Structure-efficiency relationship of newly synthesized 4-substituted donor-π-acceptor coumarins for dye-sensitized solar cells

Article abstract of DOI:10.1039/c7nj04954d

Four (MC1-MC4) 4-substituted coumarin dyes having N,N-diethyl aniline as donor and rhodanine-3-acetic acid as acceptor have been synthesized for use in nano-crystalline TiO₂-based dye-sensitized solar cells (DSSCs). The alteration at the 4-position of coumarin was carried out by substituting H atom by chlorine (-Cl), piperidine (-NC₅H₁₀), and cyano group (-CN) to study the effect of substitution on the efficiency of the DSSCs. All the dyes were characterised by ¹H-NMR and ¹³C-NMR spectroscopy and CHN analysis. The absorption and emission spectra of these coumarin dyes were recorded in eight different solvents and show positive solvatochromism. The TiO₂-based DSSCs were fabricated using the four dyes and their photovoltaic properties were estimated. A maximum efficiency of 4.60% was obtained for the MC4 device, which has an electron-withdrawing cyano group at the 4-position of coumarin, while 2.64% efficiency was obtained for the MC1 device, which has only hydrogen at the 4-position. The efficiencies of the MC2 and MC3 devices lie between those of MC1 and MC4, suggesting the significance of substitution at the 4-position. The introduction of a cyano group, which acts as an electron trap, increases the electron-withdrawing capacity of the dye; thus, more electron density is withdrawn from the donor, resulting in enhanced efficiency. These dyes were studied by using density functional theory (DFT) and time dependent density functional theory (TD-DFT) to obtain the vertical excitation, HOMO-LUMO energy levels, band gap and electron distribution in the ground and excited state. The calculated values showed good correlation with the experimental values. Our results suggest that substitution at the 4-position is essential for enhancing the efficiency of coumarin-based DSSCs.

Full text of DOI:10.1039/c7nj04954d

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Structure Efficiency Relationship in newly synthesized 4-
Substituted Donor-π-Acceptor Coumarins for Dye Sensitized Solar
Cells
Received 00th January 20xx,
Accepted 00th January 20xx
Manoj M Jadhava, Jayraj V Vaghasiyab,c, Dinesh S Patila, Saurabh S Sonib,*, Nagaiyan Sekara,*
DOI: 10.1039/x0xx00000x
Four (MC1-MC4) 4 substituted coumarin dyes having N, N-diethyl aniline as donor and rhodanine-3-acetic acid as acceptor
have been synthesized for use in nano-crystalline TiO2 based dye-sensitized solar cells (DSSCs). The alteration at 4-position
of coumarin is carried out by substituting H atom by chlorine (-Cl), piperidine (-NC5H10) and cyano (-CN) to study the effect
of substitution on efficiency in DSSCs. All the dyes were characterised by 1H-NMR, 13C-NMR and CHN analysis. The
absorption and emission spectra of these coumarin dyes recorded in eight different solvents show positive
solvatochromism. TiO2 based DSSCs were fabricated using all the four dyes and their photovoltaic properties are
estimated. Maximum efficiency of 4.60 % is obtained for MC4 having electron withdrawing cyano group at 4-position in
coumarin whereas 2.64% efficiency is obtained for MC1 which has only hydrogen at 4 position while efficiencies of MC2
and MC3 lies between those of MC1 and MC4 suggesting the significance of substitution at 4 position. Introduction of
cyano group which acts as electron trap increases the electron withdrawing capacity of dye and more electron density is
withdrawn from donor which results in enhanced efficiency. These dyes were studied by using density functional theory
(DFT) and time dependent density functional theory (TD-DFT) to obtain vertical excitation, HOMO-LUMO energy levels,
band gap and electron distribution at ground and excited state. These values show good correlation with experimental
values. Our results suggest that substitution at 4-position is very essential for enhancing the efficiency of coumarin based
DSSCs.
www.rsc.org/
transition at about 400 nm) and weak Q band (S0-S1 transition
at about 550nm).12,13 Porphyrin based DSSCs suffer from
Introduction
tedious synthetic routes and difficulty in purification. To
Organic based dye sensitized solar cells (DSSCs) capable of
harvesting light radiation have received mammoth
consideration1–4 since the first report in 1991 by Grätzel and
co-workers on nano crystalline anatase TiO2 based dye-
sensitized solar cells (DSSCs) as prospective replacements to
conventional silicon-based inorganic photovoltaic devices.5
Ruthenium based color complexes have been explored as a
sensitizer on TiO2 semiconductors, have achieved the light to
current conversion efficiency up to 11.5%.6–10 The commercial
application of these dyes is impeded substantially due to
inadequate availability, high cost of ruthenium metal, low
molar extension coefficient, bad environmental effects,
difficulty in purification.11 Porphyrin based dyes are gaining
more importance because of their broad absorption spectrum
resulting due to the combination of intense Soret band (S0-S2
overcome these limitations metal-free organic based donor-pi-
acceptor chromophores have been explored simultaneously.
