA cm-2), Voc is the open-circuit voltage (V),
Pin is the incident light power (mW cm-2), and Jmax and Vmax are the current density (mA cm-2)
and voltage (V) in the J-V curves, respectively at the point of maximum power output. All the
fabrication steps and characterization measurements were carried out in an ambient
environment without any protective atmosphere. The photovoltaic parameter values were
made by taking the average values of three DSSCs for each system.

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RESULTS AND DISCUSSION
Characterization for esCPMs and esCPMEs
The FE-SEM image of the prepared esPM and esCPM (1 wt%) are shown in Fig. 1(a
& b). The FE-SEM image of the prepared esPM and esCPM are shown in Fig. 1(a & b). It
can be seen from Fig. 1(a) that the esCPM has a three-dimensional network with fully
interconnected pores structure that capable of entrapping large amount of ionic liquid
electrolyte in their pores which favorable for the transportation of redox couple resulting in
the improvement of ionic conductivity. In Fig. 1(b), the bubble like structure observed is due
to CoS nanoparticles incorporated in host esCPM. This esCPM has sufficient mechanical
strength due to its three dimensional network structure with cross linking points 23. The
esCPM (average diameter of the fibers is 300-350 nm) has a maximum porosity, electrolyte
uptake and less leakage are 94 %, 410 % and 0.2, respectively. The increase in the electrolyte
uptake upon the addition of CoS nanoparticles is mainly due to increase in the porosity on
account of increase in surface roughness. Also, the CoS fillers decreases the degree of
crystallinity that provide a large free volume and many free surface sites able to trap ionic
liquid electrolyte which increase further the ionic conductivity as well as the electrochemical
performance. However, beyond the optimum concentration of CoS, the blocking effect is
caused by the aggregation of CoS nanoparticles which decreases the porosity thereby
reducing the ability of electrolyte uptake.
The FT-IR spectra of PVdF-HFP, CoS and esCPM (1 wt%) are shown in Fig. 2. The
peaks at about 1395, 867 and 485 cm-1 are due to the C-F2 bending, wagging and stretching
vibrations and peak at 1185 is due to the C-C bond of PVdF. It is clear that the spectrum of
PVdF-HFP contains peak at 611, 872, 1064, 1180 and 1400 cm-1 that corresponds to
vinylidene, CH2 wagging of the vinylidene band, -C-F- stretching, scissoring and bending
vibration of the vinyl group, respectively. The peaks at 680 cm-1 and 550 cm-1 correspond to
twisting in vinyl group. For cobalt sulfide nanoparticles, the appearance of band at 474.4 cm-

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1
and 1115 cm-1 corresponds to the S-O modes. The peak at 1527 cm-1 is due to the -OH
stretching. No shift in peaks are observed in esCPM indicating that there is no conjugate
bonds or interaction between PVDF-HFP and CoS nanoparticles. It reveals that the CoS
nanoparticles are incorporated in the host esCPM and there is no complex formation between
PVdF-HFP and CoS.
The variation in crystallinity of PVdF-HFP owing to the addition of different weight
percentage of CoS nanoparticles are studied by X-ray diffraction. The XRD patterns for
PVdF-HFP powder, CoS, esPM and esCPMs are shown in Fig. 3. The diffraction peaks of
CoS nanoparticles are matched with standard XRD pattern (ICSD No. 029305). No impurity
peaks were observed indicates the formation of pure CoS nanoparticles 29. In the XRD pattern
of PVdF-HFP, the major peaks at 18.2° and 20.0° corresponds to (100) and (020) crystalline
phase, respectively. It is observed that the intensity of peak weakened for electrospun PVDF-
HFP that makes the migration of polymer chain free 30. The intensity these peaks reduced
considerably with increase in the addition of CoS which indicates the addition of CoS
considerably reduced its partial crystallinity to amorphous. The decrement in peak intensity
suggests an increase in the degree of amorphicity that helps in the migration of ions in the
electrolyte system, which is responsible for the enhancement of ionic conductivity. Also, the
decrease in the crystallinity indicates the better dispersion of CoS nanoparticles in the
electrospun membrane. The lowest crystallinity is found for 1wt% of CoS incorporated
esCPM. However, on increasing the CoS content beyond 1wt%, they tend to agglomerate and
create a blocking effect on the mobility of redox couple, hereby increased the crystallinity
and deteriorate the polymer chain movement. Thus, 1wt% of CoS incorporated esCPME
provided high ionic conductivity and thereby increased the photovoltaic performance.
Fig. 4 shows the DSC thermograms of esPM and 1wt% of CoS incorporated esCPM.
The addition of CoS nanoparticles increase the amorphous phase of the host. It is observed
that 1wt% of CoS incorporated esCPM have more amorphous content than the esPM which is

