Surface Treatment of Dye-Sensitized Solar cells by Atmospheric Pressure Plasma
Shogo KANETA1, Marius BLAJAN2, Kenta OGI1, Akinori Konno3 and Kazuo SHIMIZU2
1Graduate School of Engineering, Shizuoka University
2Organization for Innovation and Social Collaboration, Shizuoka University
3Graduate School of Science and Technology, Shizuoka University

Johoku, Hamamatsu, 432-8561, Japan
E-mail：shimizu@cjr.shizuoka.ac.jp
(b)

(a)

INTRODUCTION
The dye-sensitized solid-state solar cells (DSSSCs)
could have the potential to be alternatives to theexistent DSSCs. However, solar conversion efficiency
of DSSSCs is lower than that of conventional DSSCs
efficiency [1, 2].
Surface treatment of dye-sensitized solid-state
solar cells by atmospheric pressure plasma jet wasstudied to improve its efficiency.

100 nm(a) Before treatment(b) 15 min. treatment
Fig. 5 FE-SEM images of TiO2 surface

METHODS(1)Experimental setup
Figure. 1 shows an experimental setup for surface
modification. Atmospheric pressure plasma jet wasgenerated between two electrodes. The plasma jetelectrode was powered by an AC high voltage powersupply. The process gas was fed through the glass
tube from gas cylinders. DSSSCs sample and theplasma jet electrode were placed into a chamber. AnAr/O2 mixture (5.00 + 0.25 L/min.) was used as theprocess gas. Additionally, the process gas can behumidified (relative humidity 65%). The frequency of
AC high voltage was set at 16.1 kHz. Discharge
voltage was 5.0 kV (Figure. 2 (a)). Distance between
cathode and TiO2sample was 13 mm. Figure. 2 (b)shows an image of light emission of Ar + O2 plasmadischarge.

100 nmFig. 3 I-V characteristics before and after various
treatment times (5, 10 and 15 min.).
Table 1 Characteristics of no treated and treated DSSCs.

Treatment
Jsctime[mA/cm2][min.]Voc[V]

FFh[%]

Untreated

4.25

0.54

0.69

1.60

5

4.32

0.55

0.70

1.65

10

4.82

0.49

0.71

1.67

15

5.35

0.51

0.72

1.96

(2) XPS analysis
The surface stoichiometry was determined by
calculating the relative peaks area as ratio of thetotal Ti 2p and O 1s in XPS spectra (Figure 4). Table.
2 shows chemical composition of TiO2 surface
before and after treatment. Ti3+ peaks and Ti2O3
peaks were increased after plasma treatment.

(4) Effect of humidity
Dry treatment (dry process gas with relative
humidity 0%), and wet treatment (humid process gas
with relative humidity 65%) were carried out(Figure 6).Dry treatment improved the conversion
efficiency. Improvement rate increased with about
20% after 15 min. Wet treatment worsened theconversion efficiency. After 15 min of wet
treatment, improvement rate decreased with about
45%.

Fig. 6 Effect of humidity in the carrier gas.
(5) Dye adsorption quantity

Figure. 7 shows dye adsorption quantity of TiO2
surface after plasma treatment. After Drytreatment, dye adsorption quantity increased with
about 5%. On the other hand, after Wet treatment,
dye adsorption amount decreased with about 20%.
Hydrophilic group modification could have been
occurred during both types of treatment. However,humidity in process gas inhibited the dyeadsorption and decreased the conversion efficiency.

Fig. 1 An experimental setup for TiO2 sample surface
modification.

(a)Fig.4 (a) XPS spectra of Ti 2p on the TiO2 surface(treated 15 min.).

Fig. 2 (a) current-voltage wave form.

Fig.7 Dye adsorption quantity of TiO2 surface versus
treatment time(b)Fig. 2 (b) image of Ar + O2 plasma discharge.

RESULTS(1)Photovoltaic measurements
The size of the TiO2 sample was 0.5 cm2. After theplasma exposure treatment, The TiO2 sample wassoaked to dye again for about 18 hours. N719
Ruthenium-based dye was used. I-V characteristics
were measured under simulated solar light (AM 1.5,100mW/cm2) using a solar cell evaluation system(JASCO, CEP-25BX). Treatment time of sample
surface was 5, 10 and 15 min. The target sample wasattached in the chamber and relative humidity inchamber was 0%. 3 samples were treated each time.
Figure. 3 and Table. 1 show the result of photovoltaic
measurements. Efficiency was improved withincreasing treatment time because the short circuit
photocurrent density was increased by plasma
treatment.

Fig.4 (b) XPS spectra of O 1s on the TiO2 surface(treated 15 min.).

CONCLUSIONS

Ti 2p

Ti4+ 2p1/2

Ti4+ 2p3/2

Ti3+ 2p1/2

Ti3+ 2p3/2

No treated

29.52

67.21

2.39

0.88

15 min

29.61

66.48

2.93

0.97

O 1s

TiO2

Ti2O3

No treated

72.99

27.01

In this study, the following conclusions wereobtained.
1. TheDSSSCssurfacemodification
using
atmospheric pressure plasma jet improved theconversion efficiency of DSSSCs.
2. The electric conductivity of the DSSSC sample
surface was increased after 15min of plasma
treatment.
3. Humidity in the carrier gas decreased theconversion efficiency of DSSSCs because
humidity in process gas inhibited the dye
adsorption.

15 min

67.81

32.19

REFERENCE

Table 2. Chemical composition of TiO2 surface.

(3) SEM image
As shown in Figure. 5, The photo of TiO2 surface
before and after treatment were taken by a SEM. No
significant change on the TiO2 surface was observed.

[1] B. O'Regan and M. Gratzel, Nature, 353
pp.737(1991).
[2] A. Konno and EVA Premalal, J. Photopolym. Sci.
Technol, 23 279 (2010).