result for possible application of such molecular donor–
acceptor ensembles for photovoltaic devices. Further investi-
gation will be necessary to optimize the devices structure and
fully clarify the photophysical features.
We are grateful for financial support from the National
Science Foundation of China (grant numbers 20573040,
20474024, 90501001, 50303007), the Ministry of Science and
Technology of China (grant number 2002CB6134003), 111
project (B06009) and PCSIRT.
Notes and references
z Selected data of the compounds. 6: 1H NMR (500 MHz, DMSO-
D6):
d [ppm] 8.760 (s, 2H, ArH), 8.575–8.558 (d, 2H, ArH),
8.037–8.016 (d, 2H, ArH), 7.906–7.890 (d, 2H, ArH), 7.702–7.685
(d, 2H, ArH), 7.630 (d, 2H, ArH), 7.544–7.527 (d, 2H, ArH),
7.362–7.184 (m, 26H), 7.090–6.945 (m, 30H), 6.907–6.890 (d, 4H,
ArH); Elemental analysis: calculated: C102H76N6: C, 88.41; H, 5.53;
N, 6.06; found: C, 88.43; H, 5.91; N, 5.33; MALDI-TOF MS: m/z =
1386.0 ([M+H]+), calcd.: 1384.6.
Fig. 3 Current–voltage characteristics of devices under white light
illumination (100 mA cmꢂ2).
(Table 1). These values corresponded to a power conversion
efficiency (Ze) of 0.012%, which was a satisfied result for single
layer organic photovoltaic device compared with previous
reports.12 On the other hand, the device based on compound
6 was also been inspected. The Isc, Voc and FF were 0.038 mA
cmꢂ2, 0.65 V and 0.24, respectively. The value of Ze is 0.006%,
which was only half of that obtained from 7 based devices.
Obviously, both the Isc and Voc of the devices were highly
influenced by the Re ion chelation. These two factors, espe-
cially Isc increased significantly for the device based on com-
plex 7. In addition, the external quantum efficiency value of
the 7 based device is also nearly two times higher than that of
the 6 based device (Fig. S7z). These improvements after Re ion
chelation can be attributed to enhanced exiton dissociation
ability in complex 7 compared with compound 6. Meanwhile,
since the donor and acceptor components are covalently
linked in complex 7, the problem of phase separation in some
heterojunction devices could be avoided.13 In a further experi-
ment, the organic bulk heterojunction photovoltaic cells were
fabricated by using PCBM as the acceptor for a more efficient
charge collection with a device structure ITO/PEDOT/PCBM:
7 (or 6) (1 : 1 w/w)/LiF/Al. The power conversion efficiency of
the 7/PCBM based device is 0.8%, which is about 1.6 times of
that in the compound 6 based device (0.5%).
7: 1H NMR (500 MHz, DMSO-D6): d [ppm] 8.991–8.976 (d, 2H,
ArH), 8.976 (s, 2H, ArH), 8.512–8.495 (d, 2H, ArH), 7.969–7.953 (d,
2H, ArH), 7.798–7.783 (d, 2H, ArH), 7.741 (s, 2H, ArH), 7.560–7.544
(d, 2H, ArH), 7.456–7.440 (d, 2H, ArH), 7.398–7.227 (m, 22H),
7.097–6.969 (m, 30H), 6.871–6.855 (d, 4H, ArH); Elemental analysis:
calculated: C105H76Cl N6O3Re: C, 74.56; H, 4.53; N, 4.97; found: C,
73.76; H, 4.71; N, 4.11; MALDI-TOF MS: m/z = 1691.9 ([M+H]+),
calcd.: 1690.5.
1 (a) C. W. Tang, Appl. Phys. Lett., 1986, 48, 183; (b) G. Yu, J. Gao,
J. C. Hummelen, F. Wudl and A. J. Heeger, Science, 1995, 270,
1789; (c) S. E. Shaheen, C. J. Brabec, N. S. Sariciftci, F. Padinger,
T. Fromherz and J. C. Hummelen, Appl. Phys. Lett., 2001, 78, 841;
(d) M. Al-Ibrahim, H. K. Roth and S. Sensfuss, Appl. Phys. Lett.,
2004, 85, 1481; (e) J. Y. Kim, K. Lee, N. E. Coates, D. Moses, T.
