1946
C.-Y. Lin et al. / Electrochimica Acta 56 (2011) 1941–1946
in the presence of 0.5 vol% Me-EDA-Si in the base solution was only
5.86%. The ꢁ value decreased dramatically with higher Pt loading
on the FTO surface, indicating that most of the Pt became useless
due to Pt aggregation.
Comparison of data as shown in Table 1 further indicates the suc-
cessful decrease of Pt loading with the use of Me-EDA-Si without
loss of high cell efficiency under the similar preparation method.
Although there were efficiencies reported higher than 6–7% in the
literature, they usually involve optimal combination of all the com-
ponents in DSSC or usually on a very small substrate. In any case, a
higher ꢁ (7.39%) for our low Pt-loading counter electrode than the
corresponding sputtered-Pt counter electrode (6.01%) means we
should be able to further improve our cell efficiency with existing
technology.
4. Conclusions
We have developed a process whereby low Pt-loading counter
electrode can be prepared in very short period by dc electrode-
position with appropriate addition of Me-EDA-Si. The Me-EDA-Si
additive serves as an accelerator so that the counter electrode can
Me-EDA-Si can inhibit the growth of semicircle-like Pt grains, thus
resulting in the formation of high active surface area. The DSSC with
the electrodeposited-Pt counter electrode prepared in the presence
of 0.01 vol% Me-EDA-Si already demonstrated a fairly high cell effi-
ciency of 7.39% with very low Pt loading (∼4.76 g cm−2) in our
preliminary experiment without optimization. The improved per-
formance of the DSSC was attributed to the increased relative active
surface areas and the small charge-transfer resistance (1.39 ꢀ cm2).
The whole process took only 30 s and was under ambient atmo-
sphere, and no high temperature post-annealing was required.
Fig. 6. Cyclic voltammetrics for the sputtered-Pt counter electrode and
electrodeposited-Pt counter electrodes prepared in the presence of 0 vol% and
0.01 vol% Me-EDA-Si.
presence of 0.01 vol% Me-EDA-Si as a working electrode indeed
demonstrated the largest current density for the reaction of I−/I3
.
−
The superior performance is related to high active surface area as
studied by other workers [7,13,19].
The I–V curves of the as-prepared DSSCs are shown in Fig. 7, and
the corresponding photovoltaic parameters are listed in Table 1.
The performance of the DSSC with Pt counter electrode electrode-
posited with 0.01% Me-EDA-Si additive (Pt loading ∼4.76 g cm−2
)
shows a short circuit current (Jsc) of 17.45 mA cm−2, open circuit
voltage (Voc) 0.68 V, fill factor (FF) 0.62, thus yielding a 7.39% cell
efficiency (ꢁ). As for the DSSC with a sputtered-Pt counter electrode
(Pt loading ∼100 g cm−2), the Jsc, Voc and FF were 14.9 mA cm−2
,
0.66 V, and 0.61 and a resultant ꢁ of 6.01% Moreover, we noticed
that the Jsc and the ꢁ values of the DSSCs with electrodeposited-Pt
counter electrodes increased gradually with the Me-EDA-Si con-
centration up to 0.01 vol% and then decreased with further addition
of Me-EDA-Si. This observation is indeed in consistency with the
EIS results. In addition, although the loading of Pt increased with
increasing Me-EDA-Si concentration, the cell efficiency reached a
maximum when 0.01 vol% Me-EDA-Si was added in the base solu-
tion. This might be attributed to the relative highest active surface
area in this particular case, as observed from the EIS and CV data,
Acknowledgment
The authors are very grateful to the National Science Council in
Taiwan for its financial support under Contract No. NSC-99-2221-
E-036-038.
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Fig. 7. I–V curves of the DSSCs assembled with various Pt counter electrodes.