Preparation of PAH/Graphene Oxide Layer-by-Layer Films
for Application on Solar Cells
I. C. C. Assunção
1
, P. A. Ribeiro
1
,
Q. Ferreira
2
, M. Raposo
1
and S. Sério
1
1
CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa,
2829-516 Caparica, Portugal
2
Instituto de Telecomunicações, Instituto Superior Técnico, University of Lisbon,
Av. Rovisco Pais, P-1049-001 Lisboa, Portugal
Keywords: Graphene Oxide, PAH, Hybrid Solar Cells, LBL Films.
Abstract: In this study we provide the preparation and characterization of layer-by-layer LBL films made with
poly(allylamine hydrochloride) (PAH) alternated with graphene oxide. The scanning electron microscopy
(SEM) and atomic force microscopy (AFM) showed a smooth surface with a RMS roughness of 5.74 nm.
The LBL films were also characterized by means of UV-vis spectroscopy. The I-V characteristic curve
evidenced a typical semiconductor behaviour.
1 INTRODUCTION
Since the nineteenth century, the humanity has relied
mainly on fossil fuels for energy needs. However,
with the growing concern and awareness around the
environmental problems caused by the increase in
greenhouse gases and other pollutants responsible
for the global warming, as well as the possibility of
depletion of fossil fuels, increased the demand for
energy sources environmentally friendly and
sustainable (Choe, 2013). The challenge to obtain
renewable energy sources with low-cost, led the
scientific community to develop other alternatives,
namely efficient photovoltaic cells (Günes, 2007).
Efforts to find alternative energy sources to fossil
fuels have been recorded globally. In 2006, the US
announced its "Advanced Energy Initiative", which
outlined a goal of reducing oil imports from the
Middle East by 75% by the year 2025 through the
development of new energy sources and also
renewable. The European Union (EU) approved a
plan (SET-Plan) which set the target of reducing
emissions of EU greenhouse gases emissions by at
least 20% up to 2020 compared to emissions in
1990. The Korean government established "The
second National Plan for Technology Energy
Development". With this plan, South Korea aims to
develop new renewable energy technologies and
improve energy efficiency by increasing investment
in research and development of renewable energy up
to 2020. In addition, Japan, China and Canada have
also established national agendas for the
development of new renewable energy technologies
to reduce their dependence on fossil fuels and
promote the strategic development of Green
industries.
Currently, the most widely used systems for the
conversion of solar energy are inorganic solar cells,
including silicon solar cells which dominate 85% of
photovoltaic industry market. Due to the high
production costs of silicon cells, researchers in
recent years have focused on research and
development of alternatives for this type of cells
(Sun, 2015; Rowell, 2006).
The development of organic solar cells (OSC)
based on polymer materials, is a new technology that
within a short period, can produce clean energy at a
more reasonable cost. Since the polymeric solar cells
are light and capable of becoming flexible opens up
a range of new applications. Furthermore, large OSC
(large area) can be manufactured easily and
inexpensively by employing low-cost techniques,
such as screen printing, slot-die coating, gravure and
spray coating, etc. (Sun, 2015) .
OSCs have emerged as a promising alternative to
photovoltaic technology, due to profitable
production potential of flexible devices of large
surface using processing techniques with low
environmental impact and also versatility in organic
Assunção, I., Ribeiro, P., Ferreira, Q., Raposo, M. and Sério, S.
Preparation of PAH/Graphene Oxide Layer-by-Layer Films for Application on Solar Cells.
DOI: 10.5220/0005843203750378
In Proceedings of the 4th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2016), pages 377-380
ISBN: 978-989-758-174-8
Copyright
c
2016 by SCITEPRESS Science and Technology Publications, Lda. All rights reserved
377
material “design” (Bian, 2012). For the production
of polymer thin films for application in the OSC,
several techniques are used. Among them, the layer-
by-layer technique (Layer-by-Layer, LBL) having
several advantages such as no pollutants production
and also the fact of doesn’t requires highly
sophisticated equipment, makes it an important
technique in such applications. In this context, with
the present work it is aimed to find solutions to
capture solar energy, based on the knowledge
acquired in the last two decades under organic
conductive polymers, photoluminescent and
photochromic (Ferreira 2013, Ferreira 2007 and
Ferreira 2007).
