Electrophoretic deposition of reduced graphene oxide thin films for reduction of cross-sectional heat diffusion in glass windows

Journal of Science: Advanced Materials and Devices 4 (2019) 252e259

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Journal of Science: Advanced Materials and Devices
journal homepage: www.elsevier.com/locate/jsamd

Original Article

Electrophoretic deposition of reduced graphene oxide thin films for
reduction of cross-sectional heat diffusion in glass windows
Loo Pin Yeo a, b, 1, Tam Duy Nguyen a, b, **, 1, Han Ling a, Ying Lee a, Daniel Mandler b, c,
Shlomo Magdassi b, c, Alfred Iing Yoong Tok a, b, *
a

School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798
Singapore-HUJ Alliance for Research and Enterprise, NEW-CREATE Phase II, Campus for Research Excellence and Technological Enterprise (CREATE),
Singapore 138602
c
Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel
b

a r t i c l e i n f o

a b s t r a c t

Article history:
Received 15 February 2019
Received in revised form
29 March 2019
Accepted 1 April 2019

Available online 26 April 2019

Effective management of heat transfer, such as conduction and radiation, through glass windows is one
of the most challenging issues in smart window technology. In this work, reduced Graphene Oxide (rGO)
thin films of varying thicknesses are fabricated onto Fluorine-doped Tin Oxide (FTO) glass via electrophoretic deposition technique. The sample thicknesses increase with increasing number of deposition
cycles (5, 10, 20 cycles). It is hypothesized that such rGO thin films, which are well-known for their high
thermal conductivities, can conduct heat away laterally towards heat sinks and reduce near-infrared
(NIR) transmittance through them, thus effectively slowing down the temperature increment indoors.
The performance of rGO/FTO in reducing indoor temperatures is investigated with a solar simulator and a
UV-Vis-NIR spectrophotometer. The 20-cycles rGO thin films showed 30% more NIR blocked at 1000 nm
as compared to clean FTO, as well as the least temperature increment of 0.57  C following 30 min of solar
irradiation. Furthermore, the visible transmittance of the as-fabricated rGO films remain on par with
commercial solar films, enabling up to 60% of visible light transmittance for optimal balance of transparency and heat reduction. These results suggest that the rGO thin films have great potential in blocking
heat transfer and are highly recommended for smart window applications.
© 2019 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
This is an open access article under the CC BY license ( />
Keywords:
Electrophoretic deposition
Reduced graphene oxide
Thin films
Heat conduction
Smart windows

1. Introduction
Global warming and rapid fossil fuel depletion are major issues
that have continued to intensify over the years, yet remain without
a clear resolution. Governments have been prompted to source for
renewable energy alternatives as well as methods to reduce their
energy consumption. The building industry, in particular, consumes
a large percentage of energy each year, with room heating and

cooling making up at least 32% of a building's total energy consumption [1,2]. Modern building technology, in particular, is

* Corresponding author. School of Materials Science and Engineering, Nanyang
Technological University, 50 Nanyang Avenue, Singapore 639798.
** Corresponding author. School of Materials Science and Engineering, Nanyang
Technological University, 50 Nanyang Avenue, Singapore 639798.
E-mail addresses: (T.D. Nguyen),
(A.I.Y. Tok).
Peer review under responsibility of Vietnam National University, Hanoi.
1
These authors contributed equally to this work.

typically assembled with many large scale window panels, thus
causing the effect of heat and light transfer through windows to
become increasingly significant. Therefore, smart window technologies, which can modulate the transmittance of heat and light,
are widely researched on due to their potential energy savings in
lightings, heaters and air-conditioners. Amongst smart window
technologies, electrochromic devices, which are able to electrically
modulate the transmittance of solar radiation, are one of the most
widely investigated [3]. However, heat can also be transferred in or
out of the room through the glass window due to the conduction
process, i.e. by a temperature gradient. The thermal conductivity of
glass (with a typical thickness of 3 mm) is approximately 0.9 W/mK
[4]. Depending on the temperature difference between the indoor
and outdoor ambience, the direction of heat transfer will cause an
increase or decrease in the indoor room temperature. However, the
management of heat conduction through the glass window has not
been as widely investigated.

