The comparative study of new carboxylated 1,3-indanedione sensitizers with standard cyanoacetic acid dyes using co-adsorbents in dye-sensitized solar cells

Article abstract of DOI:10.1016/j.cplett.2018.11.026

Two new carboxylated 1,3-indanedione sensitizers (MPhe-ind and BPhe-ind) were synthesized and their dye-sensitized solar cells (DSSC) performance were compared with the corresponding standard cyanoacetic acid sensitizers (MPhe-cn and BPhe-cn). The carboxylated 1,3-indanedione sensitizers have shown almost 100 nm enhanced absorption curves compared to the cyanoacetic acid dyes with an extended IPCE curve up to 800 nm. Despite greater absorption and electrochemical properties, the synthesized dyes showed moderate efficiencies (2.10% and 2.67%) than standard dyes. The low electron injection efficiency and recombination of carboxylated 1,3-indanedione might be responsible for low efficiency. Detailed investigation studies have been performed and complemented with the theoretical studies.

Full text of DOI:10.1016/j.cplett.2018.11.026

Accepted Manuscript
Research paper
The comparative study of new carboxylated 1,3-indanedione sensitizers with
standard cyanoacetic acid dyes using co-adsorbents in dye-sensitized solar cells
Hyeonjun Jeong, Ramesh Kumar Chitumalla, Dong Woo Kim, S.V. Prabhakar
Vattikuti, Suresh Thogiti, Rajesh Cheruku, Jae Hong Kim, Joonkyung Jang,
Ganesh Koyyada, Jae Hak Jung
PII:
S0009-2614(18)30947-3
DOI:
https://doi.org/10.1016/j.cplett.2018.11.026
CPLETT 36097
Reference:
Chemical Physics Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
17 August 2018
10 November 2018
12 November 2018
Please cite this article as: H. Jeong, R. Kumar Chitumalla, D. Woo Kim, S.V. Prabhakar Vattikuti, S. Thogiti, R.
Cheruku, J. Hong Kim, J. Jang, G. Koyyada, J. Hak Jung, The comparative study of new carboxylated 1,3-
indanedione sensitizers with standard cyanoacetic acid dyes using co-adsorbents in dye-sensitized solar cells,
Chemical Physics Letters (2018), doi: https://doi.org/10.1016/j.cplett.2018.11.026
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The comparative study of new carboxylated 1,3-indanedione sensitizers with standard
cyanoacetic acid dyes using co-adsorbents in dye-sensitized solar cells
Hyeonjun Jeonga, Ramesh Kumar Chitumallab, Dong Woo Kima, S. V. Prabhakar Vattikutia,
Suresh Thogitia, Rajesh Cherukua, Jae Hong Kima, Joonkyung Jangb, Ganesh Koyyadaa,*, Jae
Hak Junga,*
aDepartment of Chemical Engineering, Yeungnam University, 214-1, Dae-hakro 280, Gyeongsan,
Gyeongbuk, 712-749, South Korea.
bDepartment of Nanoenergy Engineering, Pusan National University, Busan, 46241, South Korea.
E-mail: ganeshkoyyada@gmail.com/ganeshkoyyada@ynu.ac.kr
jhjung@ynu.ac.kr.
Abstract
Two new carboxylated 1,3-indanedione sensitizers (MPhe-ind and BPhe-ind) were synthesized
and their dye-sensitized solar cells (DSSC) performance were compared with the corresponding
standard cyanoacetic acid sensitizers (MPhe-cn and BPhe-cn). The carboxylated 1,3-indanedione
sensitizers have shown almost 100nm enhanced absorption curves compared to the cyanoacetic
acid dyes with an extended IPCE curve up to 800nm. Despite greater absorption and
electrochemical properties, the synthesized dyes showed moderate efficiencies (2.10% and
2.67%) than standard dyes. The low electron injection efficiency and recombination of
carboxylated 1,3-indanedione might be responsible for low efficiency. Detailed investigation
studies have been performed and complemented with the theoretical studies.
Key words: Dye-sensitized solar cells; co-adsorbents; organic sensitizer; DFT.
1. Introduction
The past few decades have seen remarkable research efforts dedicated to dye-sensitized solar
cells (DSSCs)[1-3] owing to their synthetic and purification ease over the conventional silicon
solar cells. The initial DSSC device was reported by ÓRegan and Grátzel (1991)[4], since then
efforts to develop efficient and stable devices have been taken up by researchers all around the
globe. The photosensitizer is one of the crucial components in getting the optimum efficiency,
which harvests the solar energy and injects the photogenerated electron into the conduction band
of semiconductor oxide [5, 6]. Early reports of zinc porphyrin [7, 8], ruthenium complexes [9-11]
and metal-free organic dyes [12-15] are some of the benchmark sensitizers in DSSCs. The zinc
1