14–20
Well established synthetic protocols and purification
technique, abundant availability of starting materials, easy
structural modification and ease in optical property tuning
makes them a demanding alternative as a sensitizer in
DSSCs.21–24 Highly efficient sensitizer having donor-π-acceptor
skeleton shows broad absorption in visible and near infrared
regions, fast injection of electron on conduction band of TiO2
and slow recombination of electron with oxidized dye.21,25
Organic amine based donors in conjugation with π-extended
conjugative linkers such as coumarin,26–29 indoline,30–32
polyene,33,34
phthalocyanine43 have been explored as potential sensitizers
for DSSCs. Out of these -linkers coumarin is one of the widely
thiophene,35–37 cyanine,38,39 squaraine,40–42
π
explored chromophore44–47 in DSSCs. 6,7 and 8 position of
coumarin were being substituted by different substituents to
enhance the efficiency 21,44,48,49 but the impact of substitutions
at 4 position on efficiency of DSSCs remains unexplored till
date. In this paper, we have synthesized four rohdanine-3-
acetic acid based coumarin molecules MC1 to MC4 having
different substituent at 4-position. Systematic modification at
4 position of coumarin dyes with chlorine (Cl), piperidine (-
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NC5H10) and cyano (-CN) results in shifting the maximum simulator, PET, USA) calibrated with the light intensity
absorption to the red region. This leads to an improvement in 100mW.cm-2 at AM 1.5 G solar light conditions by a certified
photophysical response, short-circuit photocurrent and overall silicon
energy conversion efficiency have been improved significantly
which highlights the importance of 4 substitution in coumarin.
solar
cell
was
used
as
light
source.
N
O
O
O
N
OH
CHO
4-(diethylamino)-2-hydroxybenzaldehyde
b
a
O
1
Experimental Section
Computational methods
N
N
O
O
Density functional theory (DFT) was used to optimize MC1 to
MC4 in the gas phase and eight different solvents. A well-
known B3LYP method50 which is a combination of Becke’s
three parameter exchange functional (B3)51 with the nonlocal
correlation functional by Lee, Yang, and Parr (LYP)52 is explored
for optimization of molecules. The local minimum energy and
N
O
O
c
d
CHO
2
3
O
O
vertical excitation of each compound computed using TD-DFT
53
CHO
calculation
at 6-31+G(d) basis set. The polarizable
CN
4
continuum model (PCM)54,55 as implemented in Gaussian 09
was employed for optimization in solvents. All electronic
structure computations were carried out using the Gaussian 09
56 program.
N
OH
N
O
O
e
f
Chemicals and Instruments
3-(diethylamino)phenol
OH
5
All the synthetic grade reagents and solvents required for
synthesis were procured from S. D. Fine Chemicals Pvt Ltd and
used as it is without purification. The 3-methoxy propionitrile
(MNP), Titania (IV) isoporopoxide, LiI, I2, 4-tert-butyl pyridine
(TBP), TiO2 nanoparticle (<25nm particle size), ethyl cellulose
and α-terpineol were purchased from the Sigma-Aldrich, India
and used as it is without further purification. FTO doped
transparent conducting glass (12Ω, Solaronix, thickness
2.2mm, SA, Switzerland) and Meltronix tape (20µm) were used
for the fabrication of DSSC device. All the reactions were
monitored by using 0.25 mm silica gel 60, F254 percolated TLC
plates and visualized under UV light. 1H-NMR and 13C-NMR
spectra were recorded on VARIAN 500-MHz instrument (USA)
using TMS as an internal standard. Perkins-Elmer Lambda 25
spectrometer was used to record the UV-visible absorption
spectra of the compounds in different solvents. Fluorescence
emission spectra was recorded on Varian Cary Eclipse
fluorescence spectrophotometer. Electrochemical Impedance
Spectroscopy (EIS) were executed by utilizing Solartron
1260+1287 interfaces. CorrView and Zplot software were used
for interpretation of data. EIS was measured by changing the
frequency from 120 kHz to 0.1 Hz having an AC amplitude of
10 mV. Potentiometric dada of all the samples estimated by
doing cyclic voltammetry (CV) of all the samples
electrochemical workstation (CHI660E, USA). Three electrode
system in acetonitrile/TBAPF6 was used in cyclic voltammetry.
The photocurrent density to voltage (J–V curve) spectra were
recorded by employing an external potential bias to the
device. The generated photocurrent was measured with a
Keithley 2450 digital source meter. Xenon lamp (solar
N
O
N
O
N
O
O
g
CHO
CHO
Cl
6
7
Scheme 1 a) 10 mmol of DEMAP-aldehyde + 20 mmol diethyl malonate + 1 mL of
piperidine+ 30 mL ethanol, reflux for 6hrs. b) 0.1 eq of compound 1 + 20 mL acetic acid
+ 20 mL HCl, reflux for 24 hrs. c) 2.3 mL DMF+2.3 mL POCl3 + 6.91 mmol of compound 2
dissolved in 10 mL DMF, 60°C for 12 h. ( Yield 67.7%) d) 6.9mmol of compound 4 in 10
mL DMF + 7.6 mmol NaCN dissolved in 4 mL water at 0°C + 10.3mmol Br2 liquid drop
wise at 0°C, 30 mins. (Yield 52.2%) e) 0.108 mol of 3-diethylaminophenol + 0.108 mol of
magic malonate+ 100 mL dry toluene, reflux for 2 h (Yield 50%). f) 0.0557 mol of
compound 5 in 80 mL dry DMF+ stir for 3hrs at 0°C + 0.1449 mol of POCl3 stir for 30
mins (Yield 55.0%) g) 0.1 mmol of compound 6 + 0.2 mmol of piperidine in absolute
ethanol+ triethylamine 1 mL, stir at RT for 4h (Yield 60.0%).
Open-circuit voltage decay (OCVD), lifetime curves and Tafel
polarization were obtained by using Solartron (1260)
electrochemical analyser with sweeping potential at ±0.65V in
dark with 25mV/s scan rate.
Device Fabrication
TiO2 photoelectrode as a working electrode and platinized
electrode as a counter electrode were used for DSSC device. 57
.
A sandwich of these two electrodes was employed for
fabrication of solar cell. For TiO2 photoelectrode, a transparent
layer of TiO2 (18 NRT, Dyesol) with thickness 12µm, as
measured by using a profilometer (Veeco Dektak 150 Stylus
surface profiler), was employed on FTO glass plate. The
photoelectrode was immersed overnight in ethanol solution
containing 3 mM dye solution for dye adsorption on surface.
