Bi-anchoring organic sensitizers of type D-(π-A)2 comprising thiophene-2-acetonitrile as π-spacer and malonic acid as electron acceptor for dye sensitized solar cell applications

Article abstract of DOI:10.1016/j.saa.2015.03.032

Two new bi-anchoring organic sensitizers of type D-(π-A)₂ comprising the identical π-spacer (thiophene-2-acetonitrile) and electron acceptor (malonic acid) but different aryl amine as electron donors (diphenylamine and carbazole) were synthesized, characterized and fabricated metal free dye-sensitized solar cell devices. The intra molecular charge transfer property and electrochemical property of these dyes were investigated by molecular absorption, emission, cyclic voltammetric experiments and in addition, quantum chemical calculation studies were performed to provide sufficient driving force for the electron injection into the conduction band of TiO₂ which leads to efficient charge collection. Among the fabricated devices, carbazole based device exhibits high current conversion efficiency (η = 4.7%) with a short circuit current density (J_SC) 15.3 mA/cm², an open circuit photo voltage (V_OC) of 0.59 V and a fill factor of 0.44 under AM 1.5 illumination (85 mW/cm²) compared to diphenylamine based device.

Full text of DOI:10.1016/j.saa.2015.03.032

Accepted Manuscript
Bi-anchoring organic sensitizers of type D-(π-A)2 comprising thiophene-2-ace-
tonitrile as π-spacer and malonic acid as electron acceptor for dye sensitized
solar cell applications
Gachumale Saritha Reddy, Sekar Ramkumar, Abdullah M. Asiri, Sambandam
Anandan
PII:
S1386-1425(15)00328-5
http://dx.doi.org/10.1016/j.saa.2015.03.032
SAA 13446
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
To appear in:
Received Date:
Revised Date:
Accepted Date:
7 November 2014
29 January 2015
1 March 2015
Please cite this article as: G.S. Reddy, S. Ramkumar, A.M. Asiri, S. Anandan, Bi-anchoring organic sensitizers of
type D-(π-A)2 comprising thiophene-2-acetonitrile as π-spacer and malonic acid as electron acceptor for dye
sensitized solar cell applications, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015),
doi: http://dx.doi.org/10.1016/j.saa.2015.03.032
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Bi-anchoring organic sensitizers of type D-(π-A)2 comprising
thiophene-2-acetonitrile as π-spacer and malonic acid as electron
acceptor for dye sensitized solar cell applications
Gachumale Saritha Reddy[a], Sekar Ramkumar[a], Abdullah M. Asiri[b] and
Sambandam Anandan*[a]
[a]Nanomaterials and Solar Energy Conversion Laboratory, Department of Chemistry, National
Institute of Technology, Trichy-620 015, India.
[b]The Center of Excellence for Advanced Materials Research, King Abdulaziz University,
Jeddah 21413, P.O. Box 80203, Saudi Arabia.
* Corresponding author. Tel.: +91 431 2503639; fax: +91 431 2500133.
E-mail addresses: sanand@nitt.edu, sanand99@yahoo.com (S. Anandan).
ABSTRACT
Two new bi-anchoring organic sensitizers of type D-(π-A)2 comprising the identical π-spacer (thiophene-2-
acetonitrile) and electron acceptor (malonic acid) but different aryl amine as electron donors (diphenylamine and
carbazole) were synthesized, characterized and fabricated metal free dye-sensitized solar cell devices. The intra
molecular charge transfer property and electrochemical property of these dyes were investigated by molecular
absorption, emission, cyclic voltammetric experiments and in addition, quantum chemical calculation studies were
performed to provide sufficient driving force for the electron injection into the conduction band of TiO2 which leads
to efficient charge collection. Among the fabricated devices, carbazole based device exhibits high current
conversion efficiency (η= 4.7 %) with a short circuit current density (JSC) 15.3 mA/cm2, an open circuit photo
voltage (VOC) of 0.59 V and a fill factor of 0.44 under AM 1.5 illumination (85 mW/cm2) compared to
diphenylamine based device.
Keywords: DSSCs, malonic acid, binding strength, planar nature, electron lifetime.

1. Introduction
Dye-sensitized solar cells (DSSCs) have become one of the most promising alternatives to silicon-based
photovoltaic devices [1] due to its remarkable performances in converting solar energy to electricity at low cost
fabrications after the pioneering research work published by O’Regan and Gratzel in 1991 [2]. There are four main
factors: anode [3], cathode [4], electrolyte [5] and sensitizer [6], that plays a major role in the DSSCs performance
improvement. As a key part of DSSCs, the dye (metal-based and metal free) sensitizers take the function of light
absorption and generation of the electric charges [7]. Apart from precious metal-based sensitizers (ruthenium
sensitizers shows power conversion efficiency (η) ˃ 10%) [8], the metal free organic dyes have also achieved up to
10% efficiency under AM 1.5 G sunlight intensity [9]. In order to gain effective photo induced intramolecular
charge transfer characteristics, most of the efficient organic sensitizers are modelled as donor-π-spacer-
acceptor/anchoring (D-π-A) architecture [10] and it provides grand flexibility of molecular tailoring, simple
preparation process of low cost, high molar extinction coefficients, high purity and less environment issues. In
general, TiO2 semiconductor act as a photocatalyst for dye degradation and organic transformation processes [11-
14], whereas in DSSC charge regeneration takes place by bonding dye molecules towards TiO2 surface. However, to
design and syntheses of such more efficient organic dyes are still a challenge [15]. The main reason for the low
conversion efficiency of metal free DSSCs is its lower Voc [16], sharp absorption band in the visible region [17],
lower binding strength of dye on the TiO2 surface [18] and lower stability [19]. To rectify these problems
researchers tailoring the D-π-A core structure by substituting appropriate functional groups. Further, the presence of
only one anchoring functionality per molecule raise a serious constraint in organic dyes with respect to Ru (II)
sensitizers (N3 dye); where upon, minimum 4 anchoring groups are readily available for tuneable interfacial electron
transfer processes [20]. Recently, many groups reported bi-branched bi-anchoring dyes [D-(π-A)2] due to their
extended π-conjugation, double binding abilities, higher photocurrent and increased efficiencies over the mono
anchoring counterparts [21,22]. Hence, it is beneficial to synthesis the metal free sensitizers with more –COOH
groups which will improve the binding strength and also induces the efficient charge injection from dye to
semiconductor surface similar to metal based sensitizers.
A series of bi-branched bi-anchoring dyes based on cyanoacrylic acid and rodhanine-3-acetic acid
as acceptor have been reported by us earlier [23-25], and in continuation introduced here malonic acid as an acceptor
in bi-anchoring dyes which may further increase the interfacial electron injection by providing four anchoring –
COOH groups and also increase the absorption maximum values. The reason for choosing malonic acid as an
electron acceptor is: (1) it act as a better electron withdrawing group compared to cyano acetic acid and rodhanine-
3-acetic acid, and (2) it also provide better anchoring groups to nanocrystalline TiO2 [26,27]. With these designed
features, two new metal free organic dyes 2,2'-((5,5'-((1E,1'E)-(9-hexyl-9H-carbazole-3,6-diyl)bis(1-cyanoethene-
2,1-diyl))bis(thiophene-5,2-diyl))bis (methanylylidene))dimalonic acid (Car-th-Ma) and 2,2'-((5,5'-((1E,1'E)-
((hexylazanediyl)bis(4,1-phenylene))bis(1-cyanoethene -2,1-diyl))bis(thiophene-5,2-diyl))bis(methanylylidene))di