porphyrin-based sensitizers [7] have shown 13 % record efficiency in association with the cobalt
bipyridine ([Co(bpy)3]2+/3+) based redox electrolyte, whereas ruthenium (II) based dye [9, 16, 17]
have achieved above 11.4 % efficiency till date. However, the limitations corresponding to these
complexes such as the rare resources of ruthenium and zinc metals, high manufacturing cost;
heavy-metal toxicity and environmental problems would avert their widespread applications [18].
To overcome the above issues of metal complexes, the metal-free organic sensitizers have been
studied owing to their low cast preparation process, easy structural modifications and high molar
extinction coefficient. Moreover, organic dyes as a sensitizer in DSSC have reached 14%
efficiency [19] as reported earlier in the literature. Therefore, much concentration has been
devoted in the design, modification and development of new metal-free organic sensitizers as
efficient light harvesting materials for DSSCs application [20-22].
Derong Cao et al. [23] presented novel double branched (DB) phenothiazine-based D-π-A
mannered organic sensitizer, which showed enhanced efficiency compared to their mono
branched D-π-A sensitizers. In recent times, our research group also reported few new double
branched organic dyes by structural engineering of the molecule with symmetrical and
unsymmetrical anchoring groups with varying alkyl chains [24, 25]. Among them, D-A type
structural design was attracted more interest owing to their small size and remarkable optical and
efficient intramolecular charge transfer (ICT) property [26]. Generally, the D-A type dyes have
more tendency to anchoring on the TiO2 semiconductor. Efficient dye adsorption and its
structural configurations are the key factors for improving photovoltaic efficiency [26, 27].
Mishra et al. also stated that the performance of the DSSC device is not only subjected to design
of the sensitizer and also influenced by its physical properties like morphology and aggregation
[18]. The main role of anchoring group of the sensitizer is to bind strongly on semiconductor
surface through chemical bond and electron transfer from donor to the semiconductor conduction
band. So far the reported cyanoacetic acid anchoring groups have shown good performance,
however, the optimization on anchoring group side is rather limited. In this study, the anchoring
carboxylated 1,3-indanedione group was examined in D-A construction manner for a better
understanding of the effect of anchoring group on the semiconductor.
Numerous organic chromophores such as phenothiazine, triphenylamine, dithiafulvenyl,
tetrahydroquinoline, carbazole, indoline have been examined as a donor in organic dyes [28, 29].
Among all the above-mentioned chromophores, phenothiazine act as a strong donor and holds a
2

