Simple metal-free organic D-φ-A dyes with alkoxy-or fluorine substitutions: Application in dye sensitized Solar Cells

Article abstract of DOI:10.1166/jnn.2012.6183

Two new metal-free organic sensitizers with simplest structural variations have been synthesized for application in nanocrystalline TiO₂ sensitized solar cells. The donor-φ-bridge-acceptor (D-φ-A) structure dyes, Y2 and Y3 each designed with three parts, an electron donor unit (substituted phenyl), a linker unit (thiophene), and an anchor unit (cyanoacrylic acid) showed maximal monochromatic incident photon to current conversion efficiencies (IPCE) in a device reaching upto 67% and 82% respectively. The organic sensitizers with 3,4,5-trimethoxy phenyl (Y3) as donor moieties obtained better solar light to electrical energy conversion efficiencies of 3.30% where as the organic sensitizer with 2,4-difluoro phenyl as donor (Y2) showed comparatively lower efficiency of 1.02%. The efficiency obtained with the reference sensitizer N719 under similar fabrication and evaluation conditions was 5.84%. Copyright

Full text of DOI:10.1166/jnn.2012.6183

Copyright © 2012 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 12, 4489–4494, 2012
Simple Metal-Free Organic D-ꢀ-A Dyes with
Alkoxy- or Fluorine Substitutions: Application in
Dye Sensitized Solar Cells
M. Chandrasekharam1ꢀ∗, B. Chiranjeevi1, K. S. V. Gupta1,
Surya Prakash Singh1ꢀ∗, A. Islam2, L. Han2, and M. Lakshmi Kantam1
1Inorganic and Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500007, India
2Photovoltaic Materials Unit, National Institute for Materials Science, 1-2-1, Sengen, Tsukuba, Ibaraki-305-0047, Japan
Two new metal-free organic sensitizers with simplest structural variations have been synthesized
for application in nanocrystalline TiO2 sensitized solar cells. The donor-ꢀ-bridge-acceptor (D-ꢀ-
A) structure dyes, Y2 and Y3 each designed with three parts, an electron donor unit (substituted
phenyl), a linker unit (thiophene), and an anchor unit (cyanoacrylic acid) showed maximal monochro-
matic incident photon to current conversion efficiencies (IPCE) in a device reaching upto 67%
and 82% respectively. The organic sensitizers with 3,4,5-trimethoxy phenyl (Y3) as donor moieties
obtained better solar light to electrical energy conversion efficiencies of 3.30% where as the organic
sensitizer with 2,4-difluoro phenyl as donor (Y2) showed comparatively lower efficiency of 1.02%.
The efficiency obtained with the reference sensitizer N719 under similar fabrication and evaluation
conditions was 5.84%.
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Keywords: Metal-Free Sensitizers, Nanocrystalline TiO , Simple D-ꢀ-A Systems, Dye-
Copyright: American Scientific P2ublishers
Sensitized Solar Cells.
1. INTRODUCTION
should anchor strongly on semiconductor oxide (nanocrys-
talline TiO2) surface, to have good electronic communica-
tion and inject electrons efficiently into conduction band
of TiO2. Among metal free organic and metal complexes,
ruthenium polypyridinie complexes perform better as sen-
sitizers due to their appropriate redox, spectroscopic, and
excited-state properties.
There is an intense interest among scientific commu-
nity to develop metal free sensitizers5 as alternative to
conventional ruthenium complexes in dye sensitized solar
cells (DSSCs). The advantages of using metal-free organic
sensitizers are (1) The availability of diverse molecular
structures that can be easily designed and synthesized.
(2) cost effective easy purification and environmentally
benign compared to noble metal complexes. (3) high molar
extinction coefficients and therefore suitable for good light
harvesting efficiency with thinner TiO2 films. To date,
organic dyes exhibit higher efficiencies compared with that
of Ru complexes in p-type DSCs. Generally, donor-ꢁ-
bridge-acceptor (D-ꢁ-A) structure is the common charac-
ter of these organic dyes. With these features it is easy
to design new dye structures, extend the absorption spec-
tra, adjust the HOMO and LUMO levels and complete the
intramolecular charge separation.