malonic acid (Dpa-th-Ma) Fig. 1, was synthesized based on carbazole or diphenylamine as donor,
cyanovinylthiophene as π–linker and malonic acid as acceptor.
Fig. 1. Molecular structures of the new (Car-th-Ma) and (Dpa-th-Ma) sensitizers.
The synthesized dyes were characterized by 1H, 13C-NMR, FTIR and mass; and their photophysical, electrochemical
properties were investigated. The photophysical properties of the new dyes in solution and in thin films were
investigated by absorption spectroscopy and solution mode photoluminescence (PL) spectroscopy. The redox
properties of the new dyes were investigated by cyclic voltammetry and density functional theory (DFT)
calculations. The synthesized dyes were used as a sensitizer in TiO2 based DSSCs.
2. Experimental Section
2.1. Materials
All reagents and chemicals were purchased from Alfa Aesar and Sigma-Aldrich and used without further
purification unless specified otherwise. All solvents were dried by refluxing for at least 24 h over CaH2 and freshly
distilled prior to use. All column chromatographic separations were carried out on Merck silica gel (60-120 mesh).
FTO glass plates (sheet resistance 10Ω/□) were purchased from BHEL, INDIA. The photoanode was prepared by
the following procedure as follows: [28] Glacial acetic acid (5 mL), 7.5 mL of tetra isopropyl titanate (C12H28O4Ti)
and one drop of Triton X-100 were mixed with 15 mL of 2-propanol. Water (5 mL) was added to the above solution
drop wise while vigorously stirring the solution. The resulting semi colloidal suspension was dispersed on fluorine
doped tin oxide (FTO) conducting glass plate by doctor blade technique. Loose crust of particles on the TiO2 film
was removed by wiping smoothly using cotton wool. The thickness of the TiO2 film was successively controlled, by
repeating the above coating procedure. Then it was sintered at 450 °C for 1 h for removing the binder, solvent and
getting an electrically-connected network of TiO2 particles by burning under tubular furnace. After the sintering
process, when the temperature of the plate drops to 50 °C to 70 °C, it was immersed into the dye solution and leave
for 24 h. Excess non-adsorbed dye were washed with anhydrous ethanol. The Platinum catalyst counter electrode

was prepared by deposition of H2PtCl6.6H2O solution (0.005 mol/dm3 in isopropanol) onto FTO glass and then
sintering at 400 °C for 20 min [29,47]. The DSSC device was fabricated by the following method: the photo cathode
was placed on top of the photo anode and was tightly clipped together. Then, liquid electrolyte 0.05 M I2/0.1 M
LiI/0.5 M 4-tert-butyl pyridine (TBP) in 3-methoxypropionitrile was injected in-between the two electrodes.
2.2. Instruments
1H and 13C-NMR spectra were realized on a 300/400 MHz BRUKER spectrometer in deuterated
chloroform or dimethylsulfoxide solution at 298 K. Chemical shifts (δ values) were recorded in units of ppm relative
to tetramethylsilane (TMS) as an internal standard. The molecular weights of the dyes were determined by
Micromass QUATTRO 11 ESI-MS spectrometer coupled to a Hewlett Packard series 1100 degasser. ATR-FTIR
spectra were measured with a thermo spectrophotometer system equipped with a ZnSe prism. Absorption and
fluorescence spectra were measured in DMF solution on a Specord S 600 diode-array UV-Vis spectrophotometer
and Shimadzu RF-5301 PC spectrofluorophotometer respectively. Electrochemical measurements were performed
on a Metrohm Autolab PGSTAT potentiostat/galvanostat-84610. All measurements were carried out at room
temperature with a conventional three-electrode configuration consisting of a platinum disc working electrode, a
glassy carbon (GC) auxiliary electrode, and an Ag/AgCl (aq) was used as the reference electrode. The potentials
were reported vs ferrocene as standard using a scan rate of 0.1 Vs-1 and the sample solutions contained 3×10-4 M
sample and 0.1 M tetrabutylammonium hexafluorophosphate (Bu4NPF6) in anhydrous DMF as a supporting
electrolyte under Argon atmosphere. Electrochemical impedance spectroscopy (EIS) measurements were done under
85 mW/cm2 light illumination by using an Autolab PGSTAT potentiostat/galvanostat-84610. The impedance spectra
were recorded with a frequency ranging between 10 kHz to 1 Hz at their open circuit potential (OCP). The IPCE
spectra were recorded using Oriel 300W Xe Arc lamp in combination with an Oriel Cornerstone 260¼
monochromator. The number of incident photons was calculated for each wavelength using a calibrated
monocrystalline silicon diode as reference.
2.3. Synthesis
2.3.1. Synthesis of 9-hexyl-9H-carbazole (1a) [30]
1-Bromohexane (5 g, 1.7 eq), carbazole (3 g, 1 eq) and sodium hydroxide (6 g, 8.4 eq) were added to
dimethylsulfoxide (DMSO) (45 mL), followed by heating at 110 °C for 12 h. After cooling to room temperature the
resulting mixture was extracted with Ethyl acetate (EA)/water and then dried with Na2SO4. The solvent was
evaporated and the resulting crude was purified by column chromatography on silica gel (60-120 mesh) by using
hexane as solvent to give white solid with yield 88.22% (3.97 g).
1H NMR (CDCl3, ppm): δ 8.18 (d, 2H, J=7.6Hz), 7.56-7.54 (m, 2H), 7.52-7.46 (m, 2H), 7.31 (t, 2H,
J=7.2Hz), 4.33 (t, 2H, J=7.2Hz), 1.96-1.89 (m, 2H), 1.54-1.37 (m, 6H), 0.96 (d, 3H, J=6.8Hz). 13C NMR (CDCl3,
ppm): δ 140.35, 125.48, 122.75, 120.25, 118.61, 108.57, 42.90, 31.51, 28.84, 26.89, 22.48, 13.97.