Q. Nguyen, M. Dante and A. J. Heeger, Science, 2007, 317, 222.
2 P. Peumans, S. Uchida and S. R. Forrest, Nature, 2003, 425, 158.
3 N. S. Sariciftci, L. Smilowitz, A. J. Heeger and F. Wudl, Science,
1992, 258, 1474.
4 P. Peumans, A. Yakimov and S. R. Forrest, J. Appl. Phys., 2003,
93, 3693.
5 S. Kim, J. K. Lee, S. O. Kang, J. Ko, J. H. Yum, S. Fantacci, F. De
Angelis, D. Di Censo, M. K. Nazeeruddin and M. Gratzel, J. Am.
Chem. Soc., 2006, 128, 16701.
6 (a) F. He, G. Cheng, H. Q. Zhang, Y. Zheng, Z. Q. Xie, B. Yang,
Y. G. Ma, S. Y. Liu and J. C. Shen, Chem. Commun., 2003, 2206;
(b) F. He, H. Xu, B. Yang, Y. Duan, L. L. Tian, K. K. Huang, Y.
G. Ma, S. Y. Liu, S. H. Feng and J. C. Shen, Adv. Mater., 2005, 17,
2710; (c) F. He, L. L. Tian, X. Y. Tian, H. Xu, Y. H. Wang, W. J.
Xie, M. Hanif, J. L. Xia, F. Z. Shen, B. Yang, F. Li, Y. G. Ma, Y.
Q. Yang and J. C. Shen, Adv. Funct. Mater., 2007, 17, 1551; (d) A.
Zen, A. Bilge, F. Galbrecht, R. Alle, K. Meerholz, J. Grenzer, D.
Neher, U. Scherf and T. Farrell, J. Am. Chem. Soc., 2006, 128,
3914; (e) W. J. Oldham, R. J. Lachicotte and G. C. Bazan, J. Am.
Chem. Soc., 1998, 120, 2987; (f) J. N. Wilson, M. Josowicz, Y. Q.
Wang and U. H. F. Bunz, Chem. Commun., 2003, 24, 2962; (g) T.
P. I. Saragi, T. Spehr, A. Siebert, T. Fuhrmann-Lieker and J.
Salbeck, Chem. Rev., 2007, 107, 1011.
In conclusion, we report here the synthesis, characterization
and photovoltaic properties of the photoactive molecular
material bpy-DPA-TSB-Re bearing efficient charge separa-
tion, good film-forming ability and morphological stability.
The power conversion efficiency under white light illumination
was found to be moderated about 0.012% for bpy-DPA-TSB-
Re based device and showed twice larger efficiency comparing
with that of bpy-DPA-TSB (0.006%), which is an encouraging
7 G. Bott, L. D. Field and S. Sternhell, J. Am. Chem. Soc., 1980, 102,
5618.
8 H. L. Wong, L. S. M. Lam, K. W. Cheng, K. Y. K. Man, W. K.
Chan, C. Y. Kwong and A. B. Djurisic, Appl. Phys. Lett., 2004, 84,
2557.
9 Y. Shao and Y. Yang, Adv. Mater., 2005, 17, 2841.
10 W. Schuddeboom, S. A. Jonker, J. M. Warman, U. Leinhos, W.
Kuhnle and K. A. J. Zachariasse, J. Phys. Chem., 1992, 96, 10809.
11 A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
12 G. Yu, C. Zhang and A. J. Heeger, Appl. Phys. Lett., 1994, 64
1540.
13 Y. Y. Noh, C. L. Lee, J. J. Kim and K. J. Yase, Chem. Phys., 2003,
118, 2853.
Table 1 Photovoltaic data for the materials studied under white light
)
illumination (100 mW cmꢂ2
Materials
Isc/mA cmꢂ2
Voc/V
FF
Ze (%)
7
6
0.082
0.038
3.8
0.72
0.65
0.75
0.85
0.21
0.24
0.28
0.26
0.012
0.006
0.8
7 : PCBM(1 : 1, w/w)
6 : PCBM(1 : 1, w/w)
2.3
0.5
ꢀc
This journal is The Royal Society of Chemistry 2008
3914 | Chem. Commun., 2008, 3912–3914