C O M M U N I C A T I O N S
Table 1. Photophysical Studies of the HB-CPEs in MeOH and
Water
Table 2. Photovoltaic Studies of the HB-CPE Sensitized TiO2
Cellsa
λ
max [nm]
Voc
V
Jsc
absorption
λmax
emission
nm
quantum
yield %
æ
lifetime
structure
mA/cm2
FF
η
(%)
IPCE
(
ꢀ)
(τ)
ns
-
PSO3
0.42
0.42
0.43
0.48
2.7
4.1
2.1
3.2
0.51
0.36
0.35
0.36
0.57
0.62
0.33
0.55
37%
55%
38%
44%
1
HB-CPEs
M-1 cm-
PSO3-/PNMe3
+
+
PNMe3+ in MeOH 447, (2.4 × 104)
555
590
540
570
6.0
0.5
8
1.3 (91%);
15.8 (9%)
1.5 (89%);
13.9 (11%)
1.4 (92%);
15.7 (8%)
1.2 (89%);
11.0 (11%)
PNMe3
PNMe3+/ PSO3
-
PNMe3+ in H2O
PSO3- in MeOH
PSO3- in H2O
425, (1.9 × 104)
405, (2.1 × 104)
403, (1.5 × 104)
a IPCE @400 nm.
IPCE and overall efficiency compared to their respective mono-
layers owing to increased chromophore density causing more light
absorption in the bilayer as compared to either monolayer.
In conclusion, this study has led to the development of novel
anionic and cationically charged HB-CPEs which could be utilized
as polymer dyes coordinated to TiO2 and self-assembled into
bilayers for solar-cell applications. The details of hybrid film
structure using electron microscopy and atomic force microscopy
will be reported in the future. Although the performance in terms
of efficiency is lower compared to conventional cells, prospects
are high for rapid improvement. Thus, these polymers and their
self-assembly hold a viable promise for enhanced adhesion and
energy harvesting properties for future hybrid solar cells and further
investigation is underway.
0.4
Acknowledgment. The financial support for this work was
provided by the DOE/BES (Grant DE-FG02-03ER15484).
Supporting Information Available: Experimental, synthesis, and
characterization details of monomers and HB-CPEs polymers. This
References
Figure 1. (A) HB-CPE bilayer TiO2 solar cell configuration; (B-C) HB-
CPE sensitized TiO2 cells comparing monolayer and self-assembled bilayer
HB-CPEs showing (B) IPCE spectral responses and (C) J-V studies under
AM 1.5 conditions.
(1) (a) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem., Int. Ed.
Engl. 1998, 37, 402-428. (b) Yang, R.; Wu, H.; Cao, Y.; Bazan, G. C.
J. Am. Chem. Soc. 2006, 128 (45), 14422-14423.
(2) (a) Mwaura, J. K.; Zhao, X.; Jiang, H.; Schanze, K. S.; Reynolds, J. R.
Chem. Mater. 2006, 18 (26), 6109-6111. (b) Coakley, K. M.; McGehee,
M. D. Chem. Mater. 2004, 16, 4533-4542. (c) Yang, X.; Loos, J.
Macromolecules 2007, 40 (5), 1353-1362.
(3) (a) Decher, G.; Lvov, Y.; Schitt, J. Thin Solid Films 1994, 244, 772-
777. (b) Clark, A. P.-Z.; Cadby, A. J.; Shen, C. K-F.; Rubin, Y.; Tolbert,
H. J. Phys. Chem. B 2006, 110 (44), 22088-22096.
(4) (a) Tsukruk, V. V.; Rinderspacher, F.; Bliznyuk, V. N. Langmuir 1997,
13 (8), 2171-2176. (b) Tomalia, D. A.; Frechet, J. M. Prog. Polym. Sci.
2005, 30, 217-219.
