Water-in-PDMS emulsion templating of highly interconnected ...
Dye-Sensitized Solar Cells (DSSC) from Black Rice and its Performance Improvement by Depositing...
Transcript of Dye-Sensitized Solar Cells (DSSC) from Black Rice and its Performance Improvement by Depositing...
Dye-Sensitized Solar Cells (DSSC) from Black Rice and its Performance Improvement by Depositing Interconnected Copper (Copper Bridge) into
the Space between TiO2 Nanoparticles
Sahrul Saehana, Elfi Yuliza, Pepen Arifin, Khairurrijal, and Mikrajuddin Abdullaha
Department of Physics, Bandung Institute of Technology, Jalan Ganesa 10 Bandung 40132, Indonesia
Keywords: DSSC, I-V performance, copper bridge, and internal resistance
Abstract. Dye-sensitized solar cell (DSSC) which employed natural dye from black rice has been
successfully fabricated and improved its performance by depositing interconnected copper (copper
bridge) on the space between TiO2 particles. The copper bridge has significant role in minimizing
recombination of electron-hole which occurred in TiO2 surface by trapping electron and facilitating
to anode. The presence of interconnected copper nanoparticle in the space between TiO2
nanoparticles was confirmed by Scanning Electron Microscopy (SEM) and X-Ray Diffractometer
(XRD). The current-voltage (I-V) characterization of DSSC solar cells by using Keithley 617 was
also performed to investigate performance of solar cells under sun illumination in varying
intensities. It is found that performance of copper coated DSSC solar cells (efficiency 0.35% and
fill factor 0.35) is higher than DSSC without copper coating (efficiency 0.17% and fill factor 0.35).
This result is consistent with impedance spectroscopy analyzing where the internal resistance of
copper coated DSSC solar cells is lower than DSSC without coated. It is concluded that
performance of DSSC increasing with decreasing of internal resistance. Our finding is higher than
other researcher reports in Ref. [13] and [14] with similar structure and kind of natural dye. In
addition, this paper also reports the use of polymer electrolyte which employing polyvinyl acetate
(PVA) containing lithium ion to maintain long-term stability of device.
Introduction
Recently, application of TiO2 material is enormous, ranging from the fields of renewable energy
(solar cells) [1-8], to the environmental field as a photocatalyst [9] and water filter [10]. In energy
application, this material is widely used in dye-sensitized solar cells (DSSC) due to the small
particle size, wide surface area and large band gap [1,11]. A number of TiO2 unique characteristics
allowed its surface can be loaded dye molecules and play significant in electronic transport.
Some paper reports that DSSC solar cells have high efficiency [2-5] and it can be fabricated by
using a simple deposition method [12]. Moreover, photosensitive component (dye) can be derived
from materials containing anthocyanins which are widely available in nature, such as fruit, flower
and leaf [12-19]. However, some paper also reports that some unexpected phenomena, such as
recombination, still occurred in DSSC [2,22]. Other the hand, effort to optimize long-term stability
and encapsulating of this device are needed for application in industry [23].
Some efforts has been devoted to enhancing performance of DSSC, such as improving long-term
stability by employing polymer electrolyte [23-25], minimizing cost of production by depositing
carbon or graphite as counter electrode [26-27] and using the natural dye as photosensitizer [13-21].
Moreover, the use of natural dye is not only for reducing cost of production but also proposing for
environmentally-friendly [14]. Although its absorbance ability is lower than dye synthetic, such as
ruthenium complex, but the findings of Hao et al. [21] and Yuliarto et al. [13] showed that extracts
of black rice can be used as photosensitizer in DSSC. Furthermore, Hao et al. [21] also reports that
the dye of black rice extract is the best natural dye which can be used in DSSC. It is be caused, this
kind of dye can absorb wavelength in wide spectrum.
Materials Science Forum Vol. 737 (2013) pp 43-53© (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/MSF.737.43
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 192.172.226.121-07/01/13,03:12:35)
Fig.1 (a) Mechanism and (b) band diagram of DSSC solar cells [21].
