Artificial zinc chlorin dyes for dye sensitized solar cell

Article abstract of DOI:10.1016/j.ica.2015.09.027

Novel artificial zinc chlorin dyes comprising amine anchoring groups zinc aminochlorin (ZnChl-NH₂), zinc monomethylaminochlorin (ZnChl-NHMe) and zinc dimethylaminochlorin (ZnChl-NMe₂) are synthesized and their photovoltaic performances are evaluated in dye-sensitized solar cells. To the best of our knowledge, -NH₂ functionalized Zn chlorin dyes are tested in dye-sensitized solar cells for the first time. Best efficiency is obtained with ZnChl-NHMe sensitizer with a 2.67 mA/cm² short circuit photocurrent density, 414 mV of open circuit voltage, 0.64 of filling factor, and 0.68 of overall light to power conversion efficiency.

Full text of DOI:10.1016/j.ica.2015.09.027

Accepted Manuscript
Artificial Zinc Chlorin Dyes for Dye Sensitized Solar Cell
Kasim Ocakoglu, Sule Erten-Ela, K. Saleem Joya, Ersan Harputlu
PII:
S0020-1693(15)00477-6
http://dx.doi.org/10.1016/j.ica.2015.09.027
ICA 16702
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
26 January 2015
9 July 2015
22 September 2015
Please cite this article as: K. Ocakoglu, S. Erten-Ela, K. Saleem Joya, E. Harputlu, Artificial Zinc Chlorin Dyes for
Dye Sensitized Solar Cell, Inorganica Chimica Acta (2015), doi: http://dx.doi.org/10.1016/j.ica.2015.09.027
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Artificial Zinc Chlorin Dyes for Dye Sensitized Solar Cell
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a*
b*
c
a
Kasim OCAKOGLU , Sule ERTEN-ELA , K. Saleem JOYA , Ersan HARPUTLU
a
Advanced Technology Research & Application Center, Mersin University, Ciftlikkoy
Campus, TR-33343 Yenisehir, Mersin, Turkey.
b
Solar Energy Institute, Ege University, Bornova, 35100 Izmir, Turkey.
c
Leiden Institute of Chemistry, Leiden University, Einsteinweg, Leiden, The Netherlands
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Abstract
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Novel artificial zinc chlorin dyes comprising amine anchoring groups zinc aminochlorin
(ZnChl-NH
(ZnChl-NMe
sensitized solar cells. To the best of our knowledge, -NH
2
), zinc monomethylaminochlorin (ZnChl-NHMe) and zinc dimethylaminochlorin
) are synthesized and their photovoltaic performances are evaluated in dye-
functionalized Zn chlorin dyes are
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tested in dye-sensitized solar cells for the first time. Best efficiency is obtained with ZnChl-
2
NHMe sensitizer with a 2.67 mA/cm short circuit photocurrent density, 414 mV of open
circuit voltage, 0.64 of filling factor, and 0.68 of overall light to power conversion efficiency.
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Keywords: Zinc chlorin dyes, Dye sensitized solar cell, TiO nanoparticles
Corresponding authors e-mail: kasimocakoglu@gmail.com, kasim.ocakoglu@mersin.edu.tr,
Tel.: +90 3243610001 / 4961; Fax: +90 3243610153 (K. Ocakoglu), suleerten@yahoo.com,
sule.erten@ege.edu.tr, Tel.: +90 2323111231, Fax: +90 2323886027 (S. Erten-Ela).
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1. Introduction
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Capturing light energy and transforming it efficiently into electricity in a solar cell device
offers an attractive solution to the future energy quests [1-3]. Semiconductor based
photovoltaics (PV) provide an attractive solution for solar energy conversion systems [4-5].
However there is a growing room for new technologies due to the increasing demand and
competitive market for solar cells [6, 7]. In this pursuit, dye sensitized solar cells are