2 EXPERIMENTAL DETAILS
The layer-by-layer films were prepared from
aqueous solutions of poly(allylamine hydrochloride)
(PAH) (Mw ) 50 000-65 000 g/mol) and graphene
oxide (GO) 2 mg/mL, dispersion in H
2
O, with
concentrations of 10
-2
M. The chemicals were
obtained from Aldrich, and the corresponding
molecular structures are shown in Figure 1. The
ultrapure water with a resistivity of 18 M cm was
supplied by a Millipore system (Milli-Q, Millipore
GmbH). The adsorption period was 1 min for the
PAH and GO layers. After adsorption of each layer,
the films were washed with ultra pure water and
dried with a nitrogen flux.
The films were deposited on quartz, Fluorine-
doped tin oxide (FTO) coated glass and
interdigitated glass substrates for the different
characterizations (UV-spectroscopy, Atomic Force
Microscopy (AFM), Scanning Electron Microscopy
(SEM) and I-V measurements).
The quartz and interdigitated glass substrates
were cleaned with a “piranha” solution containing
hydrogen peroxide and a sulfuric acid (1:1) bath for
1h and then rinsed exhaustively with pure water. The
substrates were after dried with nitrogen flow. The
FTO coated glass substrates were ultrasonically
cleaned in a concerted sequence using acetone,
isopropanol, and deionized water, for 5 min each
step and then dried using nitrogen gas flow to
remove any adsorbed organic contamination on
substrates surface.
The films were prepared at room temperature as
well as all the characterizations.
The surface morphology of the films were
investigated by a field-emission scanning electron
microscope (JEOL 7001F) operating at 15 keV. In
order to prevent charge build up, a thin chromium
film was coated on the films surfaces before the
analysis.
(a)
(b)
Figure 1: (a) poly-(allylamine hydrochloride) (PAH); (b)
graphene oxide.
To study the films surface, Atomic Force
Microscopy (AFM) images were obtained with a
Scanning Tunneling Microscopy (STM), Agilent
Technologies, model PicoScan. For each film, scans
of 2 μm x 2 μm were obtained. The films surface
morphology was characterized by the root mean
square roughness (RMS), which was calculated by
Gwyddion software.
The UV-vis spectroscopy for the films was
carried out with a Shimadzu UV b - 2101PC
UV/VIS spectrophotometer at room temperature
within the wavelength range 200-900 nm.
The electric measurements (I-V characteristic
curve) were carried out with a DC POWER
SUPPLY model DF1730SB3A at room temperature
and ambient light, by changing the voltage between
0V and ~1V, with an increment of 20 mV.
3 RESULTS AND DISCUSSION
In figure 2 and figure 3 are depicted some
representative SEM and AFM images for the
AOMat 2016 - Special Session on Advanced Optical Materials
378
PAH/GO LBL films with 20 bilayers. In general it
can be observed from the SEM image that the films
exhibit a smooth surface, which is also consistent
with the RMS roughness value estimated from the
AFM images, which corresponds to 5.74 nm.
Figure 2: Representative SEM image of (PAH/GO)
20
LBL
film deposited on FTO coated glass substrate.
Figure 3: Representative AFM image of (PAH/GO)
20
LBL
film deposited on FTO coated glass substrate.
In figure 4 a) and b) is shown the ultraviolet-visible
absorbance spectra of different number of bilayers of
PAH/GO LBL films and the absorbance intensity at
228 nm as a function of the number of bilayers, N,
respectively. It can be observed that the absorbance
at maximum increases with the number of bilayers
indicating a linear film growth (see figure 4b).
(a)
(b)
Figure 4: (a) Absorbance spectra of PAH/GO LBL films
as a function of the number of bilayers, N. For
comparison, the absorbance spectrum of a GO film is also
present. (b) Absorbance intensity at 228 nm as a function
of the number of bilayers, N.
Figure 5: I-V characteristic curve for (PAH/GO)
20
LBL
film on interdigitated glass substrate.