Fig. 1a depicts the mechanism which occurred in DSSC solar cells. Fig. 1b shows the band
diagram of DSSC solar cells, where the desired process is marked by the green line (1) electron
injection, (2) the collection of electrons, and (3) dye regeneration. On the contrary, it also shows the
unexpected process, which is signed by red lines, namely: (4) decay, (5) recombination and (6)
recaption reaction [21].
Recombination process, as shown in Fig. 1a, is one of the crucial phenomena which occurred in
DSSC solar cells and it is reducing efficiency of solar cells [27-28]. Some papers reports [27-33,
36-39] that the deposition of metal-semiconductor contact (Schottky contacts) in the TiO2 surface is
one of effective method to reduce these phenomena. However, depositing Schottky contact to
improve DSSC performance, which conducted by other researcher [28-35], used complicated
process and employing expensive metal, such as gold.
Fig. 2 (a) Structure of our proposed solar cells, and (b) Its band diagram (Cu coated DSSC,
Cu:DSSC).
44 Nanotechnology Applications in Energy and Environment
Through this study, we fabricated DSSC solar cells by using low cost material and simple
methods to deposit Schottky contact. Design of our DSSC solar cells was depicted in Fig. 2a. It was
shown that dye coated around the interconnecting TiO2 absorbed photon and electron was
generated. The electrons are conducted through interconnecting TiO2 and copper nanoparticle to the
anode, while the holes are transfer through the polymer electrolyte of iodine in contact with
platinum catalyst at the cathode. On the other hand, Fig. 2b shows the band diagram of our solar
cells. It is shown that the interconnected copper (copper bridge) play a role to trap electrons on TiO2
conduction band and then flow it quickly to the main electrode (anode). This approach is applied to
reduce the recombination phenomena as described in our previous paper [34-36].
In this paper, we report the use of natural dyes extracted from black rice as photo sensitizer in
DSSC. We also report our significant efforts to improve performance of DSSC by deposition
Schottky contacts with a simple method (electroplating). Moreover, internal resistance of our solar
cells, which was coated by copper, was investigated by employing Electrochemical Impedance
Spectroscopy (EIS), and then it was analyzed by comparing with DSSC solar cells without copper
coating. We also demonstrate the use of polyvinyl acetate (PVA) containing lithium ion as polymer
electrolyte to support long term stability of devices. Simplicity and low cost of deposition method is
expected to facilitate its application in large-scale production (industry).
Experiment
A TiO2 film was deposited on a substrate of indium tin oxide (ITO) by using the spray method [36-
39]. A TiO2 suspension prepared by dispersion of 5 gr. of TiO2 in 10 mL water and it was stirred by
using a magnetic stirrer for 45 minutes. The suspension is then sprayed on ITO substrate which is
placed on a hotplate with temperature about 150°C [11]. Spraying process was repeated about 10
times, and then the uniform TiO2 films were obtained. Then, this film was heated at 450°C in
furnace for 45 minutes to improve contacts between the particles of TiO2 and TiO2 particles with
the substrate.
Copper (Cu) was deposited on TiO2 films by performing electroplating methods. Electroplating
process was carried out on 55°C of electrolyte solution and 50 mA of electric current for one
second. The 20 mL of copper sulfate (Cu2SO4) was used as electrolyte solution. Copper rod with
purity about 99.99% is also used as the anode.
Extracting process was begun by inserting 10 gr. black rice into the solvent and then it was
stirred by magnetic stirrer at temperature 50°C for 30 minutes. In this process, we used solvent
which contained alcohol, acetic acid, and distilled water with morality ratio about 3:2:1. Then,
solution was filtered by filter paper (1 mm mesh) and dark-red solution was obtained. TiO2 films
were immersed in dye solution for 24 hours [13,20]. Then, it was cleaned by distilled water and
then it was heated at temperature 40°C for 10 minutes.
A polymer electrolyte was made by dissolving LiOH (0.09 g) in water (10 mL) and stirring for 1
hour. Then, this solution was added into 10 mL of polyvinyl acetate (PVA) and stirring for 2 hours.