successful alternatives providing a cheaper mean than traditional semiconductor based PV
system [8,9]. During the developmental journey and technical modification of the DSSC’s,
various dye modules have been implemented, but the satisfactory results obtained only
ruthenium polypyridyl complexes [10-15]. However, ruthenium dyes are expensive and their
preparations include lengthy purification steps. In order to bypass the limitations imposed,
scientific attention has turned to go for cheaper and easy accessible light-harvesting (LH)
molecules [16-19]. In nature, plants have developed outstanding light-harvesting systems that
use supramolecular chlorophyll (Chl) aggregates for efficient energy conversion [20]. Natural
chlorophylls are derived from bacteriochlorin (BChl) units modified with long hydrophobic
side-chains [21]. The synthetic modules of the natural chlorins may offer a good building
platform to develop efficient solar cell materials sensitized with biomimetic chlorin dyes [22,
23].
Inspired by natural light-harvesting system, many people are looking for using Chl units and
their bio-inspired modifications for deployment in DSSC. Recently, many synthetic porphyrin
based dyes have been tested on TiO layer to make dye sensitized solar cell [24, 26]. Using
2
the natural concept, we started getting interest in using BChl based biomimetic dyes to make
DSSC. Here we report DSSC studies of synthetically modified zinc chlorin (ZnChl) dyes to
make a cheaper assembly for light conversion into electricity. As natural Chl or BChl are not
stable structures owing to Mg center, thus we have prepared the semi-synthetic analogues
with zinc coordinating to tetrapyrrole type rings. Moreover, the synthetically prepared ZnChls
are also modified with amino group for the attachment onto TiO
2
matrices. For the light-
harvesting chromophores, we prepared three model compounds of ZnChls, zinc aminochlorin
(ZnChl-NH
2
), zinc monomethylaminochlorin (ZnChl-NHMe) and zinc dimethylaminochlorin
1
(ZnChl-NMe
2
), in which the group in 3 -position has been substituted by an amino functional
group to make appropriate and efficient dyes for DSSCs (Fig. 1)
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2. Experimental Section
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2.1. Materials and Methods
Absorption spectra were recorded in a 1 cm path length quartz cell on a Shimadzu UV-2102
1
UV-Vis spectrophotometer. H NMR spectra performed on Bruker 400 MHz spectrometer
using residual solvent peaks as internal standards. Mass analysis was performed in Waters
LCT Premier (ESI or APCI mode) or Waters GCT (EI and CI ionization modes). All
preparations and measurements were performed in reduced light conditions.
Anhydrous solvents were either distilled from appropriate drying agents or purchased from
Merck and degassed prior to use by purging with dry argon and kept over molecular sieves.
All chemicals were purchased from commercial sources, and used as received. 2, 4, 6-
trimethylpyridine (collidine) were purchased from Fluka. Molecular sieves 4 Å activated
powder, triethylamine (99%) and OsO
4
were purchased from Aldrich. NaIO
4
(99%),
methylamine hydrochloride (99%), NaBH
3
CN (95%) and zinc acetate dehydrate (98%) were
purchased from Acros. Dye sensitized solar cells were characterized by current-voltage (J−V)
measurement. All current-voltage (J−V) measurements were done under AM 1.5 conditions.
450 W Xenon light source (Oriel) was used to give an irradiance of various intensities. J−V
data collection was made by using Keithley 2400 Source-Meter and LabView data acquisition
software.