/>2468-2179/© 2019 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi. This is an open access article under the CC BY license

( />

L.P. Yeo et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 252e259

An effective method for the management of heat conduction
can be achieved by coating a superior thermally-conductive layer
on the glass surface. This layer, which works similarly to a double
or triple-glazed window, can minimize heat diffusion through the
glass [5,6]. However, this approach can significantly reduce the
weight and fabrication cost of the window pane. The enhanced inplane thermal conductivities of such thin films enable their
application in heat transfer management, in which the heat can be
conducted away and collected at the edge of the window panels
(Figure S1). Currently, carbon-based structures such as graphene,
reduced graphene oxide (rGO) and carbon nanotubes (CNT) have
been widely reported for their extremely high thermal conductivities. Balandin et al. reported a thermal conductivity as high as
4.84e5.30 kW/mK for a suspended single-layer graphene [7],
while Seol et al. reported 600 W/mK in supported graphene [8].
Similarly, single-walled and multi-walled CNTs were reported to
have high thermal conductivities of 3500 W/mK between 300 and
800 K and 3000 W/mK at room temperature respectively [9]. As
such, these carbon-based materials have huge potentials as
thermal interface materials for heat removal, cooling systems for
the electronic industry [10,11], anti-fogging devices and in heatable smart windows etc [12]. This also gives rise to the possibility
of carbon-based windows in cool or warm climates which can
manage indoor temperatures by conducting heat inside or out
respectively. Current commercial solar films (e.g., V-Kool, Infratint, 3 M) can block UV radiation, reflect or absorb infrared (IR)
radiation and reduce glare with lower visible transmittance.
However, these films focus only on blocking wavelengths in the
solar spectrum but neglect the consideration of the warming effect of conducted heat. Carbon-based smart windows, on the
other hand, allow management of both solar radiation and heat

conduction, and thus could provide insights into novel applications in the field of smart windows.
Despite the high thermal conductivity of pristine graphene, its
cost of fabrication through techniques such as epitaxial growth,
chemical vapor deposition (CVD) and exfoliation is very high due to
limited yield or expensive substrates and is thus not an ideal material when considering scale-up productions [13,14]. Besides,
graphene and CNTs also possess low visible transparency and has
issues with homogenous, large-area surface grafting. As such, rGO
is considered the next best alternative for fabricating window
coatings due to competitive thermal conductivities as high as
1043.5 W/mK [15] and 1390 W/mK [16] as previously reported.
Furthermore, rGO also has the advantages of ease of fabrication,
mass producibility, strong infrared absorption and high transparency [17].
In this study, rGO films of varying thicknesses were electrophoretically deposited onto FTO glass substrate and their effect on
blocking heat entry were analyzed with a solar simulator. The
sample thicknesses increase with increasing number of deposition
cycles (5, 10, 20 cycles). It is hypothesized that thermallyconductive rGO can conduct heat away and reduce heat transfer
through it, thus effectively slowing down the temperature increment indoors. Electrophoretic deposition (EPD) was selected for its
potential to deposit homogenous coatings, control coating thickness and low cost [18]. As-fabricated rGO thin films can be a
promising coating material to manage the heat conduction through
glass windows.
2. Materials and experimental methods
The chemicals mentioned in this paper are obtained from
SigmaeAldrich unless otherwise stated. Fluorine-doped tin oxide
(FTO) glass substrates are also obtained from Sigma Aldrich (Model:
TEC-7, Pilkington™).