To replace fast depleting fossil fuels arising from increas-
ing global energy demands the search for clean alternate
energy sources is highly demanding.1–9 The conversion of
solar light can be considered as the important renewable
energy source that can be tapped for the generation of
mass energy. However the unviable production of solar
panels from expensive traditional inorganic semiconduc-
tors necessitated the search for alternative cheaper solar
energy technologies.10ꢀ11 In this context, since Michael
Grätzel introduced high surface area nanoporous TiO2
films as wide band gap semiconductor, a breakthrough in
the area of DSSC, the photovoltaic application of DSSC
has been enormously explored because of their low cost
and impressive conversion efficiencies.1a In DSSC, sensi-
tizers serve as solar light harvesters and their electronic
properties influence the light harvesting efficiency and the
overall photoelectric conversion efficiency. The ideal sen-
sitizer for DSSC should have high molar extinction coef-
ficient and absorb solar radiation strongly with absorption
bands preferably covering a broad range of wavelengths
across visible to near IR regions. In addition, the sensitizer
∗Authors to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2012, Vol. 12, No. 6
1533-4880/2012/12/4489/006
doi:10.1166/jnn.2012.6183
4489

Simple Metal-Free Organic D-ꢁ-A Dyes with Alkoxy- or Fluorine Substitutions
Chandrasekharam et al.
2. EXPERIMENTAL SECTION
π
Donor
Acceptor
2.1. Synthesis and Characterization of Sensitizers
All reagents were purchased from sigma-Aldrich. The
1H NMR and 13C NMR spectra of solutions in CDCl3
and DMSO were recorded on 300 and 500 MHz NMR
spectrometers. Chemical shifts were referenced relative
to TMS. The IR spectra were recorded on FTIR-5700
spectrometer. Absorption spectra were recorded on a
Perkin-Elmer spectrofluorometer.
When a dye absorbs light, intramolecular charge trans-
fer occurs from subunit D to A through the ꢁ-bridge. For
n-type DSSCs, the excited dye injects the electron into
the conduction band of the semiconductor via the elec-
tron acceptor group, A. However, in p-type DSSCs, the
excited dye captures the electron from the valence band of
the semiconductor to complete the interfacial charge trans-
fer. Many efforts have been made to change the different
parts of organic dyes to optimize DSSC performance such
as sensitizers based on polyene-triphenylamine, coumarin,
and indoline moieties.
2.1.1. Synthesis of 5-(2, 4-Di-Fluorophenyl),
Thiophene-2-Carbaldehyde (1a)
5-formyl 2-bromo thiophene (0.100 g, 0.523 mmol), 2, 4-
difiuoro phenyl boronicacid (0.090 g, 0.575 mmol), 2 M
aqNa2CO3 (3 ml), Pd [P (PPh3ꢂ]4 (0.060 g, 10 mol%) and
dimethoxyethane (3 ml) were mixed and degassed. The
whole system was refluxed for 5 h under the inert atmo-
sphere of argon. Then the reaction mixture obtained was
filtered through celite, extracted with dichloromethane,
dried over Na2SO4 and was finally purified by column
chromotography on silica gel eluting with ethyl acetate-
petroleum ether. Crystalline yellow colored solid was
obtained. Yield: 0.090 g (76%).
New less volatile redox systems such as ionic liquids6–9
and hole conductors10–12 demand thinner TiO2 films
because of mass transport limitations or insufficient
pore filling. A great variety of organic sensitizers
based on polyene-triphenylamine,13–19 coumarin,20–22 and
indoline23–26 moieties give respectable conversion efficien-
cies of 5–9% with the traditional iodide/triiodide redox
system. The introduction of long alkyl chains into donor
units can improve the photovoltaic performance and stabil-
ity of the organic dyes.27 However, still a better fundamen-
1H NMR (300 MHz, CDCl3) ꢃ 9.90 (s, 1H), 7.73 (d, J =
Delivered by Ingenta to: Nanyang Technological University
3ꢄ9 Hz, 1H), 7.69–7.61 (m, 1H), 7.48 (dd, J = 1ꢄ3ꢀ3ꢄ9Hz,
tal understanding of the energetic, kinetic and geometric
IP: 146.185.204.169 On: Thu, 09 Jun 2016 09:48:09
1H), 7.02–6.92 (m, 2H), MS (FAB) m/z 428.2.
