2009 INTERNATIONAL SYMPOSIUM ON NANO SCIENCE AND TECHNOLOGY
Tainan, TAIWAN, 20-21 November 2009
PREPARATION OF TIO2/AU COMPOSITE PARTICLES AND THEIR
APPLICATION IN DYE-SENSITIZED SOLAR CELLS
Chuen-Shii Chou*, Kuan-Hung Liu, Chun-Po Wang
Department of Mechanical Engineering, National Pingtung University of Science and Technology
Pingtung, TAIWAN
E-mail: cschou@mail.npust.edu.tw
Abstract
This study investigated the applicability of TiO2/Au composite particles on the FTO-glass (Fluorine
doped tin oxide, SnO2:F) substrate of the working electrode in a dye-sensitized solar cell (DSSC). Dry particle
coating was performed to coat the nano-sized Au powder on the surface of TiO2 particle. A layer of TiO2/Au
composite particles was fabricated on the FTO-glass substrate of the working electrode, and then sintered in a
high-temperature furnace. The working electrode with a TiO2/Au thin film was immersed in the solution of N719 (Ruthenium) dye at a temperature of 70℃ for 6 hours. Moreover, a thin film of platinum on was deposited
on the FTO-glass substrate of the counter electrode. Finally, the DSSC was assembled, and the short-circuit
photocurrent, the open-circuit photovoltage and the power conversion efficiency η of DSSC were measured
using a home-made I-V measurement system. The power conversion efficiency η of the DSSC increases with
increase in the duration of dry coating. Most importantly, this study shows that the power conversion efficiency
η of the DSSC with a film of TiO2/Au on the working electrode (2.300%) exceeds that of the conventional
DSSC (1.063%) due to a Schottky barrier, which is probably created in the TiO2/Au composite particle.
Introduction
The dye-sensitized solar cell (DSSC) that was proposed by O’Regan and Gratzel [1] has attracted
considerable interest since 1991 because it has attractive properties, such as low production cost and low
environmental impact during fabrication. However, a comparison with conventional solid-sate junction devices
made of crystalline silicon indicates that the DSSC has a relatively low conversion efficiency of 10.6% [2]. Su et
al. fabricated layer-by-layer Au nanoparicles, which were prepared using chemical reduction method, onto the
working electrode as a Schottky barrier in a water-based DSSC [3]. Accordingly, decreasing the recombination
of charges in the dye or electrolyte is one of the most important issues in increasing the conversion efficiency of
DSSC, and is worthy of ongoing study. The purpose of this work is to modify physically the surface
characteristics of nanosized TiO2 by coating the Au powder onto the surface of TiO2 in a Mechanofusion system,
and then to fabricate a DSSC with a layer of TiO2/Au composite particles as a Schottky barrier [4-5]. In a dry
coating process, tiny (guest) particles are coated onto larger (host) particles to generate value-added composite
particulate materials [6]. In this study, the TiO2/Au composite particles were prepared using the dry coating
process in a Mechanofusion system. Then, a layer of TiO2/Au composite particles (Fig. 1) was fabricated for use
in a new type of dye-sensitized solar cell to promote the conversion efficiency of DSSC.
Figure 1 Schematic of the dye-sensitized solar cell with a TiO2/Au thin-film electrode.
Experimental
The experiments involved (1) preparing the TiO2/Au composite particles, and measuring their characteristics;
(2) preparing the working electrode, and measuring its surface properties; (3) assembling the DSSC by fitting: the
working electrode, the counter electrode, the electrolyte and the copper conductive tape, and (4) making I-V
measurements of the DSSC at an energy intensity of 100mW/cm2. Figure 2 shows the procedure followed herein.
Chuen-Shii Chou, Kuan-Hung Liu, Chun-Po Wang
Figure 2 The research procedures
Results and Discussion
Table 1 presents the test conditions under which the TiO2/Au composite particle was prepared. Table 2
presents the test conditions under which the working electrode was prepared. Table 3 presents the open-circuit
photovoltage Voc and short-circuit photocurrent Isc, fill factor FF, and the power conversion efficiencyηof the
DSSC in tests D1, D2, D3, D4 and D5.
Table 1 Test conditions of preparing composite particles
Mass ratio of
TiO 2 to nano-sized Au
(g:g)
P1
P2
P3
P4
Time of dry coating (min.)
10:0.1
10:0.2
10:0.1
10:0.2
30
6000
45
Table 2 Test conditions of preparing the working electrode
First Layer
W1
W2
W3
W4
W5
Rotation speed of rotating
chamber
(rpm)
Colloid
Sintering
temperature (˚C)
Sintering Time
(hr.)
Dye
P1
P2
P3
P4
TiO2
450
1.5
N719
Second Layer
Time of dipping in the
dye
(hr.)
6
Chuen-Shii Chou, Kuan-Hung Liu, Chun-Po Wang
Table 3 Voc, Isc, FF, and η of DSSCs
D1
D2
D3
D4
D5
Counter
Electrode
Working
Electrode
A platinum film
deposited on the
FTO
W1
W2
W3
W4
W5
Open-circuit
voltage
(V)
0.690
0.680
0.710
0.740
0.770
Short-circuit
current
(mA)
5.967
4.033
4.477
6.136
3.144
Fill Factor
(FF)
η(%)
28.580
49.910
59.000
50.629
43.921
1.177
1.314
1.875
2.300
1.063
Conclusion
The TiO2/Au composite particles were prepared using dry coating. Then, the dye-sensitized solar cells
with a layer of TiO2/Au composite particles were fabricated. The power conversion efficiency of the DSSC with
a layer of TiO2/Au composite particles as the Schottky barrier exceeded that of the conventional DSSC. Most
importantly, this study supports the application of TiO2/Au composite particles to improve the performance of a
DSSC. However, the optimal process for fabricating a DSSC with a layer of TiO2/Au composite particles must
be implemented to yield a DSSC with satisfactory power conversion efficiency.
REFERENCES
[1] O’Regan, B., Gratzel, M., A Low-Cost High-Efficiency Solar Cell Based on Dye-Sensitized Colloidal TiO2
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[2] Grätzel, M., Conversion of Sunlight to Electric Power by Nanocrystalline Dye-Sensitized Solar Cells,
Journal of Photochemistry & Photobiology A:Chemistry, 164 (2004) 3.
[3] Su, Y.H., Lai, W.H., Teoh, L.G., Hon, M.H., Huang, J.L., Layer-by-layer Au nanoparticles as a schoottky
barrier in a water-based dye sensitized solar cell, Appl. Phys. A, 88 (2007) 173.
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