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YD1, confirming the viability of the present substitution strategy.
It was also found that the power conversion efficiency of the
monosubstituted ZnEP1 is superior to that of its doubly function-
alized ZnEP2, leading us to suggest that further design optimiza-
tion could produce yet-improved systems.
This work was supported by the Global Frontier R&D Program
on Center for Multiscale Energy System funded by the National
Research Foundation under the Ministry of Science, ICT & Future,
Korea (2012-8-2081; D.K.) and the U.S. NSF (CHE-1057904; J.L.S.).
Fig. 2 (a) Current–voltage characteristics and (b) action spectra at incident
photon-to-current (IPCE) conversion efficiencies of DSSCs sensitized by ZnEP1
(black) and ZnEP2 (red). Conditions: [Co(bpy)3]2+ based electrolyte in CH3CN and
AM 1.5 under simulated solar light irradiation (100 mW cmÀ2).
Notes and references
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Table 1 Photovoltaic performances of ZnEPn-sensitized cellsa
2 L.-L. Li and E. W.-G. Diau, Chem. Rev. Soc., 2013, 42, 291.
3 A. Yella, H. W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran, M. K.
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Dyes
JSC/mA cmÀ2
VOC/V
FF
Z/%
ZnEP1
ZnEP2
YD1b
11.1
8.2
12.7
0.77
0.77
0.71
0.69
0.64
0.68
5.9
4.0
6.2
5 (a) C.-W. Lee, H.-P. Lu, C.-M. Lan, Y.-L. Huang, Y.-R. Liang,
W.-N. Yen, Y.-C. Liu, Y.-S. Lin, E. W.-G. Diau and C.-Y. Yeh,
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Diau and C.-Y. Yeh, J. Mater. Chem., 2010, 20, 1127.
a
Under AM 1.5 illumination (power 100 mW cmÀ2) with an active area
of 0.25 cm2 and a TiO2 thickness of 13 mm. As a reference, the overall
efficiency of N3 sensitized solar cells was determined; JSC = 15.3 mA cmÀ2
,
b
VOC = 0.78 V, FF = 0.66, and Z = 7.7%. See ref. 5b.
6 H. Hata, H. Shinokubo and A. Osuka, J. Am. Chem. Soc., 2005,
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9 The reduced overall yield is ascribed in part to the partial hydrolysis
of the methyl ester product (3g) formed under the reaction condi-
tions. Unfortunately, in our hands the polar hydrolyzed product
could not be isolated via silica gel column chromatography.
at 450 nm that is also larger than in cells built up from ZnEP2
(27.3% at 470 nm) (Fig. 2b). This difference matched the
absorption spectral features of the corresponding porphyrins
adsorbed on the electrodes (Fig. S6, ESI†).
The photocurrent density of DSSCs is related to the effici-
encies of (i) light harvesting (LHE), (ii) charge injection (jinj),
and (iii) charge collection (Zcol).16 Among these factors, the LHE
defined as LHE = 1 À 10ÀeG (where e is the molar extinction
coefficient of the dye and G is the molar concentration of the
dye per projected surface area of the film) is thought to be 10 C. Adamo, C. Amatore, I. Ciofini, A. Jutand and H. Lakmini,
J. Am. Chem. Soc., 2006, 128, 6829.
11 Optical data for the unfunctionalized porphyrin (4) are also given in
dominant in accounting for the photocurrent generated by
the cells prepared using ZnEPn of this study. Considering the
Fig. S2 (ESI†) for the purpose of comparison.
similar absorption spectral features of the dyes, the larger 12 Electron injection from the excited state of a sensitized dye to the
G value of ZnEP1 (1.2 Â 10À7 mol cmÀ2) as determined on
TiO2 surface has been reported to take place on a time scale of
1012–1013 À1. See, Y. Tachibana, S. A. Haque, I. P. Mercer, J. R.
s
our TiO2 electrode serves to enhance the overall efficiency of
this porphyrin relative to ZnEP2 (G = 4.4 Â 10À8 mol cmÀ2).
The dye aggregates on the surface are known to be one of the
factors accounting for low efficiency.13a,17 On this basis we
consider it possible that the tilted dye geometry of ZnEP2 serves
to accelerate the back electron transfer process (Fig. S7, ESI†).
In addition, the dihedral angle between the porphyrin core and
the acceptor ethynylphenyl rings is larger in ZnEP2 than in ZnEP1
based on the optimized structures (Fig. S8, ESI;† 17.41 vs. 0.71,
respectively). This may disrupt the effective electronic communi-
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cation through the b-ethynylphenyl p-bridges. To an extent this is 16 M. K. Nazeeruddin, A. Kay, R. Rodicio, R. Humphry-Baker, E. Mu¨ller,
¨
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true, it would help to rationalize the relatively poor power conver-
sion efficiency seen for the doubly-bridged system.
17 (a) H. Imahori, S. Kang, H. Hayashi, M. Haruta, H. Kurata, S. Isoda,
´
S. E. Canton, Y. Infahsaeng, A. Kathiravan, T. Pascher, P. Chabera,
In summary, we have demonstrated the use of a direct
palladium-catalyzed oxidative alkynylation reaction of b-borylated
porphyrins to obtain b-ethynylphenyl-substituted porphyrin deri-
vatives. This has allowed us to obtain new alternative porphyrin-
based sensitizers, ZnEPn for DSSCs. The photophysical and
electrochemical properties of two ZnEPns were investigated and
proved to be similar to those of a meso-substituted control system,
¨
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c
9166 Chem. Commun., 2013, 49, 9164--9166
This journal is The Royal Society of Chemistry 2013