Synthesis of Y2
Copyright: American Scientific Publishers
interplay between the oxide/dye/electrolyte constituents is
needed in order to design new efficient and stable organic
sensitizers for future devices. In continuation of our efforts
for the synthesis and photovoltaic evaluation of new sensi-
tizers including ruthenium-complexes, metal-free organic
and tetrapyrroles for DSSC applications, we became inter-
ested in the synthesis of metal-free organic dyes with flu-
orine and trimethoxy substituted aryls as donors.28 We
report here design, synthesis and characterization of two
new sensitizers and evaluation of the photovoltaic perfor-
mance of the simplest and smallest possible metal-free
organic dyes Y2 and Y3 for application in nanocrystalline
TiO2 sensitized solar cells and compared with standard
N719 dye under similar fabrication and measurement con-
ditions (Fig. 1).
To the acetic acid (2 ml) solution of 5-(2,
4-difluorophenyl) thiophene-2-carbaldehyde (0.050 g,
0.223 mmol) cyanoaceticacid (0.018 g, 0.223 mmol),
ammonium acetate (5 mol%) were added and was refluxed
well for 2 h. The solid obtained was washed thor-
oughly with water (to remove excess of acetic acid
and cyanoaceticacid), hexane and finally with 10%
(ethylacetate+hexane) mixture to afford a fine yellow col-
ored solid, Y2 (0.060 g, 93%)
1H NMR (300 MHz, d6-DMSO) ꢃ 8.30 (s, 1H), 7.83–
7.54 (m, 3H), 7.06–7.03 (m, 2H).
2.1.2. Synthesis of 5-(2, 3, 4-Trimethoxyphenyl)
Thiophene-2-Carbaldehyde (1b)
5-formyl 2-bromo thiophene (0.100 g, 0.5234 mmol), 2, 3,
4,-trimethoxy phenyl boronicacid (0.132 g, 0.628 mmol),
2 M aqNa2CO3 (3 ml), Pd [P (PPh3ꢂ]4 (0.060 g,
10 mol %) and dimethoxyethane (3 ml) were mixed and
degassed. The whole system was refluxed for 4 h under
an inert atmosphere of argon. Then the reaction mix-
ture obtained was filtered through celite, extracted with
dichloromethane, dried over Na2SO4 and was finally puri-
fied by column chromotography on silica gel eluting with
ethyl acetate-petroleum ether. Fine yellow colored solid
was obtained. Yield: 0.110 g (75%).
NC
NC
COOH
COOH
S
O
S
F
O
F
O
Y2
Y3
Fig. 1. Structures of the new metal-free organic sensitizers.
4490
J. Nanosci. Nanotechnol. 12, 4489–4494, 2012

Chandrasekharam et al.
Simple Metal-Free Organic D-ꢁ-A Dyes with Alkoxy- or Fluorine Substitutions
1H NMR (CDCl3ꢂ ꢃ 9.87 (s, 1H), 7.66 (d, J = 3ꢄ7 Hz,
1H), 7.43 (d, J = 3ꢄ7 Hz, 1H), 6.70 (d, J = 8ꢄ30 Hz, 1H),
3.94 (s, 3H), 3.90 (s, 3H), 3.88 (s, 3H). MS (FAB) m/z
428.2.
recombination, and sintered at 500 ꢀC. The dye solu-
tions (2 × 10−4 M) were prepared in 1:1 acetonitrile and
tert-butyl alcohol solvents. Deoxycholic acid as a co-
adsorbent was added to the dye solution at a concentration
of 20 mM. The electrodes were immersed in the dye solu-
Synthesis of Y3
ꢀ
To the acetic acid (2 ml) solution of 5-(2,3,4-
trimethoxyphenyl) thiophene-2-carbaldehyde (0.100 g,
0.3597 mmol), cyanoaceticacid (0.033 g, 0.3597 mmol),
and ammonium acetate (5 mol %) were added and
was refluxed well for 5–6 h. The solid obtained was
washed thoroughly with water (to remove excess of acetic
acid and cyanoaceticacid), hexane and finally with 10%
(ethylacetate+hexane) mixture (to remove any nonpolar
and slightly polar impurities) to afford a fine red colored
solid, Y3 (0.300 g, 83%)
tions and then kept at 25 C for 20 h to adsorb the dye
onto the TiO2 surface.
2.3. Fabrication of Dye-Sensitized Solar Cell
Photovoltaic measurements were performed in a two-
electrode sandwich cell configuration. The dye-deposited
TiO2 film was used as the working electrode and a
platinum-coated conducting glass as the counter electrode.