2.2 Synthesis of Zinc Aminochlorin Derivatives
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Zinc aminochlorins were prepared from natural Chl a, which was isolated from Spirulina
Maxima algae, according to known literature procedures [31]. Further details of the
procedures and related experimental conditions for the preparation of ZnChl-NH
NHMe and ZnChl-NMe are described in Supporting Information (Scheme S1).
2
, ZnChl-
2
2.2.1 Synthesis Procedures
The synthesis of zinc aminochlorin (ZnChl-NH ), zinc methylaminochlorin (ZnChl-NHMe)
2
and zinc dimethylaminochlorin (ZnChl-NMe ) are described below.
2
2
2.2.2 Methyl 13 -demethoxycarbonylpheophorbide a (Pheo a) (3)
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Pheo a was prepared from Chl a, which was isolated from Spirulina Maxima algae, according
to known literature procedures 39, 40]. The obtained product was characterized by NMR,
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UV/Vis and mass spectroscopy [26]. UV (CH
2
C1 ) λmax: (Wavelengths and relative
2
intensities), 666 nm (0.36), 610 nm (0.06), 538 nm (0.063), 508 nm (0.07), 412 nm (0.79),
1
3
H NMR (400 MHz, CDCI ) δ ppm: 9.57 (s, 1H, CH-5), 9.45 (s, 1H, CH-10), 8.64 (s, 1H,
1
2
CH-20), 7.99 (q, 1H, J= 6.4 Hz, 3 ), 6.25, 6.19 (q, 1H + 1H, J= 16.8 Hz, 3 ), 5.25, 5.14 (d, 1H
2
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00 + 1H, J= 20 Hz, 13 -CH
2
), 4.51 (dq, 1H, J= 2 Hz, CH-18), 4.32 (dt, 1H, J= 8.4 Hz, CH-17),
1
1
1
01 3.67 (s, 3H, COOCH
02 CH ), 3.23 (s, 3H, CH
03 Hz, CH
3
), 3.61 (s, 3H, CH
3
-12 ), 3.55 (q, 2H, J= 8 Hz, CH
-7 ), 2.58-2.55, 2.34-2.27 (m, 2H + 2H, 17-CH CH
3
-18 ), 1.67 (t, J= 7.6 Hz, CH -8 ), -0.37, -2.07 (br,1H + 1H, NH). MS (ESI): m/z
2
-8 ), 3.41 (s, 3H, 2 -
1
3
3
2
2
), 1.83 (d, J= 7.2
1
2
3
+
04 calcd for C34
H
36
N
4
O [M+H] : 548.
3
05
2
06 2.2.3 Methyl 3-devinyl-3-formyl-13 -demethoxycarbonylpheophorbide a (Methyl
07 pyropheophorbide d) (4)
08 Methyl pyropheophorbide d was prepared according to the reported procedures [41, 42]. The
09 final product was obtained by colum chromatography on silica gel (15% acetone-CCl
4
) [26].
o
10 m.p. 174-176 C. UV (CH
2
C1 ) λmax: 695 (0.52), 634 (0.052), 551 (0.092), 519 (0.077), 425
2
1
11 (0.638), 386 (0.567). H NMR (400 MHz, CDCI
3
) δ ppm: 11.51 (s, 1H, CHO), 10.30 (s, 1H,
2
12 CH-5), 9.63 (s, 1H, CH-10), 8.89 (s, 1H, CH-20), 5.36, 5.16 (d, 1H + 1H, J= 20 Hz, 13 -CH
2
),
2
13 4.59 (dq, 1H, J= 2 Hz, CH-18), 4.40 (dt, 1H, J= 8.4 Hz, CH-17), 3.72 (q, 2H,J= 8 Hz, CH -
1
1
1
1
14 8 ), 3.75 (s, 3H, CH
3
-2 ), 3.69 (s, 3H, CH
3
-12 ), 3.62 (s, 3H, COOCH
3
), 3.29 (s, 3H, CH -7 ),
3
15 2.78-2.70, 2.62-2.56, 2.36-2.26 (m, 1H + 1H + 2H, 17-CH
2
CH ), 1.86 (d, J= 7.2 Hz, CH -
2
3
1
2
16 18 ), 1.69 (t, J= 7.6 Hz, CH
3
-8 ), -0.37, -2.07 (br,1H + 1H, NH). MS (EI): m/z calcd for
+
17
18
C
33
H
34
N
4
O
4
[M+H] : 551.
2
19 2.2.4 Methyl 3-devinyl-3-(methylamino)methyl-13 -demethoxycarbonylpheophorbide a
20 (5) (Chl-NHMe)
21 Metal-free aminochlorin was prepared according to the reported procedures [37]. Final
22 product was obtained with recrystallization from dichloromethane-hexane. m.p. 231-233 °C.
1
23 UV (CH
2
C1
2
) λmax: 659 (0.63), 603 (0.087), 535 (0.092), 504 (0.1), 408 (1.39); H NMR (400
24 MHz, CDCI
3
) δ ppm: 9.36 (s, 1H, 10-H), 9.17 (s, 1H, 5-H), 8.56 (s, 1H, 20-H), 5.17, 4.99 (d,
2
25 1H + 1H, J= 20 Hz, 13 -CH
2
), 4.72 (s, 2H, 3-CH2), 4.44 (dq, 1H, J= 1.6 Hz, 18-H), 4.24 (dt,
), 3.59 (s, 3H, 12-CH ), 3.48 (s, 3H,
26 1H, J= 9.2 Hz, 17-H), 3.61 (q, 2H, J= 8 Hz, 8-CH
2
3
27 COOCH ), 3.3 (s, 3H, 2-CH ), 3.2 (s, 3H, 7-CH ), 2.72 (s, 3H, NHCH
3
3
3
3
), 2.60-2.47, 2.24-2.10
4