Furthermore, the iodolyte solution (Solaronix, Switzerland) containing I-/I
3- ion added to the
polymer electrolyte. Sandwich structure solar cell devices were made by depositing a polymer
electrolyte on TiO2 films and covered with counter electrodes which made from platinum coated
indium tin oxide with a thickness about 70 nm.
Characterization of the crystal structure of TiO2 films were analyzed by using X-ray
Diffractometer (PW1710). Scanning Electron Microscopy (JEOL JSM-6360LA) which operated at
a voltage of 20 kV was also used to investigate the film morphology. On the other hand, the
performance of solar cells was measured by using Keithley 617. A measurement was done on the
dark and under sun illumination (67.08 mW/cm2). Sunlight intensity is measured by using solar
power TM-206 meter. Moreover, internal resistance of solar cell devices was investigated by
performing impedance spectroscopy (EIS) at a frequency of 20 Hz-2 MHz (Agilent E4980A
Precision LCR meter).
Materials Science Forum Vol. 737 45
Result and Discussion
Scanning Electron Microscopy (SEM) of TiO2 films which fabricated by spray method on ITO
substrate is depicted in Fig. 3. Homogeneous of the film was observed and particle size was
predicted in nanometers scale. In this size, we estimated dye molecule can occupied on its surface.
Moreover, morphology of TiO2 film which coated with copper was presented in Fig. 3b. It is shown
clearly that contact between TiO2 particles and copper was occurred. The presence of copper bridge
was expected to make electron transport to anode be quick. Although, Lai et al. [30] reported that
presence of metal bridge can reduce transmittance of TiO2 films, however, increasing performance
of DSSC solar cells was still achieved.
Fig. 3 Scanning Electron Microscopy (SEM) of TiO2 film: (a) before coated with copper, and (b)
after coated with copper nanoparticle.
In our previous paper [36-39], we have reported that the contact between TiO2 semiconductor
and the metal (Schottky contacts) can reduce recombination in solar cells. It has explained that
electrons in the conduction band of TiO2 material tends to transfer to the metal which has a higher
work function. Illustration of this process was explained by energy diagram in Fig. 4.
Fig. 4 Energy diagram of semiconductor-metal junction [38-39].
46 Nanotechnology Applications in Energy and Environment
Crystal structure of TiO2 film, which was fabricated by spray methods, was investigated by
performing X-Ray Diffraction (XRD) PW1710. Its characteristics before and after coated by copper
nanoparticle are explained in Fig. 5. Figure 5a describe clearly that the TiO2 particles (PDF number:
21-1272) are in anatase phase with a diffraction peak at 25.280°, 36.944°, 37.799°, 48.047°,
53.887°, 55.058°, 62.686°, and 75.026°, respectively. Furthermore, Fig. 5b also confirms that the
copper nanoparticle (PDF number: 04-0836) has been successfully deposited on TiO2 films and its
peaks appear at 43.295°, 50.431° and 74.127°.
Fig. 5 X-ray diffraction pattern of TiO2 film: (a) before coated with copper, and (b) after coated
with copper nanoparticle.
From above result, TiO2 and copper crystal size was calculated by using Scherrer equation [40]. It is
found that the average size both of material is about 100 nm and 40 nm, respectively. In this study,
we use dye which was extracted from black rice (Bandung, Indonesia). According to Buraidah et al.
[14] that dye from black rice contains molecules of anthocyanins (cyanidin-3-glucoside and
peonidin-3-glucoside), and it can absorb photons in a wide spectral range. The chemical structure
and its bonding with TiO2 nanoparticle is illustrated in Fig. 6 (a,b). It can be seen that TiO2 particles
can form a bond with a group hidroxyl on cyanidin-3-glucoside and peonidin-3-glucoside.
Fig. 6 (a) Chemical structure of anthocyanin (cyanidin-3-glucoside dan peonidin-3-glucoside) from
black rice, and (b) Chemical bonding of anthocyanin and TiO2 particle [13].
