Surface treatment of dye-sensitized solid-state solar cells
using atmospheric pressure plasma jet
Shogo KANETA, Marius BLAJAN, Kenta OGI, Akinori Konno and Kazuo SHIMIZU
Organization for Innovation and Social Collaboration, Shizuoka University,Johoku, Hamamatsu, 432-8561, Japan
E-mail：shimizu@cjr.shizuoka.ac.jp

RESULT

INTRODUCTION
The dye-sensitized solar cells (DSSCs) which wereinvented by Grätzel are well known as clean and low
cost photovoltaic devices, even, DSSCs has thedisadvantage of leaks and deterioration ofelectrolytic solution [1]. The dye-sensitized solidstate solar cells (DSSSCs) could have the potential tobe alternatives to the existent DSSCs. DSSSCs use CuI
as solid electrolyte, which is not leaked from the celland is not deteriorated. However, solar conversion
efficiency of DSSSCs is lower than that ofconventional DSSCs efficiency [2].
TiO2 surface modification by low pressure plasma
treatment has done, and increase of the solar
conversion efficiency has reported. By using
atmospheric pressure plasma, there is the advantagethat does not require a vacuum device or can beprocessed with low power consumption. Surface
treatment of dye-sensitized solid-state solar cellsby atmospheric pressure plasma jet was studied toimprove its efficiency. Effect on the DSSSCs byplasma exposure was investigated by photovoltaic
measurements and XPS.

(1)Photovoltaic measurements
Figure 2 shows a comparison of photocurrent
voltage (I-V) characteristics between untreated
DSSSCs and treated DSSSCs. The size of the TiO2sample was 0.5 cm square. After the plasma
exposure treatment, the sample TiO2 sample wassoaked to dye again for about 18 hours. The kindsof dye is N719 which Ruthenium-based dyes. 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 was attached in the chamber andrelative humidity in chamber was 0%. 3 samples weremade each treatment time.

METHODS(1) Experimental setup
Figure 1 shows the experimental setup for TiO2
sample surface modification by atmospheric pressureplasma jet. Atmospheric pressure plasma wasgenerated between two electrodes. The high voltage
electrode was made of tungsten wire (0.8 mm indiameter) and was fixed to the center of the glass
tube, while the grounded electrode was an Aluminumtape wrapped around a glass tube( 5.0 mm in outerdiameter). The plasma jet electrode was powered withan AC high voltage power supply. The process gas
was fed through the glass tube from gas cylinders.
DSSSCs sample and the plasma jet electrode wereplaced into a chamber. An Ar/O2 mixture (5.00 + 0.25L/min.) was used as the process gas. Additionally, theprocess gas can be humidified (relative humidity 65%).
The frequency of AC high voltage was set at 16.1
kHz. Table 2 shows the experimental conditions.

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

(b) XPS spectra of O 1s on the TiO2 surface(treated 15 min.).
Fig. 3 Ti 2p and O 1s peaks of TiO2 sample surface by XPS.
(3) Effect of humidity

Fig. 2 I-V characteristics before and after various
treatment times (5, 10 and 15 min.).
Table 2 Characteristics of no treated and treated DSSCs.
Treatmenttime [min.]Jsc[mA/cm2]

Voc[V]

FF
[%]No treated

4.25

0.54

0.69

1.60

54.32

0.55

0.70

1.65

10

4.82

0.49

0.71

1.67

15

5.35

0.51

0.72

1.96

The Improvement rate of conversion efficiency wascompared Dry treatment with Wet treatment asshown in Figure 4. 3 samples were made eachtreatment time. Dry treatment was used dry
process gas (relative humidity 0%). Wet treatment
was used humid process gas (relative humidity 65%).
Dry treatment was improved the conversion
efficiency. Improvement rate was increase about
20% after 15 min Dry treatment. Wet treatment
was worsened the conversion efficiency. After 15min Wet treatment, improvement rate wasdecreased about 45%.

As shown in Figure 2 and Table 2, the short circuit
photocurrent density (Jsc) and solar conversion
efficiency () of untreated TiO2 sample were 4.25mA/cm2 and 1.60%, respectively. Jsc and 
measured for the DSSSCs sample treated for 15 min.
were 5.35 mA/cm2 and 1.96% respectively.
However, the open circuit photovoltage (Voc)decreased and fill factor (FF) was not changed.
Efficiency was improved with increasing treatment
time.

Fig. 1 An experimental setup for TiO2 sample surface
modification.
Table 1 Experimental conditions.

Carrier gas

Ar, O2

Discharge voltage [kV]5.0Power source

AC

Distance between cathode andsample [mm]13Treatment time [min.]0, 5, 10, 15

Flow rate [L/min.]Ar : 5.0
O2 : 0.25

Frequency [kHz]16.1

Relative humidity [%]0, 65(2) XPS analysis
Ti 2p and O 1s XPS spectra of TiO2 sample surface
treated for 15 min are shown in Figure 3. Figure 3(a) shows the XPS spectra of Ti 2p on the TiO2
surface without plasma treatment (15 min.). Ti 2pspectra had analyzed with four peaks, i.e. Ti4+ 2p1/2,Ti3+ 2p1/2, Ti4+ 2p3/2, and Ti3+ 2p3/2. The surface
stoichiometry was determined by calculating therelative peaks area as ratio of the total Ti 2p and O
1s in XPS spectra. The Ti3+ surface state in Ti 2p
XPS spectra was increased from 3.27% to 3.9%
after 15 min of Ar/O2 plasma treatment. O 1s XPS
spectrum was measured as well as Ti 2p toinvestigate surface reaction. The Ti2O3 peak in O 1s
was increased from 27.01% to 32.19% after 15 minof Ar/O2 plasma treatment. Ti4+ → Ti3+ reduced
reaction could be occurred at TiO2 sample surface.
Part of TiO2 surfaces were changed to Ti2O3 asshown in Figure 3 (b). This surface reaction resulted
the increase of the electric conductivity of theDSSSC sample surface and consequently, solar
conversion efficiency could be improved.

Fig. 4 Effect of humidity in the carrier gas.

CONCLUSIONSIn this study, the following conclusions were obtained.
1. TheDSSSCs
surfacemodification
using
atmospheric pressure plasma jet made theconversion efficiency of DSSSCs improve.
2. The electric conductivity of the DSSSC sample
surface was increased after 15min plasma
treatment.
3. Humidity in the carrier gas was worsened
conversion efficiency of DSSSCs.

REFERENCE[1]

B. O’Regan and M. Grätzel, Nature. 353, 737 (1991).

[2]

G. R. A Kumara, A. Konno, K. Shiratsuchi, J. Tsukahara
and K. Tennakone, Chem. Mater. 14, 954 (2002).