Improvement of conversion efficiency of dye-sensitized solar cells
by surface modification using microplasma
N. Konagaya1, M. Blajan2, T. Onodera3, A. Konno3,4 and K. Shimizu1,2,3,4
1 Faculty of Engineering, Shizuoka University, 2 Organization for Innovation and Social Collaboration, Shizuoka University
3Graduate School of Engineering, Shizuoka University, 4Graduate School of Science and Technology, Shizuoka University

The surface modification for film dye sensitized solar cells (DSSCs) was carried out using atmospheric pressure microplasma. The DSSCs
consisted of Pt counter electrode, electrolytic solution, dye, titanium oxide (TiO2) layer and indium tin oxide (ITO) film electrode. The surfacesof TiO2 layer and ITO film were treated by argon microplasma generated by the film microplasma electrode. After microplasma treatment, thephoto conversion efficiency of DSSCs was improved by 9-27% in comparison with the untreated samples. It was observed using the contact
angle measurement that the hydrophilic property of ITO film was improved. The amount of dye adsorption of TiO2 layer was increased.

1. Introduction

3. Results

DSSCs have been gathered much attention
due to advantages such as cost effectiveness.
Although many attempts have been carriedout in recent years, the photo conversion
efficiencies of ITO and TiO2 based DSSCs
remained almost the same. Aiming toimprove film DSSCs, this study deals withsurface modification of film DSSCs using
atmospheric pressure microplasma generatedusing the film microplasma electrode.

3. 1 Contact Angle Measurement
Experimental condition (3.1)
Target

ITO film

Process gas

The solar conversion efficiency (ηC) of thecontrol sample was 1.66%. After treatmentof the ITO film and TiO2 layer, ηC was
increased to 1.81% and 2.11%, respectively.

Argon

Irradiation distance 125 ~ 1250 µm
Gas flow rate

5.0 L/min

Chamber volume

3.4 L

Treatment time0 ~ 180 s

Applied voltage

500 V

2. Experimental Methods
The electrode system was used for surface
modification of ITO film or TiO2 layer and it
consists in one high voltage electrode andone grounded electrode faced together witha 25aµm dielectric layer in between.

Cross view
Front view
Microplasma electrode

Film electrode with sample was placed in aplastic chamber. The volume of the chamber
was 3.4 L. After argon gas was supplied tothe chamber for 30 seconds, AC voltage(500aV, 27 kHz) was applied to themicroplasma electrode and plasma wasgenerated.

The water droplet
on the untreated ITO film

The water droplet on theITO film treated for 3 min
irradiation distance: 250 µm

I-V characteristics of median samples
With the increase of treatment time thecontact angle decreases. By increasing thedistance between microplasma electrode andthe target the contact angle increases. After3 minutes of treatment at a distance
between the microplasma electrode and thesample of 250 µm, a significant modificationof the surface was observed.

Average parameters of film DSSCs between
control sample and treatment sample
JSCCondition[mA/cm2]
Control
ITO film
TiO2 layer

4.54
4.78
4.68

VOC [V]FF

ηC [%]

0.72
0.72
0.75

0.50
0.53
0.60

1.66
1.81
2.11

3. 3 Dye Adsorption AmountMeasurement
Experimental condition is shown in 3.2. The
amount of dye adsorption of treated samples
was increased by 18%. The number ofsamples was 4 for each process. The dye
adsorption of TiO2 layer consists of ester
bonds which locate between hydro oxidegroups on TiO2 surface and carboxyl groupsof N719 dye. The hydrophilicity of TiO2 layer
could be considered that was improved dueto the generation of hydrophilic group.
Contact angle–Treatment time

Experimental set up for surface modification

The argon gas flowed to the sample throughΦ 1 mm holes of the microplasma electrode.
Active species, radicals and ions weregenerated and flowed by argon gas andaffected the surface of treated objects.
The surface maximum temperature ofmicroplasma electrode was 41.65 ℃ after
3aminutes of discharge.
[℃]

Contact angle-Irradiation distance3. 2 Photovoltaic Measurement
Experimental condition (3.2, 3.3)
TargetTiO2 layer

Calcining temperature

120 ℃

Calcining time

15 minProcess gas

Argon

Irradiation distance 250 µm

Thermogragh of the microplasma electrodeafter 3 min discharge

Gas flow rate

5.0 L/min

Chamber volume

3.4 L

Treatment time

3 min

Applied voltage

500 V

Comparison of dye adsorption amountbetween control samples and treated samples.

4. Conclusions■ After microplasma treatment of the surfaceof ITO film, the photo conversion efficiency
was improved by 9% in comparison withthe untreated samples. After treatment ofthe TiO2 layer, the efficiency was improvedby 27%.
■ Plasma irradiation of the ITO film caused
the increase of the hydrophilic property.
■ Increase of amount of dye adsorption wascaused by microplasma treatment of TiO2layer.