large proportion owing to its unique features like non-planar butterfly conformation, which helps
to decrease the dye aggregation and excimer formation. Moreover, the presence of the electron
rich sulfur and nitrogen heteroatoms furnish phenothiazine as a strong donor. Keeping all these
concepts in view, we herein designed two new organic dyes (Fig. S1) with single and double
branched manner along with new anchoring group i.e. carboxylated 1,3-indanedione. In
particular, we have examined the acceptance property of carboxylated 1,3-indanedione (MPhe-
ind and BPhe-ind) on mono and double branched patterns because the double branched patterns
would inhibit the electron recombination and increase the effective electron transfer into the
TiO2 semiconductor. The aggregation property of these molecules examined with co-adsorbents
like chenodeoxycholic acid (CDCA) and palmitic acids (PA) and these DSSCs performances
were compared with the corresponding cyanoacetic acid dyes (previously synthesized by our
group) [24].
2. Experimental Section
2.1. General
The phenothiazine, bromohexane, and dibromhexane starting materials were purchased from
Sigma-Aldrich. The solvents and chemicals used for this work were analytical grade and all the
reactions in this work were carried out under an argon atmosphere. Chromatographic separations
1
were performed on 60-120 mesh silica gel. H and 13C NMR have acquired on Agilent unity
inova Bat (500 MHz) spectrometers and analyzed in CDCl3 or DMSO-d6 by using
tetramethylsilane (TMS) internal standard. UV-Visible absorption spectra were measured on a
Cary 5000 UV-Vis-NIR Spectrophotometer. Emission spectra were recorded on a Jobin-Yvon
Horiba model fluorolog3 fluorescence spectrometer. The cyclic or deferential pulses
voltammograms were recorded in DMF solution contain dye (0.3mM) and
0.1Mtetrabutylammoniumhexafluorophosphate (n-Bu4NPF6). The three electrode setup was used
for recording, with pt, Pt wire, and Ag/AgCl as the working, counter and reference electrodes
with a 100 mV/s scan rate.
3

3. Result and discussion
Scheme. 1. Synthesis of MPhe-ind and BPhe-ind
The Scheme.1 depicts the synthesis steps of MPhe-ind and BPhe-ind sensitizers.The
commercially accessible phenothiazine and bromo alkanes starting material were subjected to
alkylation reaction to afford the compound 1and 4 with 80-82% yield. Compound 1 and 4 were
formylated using POCl3 and DMF to produce the intermediate compound 2 and 5with 74-77%
yield. Finally, the desired compounds (MPhe-ind and BPhe-ind) were accomplished with
moderate yields (65%) by condensation with methyl 3-hydroxy-1-oxo-1H-indene-2-carboxylate.
Detailed synthesis procedure have been explained in the electronic supporting information (ESI).
3.1. Photophysical and Electrochemical Properties
The UV-Visible absorption spectra of carboxylated 1,3-indanedione and cyanoacetic acid
dyes were measured in DMF as shown in Fig. 1a and the associated data are depicted in Table 1.
All the dyes exhibited two distinct bands. The first one ca. 250-400 nm is corresponding to the π-
π* transition and the later one ca. 400-650 nm is corresponding to the intramolecular charge
transfer (ICT). In comparison to the solution state absorption spectra of cyanoacetic acid dyes
and the synthesized carboxylated 1,3-indanedione dyes (Fig. 1a), the synthesized BPhe-ind and
MPhe-ind dyes have shown high λmax i.e. 507 and 504 nm with extended absorption curve up to
4

650 nm. On the other hand cyanoacetic acid dyes have shown 397 and 416 nm λmax and the
absorption curve was extended up to 550 nm. It indicates the strong electron withdrawing ability
of carboxylated 1,3-indanedione group over cyanoacetic acid [26]. Among, the four dyes, all
most double the molar extinction coefficient was observed for BPhe-ind (0.4 × 105 M-1 cm-1) and
BPhe-cn (0.29 × 105 M-1 cm-1) than their corresponding monomers MPhe-ind (0.25 × 105 M-1
cm-1) and MPhe-cn (0.14 × 105 M-1 cm-1). Double the number of units in dimers (BPhe-ind and
MPhe-cn) might be responsible for double the molar extinction coefficient. Fig. 1b displays the
absorption spectra of carboxylated 1,3-indanedione dyes and cyanoacetic acid dyes on TiO2 film.
Surprisingly, the absorption curves of MPhe-ind and BPhe-ind dyes on TiO2 have shown a
bathochromic shift of 40 and 70 nm, relative to their solution state absorption spectra and these
absorption curves was extended up to 750 nm. The enhanced absorption properties of dyes might
be attributed to the J-aggregation on the TiO2 surface [30]. Further, the Stokes shift values
calculated from absorption emission intercepts of MPhe-ind and BPhe-ind dyes are 252 nm and
257 nm, which indicate the excellent ICT between the donor and acceptor.
a)
b)
BPhe-ind
MPhe-ind
BPhe-cn
MPhe-cn
BPhe-ind
MPhe-ind
BPhe-cn
MPhe-cn
50000
1.0
0.8
0.6
0.4
0.2
0.0
40000
30000
20000
10000
0
300
400
500
600
700
400
500
600
700
Wavelength (nm)
Wavelength (nm)
c)
MPhe-Ind (CV)
MPhe-Ind (DPV)
BPhe-Ind (CV)
BPhe-Ind (DPV)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Potential (V)
5