Materials Science Forum Vol. 737 47
In order to get optimum efficiency of DSSC solar cells, parameter which influencing absorbance
and dye loading as reported by other researcher [13-21], namely solution pH and temperature for
extracting, were used. We also used optimum time for dipping TiO2 film in dye solution as reported
by Takeuchi et al. [20]. Moreover, alcohol as organic and an effective solvent, as reported by
Buraidah et al. [14], were also used in extraction process. This treatment is related with ability for
optimum extracting process. A number of dyes loading on TiO2 surface were not discussed in this
paper.
UV-Vis characterization result, as shown in Fig. 7, indicates that natural dye from black rice is
potential to application in DSSC solar cells, due to wide of its absorption. From this figure, it can be
observed that there are two absorption peaks, where the first and second peak is at 350 nm and 500
nm, respectively. This characterization result is consistent with other paper reports [13,14,21].
Fig. 7 Absorbance spectrum of dye molecule extracted from black rice.
To determine performance of DSSC solar cells, calculation of fill factor and efficiency was
performed by using Equation (1) and (2) [13].
FF =
, (1)
η =
. (2)
where Imax is the maximum current, Vmax is maximum voltage, Isc is the solar cell current measured
at voltage V=0, Voc is the solar cell voltage measured at zero current and Pin is input power which
was get from illumination.
Fig. 8 shows the performance of DSCC solar cells without copper which comparing with DSSC
solar cells with employing copper bridges. It can be seen that performance of copper coated DSSC
(efficiency 0.35% and fill factor 0.35) is higher than DSSC without copper coating (efficiency
0.17% and fill factor 0.35). The possible reason is that copper bridges which contact with TiO2
particles enhance the electron transport, so that DSSC solar cell efficiency increases. However,
some paper [41-50] also reports that performance of solar cell was influenced by internal resistance.
Particularly, Han et al. [41-43] explained detail that performance of solar cells increase with
decreasing of internal resistance of solar cells.
48 Nanotechnology Applications in Energy and Environment
Fig. 8 I-V characterization result: (a) Cu coated DSSC (Cu:DSSC), and (b) Cu uncoated Cu.
I-V characterization result of our solar cells, which was shown in Fig. 8, can be explained by
analyzing its circuit model as reported in some paper [2,41-48]. Simple circuit for solar cell in
steady illumination was illustrated in Fig. 9a [2]. Maximum performance of solar cells was obtained
by minimizing the series resistance, Rs, and maintaining the shunt resistance, Rsh, as high possible.
On the other hand, Fig. 9b also depicts the electrical equivalent for DSSC. The internal resistance of
solar cells is the sum of the each component given in Fig. 9b (Z = Z0+Z1+Z2+Z3). It is respectively
the contact impedance (TCO), Pt-catalyzed counter electrode impedance, complex impedance, and
Warburg impedance [2].
Fig. 9 (a) A simple equivalent circuit for DSSC, (b) a representative electrical equivalent of DSSC,
and (c) illustration of recombination process in DSSC [2].
It has explained by Lee et al. [2] that complex impedance (Z2 component), which represents the
interface between TiO2, dye and electrolyte, gives most important contribution to the total
resistance. Highly Z2 component may be caused by recombination process which may occurred in
Materials Science Forum Vol. 737 49
TiO2, as illustrated in Fig. 9c. The presence metal semiconductor junction (Schottky junction)
occurred in our DSSC was possibly minimizing recombination phenomena at TiO2 surface because
this junction can trap electron and facilitating electronic transport to the main electrode (anode). As
the consequences, resistance of Z2 component reduced and performance of DSSC, as shown in Fig.
8a, was improved.
Moreover, in order to know effect of copper bridges more detail on internal resistance of our
solar cells, investigating by Electrochemical Impedance Spectroscopy (EIS) was performed. The
data obtained by using EIS measurements are then plotted with EIS software because limitation of
EIS instrument and equivalent circuit which was formulated by Han et al. [41], as shown in inset of
Fig. 10, was used. Then, performance of the solar cells was observed under sun illumination. The
EIS analyzing was summarized in Table 1.