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28 (m, 2H + 2H, 17-CH
2
CH
2
), 1.78 (d, 3H, J= 7.2 Hz, 18-CH
3
), 1.63 (t, 3H, J= 7.6 Hz, 8-
+
29 CH
2
CH
3
), -0.09, -2.04 (br,1H + 1H, NH). MS (ESI): m/z calcd for C34
H
39
N
5
O
3
[M+H] : 565.
30
2
31 2.2.5 Methyl 3-devinyl-3-(methylamino)methyl-13 -demethoxycarbonylpheophorbide-a
32 zinc complex (6) (ZnChl-NHMe)
33 Standard zinc-metallation of chlorins was carried out according to the reported procedures [
34 28, 40]. Final zinc complex was obtained with the separation on iChroprep RP-18 (25-40 µm)
1
35 column (methanol/water/pyridine, 80:15:5, as an eluent) (75% yield). H NMR (400 MHz,
36 CDCI
37 4.99 (d, 1H + 1H, J= 20 Hz, 13 -CH
38 4.11 (dt, 1H, J= 8 Hz, 17-H), 3.67 (q, 2H, J= 8 Hz, 8-CH
39 COOCH ), 3.16 (s, 3H, 7-CH ), 3.15 (s, 3H, 2-CH ), 2.46 (br, 3H, NHCH
40 2.26, 2.22-2.13, 1.93-1.89 (m, 1H + 1H + 1H + 1H, 17-CH
3 5 5
+ 1%C D N) δ ppm: 9.48 (s, 1H, 10-H), 8.43 (s, 1H, 5-H), 8.22 (s, 1H, 20-H), 5.12,
2
1
2
), 4.58 (br, 2H, 3 -CH
), 3.60 (s, 3H, 12-CH
), 2.52-2.48, 2.35-
2
), 4.32 (dq, 1H, J= 2,7 Hz, 18-H),
2
3
), 3.48 (s, 3H,
3
3
3
3
2
CH
2
), 1.64 (d, 3H, J= 7 Hz, 18-
+
41 CH
3
), 1.61 (t, 3H, J= 7.6 Hz, 8-CH
2
CH
3
). MS (ESI): m/z calcd for C34
H
37
N
5
O
3
Zn [M+H] :
42 629.
2
43 2.2.6 Methyl 3-devinyl-3-aminomethyl-13 -demethoxycarbonylpheophorbide-a zinc
44 complex (6) (ZnChl-NH
2
)
1
45
3 5 5
H NMR (400 MHz, CDCI + 1%C D N) δ ppm: 9.45 (s, 1H, 10-H), 8.48 (s, 1H, 5-H), 8.32
2
1
46 (s, 1H, 20-H), 5.14, 5.01 (d, 1H + 1H, J= 20 Hz, 13 -CH
47 1H, J= 2,7 Hz, 18-H), 4.15 (dt, 1H, J= 8 Hz, 17-H), 3.71 (q, 2H, J= 8 Hz, 8-CH
48 12-CH ), 3.51 (s, 3H, COOCH ), 3.20 (s, 3H, 7-CH ), 3.16 (s, 3H, 2-CH
49 2.28, 2.23-2.14, 1.94-1.89 (m, 1H + 1H + 1H + 1H, 17-CH
2
), 4.81 (br, 2H, 3 -CH
2
), 4.34 (dq,
2
), 3.61 (s, 3H,
3
3
3
3
), 2.54-2.49, 2.37-
2
CH
2
), 1.66 (d, 3H, J= 7 Hz, 18-
+
50 CH
3
), 1.62 (t, 3H, J= 7.6 Hz, 8-CH
2
CH
3
). MS (ESI): m/z calcd for C33
H
35
N
5
O
3
Zn [M+H] :
51 616.
2
52 2.2.7 Methyl 3-devinyl-3-(dimethylamino)methyl-13 -demethoxycarbonylpheophorbide-
53 a zinc complex (6) (ZnChl-NMe
2
)
1
54
3 5 5
H NMR (400 MHz, CDCI + 1%C D N) δ ppm: 9.37 (s, 1H, 10-H), 8.42 (s, 1H, 5-H), 8.20
2
1
55 (s, 1H, 20-H), 5.10, 4.96 (d, 1H + 1H, J= 20 Hz, 13 -CH
56 1H, J= 2,7 Hz, 18-H), 4.06 (dt, 1H, J= 8 Hz, 17-H), 3.63 (q, 2H, J= 8 Hz, 8-CH
57 12-CH ), 3.45 (s, 3H, COOCH ), 3.15 (s, 3H, 7-CH ), 3.13 (s, 3H, 2-CH
58 NH(CH ), 2.50-2.46, 2.32-2.24, 2.20-2.11, 1.91-1.86 (m, 1H + 1H + 1H + 1H, 17-CH
59 1.63 (d, 3H, J= 7 Hz, 18-CH
2
), 4.48 (br, 2H, 3 -CH
2
), 4.29 (dq,
2
), 3.57 (s, 3H,
3
3
3
3
), 2.35 (br, 3H,
CH ),
3
)
2
2
2
3
), 1.58 (t, 3H, J= 7.6 Hz, 8-CH
2
CH
3
). MS (ESI): m/z calcd for
+
60
35 39 5 3
C H N O Zn [M+H] : 644.
5