Fig. 1. a) Comparative UV-Visible spectra of carboxylated 1,3-indanedione dyes and
cyanoacetic acid dyes in DMF b) UV-Visible absorption spectra of carboxylated 1,3-indanedione
dyes and cyanoacetic acid dyes on TiO2 thin film c) Cyclic voltammetry (CV) and differential
pulse voltammetry (DPV) of BPhe-ind and MPhe-ind dyes in DMF.
Table. 1. Optical and electrochemical data of MPhe-ind and BPhe-ind dyes.
λabs(nm)a
λabs(nm)b
Dye
ε(M-1 Cm-1)
λem(nm)c E0X (V)d E0-0 (V)e E0X*(V)f
(TiO2)
(solution)
MPhe-ind 504
0.923 V 2.04
-1.117
-1.091
-1.638
-1.517
25483
46749
14345
29075
546
572
430
441
756
765
543
644
BPhe-ind
MPhe-cn
BPhe-cn
508
397
416
0.929
0.902
0.913
2.02
2.54
2.43
b
aAbsorption spectra were measured in DMF. Absorption spectra were measured on TiO2
d
thin film. CEmission spectra were measured in DMF. Oxidation potentials were recorded by CV
e
and DPV. The band gap, E0-0, was calculated from the absorption and emission intercept plots.
fEOX* were derived by subtracting E0-0 from EOX.
Differential pulse voltammetry (DPV) and cyclic voltammetry (CV) experiments were
performed to determine the energy levels i.e. ground state oxidation potential (GSOP) and
excited state oxidation potentials (ESOP) of the carboxylated 1,3-indanedione dyes and
cyanoacetic acid dyes (Fig. S3). Fig. 1c represents the oxidation potentials of MPhe-ind and
BPhe-ind dyes, these experiments were employed in DMF solution containing 0.1M n-Bu4NPF6
supporting electrolyte and the corresponding data have been depicted in Table 1. The measured
oxidation potential values (GSOP) of MPhe-ind and BPhe-ind dyes are 0.923 V and 0.929 V
-
(vs. SHE) respectively, which are sufficiently more positive than that of I-/I3 redox potential
(~0.4 V vs SHE) thereby helping in effective dye regeneration. The ESOP (EOX*) of MPhe-ind
and BPhe-ind derived from EOX-E0-0 formula are -1.11 and -1.09 V vs SHE, respectively, where
E0-0 was determined from the intercept of fluorescence and absorption curves (Fig. S2a and b).
ESOP (EOX*) of MPhe-ind and BPhe-ind are more negative than the conduction band potential
of TiO2, which ensures enough driving force for the proficient electron injection processes [31].
6

3.2.Computational studies
To explore the effect of carboxylated 1,3-indanedione anchoring group on DSSC
photovoltaic performance over the cyanoacetic acid, the simulated optical, electrochemical, and
adsorption properties of MPhe-ind and BPhe-ind dyes have been analyzed using Gaussian 09
quantum chemical program and compared with cyanoacetic acid dyes properties [32]. The
structural geometry optimization of all the dyes was carried out by employing B3LYP functional
[33-35] in combination with the 6-31G(d) basis set and presented in Fig. 2 and S5. The optical,
electrochemical properties and molecular orbital transitions of the dyes were obtained by
employing TDDFT formalism with PBE0 [36, 37] hybrid functional and 6-31G(d) basis set. We
have calculated the first 25 singlet-singlet excitations to simulate the absorption spectra.
7

