1. UNIVERSITI MALAYSIA PERLIS Knowledge . Sincerity . Excellence
Annealing Effect on Titanium Dioxide Layer in paired Hybrid Carbon Nanotubes - Graphene as Dye Sensitized Solar Cell Working Electrode
Siti S. Mat Isa, M. R. Muda, Muhammad M. Ramli and N. A. M. Hambali
School of Microelectronics Engineering, UniMAP
Introduction of Dye Sensitized Solar Cell
Introduction of Hybrid System CNT-Graphene
Results and Discussions
Conclusion
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3. UNIVERSITI MALAYSIA PERLIS
Why DYE SENSITIZED SOLAR CELL (DSCC) ??
Relatively high efficiency, High simplicity, Environmental friendly, Low cost production
Concern in DSSCs performance : Accelerate electron transport and suppress the charge recombination
Concern in Working/Counter Electrode : Layer that has active photocatalytic activity/ conductive electrode
Concerns in Dye :
1) Chemical group: possess a chemical group (anchoring group – carboxyl & hydroxyl) that can attach (adsorb) to the TiO2 surface
2) Energy level: must have energy levels at the proper positions necessary for electron injection and sensitization
SOLUTION FOR THE CONCERNS:
CARBON BASED MATERIAL
(CARBON NANOTUBES, GRAPHENE)
High charge carrier mobility
Excellent electrical conductivity
High surface area
3) Thickness: acts as the absorber of the lights, dye must be very thin layer for active charge (electron) injection (almost every excited electron produce by light absorption can rapidly be transferred into
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STRUCTURE OF DYE SENSITIZED SOLAR CELL (DSCC)
ITO
Working Electrode
Dye
Iodide Electrolyte
Counter Electrode
ITO
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5. DSSC WORKING PRINCIPLES
Dye discharges electrons when hit by sunlight. Discharged electrons move toward a Working Electrode (-ve electrode) through TiO2 which resulted dye is oxidized in the process
2. Electrons have reached the Working Electrode move toward catalyst and Counter Electrode (+ve electrode) through and external circuit
3. Iodide electrolyte receives electrons from the Counter Electrode.
4. Electrolyte provides received electrons to dye.
DSSC Structure
EneLEAF (2014)

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CARBON NANOTUBES (CNTs)
CNTs are allotropes of carbon with a cylindrical nanostructure.
Type : Single-Walled CNTs (SWCNTs), Double-Walled CNTs (DWCNTs) and Multi-Walled CNTs (MWCNTs)
CNTs can DOUBLE the efficiency of the photochemical solar cells [1]. It has been proved that CNT itself can generate electron-hole pairs when shining the light which enhance the efficiency of the photovoltaic devices [2].
[1] A. Kongkanand, R.M. Domínguez, P. V. Kama, “Single Wall Carbon Nanotube Scaffolds for Photoelectrochemical Solar Cells. Capture and Transport of Photogenerated Electrons”, Nano Lett., (2007), 7 (3), 676–680.
[2] J.U. Lee, “Photovoltaic effect in ideal carbon nanotube diodes”, Appl. Phys. Lett. 87, (2005)
SWCNTs, DWCNTs and MWCNTs
Physicsworld (2013)
MWCNTs structure
Ijima (1991)
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GRAPHENE
Pure carbon in the form of very thin, nearly transparent sheet, one atom thick
Crystalline allotrope of carbon with 2 D properties. The carbon atoms are densely packed in a regular sp2 bonded hexagonal pattern
Graphene thin films that has been used for the similar devices has shown better performance compared to CNT devices [3]
as this material has high electron and hole transport mobility, large specific surface area and inertness against oxygen and water vapor that make graphene as a promising material in photovoltaic applications
[3] C. X. Guo, H. B. Yang, Z. M. Sheng, Z. S. Lu, Q. L. Song, C. M. Li, “Layered Graphene/Quantum Dots for Photovoltaic Devices”, Angewandte Chemie, Volume 122 Issue 17, (2010), 3078 – 3081.
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STRUCTURE OF DYE SENSITIZED SOLAR CELL (DSCC)
ITO
Working Electrode
Dye
Iodide Electrolyte
Counter Electrode
ITO
THIS STUDY
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THIS STUDY FOCUS: TIO2 (WORKING ELECTRODE) + HYBRID CNTs-G (DYE)
TIO2 (WORKING ELECTRODE)
large band gap of energy (1.8 – 4.1 ev)
high refractive index
ability of the surface to resist the continuous transfer of electron under illumination solar photon
large surface area of the porous and spongy like structure can enhance the light adsorption of the dye molecules and electron efficiency between the interfaces in DSSC
the crystal structure of TiO2 also affects the performance of the electrode layer.
Hybrid CNTs-G (DYE)
Hybrid may increase the conversion efficiency of the DSSC as the electron charge transfer can be improved by the adsorption of the dye (hybrid system) on the semiconducting layer.
The presence of hydrophilic group (carboxyl and hydroxyl) that act as a good binder on the surface of hybrid material was also believed can provide a better conducting pathways.
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10. RESULTS AND DISCUSSIONS HYBRID GRAPHENE-CARBON NANOTUBES+ GO
rGO
1 mL reduced Graphene Oxide
10 mL Functionalized SWCNTs using HNO3 washing procedure
Sonicated,filtered and washed
Hybrid G-CNTs in DI water