The two electrodes were separated by a surlyn spacer
(40 ꢅm thick) and sealed up by heating the polymer frame.
The electrolyte was composed of 0.6 M dimethylpropyl-
imidazolium iodide (DMPII), 0.05 M I2, and 0.1 M LiI in
acetonitrile (ACN).
1H NMR (300 MHz, d6-DMSO) ꢃ 8.24 (s, 1 H), 7.82–
7.75 (m, 1 H), 7.54–7.42 (m, 2 H), 6.80 (d, J = 9ꢄ06, 1 H).
MS (FAB) m/z428.2.
2.2. Preparation of TiO2 Electrode
2.4. Photovoltaic Characterization
Nanocrystalline TiO2 photoelectrodes of about 20 ꢅm
thickness (area: 0.25 cm2) were prepared using a varia-
tion of a method reported by Grätzel and co-workers.2
Fluorine-doped tin oxide-coated glass electrodes (Nippon
Sheet Glass Co., Japan) with a sheet resistance of
The working electrode was illuminated through a con-
ducting glass. The current–voltage characteristics were
measured using the previously reported method29 with
a solar simulator (AM-1.5, 100 mW/cm2, WXS-155S-
10: Wacom Denso Co., Japan). Monochromatic incident
photon-to-current conversion efficiency (IPCE) for the
solar cell, plotted as a function of excitation wavelength,
was recorded on a CEP-2000 system (Bunkoh-Keiki
Co. Ltd.). Incident photon-to-current conversion efficiency
(IPCE) at each incident wavelength was calculated from
Eq. (1), where Isc is the photocurrent density at short cir-
cuit in mA cm−2 under monochromatic irradiation, q is the
elementary charge, ꢆ is the wavelength of incident radia-
8–10 ohm−2 and an optical transmission of >80% in
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the visible range were used. Anatase TiO2 colloids (par-
Copyright: American Scientific Publishers
ticle size ∼ 13 nm) were obtained from commercial
sources (Ti-Nanoxide D/SP, Solaronix). The nanocrys-
talline TiO2 thin films of approximately 20 ꢅm thickness
were deposited onto the conducting glass by screen-
ꢀ
printing. The film was then sintered at 500 C for 1 h.
The film thickness was measured with a Surfcom 1400A
surface profiler (Tokyo Seimitsu Co. Ltd.). The electrodes
were impregnated with a 50 mM titanium tetrachloride
solution to block the TCO glass electrode to come into
direct contact with the electrolyte thus preventing the
tion in nm, and P0 is the incident radiative flux in W m−2
.
IPCE ꢇꢆꢂ = 1240ꢇIsc/qꢆP0ꢂ
(1)
B(OH)2
Br
10 mol-%Pd(PPh3)4
2M Na2CO3
O
O
S
R3
S
R3
H
R1
DME, reflux, 4 to 20h
H
R1
R2
R2
1a,1b
CN
CNCH2COOH
5mol% CH3COONH4
CH3COOH
COOH
S
R3
reflux,12h
R1
R2
Y2:R1=R3=F,R2=H
Y3:R1=R2=R3=CH3O
Scheme 1. Synthesis of Sensitizers Y2 and Y3.
J. Nanosci. Nanotechnol. 12, 4489–4494, 2012
4491

Simple Metal-Free Organic D-ꢁ-A Dyes with Alkoxy- or Fluorine Substitutions
Chandrasekharam et al.
3. RESULTS AND DISCUSSION
0.48
3.1. Synthesis
Y2
Y3
N719
0.36
0.24
0.12
0.00
Difluorophenyl and trimethoxyphenyl were chosen as
donor moieties for the two metal-free organic sensitizers
Y2 and Y3 respectively. Though there are a few reports
on the role of fluorine on ruthenium as well as metal-free
organic sensitizers, we assumed to synthesize the simplest
fluorine substituted sensitizer for DSSC application.30 In
contrast to the reported organic sensitizers where the fluo-
rine has been substituted on the spacer aryl moiety30d, we
chose to substitute fluorine on the donor moiety in Y2.
On the other hand trimethoxyphenyl is a good electron
donating unit selected for Y3. The thiophene unit is a con-
jugation moiety with two double bonds and also provides
stability to the molecule by virtue of aromaticity where as
cyanoacrylic acid group provides a strong anchor for the
sensitizer to electronically bind onto TiO2 semiconductor
particles.