Fig. 2. Optimized geometries and electron density distribution of MPhe-ind and BPhe-ind.
The percentage contribution of the molecular orbital density on anchoring group is shown as
encircled part. The Kohn-Sham eigenvalues are given in eV.
The optimized geometries and the electron density distribution in frontier molecular orbitals
of carboxylated 1,3-indanedione dyes are presented in Fig. 2 and the cyanoacetic acid based dyes
are shown in Fig. S5. It is obvious and found from optimized geometry that the phenothiazine
existed as non-planar butterfly structure in all the dyes. The study about the electron density
distribution in frontier molecular orbitals of HOMO and LUMO states was helpful to understand
the charge transfer phenomena from Fig. 4. The electron density in HOMO state is mainly
8

located over phenothiazine (donor) and is shifted to the carboxylated 1,3-indanedione group in
LUMO. The comparable electron distributions of LUMO frontier molecular orbitals of
carboxylated 1,3-indanedione and cyanoacetic acid based dyes are presented as 3d graphical
manner (Fig. 4). The calculated electron density on -COOH group in LUMOs of MPhe-ind and
BPhe-ind are 5.6 and 5.3%, respectively, while MPhe-cn and BPhe-cn have 14.6 and 14.5%,
respectively. The low electron density on -COOH group of LUMOs in MPhe-ind and BPhe-ind
dyes is due to the presence of two carbonyl groups on the carboxylated 1,3-indanedione group,
which involved in conjugation with donor molecule, as a result, the extent of electron reaches to
the carboxyl group is decreased. The low electron density on –COOH group in LUMO state
indicates the low electron injection into the TiO2 conduction band, probably it might be the
reason for low DSSCs efficiencies of MPhe-ind and BPhe-ind dyes over MPhe-cn and BPhe-
cn.
Fig. 3. Comparative electron density contribution of anchoring group in LUMO, MPhe-ind
versus MPhe-cn and BPhe-ind versus BPhe-cn.
The theoretically simulated absorption spectra of MPhe-ind and BPhe-ind are depicted in
Fig. 4 and absorption data are compiled in Table 2. To mimic the experimental solvent
conditions, we used polarizable continuum model [38, 39] in the TDDFT simulations to define
the DMF solvent. The theoretical absorption maxima are 514 and 536 nm for MPhe-ind and
BPhe-ind, respectively. The theoretical absorption maximum of MPhe-ind (514 nm) is in
9

excellent agreement with that of the experiment (504 nm). Though the theoretical absorption
maximum of BPhe-ind (536 nm) is slightly over estimated with that of experiment (508 nm), the
trend i.e., redshifted absorption has been achieved from MPhe-ind to BPhe-ind. The first two
transitions of BPhe-ind dye occurring at 536 and 515 nm which are corresponding to the
excitations of HOMO  LUMO+1 and HOMO-1  LUMO, respectively. In both the
transitions, the intramolecular charge transfer is on same MPhe-ind unit within the BPhe-ind
dye.
Fig. 4. Simulated UV-visible absorption spectra of the MPhe-ind and BPhe-ind obtained at TD-
PBE0/6-31G(d) level of theory in DMF solvent.
Table. 2. Simulated optical properties of MPhe-ind and BPhe-ind obtained at PBE0/6-31G(d)
level of theory.
Dye
Transition
Oscillator CI
Dominant
cal (nm)
strength
0.5549
0.0441
0.0028
0.4629
0.0010
0.6647
0.4576
0.0020
0.0040
Coefficient Contribution (%)
MPhe-ind S0S1
S0S2
514
433
394
374
362
536
515
485
466
0.70052
0.69628
0.63801
0.67815
0.62222
0.69383
0.69048
0.69673
0.69707
HOMOLUMO (98)
HOMOL+1 (97)
H-3LUMO (81)
H-1LUMO (92)
H-3L+1 (77)
S0S3
S0S4
S0S5
BPhe-ind
S0S1
S0S2
S0S3
S0S4
HOMOL+1 (98)
H-1LUMO (95)
HOMOLUMO (97)
HOMOL+2 (97)
10

