CL-150486
Received: May 19, 2015 | Accepted: July 14, 2015 | Web Released: July 25, 2015
High IPCE Performance of Photosensitized Dyes Having Trifluoromethylacrylic Acid
as an Acceptor-anchor Moiety
Satoru Iwata,* Shouta Oshio, Shintaro Kobayashi, Misa Aoyama, and Kiyoshi Tanaka*
Laboratory of Molecular Control, Faculty of Science and Technology, Seikei University, Musashino, Tokyo 180-8633
(
E-mail: iwata@st.seikei.ac.jp, tanaka@st.seikei.ac.jp)
Novel photosensitized dyes having trifluoromethylacrylic
acid as an acceptor-anchor moiety (MCL2629) are synthesized.
These dyes seem to suppress the back-donation currents from the
a
OHC
Br
N
S
n
OHC
S
n
1
a (n=0) Commercially available
conduction band of TiO semiconductor to the electrolyte. Their
fabricated dye-sensitized solar cells (DSCs) show high IPCE
performances (MCL27; over 80% between 400520 nm, max
1b (n=1) 61%
2
1
c (n=2) 52%
CF3
b
HOOC
1a-c
N
n
S
9
0% at 465 nm). In particular, the high IPCE properties are
N
MCL26 (n=0) 64% (E:Z = 40:60)
MCL27 (n=1) 52% (E:Z = 51:49)
MCL28 (n=2) 36% (E:Z = 61:39)
compared with more than 80 article examples.
I
c
a
1a
OHC
N
X
N
Fundamental research of photosensitized dyes for dye-
sensitized solar cells (DSCs) has been widely achieved.
However, there are few reports of the development of dyes
I
2
87%
1
having particularly new chemical structure. For this reason,
N
complicated structure is necessary for photosensitized dyes, for
example, to absorb wide wavelengths of sunlight.
3
(X: -CHO) 93%
b
MCL29 (X: -CH=C(CF )COOH ) 54 % (E:Z = 40:60)
From a different viewpoint, even though the overall
photoelectronic conversion of DSC is low, it is still important
to develop simple structure dyes absorbing a limited wavelength,
because these dyes can be applied to cocktail and/or hybrid type
3
Scheme 1. Reagents and conditions: a) 4-Diphenylamino-
phenylboronic acid, [Pd(PPh3)4], NaOH/DME, under N2; b)
CF CH COOH, TiCl /THF, Et N, rt; c) KI, KIO /AcOH, H O.
2
DSCs. In our continuing research on fluorine-containing dyes,
3
2
4
3
3
2
we have reported trifluoromethylthiazolecarboxylic acid as a
new type of acceptor-anchor in dyes for DSCs, where the
trifluoromethyl group acts as a suppressor of electron back-
CN
N
HOOC
3
donation from TiO2 semiconductor to the electrolyte. Recently,
N
S
n
fluorine-containing dyes bearing trifluoromethylacrylic acid
were synthesized, and their effectiveness as a new anchor was
reported. In this communication, we wish to report the synthesis
L0 (n=0)
L1 (n=1)
D5L6 (n=2)
CN
4
HOOC
N
of novel triphenylaminethiophene dyes having trifluoromethyl-
acrylic acid acceptor and show the high IPCE performance of
the DSCs of these simple structure dyes, in comparison with
those of the corresponding cyanoacrylic acid dyes.
The trifluoromethylacrylic acid unit was introduced by the
titanium tetrachloride mediated Knoevenagel-type reaction of
R
R
3
F C
N
S
N
HOOC
T1
MCL05 (R=Ph)
MCL06 (R=Et)
N
3
,3,3-trifluoropropanoic acid (CF3CH2COOH) with triphenyl-
5
amine-containing aldehyde, as reported by Liu et al. The
synthetic procedures of the dyes are shown in Scheme 1 (The
experimental details are shown in Supporting Information (SI)).
According to previous reports, the geometry of the formed
isomer is expected to be Z-form for the trifluoromethylacrylic
acid part, but, in our cases, isomer ratios were nearly E:Z = 1:1.
The following experiments were carried out without further
separation of the isomers.
Chart 1.
The DFT calculated- and the experimentally measured
HOMOLUMO energy levels of the dyes are summarized in
Figure 2 (data of onset, E , E energy are shown in SI). It is
ox
0-0
noticed that, due to the effect of the thiophene π conjugation
unit, HOMO energy level is higher.
The DSCs were fabricated using screen-printed TiO2 (cell
2
Absorption spectra of the obtained dyes MCL2629
size 0.25 cm , average cell thickness: about 13 ¯m) on TCO
together with the reference dye, cyanoacrylic acid dye L1
glass. The photovoltaic performances of the DSCs were
measured using an AM1.5G solar simulator. The cell perform-
ance data are summarized in Table 1. The DSC of the most
simple dye MCL26 shows the photoelectronic conversion
efficiency © = 1.1%, and the DSCs of dyes having thiophene
π conjugation unit, MCL27 and MCL28, show the improve-
ment of the cell performances © = 2.9% and 2.8%, respectively.
6
(Chart 1), are shown in Figure 1. By the introduction of
thiophene π conjugation unit, max are red-shifted and molar
absorption coefficients are increased. Compared with the
cyanoacrylic acid dye L1, MCL27 is blue-shifted by about
45 nm. MCL29 has large absorbance between 300400 nm, due
to the introduction of a lot of phenyl groups into the donor part.
© 2015 The Chemical Society of Japan