2.2.2. Synthesis of 9-hexyl-9H-carbazole-3, 6-dicarbaldehyde (1b) [31]
Freshly distilled POCl3 (36 mL, 25 eq) was added drop wise to DMF (27 mL, 23 eq) under N2 atmosphere
at 0 °C, and then it was stirred for 1 h. Compound 1a (3.89 g, 0.015 mol) was added to the above solution, and then
resulting mixture was stirred for 4 h at 95 °C. After cooling to room temperature, the mixture was poured into a
beaker containing ice-cube, and basified with 6 M NaOH. Filtered the solid and dried. The solid crude product was
purified by column chromatography on silica gel (60-120 mesh) by using Ethyl acetate/Hexane (1:4), to give a white
solid (2.94 g, yield = 63.46%).
1H NMR (CDCl3, ppm): δ 10.13 (s, 2H), 8.67 (d, 2H, J=1.5 Hz), 8.10-8.08 (m, 2H), 7.55 (d, 2H, J =8.5
Hz), 4.39 (t, 2H, J =7.5 Hz), 1.94-1.88 (m, 2H), 1.41 (d, 2H, J =7 Hz), 1.38-1.30 (m, 4H), 0.86 (m,3H). 13C NMR
(CDCl3, ppm): δ 191.43, 144.73, 129.61, 127.79, 124.19, 123.12, 109.72, 43.78, 31.39, 28.89, 26.81, 22.42, 13.90.
2.2.3. Synthesis of (2E, 2’E)-3, 3’-(9-hexyl-9H-carbazole-3, 6-diyl) bis (2-(thiophen-2-yl) acrylonitrile) (1c) [23]
Freshly distilled methanol (100 mL) was taken in a 250 mL single neck round bottom flask. The compound
1b (3 g, 1 eq) and thiophene-2-acetonitrile (2.65 g, 2.2 eq) were added to the methanol. A catalytic amount of
potassium tert-butoxide was added into this mixture at room temperature. Then the reaction mixture was stirred for
12 h at 50 °C. It was monitored by TLC. A bright yellow solid was filtered after 12 h. It was recrystallized in
dichloromethane and methanol to give the product 2.6 g (yield = 52%).
1H NMR (CDCl3, ppm): δ 8.60-8.50 (m, 2H), 8.12-8.09 (m, 2H), 7.51-7.45 (m, 2H), 7.42-7.38 (m, 2H),
7.26 (s, 2H), 7.13-7.10 (m, 2H), 7.04-7.00 (m, 2H), 4.32 (t, 2H, J=7.2 Hz), 1.93-1.55 (m,2H), 1.39-1.25 (m, 6H),
0.89-0.87 (m, 3H). 13C NMR (CDCl3, ppm): δ 142.22, 140.77, 140.08, 128.21, 127.42, 126.47, 125.60, 123.32,
122.93, 117.91, 109.87, 103.17, 43.79, 31.64, 29.14, 27.05, 22.66, 14.13.
2.2.4. Synthesis of (2E,2'E)-3,3'-(9-hexyl-9H-carbazole-3,6-diyl)bis(2-(5-formylthiophen-2-yl)acrylonitrile) (1d)
[31]
DMF (7 mL, 23 eq) was taken in a 100 mL 3 neck round bottom flask. To this freshly distilled POCl3 (9
mL, 25 eq) was added drop wise under an atmosphere of N2 at 0 °C, and then it was stirred for 1 h. 2 g of compound
1c was added to the above solution, and the resulting mixture was stirred for 4 h at 95 °C. It was monitored by TLC.
After the completion of the reaction, it was cooled to RT, and then the reaction mixture was poured into a beaker
containing ice-cubes, and basified with 6 M NaOH. It was extracted with dichloromethane/brine. After evaporating
the organic solvent the crude product was purified by column chromatography on silica using a mixture of Ethyl
acetate/Hexane (1:4, v/v), to give an orange colour solid 1.04 g (yield = 47%).
1H NMR (CDCl3, ppm): δ 10.14 (s, 2H), 8.15-8.17 (m, 2H), 7.57 (s, 2H), 7.47 (d, 2H,J=8.8 Hz), 7.39 (s,
2H), 7.39-7.29 (m, 2H), 7.26 (s, 2H), 7.10-7.08 (m, 2H), 4.33 (t,2H, J=7.2 Hz), 1.92-1.88 (m, 2H), 1.55-1.25 (m,
6H), 1.38-1.25 (m, 4H), 0.89-0.86 (m,3H). 13C NMR (CDCl3, ppm): δ 180.94, 147.37, 144.52, 140.54, 125.67,
122.92, 120.44, 118.79, 113.02, 108.76, 107.19, 90.92, 43.15, 31.71, 29.04, 27.09, 22.67, 14.15.