S0S5
453
0.0001
0.70495
H-1L+2 (97)
As the interaction between dye and TiO2 plays a vital role in deciding the device
performance, we have carried out the adsorption studies of MPhe-ind and MPhe-cn on a
(TiO2)16 cluster (Fig. 5). The chosen (TiO2)16 is reported to simulate and predict the
electronic properties of experimental TiO2 results [40]. The adsorption studies of MPhe-ind
and MPhe-cn on TiO2 were performed to evaluate the effect of anchoring group
(carboxylated 1,3-indanedione vs. cyanoacetic acid) on overall power conversion efficiency.
First, the isolated dyes were optimized and later adsorbed on pre-optimized TiO2 in a
bidentate bridging mode, then optimized the dye adsorbed TiO2. The adsorption is
dissociative i.e., the hydrogen atom of the anchoring -COOH group is transferred to the TiO2
surface. The adsorption energy is calculated by subtracting the energy of the total system
from the sum of the energies of the dye and TiO2:
The calculated adsorption energies of MPhe-ind and MPhe-cn are 2.42 and 11.91 kcal/mol,
respectively. The low adsorption energy obtained for MPhe-ind is responsible for the low JSC
and thereby low efficiency.
Eads = 2.42 kcal/mol
Eads = 11.91 kcal/mol
Fig. 5. Adsorption of MPhe-ind (left) and MPhe-cn (right) on (TiO2)16 cluster.
11

3.3. Photovoltaic Properties
The newly synthesized carboxylated 1,3-indanedione dyes were evaluated for DSSCs with
and without co-adsorbents such as CDCA or PA and these photovoltaic performances were
compared with the cyanoacetic acid based dyes under the similar experimental conditions. All
these dyes DSSCs photovoltaic device performances were examined using the 0.25 cm2 active
area of TiO2 electrode by thermally stable redox shuttle containing 0.5M 1,2-dimethyl-3-
propylimidazole iodide (DMPII), 0.05M I2 and 0.1M LiI in acetonitrile. The obtained
photocurrent-voltage curves (J-V) are shown in Fig. 6 and corresponding detailed device
photovoltaic parameters are listed in Table 3. In between the carboxylated 1,3-indanedione dyes,
BPhe-ind dye has shown high efficiency in the absence of co-adsorbents of 2.49% with Jsc =
7.33 mA. cm-2, Voc= 0.47 V, FF = 0.72 than MPhe-ind of 1.88% with Jsc = 5.57mA. cm-2, Voc =
0.46 V, FF = 0.73. The high photovoltaic conversion efficiency (PCE) of BPhe-ind dye was
attributed to the high Jsc, which was ascribed to the high light harvesting nature of the BPhe-ind
dye. These carboxylated 1,3-indanedione dyes were further evaluated with co-adsorbents (CDCA
and PA) in order to understand the aggregation phenomena. When MPhe-ind and BPhe-ind
were dyes evaluated with PA the efficiency increased to 2.67% and 2.10% respectively, whereas
with CDCA the efficiency is 2.58% and 1.95%. The PA has shown significant influence on
improving the device efficiency of carboxylated 1,3-indanedione based dyes over CDCA. These
results instigated us to investigate the reason. According to the theoretical studies, the
carboxylated 1,3-indanedione dyes were anchored on the TiO2 in a linear manner, so small size
molecules easily reach the gaps of carboxylated 1,3-indanedione dyes on TiO2. In the
comparison of PA and CDCA, PA is small in size, so it can easily take place between the gaps of
carboxylated 1,3-indanedione dyes, as a result, it shows high efficiency. In spite of having
superior absorption and electrochemical properties, the carboxylated 1,3-indanedione dyes have
shown low efficiency than cyanoacetic acid dyes. The low Jsc and unfavorable distribution of
LUMO over carboxylated 1,3-indanedione group (Fig 3) signify the low electron injection into
the conduction band of TiO2. It might be because of competitive conjugation between the
carbonyl group and carboxylic acid in carboxylated 1,3-indanedione. The same results can be
observed from DFT studies that LUMO distribution on carboxylic anchoring group is 5.6 % (Fig.
2) for carboxylated 1,3-indanedione dyes whereas for cyanoacetic acid is 14.5 % (Fig. S4). The
12