11. EFFECTS OF ANNEALING ON TITANIUM DIOXIDE
AFM images of TiO2 at different temperature
TiO2 deposit using Dr. Blade method
Uniform deposited layers
Temperature increases, the grain size increases
No significant results between pure and diluted HNO3

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SEM images of TiO2 at different temperatures
Surface morphology at 650 °C was very rough.
TiO2 particles at higher temperature were more individual.
The aggregation of particles happened because the stress-induced surface rumpling that can caused by the fast cooling after annealing process.
At lower temperatures, the surface of thin films look amorphous.
Large particle distribution was attained at 650 °C , (diameter size ̴ 5 – 20 nm).
Annealing temperature did not give any significant effect to the thickness of TiO2
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Anatase is photocatalytically active than rutile structure ( °C)
As the temperature increased (650 °C), the rutile structure was started to form
650 °C A
Formation of anatase and rutile structure at 650 °C R R A A A R A
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14. + UNIVERSITI MALAYSIA PERLIS PHOTOCATALYTIC ACTIVITY Counter Electrode
Working Electrode
An assembled DSSCs measured by 60W of simulated solar irradiance
Iodide electrolyte
DSSC
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Temperature (C)
ISC (µ)
VOC (mV)
η (%)
450
49.25 28
0.0016
550
12.55 34
0.0003
650 –
High efficiency obtained at 450 °C. It was believed that anatase content for TiO2 surface initiate to the efficient photocatalytic activity.
At 550 °C, difference photocatalytic activity was achieved although similar anatase structure as 450 °C was obtained.
At 650 °C, the measurement was unsuccessful. This might happened because the high percentage of rutile phase obtained at the surface structure was inactive, thus show no activity.
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CONCLUSION
The optimum annealing temperature for TiO2 film was at 450 °C, where active photocatalytic activity was initiated by the anatase TiO2 formation that contributed to the highest conversion efficiency of the device performance
Overall efficiencies still quite low. This fact implies that the photocatalytic activity did not only depends on the TiO2 surface structure only at certain annealing temperature but also affected by other factors like dye material.
ACKNOWLEDGEMENT : This work was partially supported by Fundamental Research Grant (FRGS) and Research Acculturation Grant Scheme (RAGS) funded by Ministry of Education Malaysia. Authors would also want to thank Cluster of Sustainable Engineering, School of Materials Engineering, University Malaysia Perlis.
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