2.2.5. Synthesis of 2,2'-((5,5'-((1E,1'E)-(9-hexyl-9H-carbazole-3,6-diyl)bis(1-cyanoethene-2,1-diyl))bis(thiophene-
5,2-diyl))bis(methanylylidene))dimalonic acid (1e)
Freshly distilled acetonitrile (30 mL) was taken in a 100 mL 2 neck round bottom flask. 1 g of compound
1d was added to the above solvent and maintains the reaction at 60 °C and piperidine (0.482 mL, 2.8 eq), malonic
acid (0.430 mg, 2.4 eq) was added to the above solution, and then refluxed it for overnight. It was monitored by
TLC. After completion of the reaction, cooled to room temperature (RT) and then distillate the solvent by using
rotovac evaporator, then the solid compound was washed with 1:1 ratio of CHCl3:CH3OH mixture. Filter the dark
red colour solid compound about 47 mg (yield = 36.5%).
1H NMR (CDCl3, ppm): 8.59 (s, 1H), 8.27 (s, 1H), 8.00 (s, 2H), 7.83 (s, 2H), 7.79 (m, 2H), 7.74 (m, 2H),
7.64 (d, 1H, J=8.4 Hz), 7.52 (m, 1H), 7.31 (d, 1H, J=8 Hz ), 7.26 (s, 1H), 4.30-4.21 (m, 2H), 1.84 (m, 2H), 1.65 (m,
2H), 1.41-1.25 (m, 4H), 0.84 (s, 3H). 13C NMR (DMSO-d6, ppm): δ 166.18, 156.34, 153.15, 146.47, 143.12, 141.42,
132.10, 126.73, 125.54, 124.86, 115.07, 105.10, 45.21, 31.45, 26.54, 22.17, 14.81. ESI-MS Anal. Calcd. for
C40H31N3O8S2: 745.82. Found: 746.
2.2.6. Synthesis of N-hexyl-N-phenylaniline (2a) [30]
It was synthesized according to the procedure of 1a whereas diphenylamine is used as starting compound
instead of carbazole. The product obtained was colourless liquid (yield = 81.7%).
1H NMR (CDCl3, ppm): δ 7.27-7.23 (m, 4H), 6.98-6.96 (m, 4H), 6.94-6.91 (m, 2H), 3.67 (t, 2H, J=8Hz),
1.66-1.62 (m, 2H), 1.35-1.26 (m, 6H), 0.88-0.85 (m, 3H). 13C NMR (CDCl3, ppm): δ 148.05, 129.15, 120.95,
120.82, 52.28, 31.59, 27.36, 26.71, 22.62, 13.99.
2.2.7. Synthesis of 4, 4'-(hexylazanediyl) dibenzaldehyde (2b) [31]
It was synthesized according to the procedure of 1b by using compound 2a. The product is brown colour
liquid (yield = 94%).
1H NMR (CDCl3, ppm): δ 9.85 (s, 2H), 7.78 (d, 4H, J=8.4 Hz), 7.13 (d, 4H, J=8.4 Hz), 3.82 (t, 2H,
J=8.0Hz), 1.67 (d, 4H, J=8.4 Hz), 1.33-1.26 (m, 6H), 0.85 (t, 3H, J=6.4 Hz). 13C NMR (CDCl3, ppm): δ 190.25,
148.89, 129.92, 121.95, 121.69, 52.31, 31.69, 27.42, 26.90, 22.69, 13.87.
2.2.8. Synthesis of (2E, 2'E)-3, 3'-(4, 4'-(hexylazanediyl) bis (4, 1-phenylene)) bis (2-(thiophen-2-yl) acrylonitrile)
(2c) [23]
It was synthesized according to the procedure of 1c by using compound 2b. The product obtained was red
colour solid (yield = 68.5%).

1H NMR (CDCl3, ppm): δ 7.79 (d, 2H, J=10.4 Hz), 7.36-7.34 (m, 2H), 7.30-7.26 (m, 2H), 7.26-7.22 (m,
2H), 7.12-7.04 (m, 4H), 6.97-6.95 (m, 2H), 3.80 (t, 2H, J=8.0 Hz), 1.72-1.66 (m, 2H), 1.38-1.25 (m, 6H), 0.91-0.87
(m, 3H). 13C NMR (CDCl3, ppm): δ 148.82 139.91, 139.26, 130.89, 128.22, 126.98, 126.54, 125.67, 120.93, 117.61,
103.21, 52.49, 31.69, 27.68, 26.82, 22.76, 14.14.
2.2.9. Synthesis of (2E,2’E)-3,3’-((hexylazanediyl)bis(4,1-phenylene))bis(2-(5-formylthiophen-2-yl)acrylonitrile)
(2d) [31]
It was synthesized from compound 2c according to the similar procedure of 1d. The product was red colour
solid (yield = 39%).
1H NMR (CDCl3, ppm): δ 9.87 (s, 2H), 7.88 (d, 4H, J=8.8 Hz), 7.71 (d, 2H, J= 4Hz), 7.47 (s, 2H), 7.41
(d,2H, J=4 Hz) 7.15-7.13 ( m, 4H), 3.84 (t, 2H, J=8.0 Hz), 1.73 -1.62 (m, 2H), 1.38-1.34 (m, 2H), 1.32-1.25 (m, 4H),
0.90-0.87 (m, 3H). 13C NMR (CDCl3, ppm): δ 182.56, 149.53, 149.01, 142.67, 142.45, 137.11, 131.74, 126.94,
126.48, 121.07, 116.80, 102.18, 52.57, 31.63, 27.72, 26.76, 22.72, 14.11.
2.2.10.
Synthesis
of
2,2'-((5,5'-((1E,1'E)-((hexylazanediyl)bis(4,1-phenylene))bis(1-cyanoethene-2,1-
diyl))bis(thiophene-5,2-diyl))bis(methanylylidene))dimalonic acid (2e)
It was synthesized according to the procedure of 1e by using compound 2d. The product was dark red
colour solid (yield = 37.9%).
1H NMR (DMSO-d6, ppm): 8.31 (s, 2H), 8.16 (s, 2H), 7.91 (d, 2H, J=8.7 Hz), 7.85-7.82 (m, 2H), 7.73-7.60
(m, 4H), 7.56-7.32 (m, 2H), 7.22-7.01 (m, 2H), 2.97 (s, 2H), 1.57 (m, 2H), 1.33 (m, 2H), 1.21 (m, 4H), 0.84 (m,
3H). 13C NMR (DMSO-d6, ppm): δ 165.87, 159.28, 157.16, 149.24, 140.72, 134.86, 130.61, 120.54, 120.12, 119.67,
114.17, 107.24, 50.64, 30.95, 29.15, 26.95, 22.54, 13.71. ESI-MS Anal. Calcd. for C40H33N3O8S2: 747.84. Found:
747.
3. Results and Discussion
3.1 Synthesis of organic dyes
The synthetic pathways of organic dyes Car-th-Ma and Dpa-th-Ma were depicted in scheme 1. The
electron-donor part, N-hexyl diphenylamine and N-hexyl carbazole are synthesized by hexylation of diphenylamine
and carbazole in basic DMSO medium and then coupled with cyanovinylthiophene π–linker via Vilsmeier-Haack
formylation reaction followed by Knoevenagel condensation. Then the product is coupled with anchoring malonic
acid group through Vilsmeier-Haack formylation reaction followed by Knoevenagel condensation. All the
intermediates and target products were purified by column chromatography and the new compounds were well
confirmed by various analytical tools (See Supporting information).

