10.1002/chem.201800938
Chemistry - A European Journal
COMMUNICATION
10-5 cm2 V-1 s-1). The measurements of GIXRD, AFM and TEM all
exhibit the similar cases (Figures S5-7).
D. Yang, Q. Luo, Y. Zhu, Y. Huang, S. Zhao, Z. Lu, J. Mater. Chem.
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To eliminate the possibility of experiment errors, two more
batches of devices in the ratio of 1:3 with/without TA were
reproduced carefully, and all the data show the same results,
even including the slightly increase of Voc and FF. And these
increases may be caused by weaker charge recombination.14
Then, light intensity (I) dependent J−V analysis of the OSCs were
performed (Figure 5) to investigate the charge recombination
kinetics. The relationship between JSC and I is defined as JSC IS,
where the S value close to the 1, which means it shows a weak
bimolecular recombination.14 As shown in the Figure 5, both of
them show the same slope of 0.96, suggesting that TA treatment
has no effects on the bimolecular recombination. The relationship
between VOC and I should be VOC = n(kBT/ e) ln(I)+ C, where n is
the ideality constant, kB the Boltzmann constant, T temperature,
e elementary charge, and C a constant.14 When n = 1 , there
exist only bimolecular recombination; when n>1, there exist the
mixture of bimolecular recombination and monomolecular
recombination. Interestingly, the value of n was decreased after
TA from 1.37 to 1.16, indicating TA treatment can significantly
decrease the monomolecular recombination. And this decrease
can lead to the increase of Jsc, FF and Voc.
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In addition, the blend film with 1:3 ratio exhibit much stronger
absorption in comparison the film with 1:5 ratio (Figure S2).
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In conclusion, a novel unsymmetrical squaraine with 3H-
benzo[e]indoline was designed, synthesized, and characterized.
The hole mobility of USQ-BI was about 5 times compared to with
that of indoline-based squaraine (ASQ-5) in pristine film. The
solution-processed small-molecule BHJ OSCs fabricated with
USQ-BI/ PC71BM exhibited a high PCE of 5.35% with the
excellent Jsc over 15 mA/cm2, which is one of the highest value
for the squaraine-based OSCs. And higher PCE could be
expected with electron deficient substituents (-F, -CN, et al.) on
the indoline. These preliminary studies demonstrate that the
simple benzene-ring-fused strategy is very effective for indoline
skeleton to increase the hole mobility and the photovoltaic
performance. At the same time, these results demonstrate that
3H-benzo[e]indoline is a promising constructing-unit for OSCs,
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Acknowledgements
We acknowledge the financial support for this work from the
National Natural Science Foundation of China (projects No.
51573108, and 21672156). We also would like to thank Dr.
Shanling Wang of Analytical & Testing Center, Sichuan University,
for his help in TEM measurements. We are grateful to the
Analytical & Testing Center of Sichuan University for providing
single crystal X-ray diffraction data for objective molecules.
Y.Chen thank the joint-Ph.D. program supported by China
Scholarship Council for fellowships.
Conflict of interest
The authors declare no conflict of interest.
Keywords: Indoline • Squaraine • Organic Solar Cells • Charge
Mobility
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