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61 2.3 Fabrication of Dye Sensitized Solar Cell
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62 FTO glass (TEC-15, 2.2 mm thickness, Solaronix) is used for the transparent conducting
63 electrodes. The glass substrates are first cleaned in the ultrasonic bath using helmanex
64 detergent solution, then water, acetone and ethanol (each step is 20 min. long). We have used
2
65 10 (transparent) + 4 (scattering) µm TiO layers in this study. This term is added to
66 experimental part. The TiO
2
coated FTO glasses are immersed into the 0.5 mM dye solutions
2
67 of chlorins. Active area is 0.16 cm . Counter electrodes are prepared by coating with a drop of
68
H
2
PtCl
6
solution. The TiO sensitized photoanode and Pt counter electrodes are assembled
2
69 into a sealed sandwich-type cell by a hot-melt ionomer film (Surlyn). Then electrolyte
70 solution is injected and the hole sealed by using surlyn patch and a cover glass. Electrolyte
71 consists of 0.6 M N-methyl-N-butyl imidazolium iodide (BMII), 0.1 M LiI, 0.05 M I
2
, 0.5 M
72 4-tert-butyl pyridine (TBP) in acetonitrile.
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74 3. Results and Discussion
75
Cyclic tetrapyrroles, such as porphyrins, bacteriochlorins, and phthalocyanines are an
76 important group of organic molecules possessing distinguished photophysical and
77 photochemical properties [20-25, 29]. Among them, porphyrins and bacteriochlorins possess
78 some intrinsic properties in photosynthesis including light-harvesting and energy- and
79 electron-transferring processes [29, 32, 33]. Semi-synthetic zinc chlorins (ZnChls) that are
80 preprogrammed for self-assembly can easily mimic the intriguing architectural principle of
81 the supramolecular organization of dyes in chlorosomes [27, 29, 33, 34]. According to this
82 model, ZnChl molecules are able to self-organize into rod-shaped supramolecular structures
83 driven by three non-covalent interactions without requiring proteins for structural control;
1
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84 coordination of the 3 -oxygen unit to the central atom, hydrogen bonding between the 3 -
85 alcohol to the 13-keto group and π-π stacking between the extended chlorin chromophores
86 yielding a strongly red-shifted J-type absorption band and extremely large exciton diffusion
87 lengths covering up to 200 monomers at room temperature [29, 35]. These supramolecular
88 arrays can function either as energy conductors (exciton transport) or as charge conductors
89 [32-34]. These highly unusual exciton and optical properties, unprecedented by any other
90 organic material known so far, let us expect novel, interesting electronic materials properties.
91 The most significant structural difference of ZnChls used in this work from other well-known
1
92 zinc chlorins is the presence of amino functional groups in 3 -position instead of hydroxyl
93 group (Figure 1). Furthermore, these compounds would form as highly robust, single stack
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94 rod structures under appropriate conditions (such as in non-polar solvents) probably due to the
95 fact that amino ligands coordinate to the central metal more strongly than oxygen ligands [26,
96 27]. Using such compounds we aim to make DSSC because of the fact that ZnChls can easily
97 bind to TiO
2
2
2
surface via its amino groups. Attachment of ZnChl-NMe to the TiO surface
98 will be a significant problem due to the steric hindrance in the presence of the methyl groups
99 attached to nitrogen, and this could be the biggest reason for low cell efficiency compared
00 with those of ZnChl-NH
01 aggregation features, which limits the injection from dyes to the TiO
02 semi-synthetic zinc chlorins used in this study. This could be responsible for lower efficiency
03 of ZnChl-NH compared with those of methyl amino derivative (ZnChl-NHMe). The high
04 efficiency of ZnChl-NHMe could be explained by the fact that the lower self-aggregation
05 features when compared to the ZnChl-NH , as well as the high attachment capacity on the
06 TiO surface.
07 Three Zinc chlorine dyes are designed for use in dye sensitized solar cells, coded ZnChl-NH
08 ZnChl-NHMe, ZnChl-NMe , with chemical structures depicted in Fig 1. All three dyes show
2
and ZnChl-NHMe. Furthermore, ZnChl-NH
2
exhibit a higher self-
2
, compared to other two
2
2
2
2
,
2
09 panchromatic absorption bands in Fig. 2. The incident photon to current conversion efficiency
10 of zinc chlorins is shown in Fig. 4. The IPCE for Zinc Chlorin dye, ZnChl-NHMe reached a
11 maxima of 7.5% at 425 nm. These results show that the ZnChl-NHMe sensitized cell revealed
12 a maximum IPCE value, extending the response of photocurrent generation to 700 nm.
13 Photovoltaic performances of dye sensitized solar cells based on Zinc Chlorins are shown and
14 summarized in Fig. 4 and Table 3. Table 3 also shows the adsorbed dye amounts on TiO
2
15 layer. Under the AM 1.5 conditions, ZnChl-NHMe sensitizer gave the best results with the
2
16 overall conversion efficiency of 0.68% (η), short-circuit photocurrent of 2.67 mA/cm (Jsc),
17 open circuit photovoltage of 414 mV (Voc), fill factor of 0.64 (FF). Photovoltaic performances
18 are determined in the order of ZnChl-NHMe > ZnChl-NH
19 Lower photovoltaic performance was obtained with ZnChl-NMe2 dye. This results could be
20 explained by the steric hindrance of -CH group in the molecular structure of ZnChl-NMe . It
21 is found that ZnChl-NHMe gives high efficiency in these classes of dye sensitizers. The UV-
22 Vis spectra of the three of NH functionalized ZnChl dyes, ZnChl-NH , ZnChl-NHMe and
23 ZnChl-NMe , are shown in Fig. 2. All three ZnChl derivatives are soluble in CH Cl and THF
2
> ZnChl-NMe
2
from I-V curves.
3
2
2
2
2
2
2
24 but the UV-Vis spectra are preferred in the later. The most common Soret band in chlorin and
25 porphyrin type compounds that originate from the electron dipole movement that allows π-π*
26 transition was observed at 428 nm for all three ZnChl derivatives. The Q bands for the three
y
27 compounds are observed in the spectral region from 650 to 659 nm (Table 1). A slight blue
7