Scheme 1. Synthetic pathway of the organic dyes. (i) 1- Bromohexane, NaOH, DMSO, 110 °C . (ii) POCl3,
DMF, 95 °C. (iii) 2-(thiophene-2-yl)-acetonitrile, t-BuOK, CH3OH, refluxed. (iv) POCl3, DMF, 95 °C. (v)
Malonic acid, piperidine, acetonitrile, refluxed.
3.2 Photophysical properties
The UV-Vis spectra of the synthesized organic dyes in DMF solution (6×10-5 M) and adsorbed on TiO2
film are presented in Fig. 2 and 3, respectively and the detailed parameters are collated in Table 1. As can be seen in
Fig. 2, Car-th-Ma and Dpa-th-Ma exhibit obvious maximum absorption peaks at two distinct regions. The higher
energy peaks at 299 nm (ε=27,971 M-1 cm-1) for Car-th-Ma and at 273 nm (ε=38,426 M-1 cm-1) for Dpa-th-Ma dyes
can be ascribed to a π-π* transition of the conjugated aromatic rings and the lower energy peaks at 537 nm
(ε=43,411 M-1 cm-1) for Car-th-Ma and at 465 nm (ε=35,080 M-1 cm-1) for Dpa-th-Ma can be attributed to the

intramolecular charge transfer (ICT) between the arylamine donating unit and malonic acid acceptor/anchoring
moiety, thereby producing an efficient charge separated state [32].
Fig. 2. Absorption and emission spectra of Car-th-Ma and Dpa-th-Ma dyes recorded in DMF.
In that spectra, the Car-th-Ma dye red shifted by 72 nm and its molar extinction coefficients were 8,331 times
greater than the Dpa-th-Ma which is reasoned out with the help of DFT calculations, that the former (Car-th-Ma) has
the dihedral angles of the corresponding ring units R1-R2 is 0.25° and R1-R3 is -179.1°, supports more planar
configuration and hence more delocalization over entire conjugate system upon compared to Dpa-th-Ma [33]. Fig. 3
shows the absorption spectra of the dye loaded TiO2 films after 24 h immersion of TiO2 films in dye solution. The
maximal absorption peaks for Car-th-Ma and Dpa-th-Ma are at 513 nm and 478 nm respectively. Upon comparing
with the absorption spectra of the corresponding dyes in solution Car-th-Ma shows blue shifted by 24 nm may be
due to the H-aggregation, i.e., the aggregation of the dyes on the surface of TiO2 nanoparticles due to strong
interactions between the dyes and semiconductor surface [34] and such phenomenon has been found in other organic
dyes reported earlier [35-37].
Whereas, Dpa-th-Ma dye shows red shifted by 13 nm may be due to the J-aggregation [38] occurred by
increased delocalization of the π* orbital of the conjugated framework caused by the interaction between the
carboxylate group and Ti4+ ions that directly decreases the energy of the π* level [39] respectively. The absorption
spectra of the dyes became broadened after adsorption on the TiO2 surface, which should favor the light harvesting
of the solar cells [40]. Further, the introduction of malonic acid electron acceptor shifts the absorption bands of the
both dyes to red region compare to cyano acetic acid electron acceptor [23]. The fluorescence spectra recorded upon

their excitation of absorption maxima value of Car-th-Ma and Dpa-th-Ma exhibit strong luminescence maxima at
661 nm (λex = 577 nm) and 578 nm (λex = 483 nm) respectively.
Fig. 3. Absorption spectra of Car-th-Ma and Dpa-th-Ma dyes adsorbed on nanocrystalline TiO2 films.
3.3 Electrochemical properties
The estimation of the energy levels, the effect of arylamine donors on the energy level of the synthesized
dyes and the electron transfer from the excited dye molecule to conductive band (Ecb) of TiO2 were measured by
ox
cyclic voltammetry (Fig. 4) and their data are summarized in Table 1. The onset oxidation potentials Eonset are
observed at 0.72 V and 1.07 V were determined from the intersection of two tangents drawn at the rising current and
background charging current of a cyclic voltammograms [41] for Car-th-Ma and Dpa-th-Ma dyes respectively. The
HOMO energy levels were calculated based on the relationship of HOMO (eV) = -e (Eonsetox V (vs Fc/Fc+) + 4.8 V)
by assuming the ferrocene (Fc) energy level to be -4.8 eV below the vacuum level [42], these HOMO values are
-
positive than I-/I3 redox couple (-4.6 eV vs vacuum) which may further improved negatively about 0.3 V by adding
-
additives such as 4-tert-butylpyridine (TBP) to the I-/I3 redox electrolyte [43]. The LUMO levels of the dyes were
calculated by (Eonsetox) - E0-0, where E0-0 is the zero-zero energy of the dyes estimated from the intersection between
absorption and emission spectra [44,45]. Probably, the LUMO energy values are negative than of conduction band
(Fig. 5), provides sufficient driving force for the electron injection into the conduction band of TiO2 which leads to
efficient charge collection [46]. Further, the HOMO and LUMO energy levels of the synthesized dyes are very
-
suitable for the electron regeneration from the electrolyte I-/I3 and electron injection to the conduction band of TiO2
respectively.

Fig. 4. Cyclic voltammograms of dyes were measured in DMF solution with Bu4NPF6 (0.1 M) as an
electrolyte. Working electrode: Pt; reference electrode: Ag/AgCl (aq); counter electrode: Glassy carbon;
calibrated with Fc/Fc+ as a standard reference; scan rate: 0.1 Vs-1.
Table 1
Optical, electrochemical data and HOMO, LUMO energy levels of Car-th-Ma and Dpa-th-Ma dyes.
ꢀꢁꢂꢃꢄ(eV)c
Dye
λabs /nm
λem/nma,b
Eox/V(vs, Fc) EHOMO(eV)d ELUMO(eV)d HOMOe LUMOe
(ε(M-1cm-1))a
Car-th-Ma 537 (43,411) 661
Dpa-th-Ma 465 (35,080) 578
1.99
2.30
0.72
1.07
5.07
5.42
3.08
3.12
-5.70
-5.47
-2.88
-3.08
a
Absorption and emission spectra were recorded in DMF solution (6×10-5 M) at room temperature.
Dyes were excited at their absorption maximum value (for Car-th-Ma, λex = 577 nm and for Dpa-th-Ma, λex = 483
b
nm).
c Optical band gap calculated from intersection between the absorption and emission spectra.
d The values of EHOMO and ELUMO were calculated with the following: HOMO (eV)= -e (Eꢅꢅꢆꢊꢇꢈꢉ V (vs Fc/Fc+) + 4.8 V) ;
LUMO (eV)=(Eꢅꢅꢆꢊꢇꢈꢉ) - E0-0 , where E0-0 is the intersection between the absorption and emission spectra of the
sensitizers.
e B3LYP/6-31G(d) calculated values.

