Journal of the American Chemical Society
COMMUNICATION
a
Table 1. Performance of Polymer Solar Cells
external quantum efficiency (EQE) curves of the polymer:
PC BM blends. The PBDT-DTNT:PC BM device exhibited
b
2
71
71
active layer
J
sc (mA/cm )
V
oc (V) FF (%) PCE (%)
a broad and high response range, covering 300À800 nm, whereas
PBDT-DTBT/PC61BM
PBDT-DTBT/PC71BM
PBDT-DTNT/PC61BM
PBDT-DTNT/PC71BM
4.00
5.80
1.05
1.00
0.80
0.80
35.3
34.6
62.2
61.0
1.56
2.11
5.32
6.00
the PBDT-DTBT:PC BM device exhibited a relatively narrow
71
and low response range, covering 300À700 nm. These results
have shown clearly that the more effective solar energy harvesting
capability and the high charge transport mobility are the main
reasons for the improved PSC performance of PBDT-DTNT
compared to PBDT-DTBT.
10.15
11.71
a
All the devices were measured under the illumination of AM1.5G at 95
mW/cm . All the weight ratios of polymer and PCBM were 1:1 and
2
b
In conclusion, two DÀA conjugated polymers using NT and
BT as acceptor units, PBDT-DTNT and PBDT-DTBT, were
developed for PSC applications. Compared with the BT-based
polymer, the NT-based polymer showed more pronounced red-
shifted absorption spectra and higher hole mobilities while
maintaining suitable energy levels for effecting reasonable Voc
and efficient charge separation between the polymer and PCBM.
Consequently, the NT-based polymer exhibited a much more
promising photovoltaic performance, with a PCE of 6.00% when
compared with the analogous PBDT-DTBT, based on the
previously widely used BT acceptor.
annealed at 130 °C for 7 min.
’
ASSOCIATED CONTENT
Figure 2. (a) JÀV curves of the PBDT-DTBT/PC71BM and PBDT-
DTNT/PC71BM devices. (b) External quantum efficiency curves of the
PBDT-DTBT/PC71BM and PBDT-DTNT/PC71BM devices.
S
Supporting Information. Complete ref 25; experimental
b
details for the synthesis, instruments, measurements, and fabrica-
tion procedures; and characterization details of the PSC devices.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(
ITO, indium tin oxide; PEDOT:PSS, poly(styrene sulfonate)-
doped poly(ethylene-dioxythiophene); PCBM, PC BM or
61
PC BM). A thin film (40 nm) of PEDOT:PSS was deposited
7
1
’ AUTHOR INFORMATION
on a pre-cleaned ITO substrate. The polymer:PCBM (1:1, w/w)
solution in 1,2-dichlorobenzene was then spin-coated, and the
substrate was subsequently annealed at 130 °C for 7 min. Finally,
the process was completed by evaporating Ca/Al metal electro-
des under high vacuum with an area of 0.16 cm , as defined by
masks. A more detailed description of the device fabrication
Corresponding Author
msfhuang@scut.edu.cn; yongcao@scut.edu.cn
2
’
ACKNOWLEDGMENT
process is available in the Supporting Information.
This work was financially supported by the Natural Science
The device performance data are presented in Table 1. Both
PBDT-DTNT and PBDT-DTBT showed much better perfor-
mance when using PC BM as the acceptor than with devices
Foundation of China (No. 50990065, 51010003, 51073058, and
20904011), the Ministry of Science and Technology, China
(MOST) National Research Project (No. 2009CB623601),
and the Fundamental Research Funds for the Central Univer-
sities, South China University of Technology (No.2009220012).
71
fabricated using PC BM, which can be explained by PC BM
6
1
71
having a considerably stronger absorption in the visible region,
32
complementing the absorption valley of the polymers. The best
cell was obtained from PBDT-DTNT:PC BM and showed a
71
’
REFERENCES
2
short-circuit current density (J ) of 11.71 mA/cm , an open-
sc
(
(
(
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1
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dx.doi.org/10.1021/ja201131h |J. Am. Chem. Soc. 2011, 133, 9638–9641