2 | J. Name., 2012, 00, 1-3
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Molecular design and synthesis
In order to correlate the effect of substituents at 4-position of
coumarin on light to current conversion efficiency, here we
have synthesized four molecules with modification at
4
position of coumarin. The systematic substitution at 4 position
in coumarin is carried out. It has been observed, the
photophysical and photo-voltaic properties of resultant
sensitizer are sensitive the substitution at 4 position. The
change in properties is observed due change in HOMO-LUMO
band gap as given in table no 2 and 3. Also the distribution of
electron density at HOMO and LUMO level is also affected
(Supporting Figure S13). The HOMO-LUMO energy level and
band gap is determined by using cyclic voltammetry and
density functional theory calculations while electron density
distribution is determined from the optimized structure by
DFT. In MC1 we have put hydrogen at 4 position which has
been utilized as a reference for comparison with other dyes. In
MC2 coumarin dye hydrogen at 4 position is substituted by
electronegative mono atomic chlorine atom to study effect of
electronegative group on properties. In MC3 hydrogen is
replaced by six membered donor piperidine ring to rationalize
the effect of bulky donor substitution at 4 position. In MC4, 4
position is altered by putting cyano group which will act as
strong electron withdrawing group to enhance the charge
separation. All the final compounds were purified with column
chromatography and successfully characterized 1H NMR, 13C
NMR, and elemental analysis.
Scheme 2 h) 0.1 mmol of aldehyde + 0.1 mmol of rhodanine-3-acetic acid + 2
drops of piperidine in 10 mL ethanol, reflux for 6h ( Yield : MC1: 66.8%; MC2:
61.8%; MC3: 58.55%; MC4: 55.3%).
-
The electrolytic solution of I-/I3 prepared by dissolving 0.5M
lithium iodide (LiI), 0.05 M Iodine (I2), 0.5 M tert-butyl pyridine
(TBP), and 0.5M guanidium thiocynate (GSCN) in 3-methoxy
propionitrile. The electrolyte was employed in cell through the
predrilled back holes onto the Pt-counter electrode. An epoxy
adhesive were used to seal the holes. The DSSCs device were
stored in dark at room temperature for 12
h before
photovoltaic measurements. Active areas of the DSSCs were
set to 0.16 cm2 and were maintained constant using the same
screen for coating.
Result and Discussion
Photo-physical Characterizations
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Figure 2 Normalised Absorption and Emission spectra of MC1 to MC4 in acetonitrile
The absorption and emission spectra of MC1 is represented in acetonitrile while highest emission maxima of 567 nm is
Figure 1 while for MC2 to MC4 the absorption and emission observed in DMSO. The lowest absorption maxima of 472 nm
spectra is given in supporting information (Figure S1 to S3). is observed in ethanol and lowest emission maxima of 550 nm
The combined absorption emission data of MC1 to MC4 is is observed in THF. The vertical excitation obtained for MC2
tabulated in Supporting Table S1. The respective normalised and MC3 by TD-DFT shows close resemblance with
absorption and emission spectra for MC1-MC4 are given in experimental values. The substitution of hydrogen by chlorine
supporting information (Figure S4 to S7). A comparative in MC2 and piperidine in MC3 shows similar impact on
correlation between structural modification and change in photophysical behaviour. This might be due to comparable
absorption and emission of MC1 to MC4 in acetonitrile for electronegativity of chlorine and nitrogen and their identical
5×10-6 mol/dm3 concentration along with vertical excitation ability to form resonating structures by donating lone pair of
obtained from TD-DFT is represented in Figure 2 while the electrons.
absorption emission maxima is given in Table 1. A correlation
Table 1 Correlation of absorption and emission of MC1-MC4 in acetonitrile with vertical
between experimental absorption and theoretical vertical
excitation
excitation obtained from TD-DFT is given in supporting Table 2-
5 in supporting information. The Stoke’s shift in cm-1 is
calculated by taking difference between the absorption and
emission maxima on wavenumber scale. For estimating the
Stoke’s shift in nm the difference between emission maxima in
nm and absorption maxima in nm is considered. In case of
MC1 where hydrogen is present at 4 position, shows highest
absorption maxima in MDC at 521 nm and highest emission
maxima is observed in methanol at 577 nm. It shows solvent
dependent absorption and emission. MC1 shows lowest
absorption maxima in methanol at 503 nm and whereas
lowest emission maxima is observed in ethyl acetate at
Samples λAbs
code
λemi
εmax
Stokes
shift
Vert.
Exct.
Orb.
Contri.