Fig.10 Schematic Nyquist plot of DSSC solar cells and its equivalent model (inset) [41].
In Fig. 10, resistance which occurred on contact between TiO2 and substrate are represented R1.
Electronic transport on the dye/TiO2/Cu junction was represented with parallel circuit between R2
and C1. However, electronic transport occurred at polymer electrolytes and counter electrode was
respectively illustrated with parallel circuit between R3 and C2, as well as R4.
Table 1. Comparisons of the internal resistance of our DSSC solar cells analyzed by using EIS
DSSC Structure Intensity
(mW/cm2)
R1(Ω) R2(Ω) R3(Ω) R4(Ω) Internal
Resistance (Ω)
TiO2/dye/polymer
electrolyte/Pt
37.08 50 4,000 180 20 4,250
TiO2:Cu/dye/polymer
electrolyte/Pt
37.08 50 200 190 20 460
Table 1 describes that, at the same intensity, the internal resistance of DSSC solar cells after
coating with copper is smaller (about 9x) than before copper coating. This data was agreed with
result which was presented by Fig. 8. It was found that increasing of solar cell performance can be
implied decreasing of solar cells resistance. As stated above, that the presence of metal
semiconductor junction (Schottky junction) occurred in our DSSC minimizing recombination
phenomena at TiO2 surface and the consequences, resistance of Z2 component reduced about twenty
50 Nanotechnology Applications in Energy and Environment
times (20x) after coating copper. So, we concluded that contact between TiO2 and copper
nanoparticle (Schottky contacts) can improve electronic transport to the main electrode (anode),
then total resistance of solar cell can be reduced.
Furthermore, we also demonstrated the use of polymer electrolyte consisting of polyvinyl acetate
(PVA) containing lithium ion. It is proposed to improve the efficiency of solar cells and also
supporting long-term stability. In order to know effect of this treatment, we compared two kinds of
solar cells which employing a polymer electrolyte and without polymer electrolyte (liquid
electrolyte). I-V measurement results of both DSSC solar cells with different electrolytes were
shown in Fig. 11.
Fig. 11 Performance of DSSC: (a) employing polymer electrolyte, and (b) liquid electrolyte
It can be seen in Fig. 11 that DSSC which employing polymer electrolyte and liquid electrolyte
has quite similar performance. However, long term stability of DSSC with polymer electrolyte is
better than without polymer electrolyte as shown in Fig. 12.
Fig. 12 Performance of DSSC solar cells under sun illumination
Performances of both solar cells for 6 days are presented in Fig. 12. DSSC with polymer
electrolytes is more stable than DSSC without polymer electrolytes. The possible reason is that
iodine ion distributed in the polymer chain, as reported by Wang et al. [25], can be exist in long
period. In the further study, optimation some parameter, such as thickness of TiO2, a number of dye
loading, TiO2 particle size, conductivity of polymer and thickness of catalyst on the counter
electrode was required to improve performance of solar cells.
Materials Science Forum Vol. 737 51
Conclusion
DSSC solar cells which employing black rice as photosensitizer has been successfully fabricated
and improved its performance by depositing interconnected copper (copper bridge) in the space
between TiO2 particles. The observation by Scanning Electron Microscopy (SEM) and X-Ray
Diffraction (XRD) shows that interconnected copper in nanometer size has been successfully
deposited. Moreover, I-V characterization shows that performance of copper coated DSSC is higher
than uncoated DSSC. It is concluded that the presence of a copper bridge reducing the internal
resistance of DSSC solar cells and facilitating electronic transfer to anode. In addition, long-term
stability of DSSC solar cells was also achieved by employing PVA-based polymer electrolytes
containing iodine ion.
Acknowledgements
This work was partially supported by the Innovations and KK ITB Research Grant and
Decentralization Research Grant of Directorate General of Higher Education, Ministry of National
Education, and the Republic of Indonesia in the fiscal years of 2011/2012.