results indicate that the carbonyl groups presented on carboxylated 1,3-indanedione group retract
the electron injection efficiency as a result Jsc and overall efficiency decreases.
The incident photon to current conversion efficiency (IPCE) curves of carboxylated 1,3-
indanedione dyes showed a similar pattern and extended up to 800 nm, while cyanoacetic acid
dyes (MPhe-cn and BPhe-cn) showed up to 660 and 680 nm respectively. The IPCE intensity of
MPhe-ind and with CDCA was 28 % at ~ 490 nm, but with PA the IPCE intensity was
improved to 30%. In the case of BPhe-ind sensitizer, the IPCE intensity was 32 % with and
without CDCA, while with PA it was improved to 33%. Improved IPCE of BPhe-ind over
MPhe-ind were attributed to the increased molar extinction coefficient (ε) of BPhe-ind as
shown in absorption spectra. In IPCE comparison of carboxylated 1,3-indanedione dyes with
CDCA or PA, the carboxylated 1,3-indanedione dyes with PA have shown higher intensity over
CDCA, it might be because of decreased dye aggregation.
a)
0.4
b) 6
5
MPhe-ind
0.3
MPhe-ind-cdca
MPhe-ind-pa
4
3
2
1
0
0.2
0.1
0.0
MPhe-ind
MPhe-ind-cdca
MPhe-ind-pa
300
400
500
600
700
800
0.0
0.1
0.2
0.3
0.4
0.5
Wavelength (nm)
Potential (V)
8
7
6
5
4
3
2
1
0
d)
c)
0.4
BPhe-ind
BPhe-ind-cdca
BPhe-ind-pa
0.3
0.2
0.1
0.0
BPhe-ind
BPhe-ind-cdca
BPhe-ind-pa
300
400
500
600
700
800
0.0
0.1
0.2
0.3
0.4
0.5
Wavelength (nm)
Potential (V)
Fig. 6. a) and b) are the IPCE and J-V curves of DSSCs based on MPhe-ind dye, c) and d) are
the IPCE and J-V curves of DSSCs based on BPhe-ind dye.
13

Table. 3. DSSCs device performance data of carboxylated 1,3-indanedione and cyanoacetic
acid dyes.
a
b
Jsc
Voc
FFc
(%)
CEd
(%)
Sensitizer
(mA cm-2)
5.57
5.55
6.12
7.33
7.37
7.61
10.16
9.06
9.01
(V)
MPhe-ind
0.460
0.477
0.473
0.472
0.482
0.486
0.558
0.596
0.564
0.543
0.541
0.544
0.73
0.73
0.72
0.72
0.72
0.72
0.71
0.71
0.72
0.71
0.71
0.71
1.88
1.95
2.10
2.49
2.58
2.67
4.07
3.90
3.71
4.23
4.15
4.19
MPhe-ind-CDCA
MPhe-ind-PA
BPhe-ind
BPhe-ind-CDCA
BPhe-ind-PA
MPhe-cn
MPhe-cn-CDCA
MPhe-cn-PA
BPhe-cn
BPhe-cn-CDCA
BPhe-cn-PA
10.92
10.79
10.86
The average values of three devices are reported in parenthesis
a Current density, b Open-circuit voltage, cFill factor, d Photovoltaic conversion efficiency
3.4. Electrochemical impedance spectroscopy
The electrochemical impedance spectroscopy (EIS) of carboxylated 1,3-indanedione and
cyanoacetic acid dyes were measured under the dark condition and the Nyquist plots were
presented in Fig. 7. All these dyes have shown three semicircles. In general, the first semicircle
indicates the charge transfer resistance at the counter electrode and the electrolyte interface [41].
The larger semicircle in the mid-frequency region represents the recombination resistance (R3) at
the TiO2/dye/electrolyte interface. The third semicircle in the low-frequency range represents the
-
Warburg diffusion process of I-/I3 in the electrolyte. The data corresponding to the Fig. 7 was
depicted in Table 4, where R1 is the series resistance, R2 is the resistance of electron transport in
the counter and R3 is the charge recombination resistance at TiO2/dye/electrolyte interfaces. In
the dark impedance analysis, the recombination resistance values of MPhe-cn, BPhe-cn, MPhe-
ind and BPhe-ind dyes are 15.71, 14.78, 13.94 and 13.41 Ω were obtained, respectively. low
recombination resistance might be responsible for low Voc of carboxylated 1,3-indanedione than
cyanoacetic acid dyes. On the other hand, among the mono (MPhe-cn and MPhe-ind) and bis
(BPhe-cn and BPhe-ind) phenothiazine dyes high R3 values are found for bis phenothiazine
14