(nm)
(nm)
572
(mol-1 cm-1)
17779
(nm)
63
(nm)
496
(%)
MC1
509
99.6
MC2
MC3
MC4
483
487
594
563
564
671
22947
11354
22245
80
77
77
519
485
567
98.9
99.0
100.3
In MC4 where 4 position is substituted by strong electron
withdrawing cyano group shows red shift in absorption and
emission maxima with respect to MC1. In MC4 the highest
absorption maxima of 613 nm in MDC and highest emission
maxima of 696 nm is observed in DMSO while the lowest
absorption maxima of 591 nm and lowest emission maxima of
660 nm is observed in ethyl acetated. The red shift in
absorption and emission is attributed to strong electron
withdrawing nature of cyano group. On comparing the data
given in Table 1 it is quite evident that substitution at 4
position has substantial effect on absorption and emission
maxima which in turn affect the Stoke’s shift values. This
substantial effect is mainly due to change in HOMO-LUMO
energy levels, alteration in band gap and electron density
distribution. In case of MC2 and MC3 where 4 position is
substituted by electron donating group, a blue shift in
absorption and emission has been observed. While for MC4
551nm. The lowest Stoke’s shift of 43 nm is observed in ethyl
acetated whereas highest Stoke’s shift of 74 nm was observed
in methanol solvent. The vertical excitation calculated by using
TD-DFT calculation shows close resemblance with
experimental absorption values. For MC2 and MC3 where we
have substituted H atom by Cl atom and bulky six membered
piperidine donor moiety respectively shows blue shift in
absorption maxima and emission maxima in comparison with
MC1, which results in larger Stoke’s shift for MC2 and MC3
with respect to MC1. For MC2 the highest absorption maxima
of 496 nm is observed in DMSO while highest emission maxima
of 577 nm is observed in DMF. The lowest absorption maxima
of 476 nm is observed in DMF and lowest emission maxima of
544 nm is observed in ethyl acetated. For MC3 the highest
absorption maxima of 487 nm is observed in MDC and
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red shift in absorption and emission has been observed. The Electrochemical properties:
lowest Stoke’s shift of MC1 suggest poor charge transfer which
The oxidation and reduction potential of MC1 to MC4 were
determined by cyclic voltammetry (CV) in deoxygenated
acetonitrile solution containing 0.1 M tetra-n-butylammonium
hexafluorophosphate (TBAPF6) as supporting electrolyte.
Conventional three-electrode electrochemical cell was used to
carry out the measurement. The electrochemical cell is made
of glassy carbon electrode as the working electrode while
platinum wire and Ag/AgCl acts as counter and reference
electrodes respectively. The cyclic voltammogram for MC1 to
MC4 is given in supporting figure S12. An oxidation wave
which indicates the removal of an electron from the amine
segment is present in all the dyes which is used to determine
Eonset value which corresponds to the excited state energy of
the dye. The Eonset values are calculated from oxidation and
reduction potential peaks of MC1 to MC4 in acetonitrile are
shown in Table 2 while HOMO and LUMO energy levels
obtained by DFT are given in Table 3.The first oxidation
potentials (EHOMO) of the dyes are positive than the redox
can be justified by using electron density distribution at HOMO
and LUMO level of MC1. In MC1 electron density distribution
at HOMO and LUMO level does not show any significant
change. MC2-MC4 show comparably high Stoke’s shift which
can be due to better charge transfer. The solvatochromic
behaviour and charge transfer properties of MC1 to MC4 was
studied with the help of Lippert-Mataga58
,
McRae59,
Bakshive60, and Reichardt-Dimroth ET(N)61 functions. To get
the good linearity for MC1 and MC3 we have removed two
solvents (acetonitrile and ethanol) form consideration. For
MC2 we have removed DMF and ethanol from consideration.
For MC4 we have removed acetone and DMSO from
consideration. These plots show good linearity confirming
considerable charge transfer within the molecule. The plots
are shown in Supporting Information (Supporting Figure S8 to
S10).The excess dipole moment (the difference between the
excited and ground state dipole moments) calculated using the
slopes of the linear plots are given in Supporting Table 6.
potential of the (I-/I3
̄
)
redox couple. This signifies
thermodynamic possibility for reduction of oxidized dyes with
I- ions. The excited state oxidation potentials (ELUMO) is
obtained from following eq:
c
e
E0
EHOMO
Egd
ELUMO
a
Samples λAbs
code
εmax
onsetb
ELUMO = Eg-EHOMO
The ELUMO values of the dyes are negative than the conduction
band potential of TiO2. This signifies the possibility of electron
injection from the excited dyes to the TiO2 conduction. The
HOMO-LUMO energy levels obtained by DFT and band gap
show similar trend and are comparable with experimental
values. The graphical representation of electron density
distribution at HOMO and LUMO levels for MC1 to MC4 is
shown in supporting information (Figure S13). In MC1 electron
density lies more on donor nitrogen atom and sulphur atom
present in rhodanine-3-acetic acid at HOMO level. Upon
excitation it shifts to carbonyl carbon at LUMO level. The
change in electron density distribution upon excitation for
MC1 is very poor. In case of MC2 and MC3 electron density
resides more on chlorine or nitrogen atom of piperidine at
HOMO level rather than the nitrogen of diethylamine donor
group and shifts on carbonyl carbon at LUMO level. The
presence of electron density on chlorine or nitrogen atom for
MC2 or MC3 suggest their importance as donor. The diethyl
amine group in these two chromophores may be acting as
auxiliary donor and chlorine in MC2 and piperidine in MC3 is
(nm)
(mol-1
cm-1)
(eV)
(eV)
(eV)
MC1
MC2
MC3
MC4
509
483
487
594
17779
22947
11354
22245
-0.128
-0.176
0.136
0.403
-4.972
-4.924
-5.236
-5.503
2.115
2.068
2.055
1.859
-2.856
-2.855
-3.181
-3.644
Table 2 The Eonset values calculated from oxidation and reduction potential peaks
of MC1 to MC4 in acetonitrile.
a
Measured in acetonitrile. b Measured from cyclic voltammetry spectra. c All
potentials were obtained from cyclic voltammograms. EHOMO= - (Eonset- (Ag/Ag+) +
4.8) eV. d: calculated from UV-Visible spectra. e: Calculated from ELUMO = Eg-
EHOMO
.
Table 3 HOMO and LUMO energy values in eV for MC1 to MC4 in acetonitrile obtained
from optimized geometry.
MC1
MC2
MC3
MC4
LUMO+1
LUMO
-1.9336
-2.9682
-2.0756
-3.0756
-1.7921
-2.7627
-2.3032
-3.5312
acting as primary donor. In MC4 where
4 position is
HOMO
-5.7005
-6.6915
2.7323
-5.7917
-6.7835
2.1751
-5.6553
-6.1612
2.8925
-5.8646
-6.7743
2.3334
substituted by strong electron withdrawing cyano group,
electron density lies more on donor nitrogen atom and later
on it shifts on cyano group and carbonyl carbon at LUMO level.