References
[1] M. Grätzel, J. Photochem. Photobiol. C, Photochem. Rev. 4 (2003) 145.
[2] B. Lee, D-K. Hwang, P. Guo, S-T. Ho, D.B. Buchholtz, C-Y. Wang and R.P.H. Chang, J.
Phys. Chem. B 114 (2010) 14582.
[3] A. Islam, S.P. Singh, M. Yanagida, M.R. Karim and L. Han, Int. J. Photoen. 201 (2011) 1.
[4] S.P. Singh, A. Islam, M. Yanagida and L. Han, Int. J. Photoen. 2011 (2011) 1.
[5] Y. Chiba, A. Islam, Y. Watanabe, R. Komiya, N. Koide and L. Han, Jpn. J. Appl. Phys. 45
(2006) L638.
[6] F.O. Lenzmann and J.M. Kroon, Adv. OptoElectron. 27 (2007) 1.
[7] Z. Huang, X. Liu, K. Li, D. Li, Y. Luo, H. Li, W. Song, L.Q. Chen and Q. Meng,
Electrochem. Commun. 9 (2007) 596.
[8] B. O'Regan and M. Grätzel, Lett. Nature 353 (1991) 737.
[9] V.A. Isnaeni, O. Arutanti, E. Sustini, H. Aliah, Khairurrijal and M. Abdullah, Environ. Prog.
Sustain. Energy 01 (2011) 1.
[10] Masturi, Silvia, M.P. Aji, E. Sustini, Khairurrijal and M. Abdullah, Am. J. Environ. Sci. 8
(2012) 79.
[11] M. Abdullah, Y. Virgus, Nirmin and Khairurrijal, J. Nano Saintek. 1 (2008) 33.
[12] J. Halme, J. Saarinen and P. Lund, Solar Energy Mat. Solar Cells 90 (2006) 887.
[13] B. Yuliarto, W. Septina, K. Fuadi, F. Fanani, L. Muliani and Nugraha, Adv. Mat. Sci. Eng.,
2010 (2010) 1.
[14] M.H. Buraidah, L. P. Teo, S.N.F. Yusuf, M.M. Noor, M.Z. Kufian, M.A. Careem, S. R.
Majid, R.M. Taha and A. K. Arof, Int. J. Photoen. 2011 (2011) 273683.
[15] M.R. Narayan, Renew. Sustain. Energy Rev. 16 (2012) 208.
[16] Q. Dai and J. Rabani, J. Photochem. Photobiol. A, Chem. 148 (2002) 17.
[17] H. Zhou, L. Wu, Y. Gao and T. Ma, J. Photochem. Photobiol. A, Chem. 219 (2011) 188.
[18] G. Calogero, G.D. Marco, S. Cazzanti, S. Caramori, R. Argazzi, A.D Carlo and C.A.
Bignozzi, Int. J. Mol. Sci. 11 (2010) 254.
[19] M.H. Bazargan, M.M. Byranvand, A.N. Kharat and L. Fatholahi, Optoelectro. Adv. Mat.
Rapid Comm. 5 (2011) 360.
[20] H. Takeuchi and S. Furukawa, IEICE Trans Electron. E94-C 12 (2011) 1832.
[21] S. Hao, J. Wu, Y. Huang and J. Lin, Solar Energy 80 (2006) 209.
[22] F. Xu and L Sun, Energy Environ. Sci. 4 (2011) 818.
[23] M-S. Kang, J.H. Kim, Y.J.Kim, J. Won, N-G. Park and Y.S. Kang, Chem. Commun. 889
(2005) 889.
[24] K.J. Jiang, Y.L. Sun, K.F. Shao, J.F. Wang and L.M. Yang, Chin. Chem. Lett. 14 (2003) 1093
52 Nanotechnology Applications in Energy and Environment
[25] Q. Wang, Z. Zhang, S.M. Zakeeruddin and M. Gratzel, J. Phys. Chem. C 2008 112 (2008)
7084.
[26] P. Johshi, Y. Xie, M. Ropp, D. Galipeau, S. Bailey and Q. Qiao, Energy Environ. Sci. 2009
(2009) 426.
