Preparation of PAH/Graphene Oxide Layer-by-Layer Films

for Application on Solar Cells

I. C. C. Assunção

, P. A. Ribeiro

Q. Ferreira

, M. Raposo

and S. Sério

CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa,

2829-516 Caparica, Portugal

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

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

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 MΩ 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)

LBL

film deposited on FTO coated glass substrate.

Figure 3: Representative AFM image of (PAH/GO)

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)

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)

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

(P A H /G O )

C urre nt

(

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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