2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
28 shift is observed in all three cases that might be due to the presence of the -NH
2
, -NHMe and -
29 NMe groups which cause to the different self-aggregation features [26]. These UV-Vis
2
30 images are characteristics for the presence of chlorins and derivative in the solution in
31 monomeric form which is essential to develop the dye-solar cell [36, 38] .
-3
32
The electrochemical study of the three synthetic amino-functionalized ZnChl dyes (1x10
33 M) is conducted on a platinum working electrode (WE) electrode in dichloromethane system
34 in the presence of 0.1 M tetrabutyl ammonium hexafluorophosphate TBA(PF ). Figure 3
35 shows the cyclic voltammetry (CV) curves for the ZnChl-NH , ZnChl-NHMe and ZnChl-
36 NMe in the presence of ferrocene as internal standard. All CV’s show the oxidative currents
6
2
2
37 from 0.65 V to 0.85 V (with reference to the ferrocene as internal standard). The
38 corresponding reduction waves are also observed at 0.75 V to 0.58 V. These redox waves
39 with at E1/2 ~ 0.70 V (vs. Ag/AgCl) are due to the ferrocenium/ferrocene redox couple. For
40 ZnChl-NH , an oxidation wave appears in the potential region from 1.05 V to 1.30 V in the
2
41 present potential scale. This is attributed to the oxidation of the corresponding dye molecules
42 in the solution (Fig. 3). During the reverse sweep, this current wave is followed by a reduction
43 wave from 1.30 V to 0.09 V. The E1/2 for the ZnChl-NH
44 Similarly, the electrochemical data for the zinc amino chlorins with mono- and di- substituted
45 methyl groups; ZnChl-NHMe and ZnChl-NMe , under similar condition show the redox
2
sample is observed about 1.07 V.
2
46 behavior in the potential window from 0.09 V to 1.30 V. In case on mono-methyl the zinc
47 amino chlorins derivative, the oxidative peak currents appear prior to that of the dimethyl
48 complex (Fig. 3). The oxidation currents for the simple ZnChl-NH
2
and ZnChl-NMe , under
2
49 same set-up are very much similar indicating no net effect on the dye. It is also observed that
50 these oxidative currents for the three compounds are followed by the corresponding reduction
51 responses with current peaks at about 1.00 V for ZnChl-NMe
2
, whereas it is around 110 mV
52 for ZnChl-NH and ZnChl-NHMe.
2
53 The CV’s for three zinc amino chlorins compounds are extended until 1.75 V in order to get
54 reduction insights of these samples. Reduction peaks appear to be very similar of these three
55 complexes. Electrochemical data were collected in CH
2
Cl . Potentials are quoted with
2
56 reference to the internal ferrocene standard. The electrochemical data for zinc amino chlorine
57 complexes are compiled in Table 2. Cyclic voltammogram (Fig. 3) of chlorin dyes shows both
58 reversible oxidation and reduction peaks (Table 2). The lowest unoccupied molecular
59 (LUMO) energy of ZnChl-NHMe, ZnChl-NH
60 eV, respectively. LUMO energies of dyes are clearly higher than the conduction band of TiO
61 (~ 4.2 eV), which suggests an efficient electron transfer from chlorin to TiO electrode.
2
, ZnChl-NMe
2
are 3.07 eV, 3.05 eV and 3.08
2
2
8