Introduction of cyano group lowers LUMO energy levels
significantly which in turn decreases the band gap. The band
gap of MC4 is lowest among all the dyes.
HOMO-1
Band Gap
MC2 shows highest excess dipole moment for all the equation
followed by MC3 and MC4 while MC1 has lowest excess dipole
moment which also suggest MC2-MC4 has better charge
transfer in comparison with MC1.
Photovoltaic Characterisation
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Photophysical properties, cyclic voltammetry characterization enhancement in open circuit voltage. Introduction of donor
and density functional theory calculation of MC1 to MC4 group at 4 position enhances the cell efficiency by improving
suggest the availability of suitable HOMO-LUMO energy levels short circuit current, open circuit current and Pmax. The
required for electron injection from excited dye to conduction extended conjugation in sensitizers usually results in
band of TiO2 and feasibility of dye regeneration. The enhancement in efficiency62,63 but for MC4 introduction of
preliminary data suggest the potential use of these dyes as a cyano group at 4 position of coumarin breaks the extended
sensitizers for DSSCs. The photovoltaic devices based on MC1 conjugation. In MC4, strong electron withdrawing cyano group
to MC4 as a sensitizers were freshly fabricated and measured which acts as an electron trap shows efficiency of 4.60% due
under 1.5 AM solar irradiation (100 mW.cm-2). The to enhancement in short-circuit current (11.18 mA) open
circuit voltage (0.637 V), Pmax (4.59). The enhancement in
short circuit current and PCE for MC4 signifies the role of
cyano group as electron trap. From the comparison it is
evident that introduction of substituent at 4 position enhances
the efficiency of devices by significantly improving short-circuit
current density (JSC) and Pmax which is due the better charge
separation and ease in injection of electrons from sensitizer to
conduction band of TiO2. The PCE of these chromophores are
in the order of MC1< MC2< MC3<MC4. The HOMO-LUMO
band gap of MC1 to MC4 increase in order of
corresponding
J
–
V
characteristics graph and electrical
impedance spectra of the cells are shown in Figure 3(a). Cell
parameters such as the short-circuit current density (JSC),
open-circuit voltage (VOC), fill factor (FF) and overall conversion
efficiency (η) were tabulated in Table 4. Results clearly suggest
the importance of substituents at 4 position of coumarin to
enhance the light to current conversion efficiency. For
instance, taking MC1 as a prototype, comparison of MC2 to
MC4 was carried out to outline the correlation between 4
position substituent and light to current conversion efficiency
for coumarin as sensitizer. MC1 shows lowest efficiency of
2.64% which is attributed due to poor short-circuit current
density (JSC) (6.85 mA) and Pmax (2.64). The open circuit
voltage is 0.615V and fill factor is 0.62 for MC1. In case of MC2,
4 position is altered by incorporating electron negative
chlorine atom.
MC1< MC2< MC3<MC4. The lowest PCE of MC1 is due to
highest HOMO-LUMO band gap and poor charge separation in
comparison with other dyes which is evident from lowest
Stoke’s shift and electron density distribution.s The highest
Table 4 Photovoltaic Performance of MC1 to MC4
Photovoltaic
MC1
MC2
MC3
MC4
parameters
a
6.85
0.615
2.64
0.62
2.64
7.79
0.636
3.18
0.64
3.19
8.62
0.626
3.71
0.66
3.79
11.18
0.637
4.59
Jsc (mA)
a
Voc(V)
Pmax
a
FF
a
PCE (%)
b
0.65
4.60
RCT(Ω)
b
Rrec(Ω)
22.31
102
22.28
131
22.79
147
21.96
162
0.65
0.31
0.68
0.39
0.67
0.41
0.70
0.46
CPE-P
-2
c
(nA.cm )
J0
βa
191
295
202
295
201
299
216
316
(mV/decade)
βc
(mV/decade)
a
Performances of DSSCs were measured with 0.16 cm2 working area (measurements
were performed under AM1.5, 1 sun irradiation), b Values obtain by fitting Nyquist plot
and c value obtain by fitting Tafel plots
The chlorine in MC2 acts as electron donor due to its positive
inductive effect shows enhancement in efficiency to 3.19%.
MC3 shows short-circuit current density of 7.79mA, open
circuit voltage 0.636V and Pmax 3.18 but fill factor remains
unaffected. For MC3, 4 position is substituted by piperidine
group shows efficiency of 3.79% due to increase in short-
circuit current (8.62mA) and, Pmax (3.71) with marginal
Figure 3 (a) Photovoltaic characterization (I-V) and (b) Nyquist plots of DSSC devices
fabricated using various MC chromophores.
6 | J. Name., 2012, 00, 1-3
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efficiency of MC4 signifies the importance of cyano group as
electron trap.
The electron-carrier lifetime (τe) of DSSCs, which is derived
To evaluate the impact of modification on efficiency we have from the following equation64 is represented in Figure 4a.
ꢎꢏ
measured EIS in the two-electrode configuration under a
forward bias in the dark and spectra is given in Figure 3(b).