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realized from the XRD results. In the esCPME, the solar conversion efficiency strongly
depends on the ionic conductivity. On incorporation of 1 wt% of CoS, the amorphous content
increased considerably. The amorphous content has high ionic mobility and thereby enhanced
the ionic conductivity. The percentage of crystallinity is calculated using equation 1. The
1wt% of CoS incorporated esCPM has the lower crystallinity (22.84%) than that of esPM
(31.97%), which ensure its higher electrolyte uptake that leads to enhance the charge carriers
mobility and thereby increased the ionic conductivity.
The ionic conductivity of different weight percentage of CoS incorporated esCPMEs
are calculated from the bulk resistance obtained from complex impedance measurements at
ambient temperature is given in Table 1 (Fig. 5). The inclusion of CoS nanoparticles
improved the amorphicity content and provides the diffusion path in the electrospun
membrane. Thus, an excellent improvement attributed to esCPME is due to high amorphicity
content, which endorses the dissociation of charge carriers from the interactive bonds and
provides a favorable condition for the fast migration of iodide and triiodide ions to favor an
improvement in the conductivity of ionic liquid. The esCPME is thought to comprise a solid
fibrous phase, an amorphous swollen fibrous phase and a liquid phase in its pores. This
indicates that the partial swelling of the polymer fibers with a large surface area significantly
contribute to increase in stability of the electrolyte under electrochemical environments,
although the ionic conduction occurred mainly through the entrapped liquid electrolyte in a
fully interconnected pore structure. The liquid electrolyte which accumulated in between the
interconnected pores present in the esCPM to act as gel like as well as liquid electrolytes.
The increase in ionic conductivity with the addition of CoS is related to both the
generation of free volume at the interface of inorganic materials and the surface interactions
with the inorganic iodide. The CoS provides increase in molecular ordering and ionic
conductivity as well as the formation of diffusion path for the redox species thereby increases
the electrochemical activity of CoS incorporated esCPMEs. The reduction in the ionic

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conductivity on increasing the CoS content beyond 1wt% is due to the agglomeration of CoS
nanoparticles. The agglomeration makes the polymer membrane stiffer and thereby obstructs
the segmental motion of the polymer chains that hinder the transportation of the charge
carriers. The hindrance in charge transportation (blocking effect) decreases the ionic
conductivity. Fig. 6 shows the illustration of formation of esCPME and the blocking effect
due the agglomeration of CoS beyond its optimum concentration. The ionic conductivity of 1
wt% of CoS incorporated esCPME has the maximum value of 36.43×10-3 S cm-1. The PCE of
DSSC depends on the ionic conductivity of esCPME. Thus, 1wt% of CoS incorporated
esCPME may have high PCE.
Fig. 7 shows the Tafel curves of different wt% of CoS incorporated esCPMEs. The
slope of the polarization zone represents the charge transfer resistance (Rct), which is
inversely proportional to the exchange current density (J0). It is an important indicator for
assessing the electrochemical reaction kinetics. The steep slope of Tafel zone has a large J0
and small Rct values. It is observed that 1wt% of CoS incorporated esCPME has larger slope
and higher Jlim than that of the other weight percentages. The values of J0 can be obtained
from the intersection of linear cathodic and anodic region and the values of Jlim can be
obtained by drawing a straight line towards the current density axis from a point of both
anodic and cathodic region in the Tafel polarization curves. This results indicate the higher
catalytic activity towards triiodide couple and the higher diffusion velocity of facial redox
reaction in esCPME 31.
Photovoltaic performance of DSSCs
The photocurrent density-voltage (J-V) curves were obtained at a light intensity of
100 mW cm-2 under the standard global AM 1.5 irradiation are shown in Fig. 8 (Table 2). The
DSSCs assembled using esCPME (1wt% CoS) provides power conversion efficiency of
7.34% higher than that of esPME (6.42%). The increasing amorphous nature of the esCPME
on addition of CoS nanoparticles, improve the penetration of esCPME into porous TiO2