253

2.1. Fabrication of graphene oxide via modified Hummer's method
Graphene Oxide (GO) was obtained from pure graphite flakes

via modified Hummer's method [19,20]. The fabrication procedure
is illustrated in Fig. 1. Graphite powder (1 g) was added into 98%
H2SO4 (40 ml) under continuous stirring. Subsequently, KMnO4
(6 g) was gradually added into the mixture. The oxidation of
graphite to graphite oxide in this step is highly exothermic, thus
small portions of KMnO4 was added in 5e10 min interval. Deionized (DI) water (50 ml) was slowly added to minimize heat generation and the mixture was stirred for 2 h. 30% H2O2 (10 ml) was
then added to the mixture and further stirred for 10 min to remove
excess KMnO4. Next, the resultant mixture was centrifuged
(Thermo Scientific Sorvall Legend X1R) at 8000 rpm for 10 min. The
residue was washed with 6% HCl and DI water before being
centrifuged again. The washing step was repeated for at least 4
times. The residue was then mixed with DI water (200 ml). Lastly,
the graphite oxide was exfoliated with a probe sonicator (SONICS
Vibra-Cell) at 70% amplitude for 1 h to obtain a homogenous GO
suspension.
2.2. Reduction of GO via electrophoretic deposition
The GO suspension was first diluted to 1 mg/ml using
Phosphate-buffered Saline (PBS) solution and subsequently, its pH
was adjusted to 10 with NaOH. The electrophoretic deposition
(EPD) procedure of GO was carried out in a three-electrode set-up
consisting of clean FTO as the working electrode, platinum sheet as
the counter electrode and Ag/AgCl as the reference electrode
(Figure S2) [21]. Before EPD, N2 gas was bubbled into the GO suspension under continuous stirring throughout the EPD procedure,
starting from 30 min before the actual deposition. A potential range
of þ0.6 to À1.5 V was used to deposit reduced graphene oxide (rGO)
onto the FTO substrate to obtain samples of 5, 10 and 20 cycles.
2.3. Characterization
Surface morphology of the deposited rGO thin films was
analyzed with a Field Emission Scanning Electron Microscope
(FESEM, JEOL JSM-7600F) and Atomic Force Microscopy (AFM, Park

Systems NX10). Thickness of the film samples were measured with
the surface profiler (Alpha-Step IQ). X-ray Diffractometer (XRD,
Panalytical X'Pert Pro), equipped with Cu-Ka radiation, was carried
out to analyze the crystallographic structure of the samples. Fourier
Transform Infrared Spectroscopy (FTIR, PerkinElmer Frontier) was
carried out to observe the changes in molecular bonding following
the reduction of GO. The surface chemistry of as-fabricated rGO
thin films was characterized by X-ray Photoelectron Spectrometer
(XPS, Kratos AXIS Supra). The UV-Vis-NIR Spectroscopy (Agilent
Cary 5000) was carried out to measure the visible light and NIR
transmittance across the rGO/FTO samples.
The performance of the different rGO films in blocking heat was
analyzed with a solar simulator (Class 150 W XES-40S2-CE)
equipped with a xenon lamp. The set-up prepared for the solar
simulation is depicted in Fig. 2. The set-up shown was enclosed in
an opaque acrylic box to prevent entry of external lighting. With an
irradiance of 1000 W/m2, the equipment simulates the sun,
allowing the effect of rGO on blocking heat entry into the box to be
analyzed. Thermocouples were attached in the box to measure the
increase in temperature in the internal environment during solar
irradiation. The samples were irradiated for 30 min and the internal
temperature of the box was recorded at every minute. The initial
internal temperature of the box was maintained between 24.75 and
24.79  C at the start of each analysis. Irradiance of air and plain FTO
glass substrate were also measured as references.


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L.P. Yeo et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 252e259

Fig. 1. Illustration of the GO fabrication procedure by modified Hummer's Method.

Fig. 2. Illustration of the solar simulation experimental set-up.

3. Results and discussion
3.1. Morphology, crystal and chemical structures of
electrophoretically-deposited rGO thin films
Fig. 3 a-c present the FESEM images of electrophoreticallydeposited rGO film (5, 10, 20-cycles) on FTO glass substrate. The
formation of rGO thin films after the electrophoretic deposition
process can be clearly observed. The deposited rGO films are
relatively large, in the range of several micrometres. They consist
of multiple, thin layers of overlapping rGO due to the layer-bylayer alignment typical of EPD. Irregular folds can be observed
on the films which become more prominent as the number of

