C O M M U N I C A T I O N S
system (3% error). The reflective absorption spectrum of the
complete device was measured using a Cary 50 UV-vis spectrom-
eter. The internal quantum efficiency (IQE) of PBDTTT-C-based
device was then calculated using EQE and absorption data. The
result is shown in Figure 2. In almost the whole response range,
i.e., 400 to 750 nm, the IQE of the PBDTTT-C-based device
averaged at ∼95%, which implied that charge separation, trans-
portation, and collection of the device are quite efficient and photons
absorbed by the active layer efficiently convert into electricity.
In conclusion, the HOMO level of the PBDTTT-based polymer
was successfully reduced by introducing the ketone group in place
of the ester group. The average PCE of the PBDTTT-based devices
reached 6.3% with a champion PCE result of 6.58%. Due to its
highly efficient photovoltaic performance and more feasible syn-
thesis approach, PBDTTT-C has the potential to be successfully
Figure 1. ( a) Absorption spectra of PBDTTT-C as film and in chloroform
solution. (b) J-V curve of PBDTTT-C/PC70B2M based solar cell device
under illumination of AM 1.5 G, 100 mW/cm .
1
6
applied in the large-scale manufacturing of polymer solar cells.
Supporting Information Available: Experimental details of the
synthesis of the polymer, device fabrication, and characterization of
the polymer solar cells (i.e., measurements and instruments used). This
material is available free of charge via the Internet at http://pubs.acs.org.
References
(
1) Brabec, C. J.; Dyakonov, V.; Scherf, U. In Organic PhotoVoltaics:
Materials, DeVice Physics, and Manufacturing Technologies;, John Wiley
&
Sons: 2008.
Figure 2. External quantum efficiency (EQE), Internal quantum efficiency
(
2) Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Science 1995,
70, 1789.
3) (a) Jorgensen, M.; Norrman, K.; Krebs, F. C. Sol. Energy Mater. Sol. Cells
(IQE), and absorption curves of PBDTTT-C/PC70BM based solar cell device.
2
(
2008, 92, 686. (b) Krebs, F. C. Sol. Energy Mater. Sol. Cells 2009, 93,
394.
polymer and promising solar cell performance shows strong
potential of the new polymer for use in PSC manufacturing.
Absorption spectra of PBDTTT-C in the solid state and in
chloroform solution are shown in Figure 1a. The optical band gap
of PBDTTT-C in the solid state was calculated from the absorption
edge and found to be ∼1.61 eV. The value is consistent with other
(
4) (a) Blom, P. W. M.; Mihailetchi, V. D.; Koster, L. J. A.; Markov, D. E.
AdV. Mater. 2007, 19, 1551. (b) Dennler, G.; Scharber, M. C.; Brabec,
C. J. AdV. Mater. 2009, 21, 1323. (c) Kim, J. Y.; Lee, K.; Coates, N. E.;
Moses, D.; Nguyen, T.-Q.; Dante, M.; Heeger, A. J. Science 2007, 317,
2
22.
(
5) Hou, J.; Tan, Z.; Yan, Y.; He, Y.; Yang, C.; Li, Y. J. Am. Chem. Soc.
2006, 128, 4911.
1
3a,b
(6) (a) Hou, J.; Park, M.-H.; Zhang, S.; Yao, Y.; Chen, L.-M.; Li, J.-H.; Yang,
Y. Macromolecules 2008, 41, 6012. (b) Kroon, R.; Lenes, M.; Hummelen,
J. C.; Blom, P. W. M.; Boer, B. Polym. ReV. 2008, 48, 531.
PBDTTT-based polymers reported previously,
which means
the replacement of ester by keton almost has no influence on the
band gap for this kind of polymers. Electrochemical cyclic
voltammetry (CV) was also performed to determine the HOMO
level of the conjugated polymers. HOMO and LUMO levels of
(7) Peet, J.; Kim, J. Y.; Coates, N. E.; Ma, W. L.; Moses, D.; Heeger, A. J.;
Bazan, G. C. Nat. Mater. 2007, 6, 497.
(8) Hou, J.; Chen, H. Y.; Zhang, S.; Li, G.; Yang, Y. J. Am. Chem. Soc. 2008,
1
30, 16144.