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electrode, thereby decreasing the interfacial recombination of electrons, which leads to higher
in Jsc and fill factor values. Moreover, the electrocatalytic activity of esCPME reduces the
over potential which in turn increases the Voc value. The increasing amorphous nature of
esCPME on the addition of CoS, improve the penetration of esCPME into porous TiO2
photoanode, thereby decreasing the interfacial recombination of electrons, which leads to
increased Jsc and fill factor. Moreover, the electrocatalytic activity of esCPME reduces the
over potential which in turn increases the Voc value. Fig. 9 illustrates the mechanism of
increased reaction kinetics of DSSC assembled using esCPME. At optimal concentration of
CoS (1 wt%), the reaction kinetics increases and hence photovoltaic performance is also
increased. This may be due to the direct conductive pathway of electrons provided by CoS
nanoparticles and their electrocatalytic activity. However, further increase in the
concentration of CoS, cause poor penetration of esCPME into TiO2 photoanode due to
stiffness caused by agglomeration and also direct contact of CoS nanoparticles which may
form short circuit, that lead to the depletion of photovoltaic performance. The increment in
values of Jsc values from 13.10 to 14.42 is mainly attributed to the low charge transfer
−
resistance and higher electrocatalytic activity in the reduction of I3 /I− electrolyte. Thus, the
CoS incorporated esCPME ensured an effective charge transfer at the CE/electrolyte interface
with lower recombination rate in the DSSC, which ultimately increased the PCE.
The stability of DSSCs assembled with both esPME and esCPME (1 wt%) was
studied over a period of 30 days (Fig. 10). Both DSSCs retain ca. 99% of their initial value.
Notably, no decay was observed in the overall PCE of both the DSSCs. This might be due to
their three dimensional network with interconnected pores. These interconnected pores are
able to trap the liquid electrolyte and consequently, the resulting esPME/esCPME appears to
act as liquid as well as gel electrolytes. Thus, both the esPME and esCPME appears to
promote interfacial contact between the dye-adsorbed TiO2 electrode and the Pt counter
electrode, which helps to give more stable photovoltaic performance.

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CONCLUSIONS
The CoS incorporated esCPMs were prepared successfully by electrospinning
technique and compared with esPM. Their surface morphology, crystallinity, thermal
behavior, % porosity and % electrolyte uptake were studied. They were then activated by a
liquid electrolyte and their ionic conductivity and Tafel polarization measurements were
made. The esCPME (1 wt% of CoS) shows higher ionic conductivity of 36.43×10-3 S cm-1.
The 1wt% CoS incorporated esCPME showed superior photovoltaic performance. The
increased active surface area of esCPME by the incorporation of CoS could promote
−
electrocatalytic activity of I3 reduction and the total current for I3− / I− redox reaction, which
enhanced the Jsc value of the DSSC. Thus, DSSC assembled using 1wt% of CoS
incorporated esCPME shows an improved PCE of 7.34%, which is higher than that
assembled using esPME (6.42%).
ACKNOWLEDGEMENTS
The authors gratefully acknowledge the CSIR (Ref. No.01/2359/10/EMR-II) New Delhi for
the financial support and also the CIF of Pondicherry University for extending the
instrumentation facilities.
REFERENCES
1.
2.
3.
I.-K. Ding, J. Melas-Kyriazi, N.-L. Cevey-Ha, K. G. Chittibabu, S. M. Zakeeruddin,
M. Grätzel, and M. D. McGehee, Org. Electron., 2010, 11, 1217–1222.
P. Wang, S. M. Zakeeruddin, J.-E. Moser, and M. Grätzel, J. Phys. Chem. B, 2003,
107, 13280–13285.
S. Cetiner, F. Kalaoglu, H. Karakas, and A. Sezai Sarac, Fibers Polym., 2011, 12, 151–
158.
4.
5.
6.
7.
N. Angulakshmi and A. M. Stephan, Electrochim. Acta, 2014, 127, 167–172.
J. Zhao, S.-G. Jo, and D.-W. Kim, Electrochim. Acta, 2014, 142, 261–267.
Q.-H. Huang, T. Ling, S.-Z. Qiao, and X.-W. Du, J. Mater. Chem. A, 2013, 1, 11828.
Y.-C. Wang, D.-Y. Wang, Y.-T. Jiang, H.-A. Chen, C.-C. Chen, K.-C. Ho, H.-L.
Chou, and C.-W. Chen, Angew. Chem. Int. Ed. Engl., 2013, 52, 6694–8.