deposition cycles increases. The thicknesses of the rGO films were
also measured with a surface profiler and the average thickness is
0.374 mm, 0.578 mm and 1.759 mm for 5, 10 and 20 cycles rGO films
respectively. The view of the rGO thin films with varying electrophoretically deposited cycles is included in Figure S3. The
cyclic-voltammetry (CV) curves recorded during the electrophoretic deposition and reduction of GO are shown in Figure S4. A
large reduction peak was recorded for 5-cycles reduction
at À1.2 V, with a starting potential of e 0.85 V; 10-cycles reduction
at À1.32 V, with a starting potential of À0.9 V; 20-cycles reduction
at À1.06 V, with a starting potential of À0.4 V. The large reduction
peaks observed are due to the removal of oxygen functional
groups in GO to form rGO [22].

Fig. 3. FESEM images of 5-cycles (a), 10-cycles (b), and 20-cycles (c) rGO thin films deposited on FTO glass observed at 10 K magnification.

L.P. Yeo et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 252e259

Fig. 4 a-c present the AFM images of rGO thin films of different
thicknesses. The average surface roughness of 5, 10 and 20-cycles
rGO are estimated to be about 33.3, 39.8 and 58.3 nm, respectively, as presented in Fig. 4d. As expected, there is an increase in
the film surface roughness when an increasing amount of rGO was
deposited. Despite the presence of folds observed in the FESEM
images, the surface roughness remains relatively low. This suggests
that the current electrophoretic deposition and reduction method
is capable of producing relatively smooth films regardless of the
deposited thickness. A study by Chen et al. reported that cluttering
in the arrangement of graphene atoms could reduce the speed of
thermal phonon propagation and thus decrease the thermal conductivity of graphene [23]. As such, a smooth rGO film is highly
desirable for quick heat transfer across the film.
Fig. 5 presents the FTIR spectra of rGO and drop-casted graphene oxide (DC-GO) films to confirm the successful reduction of
GO to rGO with the electrophoretic deposition method. The procedure for the fabrication of DC-GO is illustrated in Figure S4. From
the DC-GO spectra, it can be observed that GO was successfully
oxidized from graphite due to the presence of oxygen-containing
functional groups [24]. The GO spectrum consists of a broad peak
centered at 3435 cmÀ1 which originates from the stretching mode
of OeH group, while the peak at 1642 cmÀ1 is associated with aromatic C]C ring stretching, the broad peak at 1186-1458 cmÀ1 and
the peak at 1085 cmÀ1 is related to stretching of epoxy CeO groups
[25e27]. Following reduction into rGO, it can be observed that peak
intensities associated with the alkoxy and hydroxyl groups are
significantly reduced or have disappeared, suggesting successful
reduction of GO.
Fig. 6 presents the XRD patterns of the rGO films. As the films
were deposited onto an FTO glass substrate, characteristic peaks of
FTO were observed at 2q ¼ 26.6 , 33.9 , 37.9 , 51.7, 61.8 and 66.0

255

Fig. 5. FTIR spectra of RGO and drop-casted graphene oxide (DC-GO).

which corresponds to the (110), (101), (200), (211), (310) and (301)
planes of SnO2 (ICDD 01-070-4176), respectively. The XRD pattern
of drop-cast graphene oxide (DC-GO) obtained from modified
Hummer's method produced a peak at 2q ¼ 9.3 with an average dspacing of 0.95 nm, which corresponds to the (001) plane [28e30].
Following reduction of GO, the GO peak disappears, indicating the
successful removal of oxygen-containing functional groups.
Although there is an overlap in peaks, the diffraction peak characteristic of rGO is also located at 2q ¼ 26.6 in the rGO films, which

Fig. 4. AFM images of 5-cycles (a), 10-cycles (b), and 20-cycles (c) rGO thin films and (d) their corresponding surface roughness.