The synthesis of two new organic sensitizers was car-
ried out according to the Scheme 1. 2-bromo-5-formyl
thiophene was subjected to Pd catalyzed Suzuki coupling
with the corresponding substituted phenyl boronic acid
in presence of aq. Na2CO3 and dimethoxy ethane. The
crude reaction mixture after work up was column chro-
matographed to obtain pure 2-aryl-5-formyl thiophenes 1a
300
400
500
600
700
Wavelength (nm)
Fig. 2. UV-Visible spectra of Y2, Y3 and N719.
Gaussian reconvolution method, which enabled to integrate
emission peak to estimate their emission maxima centred
at 451 and 418 nm for Y2 and Y3 sensitizers respectively.
Electrochemical properties of Y2 and Y3 dyes were
scrutinized by cyclic voltammetry using tetra-butyl ammo-
nium perchlorate (0.1 M in acetonitrile) as electrolyte
and ferrocene as an internal standard at 0.42 V versus
SCE. The reduction potentials obtained for these sensitiz-
ers −1ꢄ58 V and −1ꢄ71 V versus SCE, respectively are
more negative (or higher in energy) than the conduction
band edge of TiO2 (−0ꢄ80 V versus SCE) providing a ther-
modynamic driving force to inject electron from the dye
to TiO2.
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and 1b in good yield. Knoevenagel condensation of the
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aryl substituted formyl thiophenes with cyanoacetic acid in
Copyright: American Scientific Publishers
presence of acetic acid and ammonium acetate for 7 hours
under refluxing conditions yielded the crude dye which
was purified by recrystallization to give the sensitizers Y2
and Y3. The formyl thiophenes (1a & 1b) and the sensitiz-
1
ers were characterized by FTIR, HNMR and ESI-MASS
3.3. Photovoltaic Measurements
spectroscopes.
The incident photon-to-current conversion efficiencies
(IPCEs) of DSSCs constructed based on Y2 and Y3 sen-
sitizers are plotted as function of excitation wavelength
3.2. Electronic Absorption, Emission and
Electrochemical Properties
Equimolar dye solutions of Y2 and Y3 were prepared
in dimethylformamide to obtain the molar absorptivities,
and the electronic absorption spectra recorded as a func-
tion of wavelength were compared with that of N719
(Fig. 2). The electronic absorption spectra of Y2 and Y3
dyes show well defined absorption bands and their molar
extinction coefficients (ꢈ) are 31000 M−1cm−1 at 355 nm
and 42000 M−1cm−1 at 378 nm respectively under sim-
ilar conditions. The molar extinction coefficient (ꢈ) of
alkoxy substituted sensitizer (Y3) is higher while di-fluoro
substituted sensitizer (Y2) showed relatively lower value,
however much higher molar extinction coefficient than the
standard N719, ruthenium complex.
48000
Y2
Y3
36000
24000
12000
0
The emission spectra of the new sensitizers were
recorded in DMF medium by exciting the complexes
with their corresponding absorbance maximum obtained in
DMF (Fig. 3). Their emission spectra were analyzed by
375
450
525
600
Wavelength (nm)
Fig. 3. Emission spectra of Y2 and Y3 sensitizers.
J. Nanosci. Nanotechnol. 12, 4489–4494, 2012
4492

Chandrasekharam et al.
Simple Metal-Free Organic D-ꢁ-A Dyes with Alkoxy- or Fluorine Substitutions
7.0
and their IPCE spectra were compared with that of N719
sensitized cell. Figure 4 presents the typical photocur-
rent action spectra of the DSSCs fabricated using the dye
solutions (2 × 10−4 M) prepared in 1:1 acetonitrile and
tert-butyl alcohol solvents. The maximum IPCE observed
for these two dyes are within the spectral range of 300–
600 nm. The DSSCs constructed based on Y2 and Y3
sensitizers in combination with the electrolyte composed
of 0.6 M dimethylpropyl-imidazolium iodide (DMPII),
0.05 M I2, and 0.1 M LiI in acetonitrile exceeds IPCE
values of 67% and 82% respectively reaching maximum
at 425 nm. Considering the light absorption and scattering
loss by the conducting glass, the maximum efficiencies for
absorbed photon-to-collected electron conversion efficien-
cies (APCEs) of Y2 and Y3 sensitizers are almost close to
unity over a broad spectral range of 300 to 600 nm.