RSC Advances
Page 14 of 27
View Article Online
DOI: 10.1039/C5RA04944J
8.
9.
H. Sun, D. Qin, S. Huang, X. Guo, D. Li, Y. Luo, and Q. Meng, Energy Environ. Sci.,
2011, , 2630.
4
Z. Ku, X. Li, G. Liu, H. Wang, Y. Rong, M. Xu, L. Liu, M. Hu, Y. Yang, and H. Han,
J. Mater. Chem. A, 2013, , 237.
1
10. J.-Y. Lin, J.-H. Liao, and T.-C. Wei, Electrochem. Solid-State Lett., 2011, 14, D41.
11. J.-Y. Lin and J.-H. Liao, J. Electrochem. Soc., 2012, 159, D65.
12. X. Miao, K. Pan, G. Wang, Y. Liao, L. Wang, W. Zhou, B. Jiang, Q. Pan, and G. Tian,
Chemistry, 2014, 20, 474–82.
13. X. Zhang, P. Suresh Kumar, V. Aravindan, H. H. Liu, J. Sundaramurthy, S. G.
Mhaisalkar, H. M. Duong, S. Ramakrishna, and S. Madhavi, J. Phys. Chem. C, 2012,
116, 14780–14788.
14. X. Zhang, H. Liu, S. Petnikota, S. Ramakrishna, and H. J. Fan, J. Mater. Chem. A,
2014, 2, 10835–10841.
15. Z. Xiang, B. R. S. Rajaraman, H. Liu, and S. Ramakrishna, RSC Adv., 2014, 28987–
29011.
16. X. Zhang, V. Thavasi, S. G. Mhaisalkar, and S. Ramakrishna, Nanoscale, 2012, 4,
1707.
17. S. Homaeigohar and M. Elbahri, Materials, 2014, 7, 1017–1045.
18. S. Sundarrajan, K. Luck, S. Huat, and S. Ramakrishna, Procedia Eng., 2014, 75, 159–
163.
19. K. Yoon, K. Kim, X. Wang, D. Fang, B. S. Hsiao, and B. Chu, Polymer, 2006, 47
2434–2441.
,
20. S. Ramakrishnan, M. Dhakshnamoorthy, E. J. Jelmy, R. Vasanthakumari, and N. K.
Kothurkar, RSC Adv., 2014, , 9743.
4
21. Vijayakumar E, Subramania A, Z. Fei, and P. J. Dyson, J. Appl. Polym. Sci, 2015, 132
42032 (1–7).
,
22. Y.-L. Lee, Y.-J. Shen, and Y.-M. Yang, Nanotechnology, 2008, 19, 455201.
23. A. R. S. Priya, A. Subramania, Y.-S. Jung, and K.-J. Kim, Langmuir, 2008, 24, 9816–
9.
24. S.-J. Bao, C. M. Li, C.-X. Guo, and Y. Qiao, J. Power Sources, 2008, 180, 676–681.
25. A. Subramania, N. T. K. Sundaram, A. R. S. Priya, and G. V. Kumar, J. Memb. Sci.,
2007, 294, 8–15.
26. J. Hao, Q. Xiao, G. Lei, Z. Li, and L. Wu, Electrochim. Acta, 2014, 125, 450–456.