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L.P. Yeo et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 252e259

Fig. 6. XRD patterns of rGO thin films fabricated with different deposition cycles (5cycles, 10-cycles, 20-cycles).

corresponds to the (002) plane [29]. The d-spacing of rGO was
observed to be approximately 0.34 nm, with negligible differences
amongst the 5, 10 and 20-cycle samples.
3.2. Surface chemistry and UV-Vis eNIR absorption of rGO thin
films
Fig. 7 shows the XPS spectra of as-fabricated rGO thin films. The
wide scan spectra (Fig. 7a) of all samples indicate the presence of
C1s and O1s, which again confirms the formation of rGO thin films.
The Sn3d peaks are present due to the FTO substrate, with the

Sn3d5/2 and Sn3d3/2 components located at approximately 487 and
496 eV, respectively. There are small energy shifts observed as
compared to typical SnO2 XPS spectra (where Sn3d5/2 and Sn3d3/2
components are located at 485 and 494 eV, respectively) due to
fluorine doping in FTO glass substrate. The fine XPS spectra of C1s
(b), O1s (c) and Sn3d (d) of 5-cycles rGO thin film are presented in
Fig. 7 b-d. By curve-fitting analysis (Gauss*Lorentz Algorithm), the
C1s core-level spectrum of 5-cycles rGO thin films was deconvoluted to obtain 3 main peaks: CeC (~284.4 eV), CeO (~285.8 eV),
and C]O (~288 eV). The CeC peak is attributed to carbon with sp2
and sp3 hybridization, with some shoulders at higher binding energies due to the oxygen linkages (CeO, C]O). The O1s core-level
spectrum was deconvoluted into three peaks: C]O (~531.1 eV),
CeO (~533.7 eV), C(O)OH (~535.7 eV) [31]. The fine XPS spectra of
10 and 20-cycles rGO thin films are also presented in Figure S5. The
detailed elemental composition of the various rGO thin films is
presented in Table 1. In general, the atomic ratio of C/O is about 7:3
for all three rGO samples. Interestingly, in the C1s deconvolution,
while the CeC and CeO components remain unchanged, the C]O
component mostly decreases with increasing number of deposition
cycles. For O1s deconvolution, the C]O component and carboxylic
groups reduce while the CeO component increases with increasing
number of deposition cycles. This may imply the presence of less
eCOOH and eCOH functional groups in the electrophoreticallydeposited rGO thin films with increasing film thickness. This is
also in agreement with the observation from the FTIR and XRD
analyses.
Fig. 8 presents the UV-Vis-NIR spectra of the rGO films with
different number of deposition cycles (5, 10, 20-cycles) within the
range of 300e1600 nm [32]. Wavelengths above 1600 nm were not
included as the FTO glass substrate itself allows less than 30%
infrared transmittance above 1600 nm [33]. The effect of

increasing rGO thickness on NIR transmittance thus cannot be
observed clearly in that wavelength range and was subsequently

Fig. 7. Wide scan XPS spectra (a) of various rGO thin films. The fine XPS spectra of C1s (b), O1s (c) and Sn3d (d) of 5-cycles rGO thin films.


L.P. Yeo et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 252e259

257

Table 1
Elemental composition of rGO thin films determined by XPS.
Sample

5-cycles rGO
10-cycles rGO
20-cycles rGO

Elemental composition (at.%)

C1s deconvolution (at.%)

C

O

CeC

CeO

C¼O

O1s deconvolution (at.%)
C¼O

CeO

C(O)OH

70.6
70.2
73.4

29.4
29.8
26.6

55.6
55.3
60.4

31.9
26.5
34.8

12.5
18.2
4.8

42.2

31.3
25.1

34.4
51.5
73.2

23.4
17.2
1.7

further increasing rGO deposition cycles to reduce the NIR
blockage indefinitely. Nonetheless, the visible transmittance of the
as-fabricated rGO films remains on par with commercial solar
films [34,35], enabling up to 60% of visible light transmittance for
optimal balance of transparency and heat reduction.
3.3. Reduction of heat transfer through glass using rGO thin films

Fig. 8. UV-Vis-NIR transmittance spectra of rGO films (5-cycles, 10-cycles, 20-cycles)
over the wavelength range of 300e1600 nm.