2
2
2
62 HOMO energy levels of ZnChl-NHMe, ZnChl-NH
2
, ZnChl-NMe are 5.01 eV, 4.99 eV, 4.99
2
63 eV.
64
2
2
2
65 4. Conclusion
66
67 The dye sensitized solar cells based on ZnChl-NHMe exhibits the power conversion
1
2
2
2
2
2
68 efficiency of 0.68%. This result is promising and shows that the addition of vinyl units at 3 -
69 position which provide a more effective electronic conjugation could give rise to the higher
70 power conversion efficiency. Considering the fact that chlorin dyes show an impressive
71 performance, these class of sensitizers are very promising candidates in dye sensitized solar
72 cells.
2
2
73
74 Acknowledgements
2
2
2
2
2
2
2
75 This research has been financially supported by The Scientific and Technological Research
76 Council of Turkey, TUBITAK (Grant: 110M803) in the framework of European Science
77 Foundation (ESF-EUROCORES-EuroSolarFuels-10-FP-006), and we thank to Alexander von
78 Humboldt Foundation and (TUBA) Turkish Academy of Sciences.
79
80
81 References
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2
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92
93
94
3
3
3
95
96
97
1
2

3
3
4
98 Figure Captions
99
00 Figure 1. Chemical structures of zinc aminochlorin derivatives; zinc aminochlorin (ZnChl-
4
4
4
4
4
4
01 NH
02 NMe
03 Figure 2. UV-Vis Absorption spectra for zinc chlorin amino- derivatives ZnChl-NH
2
), zinc methylaminochlorin (ZnChl-NHMe) and zinc dimethylaminochlorin (ZnChl-
2
).
2
, ZnChl-
-5
04 NHMe and ZnChl-NMe , obtained in THF (c: 1.5x10 M).
2
05 Figure 3. Cyclic voltammogram of zinc amino-chlorin derivatives.
06 Figure 4. J-V and IPCE spectrum of Dye Sensitized Solar Cells
4
4
4
4
4
4
07
08
09 Table Captions
10
11
12 Table 1. UV-Vis Absorption spectral data for zinc chlorin amino-derivatives ZnChl-NH
2
,
-5
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
13 ZnChl-NHMe and ZnChl-NMe , measured in THF (c: 1.5x10 M).
2
14 Table 2. Electrochemical Properties of the Zinc Chlorin Sensitizers.
15 Table 3. DSSC Performances of Chlorin Dyes.
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
1
3

4
4
4
4
4
4
34
35
36
37
38
39
CH
3
CH3
N
NH2
1
NH
CH
3
3
CH
3
1
1
3
3
CH
3
CH3
CH3
CH
3
CH3
CH
3
CH
3
CH3
N
N
N
N
N
N
Zn
Zn
Zn
N
N
N
N
N
N
CH
3
CH3
CH3
CH
3
CH
3
CH
3
1
1
1
1
3
13
13
O
O
O
ZnChl-NHMe
ZnChl-NMe2
ZnChl-NH2
O
O
O
O
O
CH
3
CH
3
O
CH
3
4
4
4
40
41 Figure 1. Chemical structures of zinc aminochlorin derivatives; zinc aminochlorin (ZnChl-
42 NH ), zinc methylaminochlorin (ZnChl-NHMe) and zinc dimethylaminochlorin (ZnChl-
2
4
4
4
4
4
4
4
4
4
4
4
4
4
4
43 NMe
44
2
).
45
46
47
48
49
50
51
52
53
54
55
56
1
4