Page 15 of 27
RSC Advances
View Article Online
DOI: 10.1039/C5RA04944J
27. S. Yuan, Q. Tang, B. He, and P. Yang, J. Power Sources, 2014, 254, 98–105.
28. A. Subramania, E. Vijayakumar, N. Sivasankar, A. R. Sathiya Priya, and K.-J. Kim,
Ionics, 2013, 19, 1649–1653.
29. G. Panthi, N. A. M. Barakat, K. Abdelrazek, A. Yousef, K. Jeon, and H. Yong, Ceram.
Int., 2013, 39, 1469–1476.
30. R. Miao, B. Liu, Z. Zhu, Y. Liu, J. Li, X. Wang, and Q. Li, J. Power Sources, 2008,
184, 420–426.
31. Q. Li, X. Chen, Q. Tang, H. Cai, Y. Qin, B. He, M. Li, S. Jin, and Z. Liu, J. Power
Sources, 2014, 248, 923–930.

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Figure Captions
Fig. 1 FE-SEM photograph of a) esPM and b) 1wt% of CoS incorporated esCPM
Fig. 2 FTIR spectra of esPM, CoS and 1wt% of CoS incorporated esCPM
Fig. 3 XRD patterns of PVdF-HFP powder, CoS and different wt% of CoS incorporated
esCPMs
Fig. 4 DSC analysis of esPM and 1wt% of CoS incorporated esCPME.
Fig. 5 Nyquist plots for different wt% of CoS incorporated esCPMEs on ionic conductivity
Fig. 6 Illustration of formation of esCPME and the blocking effect due to the agglomeration
of CoS beyond its optimum concentration.
Fig. 7 Tafel polarization curves of the symmetrical cells assembled with different wt% of
CoS incorporated esCPME
Fig. 8 Photocurrent density-voltage (J-V) curves for DSSC based on (a) esPME (b) 1wt% of
CoS incorporated esCPME.
Fig. 9 Illustrates the mechanism of increased reaction kinetics of DSSC assembled using
esCPME.
Fig. 10 Normalized efficiency of a) esPME and b) 1wt% of CoS incorporated esCPME.

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Tables
Table 1 Influence of different wt% of CoS incorporated esCPMEs
on ionic conductivity
Electrolyte
Ionic conductivity
(×10-3 S cm-1)
5.83
U (%) P (%)
esPME
340
410
392
376
84
94
90
87
esCPME (1 wt% CoS)
esCPME (2 wt% CoS)
esCPME (3 wt% CoS)
36.43
29.17
16.22
Table 2 Photovoltaic performances of DSSCs based on esPME and 1wt% of CoS
incorporated esCPME .
Electrolyte
Jsc
(mA cm-2)
13.10
Voc
(V)
FF
69
70
Efficiency
(%)
6.42
esPME
0.71
esCPME (1wt% CoS)
14.42
0.73
7.34

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Fig. 1 FE-SEM photograph of a) esPM and b) 1wt% of CoS incorporated esCPM

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Fig. 2 FTIR spectra of esPM, CoS and 1wt% of CoS incorporated esCPM

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Fig. 3 XRD patterns of PVdF-HFP powder, CoS and different wt% of CoS incorporated esCPMs

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Fig. 4 DSC analysis of esPM and 1wt% of CoS incorporated esCPME.

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Fig. 5 Nyquist plots for different wt% of CoS incorporated esCPMEs on ionic conductivity

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Fig. 6 Illustration of formation of esCPME and the blocking effect due to the agglomeration of CoS beyond its
optimum concentration.
62x37mm (300 x 300 DPI)

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Fig. 7 Tafel polarization curves of the symmetrical cells assembled with different wt% of CoS incorporated
esCPME

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Fig. 8 Photocurrent density-voltage (J-V) curves for DSSC based on (a) esPME (b) 1wt% of CoS
incorporated esCPME.

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Fig. 9 Illustrates the mechanism of increased reaction kinetics of DSSC assembled using esCPME.
43x41mm (300 x 300 DPI)

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Fig. 10 Normalized efficiency of a) esPME and b) 1wt% of CoS incorporated esCPME.