omitted. With an increasing thickness of rGO films deposited, the
transmittance of Vis and NIR wavelengths sees a general
decreasing trend. The NIR transmittance of clean FTO, 5, 10 and 20cycles rGO thin films is in the range of 16.75e80.14%,
22.52e60.07% 16.47e45.19% respectively. By increasing from 5 to
10 deposition cycles, there is approximately 12.63% more NIR
blocked at 1000 nm. Increasing from 10 to 20 cycles shows
negligible difference in NIR blockage. However, a 20-cycle rGO thin
film still enables 30% more NIR blocked at 1000 nm as compared to
clean FTO. In the visible range, there is a consistent reduction in

transmittance as the number of rGO film thickness increases. The
visible transmittance decreases from 50.61 e 60.07% to
36.30e45.19% to 24.27e40.40% when the number of cycles
increased from 5 to 20 cycles. In order for the rGO thin films to be
used in windows, the visible transparency has to be sufficiently
high. Hence, these results suggest that there are limitations in

Fig. 9 presents the results from the solar simulation test. As
previously mentioned, the rGO samples (5, 10, 20-cycles) were
irradiated with artificial light for a period of 30 min and the internal
temperature of the box was recorded every minute. Air and plain
FTO glass substrate were also irradiated under the same parameters
as references. As shown in Fig. 9a, following 30 min irradiation, the
FTO samples coated with rGO films showed an increase in temperature of only 0.76  C, 0.68  C and 0.57  C for 5, 10 and 20-cycles
samples, respectively. On the other hand, irradiating air and plain
FTO glass substrates caused an increase by 4.40  C and 1.80  C,
respectively. Fig. 9b shows the % increment in temperature with
different samples. A magnified graph of the DT of 5, 10, 20-cycles
films is also included. A steep decline in temperature increment
can be observed once the rGO thin films were utilized. The 5-cycles
rGO thin films alone shows approximately 5.8 times and 2.4 times
reduction in interior temperature increment as compared to air and
FTO glass substrate, respectively. The interior temperature increment showed a 13% reduction when the rGO film thickness is
increased from 5 to 10-cycles and a further 15.5% reduction when
the film thickness increased from 10 to 20-cycles. Increasing the
film thickness show, as expected, lower increment in interior
temperature. There are 2 possible reasons for this explanation:

DQ =Dt ¼ Àk  ðDT=LÞ

(1)

Firstly, according to the heat transfer equation - where DQ/Dt is
the rate of heat conduction, Кis the thermal conductivity of the
material per unit thickness, A is the area of the material, L is the
layer thickness and DT is the temperature difference across the
material - increasing film thickness would result in a slower heat
transfer through the rGO film by conduction, due to the presence

Fig. 9. The temperatureetime plots (a) and temperature change analysis (b) of the solar simulation results for different samples.


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L.P. Yeo et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 252e259

of more conduction pathways in the thicker film. Furthermore,
increasing thickness of the rGO film gives rise to denser films with
better connectivity, thus increasing the ease of in-plane thermal
phonon propagation [36]. Within the testing period, most of the
heat was likely conducted laterally across the rGO thin film instead
of through the sample, resulting in a postponement of perpendicular heat entry. Secondly, as previously observed in Fig. 8,
increasing the rGO film thickness has the effect of reducing NIR
transmittance across the thin film. The reduced entry of radiant
heat into the room also contributed to the lower room temperature
increment. However, since there is a limit to how much NIR
transmittance can be blocked by increasing rGO thickness, this
suggests that the further reduction in interior temperature increment between the 10 and 20 cycle film is likely due to the
preferred propagation of the thermal phonons through other
conduction pathways.