(
9) Scharber, M. C.; M u¨ hlbacher, D.; Koppe, M.; Denk, P.; Waldauf, C.;
15
the polymers can be obtained by the reported method. Its HOMO
and LUMO were -5.12 and -3.55 eV, respectively.
Heeger, A. J.; Brabec, C. J. AdV. Mater. 2006, 18, 789.
(
10) (a) Svensson, M.; Zhang, F.; Veenstra, S. C.; Verhees, W. J. H.; Hummelen,
J. C.; Kroon, J. M.; Ingan a¨ s, O.; Andersson, M. R. AdV. Mater. 2003, 15,
988. (b) Chen, M. -H.; Hou, J.; Hong, Z.; Yang, G.; Sista, S.; Chen, L.
Polymer solar cells were fabricated using the polymer as an
electron donor material and (6,6)-phenyl-C71-butyric acid methyl
ester (PC71BM) as an electron acceptor material. The device
structure is ITO/PEDOT-PSS/Polymer:PC71BM/Ca/Al. Hole mo-
-
M.; Yang, Y. AdV. Mater. 2009,in press.
(
11) Wang, E.; Wang, L.; Lan, L.; Luo, C.; Zhuang, W.; Peng, J.; Cao, Y. Appl.
Phys. Lett. 2008, 92, 033307.
(
12) (a) Blouin, N.; Michaud, A.; Gendron, D.; Wakim, S.; Blair, E.; Neagu-
Plesu, R.; Belletete, M.; Durocher, G.; Tao, Y.; Leclerc, M. J. Am. Chem.
Soc. 2008, 130, 732. (b) Park, S. H.; Roy, A.; Beaupre, S.; Cho, S.; Coates,
N.; Moon, J. S.; Moses, D.; Leclerc, M.; Lee, K.; Heeger, A. J. Nat.
Photonics 2009, 3, 297.
13) (a) Liang, Y.; Wu, Y.; Feng, D.; Tsai, S.-T.; Son, H.-J.; Li, G.; Yu, L.
J. Am. Chem. Soc. 2009, 131, 56. (b) Liang, Y.; Feng, D.; Wu, Y.; Tsai,
S.-T.; Li, G.; Ray, C.; Yu, L. J. Am. Chem. Soc. 2009, 131, 7792. (c) Pan,
H.; Li, Y.; Wu, Y.; Liu, P.; Ong, B. S.; Zhu, S.; Xu, G. J. Am. Chem. Soc.
2007, 129, 4112.
(14) Shi, C.; Yao, Y.; Yang, Y.; Pei, Q. J. Am. Chem. Soc. 2006, 128, 8980.
15) Li, Y. F.; Cao, Y.; Gao, J.; Wang, D. L.; Yu, G.; Heeger, A. J. Synth. Met.
1999, 99, 243.
16) (a) Krebs, F. C.; Jorgensen, M.; Norrman, K.; Hagemann, O.; Alstrup, J.;
Nielsen, T.; Fyenbo, J.; Larsen, K.; Kristensen, J. Sol. Energy Mater. Sol.
Cells 2009, 93, 422. (b) Krebs, F. C.; Gevorgyan, S. A.; Alstrup, J. J.
Mater. Chem. 2009, 19, 5442.
-4
2
bilities are 2 × 10 cm /V s for the device. The J-V curve of the
fabricated PBDTTT-C/PC71BM device is shown in Figure 1b, where
V
oc is 0.70 V, 0.12 V higher than that of the PBDTTT-E/PC71BM-
(
1
3a
based device,
PBDTTT, which is 0.74 V as reported.
but it is similar with the fluorine substituted
1
3b
The average PCE
obtained from more than 200 devices reached 6.3%. The champion
2
result reached 6.58%, with a Voc of 0.70 V, a Jsc of 14.7 mA/cm ,
(
and an FF of 0.64, which is the highest value so far for polymer
solar cells. The external quantum efficiency (EQE) curve of the
PBDTTT-C-based device was shown in Figure 2. The Jsc calculated
(
2
from the integral of EQE curves is 14.1 mA/cm which is very
consistent with the Jsc value obtained from the J-V measurement
JA9064975
J. AM. CHEM. SOC. 9 VOL. 131, NO. 43, 2009 15587