(5) (a) Fomine, S.; Fomina, L.; Guadarrama, P. Macromol. Symp. 2006, 192
(1), 43-62. (b) Voit, B. J. Polym. Sci., Part A: Polym. Chem. 2005, 43,
2679-2699.
separation within a TiO2/HB-CPE regenerative photochemical cell
in which the HB-CPE operates as the light absorbing material.
Nanostructured TiO2 solar cells with adsorbed layers of HB-
CPEs were fabricated as monolayers and self-assembled bilayers
with the latter shown schematically (details in SI) in Figure 1A.
For clarity we have only shown the comparison of incident photon
to electron conversion efficiencies (IPCE) and current density-
-
voltage (J-V) characteristics of monolayer PSO3 and self-
+
assembled PSO3-/PNMe3 bilayer sensitized TiO2 cells in Figure
(6) (a) Tomalia, D. A.; Naylor, A. M.; Goddard, W. A. Angew. Chem. 1990,
29, 138-175. (b) Voit, B. I. Acta Polym. 1995, 46, 87. (c) Sun, M.; Bo,
Z. J. Poly. Sci., Part A: Polym. Chem. 2007, 45 (1), 111-124.
(7) (a) Yang, J. L.; He, Q. G.; Lin, H. Z.; Fan, J. J.; Bai, F. L. Macromol.
Rapid Commun. 2001, 22, 1152-1157. (b) Ramakrishna, G.; Ghosh, H.
N. J. Phys. Chem. A 2002, 106 (11), 2545-2553.
(8) (a) Choi, J.-Y.; Tan, L.-S.; Baek, J.-B. Macromolecules 2006, 39 (26),
9057-9063. (b) Tanaka, S.; Iso, T.; Sugiyama, J-I.; Takeuchi, K.; Ueda,
M. Synth. Met. 2005, 154, 125-128.
(9) (a) Choi, J.-Y.; Tan, L.-S.; Baek, J.-B. Macromolecules 2006, 39 (26),
9057-9063. (b) Baek, J.-B.; Tan, L. S. Macromolecules 2006, 39 (8),
2794-2803.
1B/C. It is immediately evident that the bilayer cell yields a higher
IPCE and Jsc than the monolayer cell.
This is confirmed in SI Figure S5 for IPCE and J-V for
+
-
monolayer PNMe3 and self-assembled bilayer PNMe3+/PSO3
,
where PNMe3+ is the first layer monolayer deposited on the TiO2.
Table 2 details a comparative analysis of both monolayers and
bilayers.
The cells with only a monolayer of either HB-CPE have nearly
identical IPCE values, however PSO3- results in a higher η due to
an enhanced FF and Jsc when compared to PNMe3+. This is likely
due to the sulfonate groups which can coordinate to TiO2 in a similar
manner to -COOH groups13 promoting forward interfacial electron
transfer and reducing the number of trap sites.11b The same argument
can be made when forming the bilayer PSO3-/PNMe3+ cell, where
(10) Jiang, H.; Zhao, X.; Schanze, K. S. Langmuir 2006, 22, 5541-5543.
(11) (a) Lenzmann, F.; Krueger, J.; Burnside, S.; Brooks, K.; Gratzel, M.; Gal,
D.; Ruhle, S.; Cahen, D. J. Phys. Chem. B 2001, 105, 6347-6352. (b)
Ramakrishna, G.; Ghosh, H. N. Langmuir 2003, 19 (3), 505-508.
(12) (a) Palomares, E.; Clifford, J. N.; Haque, S. A.; Lutz, T.; Durrant, J. R.
J. Am. Chem. Soc. 2003, 125 (2), 475-482. (b) Staniszewski, A.; Morris,
A. J.; Ito, T.; Meyer, G. J. J. Phys. Chem. B 2007, 111, 6822-6828.
(13) Krebs, F. C.; Spanggaard, H. Chem. Mater. 2005, 17 (21), 5235-5237.
-
+
PSO3 is the first layer as compared to the bilayer of PNMe3
/
PSO3-. Nevertheless, both bilayers show a superior response in
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