From the figure it is evident that, the high frequency range arc
ꢃꢄꢅ ꢈꢉ
ꢊꢋꢍ
ꢈꢌ
ꢀꢁ
ꢂ
ꢇ
ꢆ
-
Rct at platinum FTO/I-/I3 electrolyte interface is a depressed
The τe of the MC4 device is higher in comparison with the
other remaining device at all voltages. MC1 shows sharp
decrease in electron carrier lifetime with increase in potential
whereas τe of MC2 and MC3 remains in-between.
semicircle and can’t be visualized clearly. Rrec and CPE-P (a
component of CPE) are determined from middle frequency
range arc. CPE-P is almost constant for all the devices which
represents surface roughness and porosity of the
photoelectrode which is constant for all the devices. Rct at
platinized CEs is approximately same for all the devices but the
recombination resistance (Rrec) shows drastic change. The last
low frequency response is attributed to the ion diffusion in the
The Tafel polarization measurement were carried out on
CHI660E electrochemical workstation and the plot is
reproduced in Figure 4b. All the cells were swept with DC
potential from ±0.65V with scan rate of 10 mV s-1 in dark. This
-
I-/I3 electrolyte57. The rate of electron transport through
techniques is subjected to gain the insight about charge
transfer of the I- and I3 redox couple on the titania surface65
-
.
external circuit for MC4 sensitizer based device is very high
which has been reflected by mid-frequency. The higher value
of recombination resistance (Rrec) for MC4, suggest that the
recombination of injected electrons with electrolyte is
retarded more effectively in MC4.
The rate of cathodic (αc) and anodic (αa) reaction at the titania
electrode and I-/I3- electrolyte interface can be describe by the
equation66 is,
ꢗꢘꢙꢚ
ꢗꢢꢙꢚ
ꢝ
ꢝ
ꢐ ꢂ ꢑꢐꢒ ꢓꢔꢕꢖ
ꢞꢟ ꢑ ꢟꢔꢠꢡ ꢑ ꢔꢕꢖ
ꢞꢟ
ꢛꢜ
ꢑ ꢟꢔꢠꢡꢣ
ꢛꢜ
Eeq, J0, E, are the equilibrium potential of redox mediator,
current exchange density and applied voltage, respectively. In
dark condition equation that j = jo as E = Eeq, and J0 is depends
on the concentrations of I-/I3- and reaction area on the titania
surface. The values of βc and βa current for MC1 to MC4 are
depicted in Table 4. The βa slope values and βc slope values
are increasing from MC1 to MC4. The βa slope values are
lower than βc, which indicates feasibility of recombination
reaction at the dye + titania electrode/electrolyte interface
between electron from the conduction band of TiO2 and I3- in
the electrolyte.
Conclusion:
In this paper we have reported synthesis of coumarin based
four chromophores MC1 to MC4 along with its DFT and TD-DFT
studies and their application in DSSCs. All the compounds were
confirmed using 1H NMR, 13C NMR and elemental analysis. The
photophysical characterization of MC1 to MC4 were studied in
eight different solvents and successfully correlated with
alteration of 4 position in coumarin skeleton. The vertical
excitation, HOMO and LUMO energy levels are estimated by
using the Density Functional Theory (DFT) and Time-
Dependent Density Functional Theory (TD-DFT) shows good
correlation with observed experimental values. Structural
modification attributes a major role in deciding photophysical
and photovoltaic properties. The observed photovoltaic
properties were successfully correlated with structural
alteration at 4 position in coumarin. Any group at 4 position of
Figure 4 (a) Electron carrier lifetime plot and (b) Tafel polarization plot
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coumarin enhances the light to current conversion efficiency
by significantly improving short circuit current and Pmax value.
8977–8985.
17
S. S. Soni, K. B. Fadadu, J. V. Vaghasiya, B. G. Solanki, K. K.
Sonigara, A. Singh and P. K. Iyer, J. Mater. Chem. A, 2015,
43, 21664-21671.
18
19
20
21
22
23
24
J. V. Vaghasiya, K. K. Sonigara, T. Beuvier, A. Gibaud and S.
S. Soni, Nanoscale, 2017, 9, 15949-15957.
Z.-S. Huang, H. Meier and D. Cao, J. Mater. Chem. C, 2016,
Conflicts of interest
There are no conflicts to declare.
4
, 2404–2426.
H. Meier, Z.-S. Huang and D. Cao, J. Mater. Chem. C, 2017,
, 9828–9837.
Acknowledgements:
5
A. Mishra, M. K. R. Fischer and P. Büuerle, Angew. Chemie -
Int. Ed., 2009, 48, 2474–2499.
A. Venkateswararao, K. R. J. Thomas, C. P. Lee, C. T. Li and
K. C. Ho, ACS Appl. Mater. Interfaces, 2014, 6, 2528–2539.
D. Kumar, K. R. J. Thomas, C. P. Lee and K. C. Ho, Org. Lett.,
2011, 13, 2622–2625.
M. K. R. Fischer, S. Wenger, M. Wang, A. Mishra, S. M.
Zakeeruddin, M. Grätzel and P. Bäuerle, Chem. Mater.,
2010, 22, 1836–1845.
S. Haid, M. Marszalek, A. Mishra, M. Wielopolski, J.
Teuscher, J. E. Moser, R. Humphry-Baker, S. M.
Zakeeruddin, M. Grätzel and P. Bäuerle, Adv. Funct. Mater.,
2012, 22, 1291–1302.
K. Hara, Z. S. Wang, T. Sato, A. Furube, R. Katoh, H.
Sugihara, Y. Dan-Oh, C. Kasada, A. Shinpo and S. Suga, J.
Phys. Chem. B, 2005, 109, 15476–15482.
K. Hara, K. Miyamoto, Y. Abe and M. Yanagida, J. Phys.
Chem. B, 2005, 109, 23776–23778.
Manoj M Jadhav is grateful to Department of Science and
Technology (Government of India) and Technical Education
Quality Improvement Programme, Ministry of Human
Resource Development for financial support. SSS thanks to
Department of Science and Technology, New Delhi for financial
support (DST/TM/CERI/C285) for fabrication of devices and
characterization. Dinesh Patil is thankful to University Grants
Commission for Junior and Senior Research Fellowships under
Special Assistance (SAP) program.