In order to characterize the deposited LBL film
regarding the electric behaviour, it was measured the
I-V characteristic curve at ambient light, which is
presented in figure 5. The observed curve evidences
200 250 300 350 400 450 500 550 600
0,0
0,5
1,0
1,5
2,0
Absorbance (a.u.)
Wavelenght (nm)
1
5
10
15
20
GO
0 5 10 15 20
0,0
0,5
1,0
1,5
2,0
Abs 228 nm
Linear Fit
Absorbance 228 nm (a. u.)
Number of Bilayers
02468101214
0.1
1
10
(P A H /G O )
20
C urre nt
(
μ
A)
Voltage
(V )
Preparation of PAH/Graphene Oxide Layer-by-Layer Films for Application on Solar Cells
379
for the produced PAH/GO with 20 bilayers a
semiconductor behaviour. More studies regarding
the optimization of the PAH/GO LBL films
preparation are currently under progress in order to
improve the electric behaviour.
4 CONCLUSIONS
In this work we report the preparation of
PAH/Graphene oxide layer-by-layer (LBL) films for
application in hybrid solar cells. The surface
morphology characterization carried out by scanning
electron microscopy (SEM) and atomic force
microscopy (AFM) evidenced that the deposited
LBL films exhibit a smooth surface with a RMS
roughness of 5.74 nm. The UV-vis spectroscopy
showed a linear film growth and the I-V
characteristic curve revealed a typical semiconductor
behaviour evidencing a promising combination of
films for the development of hybrid solar cells.
ACKNOWLEDGEMENTS
The authors acknowledge the financial support from
FEDER, through Programa Operacional Factores de
Competitividade COMPETE and Fundação para a
Ciência e a Tecnologia FCT, for the project
UID/FIS/00068/2013.
REFERENCES
Choe, H. et al. 2013. Patent citation network analysis for
the domain of organic photovoltaic cells: Country,
institution, and technology field. Renew. Sustain.
Energy Rev. 26, 492–505.
Günes, S., Neugebauer, H. & Sariciftci, N. S., 2007.
Conjugated polymer-based organic solar cells. Chem.
Rev. 1324–1338.
Sun, Y. et al. 2015. Recent development of graphene
materials applied in polymer solar cell. Renew.
Sustain. Energy Rev. 43, 973–980.
Rowell, M. W. et al. 2006. Organic solar cells with carbon
nanotube network electrodes. Appl. Phys. Lett. 88,
233506.
Bian, L. et al. 2012. Progress in Polymer Science Recent
progress in the design of narrow bandgap conjugated
polymers for high-efficiency organic solar cells. Prog.
Polym. Sci. 37, 1292–133.
Ferreira, Q.,Gomes, P. J., Ribeiro, P. A., Jones, N. C.,
Hoffmann, S. V. , Mason, N. J., Oliveira Jr., O. N.,
Raposo, M.,. 2013. Determination of Degree of
Ionization of Poly(allylamine hydrochloride) (PAH)
and Poly[1-[4-(3-carboxy-4 hydroxyphenylazo)
benzene sulfonamido]-1,2-ethanediyl, sodium salt]
(PAZO) in Layer-by-Layer Films using Vacuum
Photoabsorption Spectroscopy”, Langmuir, 29 (1),
448–455.
Ferreira, Q., Gomes, P. J., Raposo, M.,. Giacometti, J. A,
Oliveira Jr., O. N., Ribeiro, P. A., 2007. Influence of
Ionic Interactions on the Photoinduced Birefringence
of Poly[1-[4-(3-Carboxy-4 Hydroxyphenylazo)
Benzene Sulfonamido]-1,2-Ethanediyl, Sodium Salt]
Films, J. Nanosci. Nanotechnol. 7, 2659–2666.
Ferreira, Q., Gomes, P.J., Maneira, M. J. P., Ribeiro, P. A.,
Raposo, M.. 2007. Mechanisms of Adsorption of an
Azo-polyelectrolyte onto Layer-by-Layer Films.
Sensors and Actuators B: Chemical, 126, 311-317.
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