Y2
Y3
5.6
4.2
2.8
1.4
0.0
0.0
0.2
0.4
0.6
0.8
1.0
Potential (V)
An electrolyte system containing MPII (0.6 M), I2
(0.1 M) LiI (0.5 M) and TBP (0.5 M) in methoxypropioni-
trile was employed to study the photovoltaic performance
of the new organic sensitizers in the DSSC test cells with
0.25 cm2 active area. The IV characteristics of the sensi-
tizers Y2 and Y3 are shown in Figure 5. Among the two
new sensitizers, Y3 sensitizer exhibited the best photo-
voltaic performance Jsc of 6.055 mA/cm2, Voc of 716 mV
and fill factor of 0.762, yielding an overall power conver-
sion efficiency of 3.30%, at AM 1.5 sunlight, Y2 sensitizer
exhibited Jsc of 3.214 mA/cm2, Voc of 448 mV and fill
factor of 0.711, yielding an overall power conversion effi-
Fig. 5. Photocurrent density versus voltage curves for DSSCs based
on Y2 and Y3 under irradiation of AM 1.5 G simulated solar light
(100 mW cm−2).
introduced two fluorine atoms in the sensitizer Y2. How-
ever, from the photovoltaic parameters obtained it seems
that without any electron donating moieties, fluorine alone
results in poor performance. Although the Y2 and Y3 sen-
sitizers show lower IPCE values than that of N719, this
problem could be solved using tandem DSSCs, a sub-
ject for further study. We are currently investigating the
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optimization of this series of sensitizers by introduction
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of various electron-donating groups (alkoxy, TPA, etc.) in
ciency of 1.02% (Table I). Under similar conditions, N719
sensitized solar cell fabricated using the same electrolyte
gave a short-circuit photocurrent density of 17.53 mA/cm2,
an open-circuit photovoltage of 517 mV and fill factor of
0.645, yielding an overall conversion efficiency of 5.84%.
To evaluate the effect of electron with drawing difluoro
substituted phenyl in the metal free organic sensitizer, we
Copyright: American Scientific Publishers
the electron donor unit which can extend the absorption
towards red region.
In conclusion, we strategically designed and synthesized
two simplest new metal-free organic sensitizers for appli-
cation in nanocrystalline TiO2 sensitized solar cells. The
monochromatic incident photon to current conversion effi-
ciencies (IPCE) of the sensitizers Y2 and Y3 in a device
reaching upto 67% and 82% were achieved. The organic
sensitizer with 3,4,5-trimethoxy phenyl (Y3) as donor moi-
ety obtained better solar light to electrical energy con-
version efficiencies of 3.30% where as the sensitizer Y2
showed comparatively lower efficiency of 1.02%. In con-
trast to reported sensitizers, these sensitizers are the sim-
plest and particularly Y2 has fluorine substituted on donor
moiety. The low efficiency of Y2 is attributed to the lack of
absorption in the region >400 nm. Efforts are on for study-
ing this class of fluoro substituted metal-free organic dyes
towards achieving higher solar to electricity conversion
efficiency.
90
80
70
Y2
Y3
60
50
40
30
20
10
0
N719
Table I. Photovoltaic Performance of DSSCs for Y2 and Y3 dyes com-
pared with N719.
300
400
500
600
700
800
Wavelength (nm)
Dye
Jsc [mA]
Voc [V]
ff
Eff [%]
Fig. 4. Photocurrent action spectra (IPCE) of nanocrystalline TiO2 film
(20 ꢅm) sensitized by Y2, Y3 and N719. The redox electrolyte solution
was a mixture of 0.6 M DMPII, 0.05 M I2, 0.1 M LiI and 0.3 M TBP
in acetonitrile.
Y2
Y3
N719
3ꢄ214
6ꢄ055
17ꢄ53
0.448
0.716
0.517
0.711
0.762
0.645
1.02
3.30
5.84
J. Nanosci. Nanotechnol. 12, 4489–4494, 2012
4493

Simple Metal-Free Organic D-ꢁ-A Dyes with Alkoxy- or Fluorine Substitutions
Chandrasekharam et al.
Acknowledgments: BC and KSVG thank CSIR and
UGC New Delhi respectively for Junior Research Fel-
lowships. Authors acknowledge the financial support from
EU-DST project entitled “Efficient Solar Cells based on
Organic and hybrid Technology (ESCORT)”.
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Received: 3 November 2011. Accepted: 17 February 2012.
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