25
26
References
1
G. Di Carlo, A. Orbelli Biroli, F. Tessore, M. Pizzotti, P. R.
Mussini, A. Amat, F. De Angelis, A. Abbotto, V. Trifiletti and
R. Ruffo, J. Phys. Chem. C, 2014, 118, 7307–7320.
27
28
29
30
2
3
A. Baheti, K. R. Justin Thomas, C. T. Li, C. P. Lee and K. C.
Ho, ACS Appl. Mater. Interfaces, 2015,
K. R. J. Thomas, Y. C. Hsu, J. T. Lin, K. M. Lee, K. C. Ho, C. H.
Z.-S. Wang, Y. Cui, Y. Dan-oh, C. Kasada, A. Shinpo and K.
Hara, J. Phys. Chem. C, 2008, 112, 17011–17017.
7, 2249–2262.
S. Verma and H. N. Ghosh, J. Phys. Chem. C, 2014, 118
,
Lai, Y. M. Cheng and P. T. Chou, Chem. Mater., 2008, 20
1830–1840.
,
10661–10669.
Z. Wang, X.-F. Wang, D. Yokoyama, H. Sasabe, J. Kido, Z.
Liu, W. Tian, O. Kitao, T. Ikeuchi and S. Sasaki, J. Phys.
Chem. C, 2014, 118, 14785–14794.
A. M. El-Zohry, D. Roca-Sanjuán and B. Zietz, J. Phys. Chem.
C, 2015, 119, 2249–2259.
N. Ohta, K. Awasthi, K. Okoshi, K. Manseki, H. Miura, Y.
Inoue, K. Nakamura, H. Kono and E. W.-G. Diau, J. Phys.
Chem. C, 2016, 120, 26206–26216.
C.-J. Tan, C.-S. Yang, Y.-C. Sheng, H. W. Amini and H.-H. G.
Tsai, J. Phys. Chem. C, 2016, 120, 21272–21284.
E. M. J. Johansson, T. Edvinsson, M. Odelius, D. P. Hagberg,
L. Sun, A. Hagfeldt, H. Siegbahn and H. Rensmo, J. Phys.
Chem. C, 2007, 111, 8580–8586.
N. Zhou, K. Prabakaran, B. Lee, S. H. Chang, B.
Harutyunyan, P. Guo, M. R. Butler, A. Timalsina, M. J.
Bedzyk, M. A. Ratner, S. Vegiraju, S. Yau, C.-G. Wu, R. P. H.
Chang, A. Facchetti, M.-C. Chen and T. J. Marks, J. Am.
Chem. Soc., 2015, 137, 4414–4423.
Z. S. Wang, Y. Cui, Y. Dan-oh, C. Kasada, A. Shinpo and K.
Hara, J. Phys. Chem. C, 2007, 111, 7224–7230.
S. Maniam, A. B. Holmes, G. A. Leeke, A. Bilic and G. E.
Collis, Org. Lett., 2015, 17, 4022–4025.
4
D. Bi, A. Mishra, P. Gao, M. M. Franckevičius, C. Steck, S. M.
Zakeeruddin, M. K. Nazeeruddin, P. Bauerle, M. Gratzel and
A. Hagfeldt, ChemSusChem, 2016, 9, 433–438.
31
32
5
6
B. O’Regan and M. Grätzel, Nature, 1991, 353, 737–740.
A. H. Younes and T. H. Ghaddar, Inorg. Chem., 2008, 47
3408–3414.
,
7
8
H.-Y. Hsu, C.-W. Cheng, W.-K. Huang, Y.-P. Lee and E. W.-G.
Diau, J. Phys. Chem. C, 2014, 118, 16904–16911.
S. Sinn, B. Schulze, C. Friebe, D. G. Brown, M. Jäger, J.
Kübel, B. Dietzek, C. P. Berlinguette and U. S. Schubert,
Inorg. Chem., 2014, 53, 1637–1645.
33
34
9
S. Sinn, B. Schulze, C. Friebe, D. G. Brown, M. Jäger, E.
Altuntaş, J. Kübel, O. Guntner, C. P. Berlinguette, B. Dietzek
and U. S. Schubert, Inorg. Chem., 2014, 53, 2083–2095.
W.-K. Huang, H.-P. Wu, P.-L. Lin, Y.-P. Lee and E. W.-G.
Diau, J. Phys. Chem. Lett., 2012, 3, 1830–1835.
L. Han, A. Islam, H. Chen, C. Malapaka, B. Chiranjeevi, S.
35
10
11
Zhang, X. Yang and M. Yanagida, Energy Environ. Sci., 2012,
36
37
38
39
40
5
, 6057–6060.
C. Li, L. Luo, D. Wu, R. Jiang, J. Lan, R. Wang, L. Huang, S.
Yang and J. You, J. Mater. Chem. A, 2016, , 11829–11834.
S. Biswas, S. De and A. Kathiravan, Dalt. Trans., 2014, 43
15065–15074.
J.-Y. Su, C.-Y. Lo, C.-H. Tsai, C.-H. Chen, S.-H. Chou, S.-H. Liu,
P.-T. Chou and K.-T. Wong, Org. Lett., 2014, 16, 3176–3179.
L.-Y. Lin, C.-H. Tsai, K.-T. Wong, T.-W. Huang, L. Hsieh, S.-H.
Liu, H.-W. Lin, C.-C. Wu, S.-H. Chou, S.-H. Chen and A.-I.
Tsai, J. Org. Chem., 2010, 75, 4778–4785.
12
13
14
15
4
,
Y. Lu, M. T. Spitler and B. A. Parkinson, Langmuir, 2007, 23
,
11637–11642.