dyes, which suggest that the double branched molecular engineering is beneficial for restricting
the electron recombination.
-14
MPhen-Cn
BPhen-Cn
MPhen-Ind
BPhen-Ind
-12
-10
-8
-6
-4
-2
0
20
25
30
35
40
45
50
Z' (ohm)
Fig. 7. Electrochemical impedance spectra carboxylated 1,3-indanedione and cyanoacetic acid
dyes under dark conditions
Table. 4. EIS analysis of DSSC under dark condition
Sample
R1
R2
R3
22.37
23.14
22.92
22.85
3.73
4.41
4.34
4.99
15.71
14.78
13.41
13.94
Mphen-cn
Bphen-cn
Mphen-ind
Bphen-ind
4. Conclusions
In summary, the replacement of cyanoacetic acid anchoring groups with carboxylated 1,3-
indanedione anchoring group resulted in 100 nm enhanced absorption curve with higher molar
absorption coefficient and IPCE have been extended up to 800 nm. This is due to high
acceptance nature and extended conjugation of carboxylated 1,3-indanedione anchoring group
15

over cyanoacetic acid. In spite of these superior absorption properties, the dyes have shown
lower efficiency than cyanoacetic acid dyes. The DFT studies have revealed that the unfavorable
LUMO localization over the carboxylated 1,3-indanedione group (i.e. 5.6 and 5.3%) is
responsible for low DSSC efficiencies than cyanoacetic acid dyes (14.6 and 14.5%). The
observed low LUMO localization on carboxylated 1,3-indanedione group might be because of
competitive conjugation between the two carbonyls groups. It diminishes the extent of electron
transfer towards carboxylic acid as a result of which Jsc and efficiency decreases. The DSSC
device efficiency of theses synthesized dyes were not increased much even after the addition of
co-adsorbents (CDCA and PA) indicating that these dyes are not aggregating. Further, structural
modifications on carboxylated 1,3-indanedione in order to enhance the photovoltaic conversion
efficiency by complete utilization of its high light harvesting property are underway.
Acknowledgments
This work was supported by the Korea Institute of Energy Technology Evaluation and
Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of
Korea (No. 20163010012310). The Human resources program in energy technology of the
KETEP, granted from the MOTIE, Republic of Korea (No. 20174030201760). Fundamental
R&D program for Core Technology of Materials (10050966) funded by the Knowledge
Economy, Republic of Korea.
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Table of Contents
The comparative study of new carboxylated 1,3-indanedione sensitizers with standard
cyanoacetic acid dyes using co-adsorbents in dye sensitized solar cells
Hyeonjun Jeonga, Ramesh Kumar Chitumallab, Dong Woo Kima, S. V. Prabhakar Vattikutia,
a
Suresh Thogitia, Rajesh Cherukua, Joonkyung Jangb, Jae Hong Kim , Ganesh Koyyadaa,*, Jae
Hak Junga,*
The effect of carboxylated 1,3-indanedione anchoring group have been investigated and
compared with standard cyanoacetic acid dyes for dye-sensitized solar cells application
19

Highlights
 The synthesized carboxylated 1,3-indanedione dyes DSSC performance were evaluated.
 The carboxylated 1,3-indanedione dyes showed 100nm red-shifted absorption spectra.
 The IPCE of carboxylated 1,3-indanedione sensitizers have been extended upto 800nm.
 The reasons for low efficiency of 1,3-indanedione sensitizers were discussed
20