Fig. 5. Energy level diagrams of Car-th-Ma and Dpa-th-Ma dyes from electrochemical data.
3.4. Computational analysis
To get an insight into the molecular structure and electron distribution of the synthesized organic dyes, their
geometries have been optimized by density functional theory (DFT) calculations using B3LYP/6-31 G (d) level in
gas phase with Gaussian 09 program. The electron distribution of HOMO and LUMO of the dyes with optimized
structures were shown in Fig. 6 and the calculated HOMO and LUMO energies of the dyes were listed in Table 1.
The dihedral angle in ∠C-N-C-C (R2-R3) is -142.6° and in ∠C-N-C-C (R3-R2) is -155.5° for Dpa-th-Ma, and the
dihedral angle in ∠C-N-C-C (R1-R2) 0.25° and in ∠C-N-C-C (R1-R3) -179.1° for Car-th-Ma dye. However in Car-
th-Ma and Dpa-th-Ma, the electron density is mainly localized at the electron donors as well as thiophene moieties at
both sides in HOMO, whereas in LUMO electron density is localized only at the thiophene and electron
withdrawing malonic acid moieties. This indicates that in both dyes the intra molecular charge transfer (ICT) takes
place from donor moiety to withdrawing group through the π-bridge. Therefore, the expected spatial orientation of
HOMO and LUMO levels for the dyes is suitable for DSSCs, which can facilitate the interfacial electron injection
from the excited dye to the conduction band of TiO2.

Fig. 6. The frontier HOMO and LUMO orbitals of Car-th-ma and Dpa-th-ma dyes.
3.5. Photovoltaic performance of the DSSCs
TiO2 nanoparticles were prepared according to the literature [28] and it was coated on a FTO glass substrate
with an effective area of 0.49 cm2. This plate was immersed in a DMF solution containing 3×10-4 M dye sensitizers
for 24 h. The photo cathode was prepared by H2PtCl6 (50 mM in isopropyl alcohol) solution which is deposited on
the FTO glass by drop casting and heated at 400 °C for 20 min [29,47]. The device was fabricated as follows: the
photo cathode was placed on top of the photo anode and was tightly clipped together. Then, 0.05 M I2/0.1 M LiI/0.5
M 4-tert- butyl pyridine (TBP) in 3-methoxypropionitrile electrolyte was injected in-between the two electrodes.
The current-voltage (I-V) curves of the fabricated DSSCs sensitized by the Car-th-Ma and Dpa-th-Ma dyes
are shown in Fig. 7 and the performance statistics were tabulated in Table 2. Among the two dyes, Car-th-Ma dye
showed high efficiency due to high JSC and VOC, mainly high JSC contributed by longer wavelength absorption with
high molar extinction coefficient in the series. Probably, the low band gap value of Car-th-Ma suggest an increase in
JSC values, which may leads to further increase in device efficiency. Further, the planar nature of carbazole moiety
facilitates the good adsorption on TiO2 surface which may be reason for the higher efficiency of Car-th-Ma.
The spectra of incident photon to current conversion efficiency (IPCE) (Fig. 8) almost covers the entire
visible region, similar to the absorption spectrum of the dye adsorbed thin TiO2 layer, facilitating the DSSCs to
efficiently convert solar light to electricity. The IPCE spectra of Car-th-Ma showed 24% in the range of 444 - 508
nm. In contrast, the IPCE of Dpa-th-Ma gives relatively low values (15%) at the wavelength maximum (478 nm),
which might be due to the poor injection efficiency arising from the unfavourable binding at the TiO2 surface [48].

Fig. 7. Current density-voltage characteristics for Car-th-Ma and Dpa-th-Ma based devices for DSSCs under
illumination of simulated solar light (AM 1.5, 85 mW/cm2).
Fig. 8. IPCE spectra of the fabricated devices based on Car-th-Ma and Dpa-th-Ma dyes.

Fig. 9. Nyquist plots of DSSCs based on Car-th-Ma and Dpa-th-Ma dyes under illumination of simulated solar
light (AM 1.5, 85 mW/cm2).
This is further confirmed by calculating the adsorbed amounts (Γ) of dyes on TiO2 surface by desorption of
the dye from the TiO2 surface using 0.1 M NaOH in DMF/H2O (1:1) mixture [34]. From these results, Car-th-Ma
adsorbs comparatively more than Dpa-th-Ma dye may be due to the planar nature of Car-th-Ma dye on TiO2 surface,
probably this may augment the device efficiency.
The electrochemical impedance spectroscopy (EIS) analysis [49] was performed to understand the
correlation between the improved cell performance and internal resistance, and to confirm relation between VOC and
the charge recombination rate of the fabricated DSSCs over a frequency range of 100-104 Hz under AM 1.5. The
Nyquist plot displayed in Fig. 9 looks like a semicircle which corresponds to the charge transfer resistance at the
counter electrode and TiO2/dye/electrolyte interface. The diameter of the bigger semicircle in the order of Dpa-th-
Ma∠ Car-th-Ma, which means that the electron recombination resistance is high for Car-th-Ma dye on the
TiO2/electrolyte interface, and it is in accordance with the VOC value of the device [10,50]. The electron lifetime for
Car-th-Ma (7.16 ms) is high compare to Dpa-th-Ma (2.79 ms), which can be measured from bode plot Fig. 10.
Probably, the lower electron recombination and longer electron lifetime of Car-th-Ma further induce the device
efficiency [51]. Malonic acid based device exhibit more surface concentration as well as longer electron lifetime
compare to cyano acetic acid based device [23], which may be the reason for higher efficiency of malonic acid
based device.

Fig. 10. Bode plots of DSSCs based on Car-th-Ma and Dpa-th-Ma dyes under illumination of simulated solar light
(AM 1.5, 85 mW/cm2).
Table 2
DSSC performance parameters of the fabricated devices.
Dye
Jsc (mA/cm2)
Voc (mV)
FF
η (%)a
Electron
lifetime
(τeff) (ms)
7.16
Surface
concentration
Γ(mol/cm2)
15.3
13.3
590
558
0.44
0.47
4.7
4.1
4.0 x 10-5
1.0 x 10-5
Car-th-Ma
Dpa-th-Ma
2.79
a Illumination: 85 mW/cm2 simulated AM 1.5 G solar light; electrolyte containing: 0.05 M I2/0.1 M LiI/0.5 M 4-
tert-butyl pyridine in 3-methoxypropionitrile.
3.6. Adsorption of Dyes on the TiO2 surface: ATR-FTIR Studies
Fourier-transform infrared (FTIR) spectra of the Car-th-Ma (Fig. 11a) dye shows most prominent bands for
C=O stretching at 1674 cm-1, -C≡N stretching at 2210 cm-1, and asymmetric and symmetric stretching modes of the
aliphatic –CH2 groups at 2931 and 2858 cm-1 respectively. And the Dpa-th-Ma dye (Fig. 12a) shows prominent
bands for C=O stretching at 1672 cm-1, -C≡N stretching at 2210 cm-1, and asymmetric and symmetric stretching
modes of the aliphatic –CH2 groups at 2921 and 2856 cm-1 respectively. An attenuated total reflectance Fourier-
transform infrared (ATR-FTIR) spectroscopy has been shown to be a powerful tool to extract structural information
about the dye adsorbed onto the TiO2 surface [52]. The spectrum of Car-th-Ma dye (Fig. 11b) anchored on TiO2
shows bands at 1627 and 1389 cm-1 for the asymmetric and symmetric stretching modes of the carboxylate group
and complete disappearance of C=O stretching peak at 1674 cm-1.