4. Conclusion
In this study, the rGO thin films were investigated for its potential to be incorporated into smart windows to block heat
transfer. The GO suspension was fabricated via modified Hummer's
method and was reduced and deposited onto FTO substrates using
electrophoretic deposition technique. Three different rGO thin
films of varying number of deposition cycles (5, 10, 20-cycles) were
fabricated and tested in a UV-Vis-NIR spectrophotometer and a
solar simulator to determine their ability to block NIR wavelengths
and reduce indoor temperatures. The 20-cycles rGO thin films
showed an NIR transmittance of 18.8e40.4%, which is 30% more NIR
blocked at 1000 nm as compared to clean FTO. It also showed the
least temperature increment of 0.57  C following 30 min of solar
irradiation. While maintaining excellent heat transfer reduction,
the visible transmittance of the films was also on par with commercial solar films, enabling up to 60% of visible light transmittance
for optimal balance of transparency and heat reduction. It is suggested that the excellent heat blocking results of rGO thin films are
due to a combination of good heat conduction and reduced NIR
transmittance and as such, possesses great potential in heatblocking window technologies.
Declaration of interest statement
The authors declare no conflict of interest.
Acknowledgements
This research is supported by grants from the National Research
Foundation, Prime Minister's Office, Singapore under its Campus
of Research Excellence and Technological Enterprise (CREATE)
Program.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
/>References
[1] D. Perera, N.-O. Skeie, Comparison of space heating energy consumption of
residential buildings based on traditional and model-based techniques,
Buildings 7 (2) (2017) 27. />[2] D. Ürge-Vorsatz, L.F. Cabeza, S. Serrano, C. Barreneche, K. Petrichenko, Heating

and cooling energy trends and drivers in buildings, Renew. Sustain. Energy
Rev. 41 (2015) 85e98. />[3] G.N. Tiwari, Solar Energy: Fundamentals, Design, Modelling and Applications,
Alpha Science Int'l Ltd, 2002.

[4] M. Rubin, Calculating heat transfer through windows, Int. J. Energy Res. 6 (4)
(1982) 341e349. />[5] B.P. Jelle, Solar radiation glazing factors for window panes, glass structures
and electrochromic windows in buildingsdmeasurement and calculation, Sol.
Energy Mater. Sol. Cell. 116 (2013) 291e323. />2013.04.032.
[6] M. Gr. Vrachopoulos, M.K. Koukou, G. Filos, C. Moraitis, Investigation of heat
transfer in a triple-glazing type window at Greek climate conditions, Cent.
Eur. J. Eng. 3 (4) (2013) 750e763. />[7] A.A. Balandin, S. Ghosh, W. Bao, I. Calizo, D. Teweldebrhan, F. Miao, C.N. Lau,
Superior thermal conductivity of single-layer graphene, Nano Lett. 8 (3)
(2008) 902e907. />[8] J.H. Seol, et al., Two-dimensional phonon transport in supported graphene,
Science 328 (5975) (2010) 213. />[9] E. Pop, D. Mann, Q. Wang, K. Goodson, H. Dai, Thermal conductance of an
individual single-wall carbon nanotube above room temperature, Nano Lett. 6
(1) (2006) 96e100. />[10] A.A. Balandin, Thermal properties of graphene and nanostructured carbon
materials, Nat. Mater. 10 (2011) 569. />[11] N. Han, et al., Improved heat dissipation in gallium nitride light-emitting diodes with embedded graphene oxide pattern, Nat. Commun. 4 (2013) 1452.
/>[12] B.H. Nguyen, V.H. Nguyen, Promising applications of graphene and graphenebased nanostructures, Adv. Nat. Sci. Nanosci. Nanotechnol. 7 (2) (2016),
023002. />[13] H. Tan, D. Wang, Y. Guo, Thermal growth of graphene: a review, Coatings 8 (1)
(2018). />[14] Md.S.A. Bhuyan, Md.N. Uddin, Md. M. Islam, F.A. Bipasha, S.S. Hossain, Synthesis of graphene, Int. Nano Lett. 6 (2) (2016) 65e83. />s40089-015-0176-1.
[15] N.-J. Song, C.-M. Chen, C. Lu, Z. Liu, Q.-Q. Kong, R. Cai, Thermally reduced
graphene oxide films as flexible lateral heat spreaders, J. Mater. Chem. 2 (39)
(2014) 16563e16568. />[16] P. Kumar, F. Shahzad, S. Yu, S.M. Hong, Y.-H. Kim, C.M. Koo, Large-area
reduced graphene oxide thin film with excellent thermal conductivity and
electromagnetic interference shielding effectiveness, Carbon 94 (2015)
494e500. />[17] S.J. Rowley-Neale, E.P. Randviir, A.S.A. Dena, C.E. Banks, An overview of recent
applications of reduced graphene oxide as a basis of electroanalytical sensing
platforms, Appl. Mater. Today 10 (2018) 218e226. />apmt.2017.11.010.
[18] H. Zhang, X. Zhang, D. Zhang, X. Sun, H. Lin, C. Wang, Y. Ma, One-step electrophoretic deposition of reduced graphene oxide and Ni(OH)2 composite
films for controlled syntheses supercapacitor electrodes, J. Phys. Chem. B 117