4
4
4
4
4
57
58
59
60
61
4
62
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
63 Figure 2. UV-Vis Absorption spectra for zinc chlorin amino- derivatives ZnChl-NH , ZnChl-
2
-5
64 NHMe and ZnChl-NMe , obtained in THF (c: 1.5x10 M).
2
65
66
67
68
69
70
71
72
73
74
75
76
77
1
5

4
4
4
4
4
4
4
4
78
79
80
81
82
83
84
85
1
0
0
.0
.5
.0
ZnChl-NH2
ZnChl-NHMe
ZnChl-NMe2
-
-
0.5
1.0
-
2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Potential / V
4
4
86
87 Figure 3. Cyclic voltammogram of zinc amino-chlorin derivatives.
4
4
4
88
89
90
4
4
4
4
4
4
91
92
93
94
95
96
1
6

4
97
-
-
-
3
2
1
0
1
2
3
ZnChl-NHMe under illumination
ZnChl-NHMe in dark
ZnChl-NH under illumination
2
ZnChl-NH in dark
2
ZnChl-NMe under illumination
2
ZnChl-NMe in dark
2
0
,0
0,1
0,2
0,3
0,4
0,5
Voltage (V)
4
98
3
2
2
1
1
0
5
0
5
0
5
0
ZnChl-NH2
ZnChl-NHMe
ZnChl-NMe2
3
00
350
400
450
500
550
600
650
700
W avelength (nm )
4
5
99
00
Figure 4. J-V and IPCE spectrum of Dye Sensitized Solar Cells.
5
5
5
5
5
5
5
5
5
5
5
5
5
01
02
03
04
05
06
07
08
09
10
11
12
13
1
7

5
14
5
5
5
5
15
16
17
18
5
5
19 Table 1. UV-Vis Absorption spectral data for zinc chlorin amino-derivatives ZnChl-NH
2
,
-5
20 ZnChl-NHMe and ZnChl-NMe , measured in THF (c: 1.5x10 M).
2
+4
1
-1
Dye
λmax (nm) (ε/10 M .cm )
ZnChl-NMe
2
655 (8.53), 609 (1.72), 576 (0.92), 529 (0.32), 426 (10.8), 409 (8.7)
656 (7.35), 610 (1.49), 576 (0.80), 529 (0.36), 427 (10.1), 409 (7.83)
657 (5.75), 612 (1.13), 569 (0.46), 523 (0.30), 428 (9.45), 412 (8.35)
ZnChl-NHMe
ZnChl-NH
2
5
5
5
5
5
5
5
21
22
23
24
25
26 Table 2. Electrochemical Properties of the Zinc Chlorin Sensitizers.
27
E
red
Dye
E
ox (V)
E
fer
HOMO (eV)
LUMO (eV)
(V)
ZnChl-NHMe
0.75
0.70
0.72
0.50
0.50
0.50
-1.190
-1.240
-1.190
5.01
4.99
4.99
3.07
3.05
3.08
ZnChl-NH
ZnChl-NMe
2
2
5
5
5
5
5
5
28
29
30
31
a
32 Table 3. DSSC Performances of Chlorin Dyes.
33
-
Dye
Voc (mV)
Jsc (mA cm
ff
η(%)
Adsorbed dye
-7
(
x10
2
mol/cm )
ZnChl-NHMe
414
417
350
2.67
2.42
0.82
0.64
0.62
0.52
0.68
0.59
0.15
3.2
2.9
1.6
ZnChl-NH
ZnChl-NMe
2
2
a
5
5
34
35
V
oc is the open-circuit potential, Jsc, short curcuit current, ff is the fill factor, and η is the overall efficiency of the cell under standard
conditions.
5
5
5
5
36
37
38
39
5
5
5
5
5
40
41
42
43
44
1
8

5
5
5
5
45 Highlights
46 • Novel artificial zinc chlorin dyes have been synthesized
47 • Bio-inspired dyes have been characterized
48 • DSSC performances were evaluated.
5
5
5
5
49
50
51
52
1
9