Fig. 11. ATR-FTIR spectra of the Car-th-Ma dye obtained using a solid sample and adsorbed on a
nanocrystalline TiO2 film.
Similarly, Dpa-th-Ma dye (Fig. 12b) also shows bands at 1630 and 1390 cm-1 for the asymmetric and symmetric
stretching modes of the carboxylate group and complete disappearance of C=O stretching peak at 1672 cm-1. From
these ATR-FTIR data, it can be inferred that the dye is anchored on the surface through the carboxylate groups via a
bidentate chelation or a bridging of surface titanium ions rather than an ester type linkage [53]. In addition, the
peaks observed for Car-th-Ma dye (at 2952, 2856 cm-1) and for Dpa-th-Ma dye (at 2926, 2857 cm-1) are corresponds
to the asymmetric and symmetric stretching modes of the aliphatic –CH2 groups, while peaks for -C≡N group
stretching for Car-th-Ma (at 2221 cm-1) and for Dpa-th-Ma (2211 cm-1), and finally the observed large and broad
absorption band centered at 3423 cm-1 may be due to adsorbed moisture presumably from the dye solution since the
TiO2 film is heated prior to staining.

Fig. 12. ATR-FTIR spectra of the Dpa-th-Ma dye obtained using a solid sample and adsorbed on a
nanocrystalline TiO2 film.
4. Conclusion
In summary, two metal free organic dyes Dpa-th-Ma and Car-th-Ma featuring thiophene-2-acetonitrile as
the ꢋ-spacer and malonic acid as the electron acceptor with different arylamine (diphenylamine and carbazole) as
electron donors were designed and synthesized. The photophysical, electrochemical, photovoltaic and ATR-FTIR
properties of the dyes were extensively studied illustrates such metal free organic dyes may be suitable for DSSCs.
Among the fabricated devices, the device based on Car-th-Ma dye showed higher efficiency (η) compared to Dpa-
th-Ma dye based device. This is due to the higher JSC and VOC, mainly the higher JSC values contributed by high
absorption and high molar extinction coefficient values of Car-th-Ma as well as the low band gap energy level, the
energy levels of Car-th-Ma provides sufficient driving force for the electron injection and dye regeneration. In
addition to this the high electron recombination resistance and longer electron life time augment the device
efficiency. From this conclusion the malonic acid provide stronger binding ability to TiO2 film.
Acknowledgment
Author SA thank SERI-DST, New Delhi (Ref. No. DST/TM/SERI/2k12/109(C)) and DST-FIST, New
Delhi (SR/FT/CSI-190/2008 dated 16th Mar 2008) for the sanction of research fund towards development of new
facilities. Author GSR thanks MHRD, New Delhi for the junior research fellowship position.
References
[1] [1] G. Li, K.J. Jiang, Y.F. Li, S.L. Li, L.M. Yang, J. Phys. Chem. C 112 (2008) 11591–11599.
[2] B. O'Regan, M. Grätzel, Nature 353 (1991) 737–740.

[3] N.G. Park, J. Van de Lagemaat, A.J. Frank, J. Phys. Chem. B 104 (2000) 8989-8994.
[4] A. Hauch, Electrochimi. Acta 46 (2001) 3457–3466.
[5] Q.B. Meng, K. Takahashi, X.T. Zhang, I. Sutanto, T.N. Rao, O. Sato, A. Fujishima, Langmuir 19 (2003) 3572-
3574.
[6] N. Robertson, Angew. Chem. Int. Ed. 45 (2006) 2338-2345.
[7] M. Katono, T. Bessho, M. Wielopolski, M. Marszalek, J.E. Moser, R.H. Baker, S.M. Zakeeruddin, M. Gratzel, J.
Phys. Chem. C 116 (2012) 16876−16884.
[8] K.J. Jiang, J.B. Xia, N. Masaki, S. Noda, S. Yanagida, Inorganica Chimi. Acta 361 (2008) 783–785.
[9] L. Zhou, C. Jia, Z. Wana, X. Chen, X. Yao, Org. Electron. 14 (2013) 1755–1762.
[10] M. Cheng, X. Yang, F. Zhang, J. Zhao, L. Sun, J. Phys. Chem. C 117 (2013) 9076-9083.
[11] K. Muthu, K. Selvam, B. Krishnakumar, M. Swaminathan, Appl. Catal. A 358 (2009) 259–263.
[12] B. Krishnakumar, R. Velmurugan, S. Jothivel, M. Swaminathan, Catal. Commun. 11 (2010) 997–1002.
[13] B. Krishnakumar, M. Swaminathan, J. Mol. Catal. A Chemical 334 (2011) 98–102.
[14] R. Velmurugan, B. Krishnakumar, Rajendra Kumar, M. Swaminathan, Arabian J. Chem. 5 (2012) 447–452.
[15] A. Mishra, M.K.R. Fischer, P. Buerle, Angew. Chem. Int. Ed. 48 (2009) 2474 – 2499.
[16] F. Zhang, Y.H. Luo, J.S. Song, X.Z. Guo, W.L. Liu, C.P. Ma, Y. Huang, M.F. Ge, Z. Bo, Q.B. Meng, Dyes
Pigm. 81 (2009) 224–230.
[17] K. Sayama, M. Sugino, H. Sugihara, Y. Abe, H. Arakawa, Chem. Lett. (1998) 753-754.
[18] K.S.V. Gupta, T. Suresh, S.P. Singh, A. Islam, L. Han, M. Chandrasekharam, Org. Electron. 15 (2014) 266–
275.
[19] H. Choia, J.K. Leea, K. Songb, S.O. Kanga, Mation, A Ko, Tetrahedron 63 (2007) 3115–3121.
[20] R. Sirohi, D.H. Kim, S.C. Yu, S.H. Lee, Dyes Pigm. 92 (2012) 1132-1137.
[21] K.D. Seo, B.S. You, I.T. Choi, M.J. Ju, M. You, H.S. Kang, H.K. Kim, ChemSusChem 6 (2013) 2069-2073.
[22] A. Baheti, K.R. Justin Thomas, C.P. Lee, K.C. Ho, Org. Electron. 14 (2013) 3267–3276.
[23] S. Ramkumar, S. Anandan, Dyes Pigm. 97 (2013) 397-404.