[27] Y-S. Wei, Q-Q. Jin and T-Z. Ren, Sol.-Sta. Electro. 63 (2011) 76.
[28] X. Wang, D.R.G. Mitchell, K. Prince, A.J. Atanacio and R.A. Caruso, Chem. Mater. 20
(2008) 3917.
[29] Y.H. Su, W.H. Lai, L.G. Teoh, M.H. Hon and J.L. Huang, Appl. Phys. A 88 (2007) 173.
[30] W.H. Lai, Y.H. Su, L.G. Teoh and M.H. Hon, J. Photochem. Photobiol. A, Chemistry 195
(2008) 307.
[31] U. Pal, E.A. Almanza, O.V. Cuchilloa, N. Koshizaki, T. Sasaki and S. Terauchi, Solar Energy
Mat. Solar Cells 70 (2001) 363.
[32] Y. Tian, H. Notsu and T. Tatsuma, Photochem. Photobiol. Sci. 4 (2005) 598.
[33] V. Dhas, S. Muduli, W. Lee, S-H. Han and S. Ogale, Appl. Phys. Lett. 93 (2008) 243108.
[34] C.K.N. Peh, L. Ke and G.W. Ho: Mat. Lett. 64 (2010) 1372.
[35] T. Bora, H.H. Kyaw, S. Sarkar, S.K. Pal and J. Dutta, Beilstein J. Nanotechnol. 2 (2011) 681.
[36] S. Saehana, R. Prasetyowati, M.I. Hidayat, Khairurrijal and M. Abdullah, AIP Conf. Proc.
1284 (2010) 154.
[37] S. Saehana, R. Prasetyowati, M.I. Hidayat, P. Arifin, Khairurrijal and M. Abdullah, AIP Conf.
Proc. 1415 (2011) 163.
[38] S. Saehana, R. Prasetyowati, M. I. Hidayat, P. Arifin, Khairurrijal and M. Abdullah,
IJBAS/IJENS 11 (2011) 15.
[39] S. Saehana, P. Arifin, Khairurrijal and M. Abdullah, J. Appl. Phys. 111 (2012) 123109
[40] M. Abdullah dan Khairurrijal, Karakterisasi Nanomaterial, Teori, Penerapan dan Pengolahan
Data, Rezeki Putra Bandung Press, Bandung, 2010.
[41] L. Han, Y. Koide, Y. Chiba, A. Islam and T. Mitate, Comptes Rendus Chimie 9 (2006) 645.
[42] L. Han, N. Koide, Y. Chiba, A. Islam, R. Komiya, N. Fuke, A. Fukui and R. Yamanaka,
Appl. Phys. Lett. 86 (2005) 213501.
[43] L. Han, N. Koide, Y. Chiba and T. Mitate, Appl. Phys. Lett. 84 (2004) 2433.
[44] R. Kern, R. Sastrawan, J. Ferber, R. Stangl and J. Luther, Electrochim. Acta 47 (2002) 4213.
[45] M. Radecka, M. Wierzbicka and M. Rekas, Physica B, Cond. Matt. 351 (2004) 121.
[46] T. Hoshikawa, R. Kikuchi and K. Eguchi, J. Electroanal. Chem. 588 (2006) 59.
[47] T. Hoshikawa, T. Ikebe, R. Kikuchi and K. Eguchi, Electrochim. Acta 51 (2006) 5286.
[48] M. Adachi, M. Sakamoto, J. Jiu, Y. Ogata and S. Isoda, J. Phys. Chem. B 110 (28) (2006)
2053.
[49] V. Yong, S-T. Ho and R.P.H. Chang, Appl. Phys. Lett. 92 (2008) 143506.
[50] T. Hanmin, Z. Xiaobo, Y. Shikui, W. Xiangyan, T. Zhipeng, L. Bin, W. Ying, Yu Tao and Z.
Zhigang, Solar Energy 83 (2009) 715.
Materials Science Forum Vol. 737 53