D. Choi, J. G. Rowley, M. Spitler and B. A. Parkinson,
Langmuir, 2013, 29, 9410–9419.
N. Shahzad, F. Risplendi, D. Pugliese, S. Bianco, A. Sacco, A.
Lamberti, R. Gazia, E. Tresso and G. Cicero, J. Phys. Chem.
C, 2013, 117, 22778–22783.
16
J.-H. Chen, C.-H. Tsai, S.-A. Wang, Y.-Y. Lin, T.-W. Huang, S.-
41
A. Alagumalai, M. F. M. K., P. Vellimalai, M. C. Sil and J.
F. Chiu, C.-C. Wu and K.-T. Wong, J. Org. Chem., 2011, 76
,
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 9 of 10
View Article Online
DOI: 10.1039/C7NJ04954D
Journal Name
ARTICLE
Nithyanandhan, ACS Appl. Mater. Interfaces, 2016,
35353–35367.
C.-H. Chang, Y.-C. Chen, C.-Y. Hsu, H.-H. Chou and J. T. Lin,
Org. Lett., 2012, 14, 4726–4729.
D. F. Pickup, I. Zegkinoglou, B. Ballesteros, C. R. Ganivet, J.
M. García-Lastra, P. L. Cook, P. S. Johnson, C. Rogero, F. de
Groot, A. Rubio, G. de la Torre, J. E. Ortega and F. J.
Himpsel, J. Phys. Chem. C, 2013, 117, 4410–4420.
X. Liu, J. M. Cole, P. C. Y. Chow, L. Zhang, Y. Tan and T.
Zhao, J. Phys. Chem. C, 2014, 118, 13042–13051.
C. J. Flynn, E. E. Oh, S. M. McCullough, R. W. Call, C. L.
Donley, R. Lopez and J. F. Cahoon, J. Phys. Chem. C, 2014,
118, 14177–14184.
8
,
H. X. Li, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg,
M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M.
Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven,
J. J. A. Montgomery, J. E. Peralta, F. Ogliaro, M. Bearpark, J.
J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, T. Keith,
R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C.
Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M.
Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C.
Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O.
Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski,
R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P.
Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O.
Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J.
Fox, Gaussian 09, Revision D.01, 2013.
42
43
44
45
46
Z.-S. Wang, K. Hara, Y. Dan-oh, C. Kasada, A. Shinpo, S.
Suga, H. Arakawa and H. Sugihara, J. Phys. Chem. B, 2005, 57
109, 3907–3914.
J. V. Vaghasiya, K. K. Sonigara, J. Prasad, T. Beuvier, A.
Gibaud and S. S. Soni, J. Mater. Chem. A, 2017, 5, 5373–
47
48
49
50
A. Morandeira, G. Boschloo, A. Hagfeldt and L.
5382.
Hammarström, J. Phys. Chem. C, 2008, 112, 9530–9537.
A. Morandeira, G. Boschloo, A. Hagfeldt and L.
Hammarström, J. Phys. Chem. B, 2005, 109, 19403–19410.
S. E. Koops, P. R. F. Barnes, B. C. O’Regan and J. R. Durrant, 60
J. Phys. Chem. C, 2010, 114, 8054–8061.
58
59
R. Wortmann, K. Elich, S. Lebus, W. Liptay, P. Borowicz and
A. Grabowska, J. Phys. Chem., 1992, 96, 9724–9730.
E. G. McRae, J. Phys. Chem., 1957, 61, 562–572.
B. G. Evale, S. M. Hanagodimath, I. A. Khan and M. V
Kulkarni, Spectrochim. Acta Part A Mol. Biomol. Spectrosc.,
2009, 73, 694–700.
O. Treutler and R. Ahlrichs, J. Chem. Phys., 1995, 102, 346–
354.
61
M. M. Husain, R. Sindhu and H. C. Tandon, Eur. J. Chem.,
51
52
A. D. Becke, J. Chem. Phys., 1993, 98, 1372–1377.
C. Lee, W. Yang and R. G. Parr, Phys. Rev. B, 1988, 37, 785– 62
789.
2012, 3, 410–416.
L.-W. Ma, Z.-S. Huang, S. Wang, H. Meier and D. Cao, Dye.
Pigment., 2017, 145, 126–135.
53
54
55
56
M. E. Casida, C. Jamorski, K. C. Casida and D. R. Salahub, J. 63
Chem. Phys., 1998, 108, 4439–4449.
M. Cossi, V. Barone, R. Cammi and J. Tomasi, Chem. Phys. 64
Lett., 1996, 255, 327–335.
J. Tomasi, B. Mennucci and R. Cammi, Chem. Rev., 2005, 65
105, 2999–3094.
M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. 66
A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B.
Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, H. P.
Z. Iqbal, W.-Q. Wu, Z.-S. Huang, L. Wang, D.-B. Kuang, H.
Meier and D. Cao, Dye. Pigment., 2016, 124, 63–71.
A. Zaban, M. Greenshtein and J. Bisquert, ChemPhysChem,
2003, 4, 859–864.
Z. Huo, C. Zhang, X. Fang, M. Cai, S. Dai and K. Wang, J.
Power Sources, 2010, 195, 4384–4390.
O. A. Petrii, R. R. Nazmutdinov, M. D. Bronshtein and G. A.
Tsirlina, Electrochim. Acta, 2007, 52, 3493–3504.
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Table of Contents:
S
HO
N
O
X
O
S
O
TiO2
N
O
MC4 : X =CN; Efficiency : 4.60%
MC3 : X =NC5H10; Efficiency : 3.79%
MC2 : X =Cl; Efficiency : 3.19%
MC1 : X =H; Efficiency : 2.64%
Substitution at 4 position of coumarin alters the photophysical, electrochemical and
photovoltaic properties.