[24] S. Ramkumar, S. Manoharan, S. Anandan, Dyes Pigm. 94 (2012) 503-511.
[25] S. Ramkumar and S. Anandan, RSC Adv. 3 (2013) 21535-21543.
[26] N.W. Duffy, K.D. Dobson, K.C. Gordon, B.H. Robinson, A.J. McQuillan, Chem. Phys. Lett. 266 (1997) 451-
455.
[27] L. Giribabu, M. Chandrasekheram, M. Lakshrni Kanthamn, V. Gopal Reddy, D. Satyanarayana, O.S. Rao, P.
Yella eddy, Indian J. Chem. 45A (2006) 629-634.
[28] P.M. Sirimanne, H. Tributsch, J. Solid State Chem. 177 (2004) 1789-1795.
[29] J. He, W. Wu, J. Hua, Y. Jiang, S. Qu, J. Li, Y. Long, H. Tian, J. Mater. Chem. 21 (2011) 6054-6062.
[30] J.H. Park, N.S. Cho, Y.K. Jung, H.J. Cho, H.K. Shim, H. Kim, Org. Electron 8 (2007) 272-285.
[31] T. Mallegol, S. Gmouh, M.A.A. Meziane, M.B. Desce, O. Mongin, Synthesis 11 (2005) 1771-1774.
[32] Z. Ci, X. Yu, M. Bao, C. Wang, T. Ma, Dyes Pigm. 96 (2013) 619-625.
[33] W. Wu, J. Yang, J. Hua, J. Tang, L. Zhang, Y. Long, H. Tian, J. Mater. Chem. 20 (2010) 1772-1779.
[34] H. Tian, X. Yang, R. Chen, R. Zhang, A. Hagfeldt, L. Sun, J. Phys. Chem. C 112 (2008) 11023-11033.
[35] K. Hara, Z.S. Wang, T. Sato, A. Furube, R. Katoh, H. Sugihara, et al, J. Phys. Chem. B 109 (2005) 15476-
15482.
[36] H.N. Tian, X.C. Yang, R.K. Chen, Y.Z. Pan, L Li, A Hagfeldt, et al, Chem. Commun. (2007) 3741-3743.
[37] M.K.R. Fischer, S. Wenger, M.K. Wang, A. Mishra, S.M. Zakeeruddin, M. Grätzel, et al, Chem. Mater. 22
(2010) 1836-1845.
[38] M. Guo, P. Diao, Y.J. Ren, F. Meng, H. Tian, S.M. Cai, Sol. Energy Mater. Sol. Cells 88 (2005) 23-35.
[39] Y. Ooyama, Y. Harima, Eur. J. Org. Chem. (2009) 2903-2934.
[40] J. Shi, Z. Chai, C. Zhong, W. Wu, J. Hua, Y. Dong, J. Qin, Q. Li, Z. Li, Dyes Pigm. 95 (2012) 244-251.
[41] A.K. Agrawal, S.A. Jenekhe, Chem. Mater. 8 (1996) 579-589.
[42] B.J. Pomrnerehne, H. Vestweber, W. Gun, R.F. Muhrt, H. Bassler, M. Porsch, et al, Adv. Mater. 7 (1995) 551-
554.
[43] G. Boschloo, L. Ha1ggman, A. Hagfeldt, J. Phys. Chem. B 110 (2006) 13144-13150.

[44] S.T. Huang, Y.C. Hsu, Y.S. Yen, H.H. Chou, J.T. Lin, C.W. Chang, C.P. Hsu, C.T sai, D.J. Yin, J. Phys. Chem.
C 112 (2008) 19739-19747.
[45] H. Tian, X. Yang, J. Cong, R. Chen, J. Liu, Y. Hao, et al, Chem. Commun. (2009) 6288-6290.
[46] P. Singh, A. Baheti, K.R. Justin Thomas, C.P. Lee, K.C. Ho, Dyes Pigm. 95 (2012) 523-533.
[47] W. Xu, B. Peng, J. Chen, M. Liang, F. Cai, J. Phys. Chem. C 112 (2008) 874-880.
[48] D.P. Hagberg, T. Marinado, K.M. Karlsson, K. Nonomura, P. Qin, G. Boschloo, T. Brinck, A. Hagfeldt, L.
Sun. J. Org. Chem. 72 (2007) 9550-9556.
[49] R. Kern, R. Sastrawan, J. Ferber, R. Stangl, J. Luther, Electrochim. Acta 47 (2002) 4213-4225.
[50] J. Zhao, X. Yang, M. Cheng, S. Li, L. Sun, J. Phys. Chem. C 117 (2013) 12936-12941.
[51] K.W. Ko, M. Lee, S.S. Sekhon, S. K. Balasingam, C.H. Han and Y. Jun, ChemSusChem 6 (2013) 2117–2123.
[52] C. Klein, Md.K. Nazeeruddin, D. Di Censo, P. Liska, M. Gratzel, Inorg. Chem. 14 (2004) 4216-4226.
[53] V. Shklover, Y.E. Ovehinnikov, L. S. Braginsk, S.M. Zakeeruddin, M. Gratzel, Chem. Mater. 10 (1998) 2533-
2541.

Bi-anchoring organic sensitizers of type D-(π-A)2 comprising
thiophene-2-acetonitrile as π-spacer and malonic acid as electron
acceptor for dye sensitized solar cell applications
Gachumale Saritha Reddy[a], Sekar Ramkumar[a], Abdullah M. Asiri[b] and
Sambandam Anandan*[a]
[a]Nanomaterials and Solar Energy Conversion Laboratory, Department of Chemistry, National
Institute of Technology, Trichy-620 015, India.
[b]The Center of Excellence for Advanced Materials Research, King Abdulaziz University,
Jeddah 21413, P.O. Box 80203, Saudi Arabia.
* Corresponding author. Tel.: +91 431 2503639; fax: +91 431 2500133.
E-mail addresses: sanand@nitt.edu, sanand99@yahoo.com (S. Anandan).
GRAPHICAL ABSTRACT

23
Two new bi-anchoring organic sensitizers of type D-(π-A)2 comprising the identical π-spacer as
thiophene-2-acetonitrile,electron acceptor as malonic acid but different aryl amine as electron
donors (diphenylamine and carbazole) were synthesized for dye sensitized solar cell fabrication.
Among two dyes, carbazole based device exhibits high current conversion efficiency (η= 4.7%)
under AM 1.5 illumination (85 mW cm-2) compared to Diphenylamine based device.

24
Highlights
• Two new bi-anchoring organic sensitizers of type D-(π-A)2 were synthesized and
characterized
• Carbazole based device exhibits high current conversion efficiency (η= 4.7%) under AM
1.5 illumination
• More negative LUMO energy levels provides sufficient driving force for the electron
injection into TiO2