(6) (2013) 1616e1627. />[19] M. Larisika, J. Huang, A. Tok, W. Knoll, C. Nowak, An improved synthesis route
to graphene for molecular sensor applications, Mater. Chem. Phys. 136 (2)
(2012) 304e308. />[20] J.T. Han, B.J. Kim, B.G. Kim, J.S. Kim, B.H. Jeong, S.Y. Jeong, H.J. Jeong, J.H. Cho,
G.-W. Lee, Enhanced electrical properties of reduced graphene oxide multilayer films by in-situ insertion of a TiO2 layer, ACS Nano 5 (11) (2011)
8884e8891. />[21] S.J. An, Y. Zhu, S.H. Lee, M.D. Stoller, T. Emilsson, S. Park, A. Velamakanni, J. An,
R.S. Ruoff, Thin film fabrication and simultaneous anodic reduction of
deposited graphene oxide platelets by electrophoretic deposition, J. Phys.
Chem. Lett. 1 (8) (2010) 1259e1263. />[22] H.-L. Guo, X.-F. Wang, Q.-Y. Qian, F.-B. Wang, X.-H. Xia, A green approach to
the synthesis of graphene nanosheets, ACS Nano 3 (9) (2009) 2653e2659.
/>[23] L. Chen, Y. Zhang, Q. Wu, Effect of graphene coating on the heat transfer
performance of a composite anti-/deicing component, Coatings 7 (10) (2017).
/>[24] T.F. Emiru, D.W. Ayele, Controlled synthesis, characterization and reduction of graphene oxide: a convenient method for large scale production,
Egypt. J. Basic Appl Sci 4 (1) (2017) 74e79. />2016.11.002.
[25] N. Sharma, V. Sharma, Y. Jain, M. Kumari, R. Gupta, S.K. Sharma, K. Sachdev,
Synthesis and characterization of graphene oxide (GO) and reduced graphene
oxide (rGO) for gas sensing application, Macromol. Symp. 376 (1) (2017)
1700006. />[26] V. Loryuenyong, K. Totepvimarn, P. Eimburanapravat, W. Boonchompoo,
A. Buasri, Preparation and characterization of reduced graphene oxide sheets
via water-based exfoliation and reduction methods, Adv Mater Sci Eng 2013
(2013) 5. />[27] D. Ickecan, R. Zan, S. Nezir, Eco-friendly synthesis and characterization of
reduced graphene oxide, J. Phys. Conf. Ser. 902 (1) (2017), 012027. https://doi.
org/10.1088/1742-6596/902/1/012027.
[28] Q. Zhuo, J. Gao, M. Peng, L. Bai, J. Deng, Y. Xia, Y. Ma, J. Zhong, X. Sun, Largescale synthesis of graphene by the reduction of graphene oxide at room
temperature using metal nanoparticles as catalyst, Carbon 52 (2013)
559e564. />[29] M.J. McAllister, et al., Single sheet functionalized graphene by oxidation and
thermal expansion of graphite, Chem. Mater. 19 (18) (2007) 4396e4404.
/>

L.P. Yeo et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 252e259
[30] P. Chen, H. Li, S. Song, X. Weng, D. He, Y. Zhao, Adsorption of dodecylamine

hydrochloride on graphene oxide in water, Results Phys. 7 (2017) 2281e2288.
/> ska,
[31] S. Drewniak, R. Muzyka, A. Stolarczyk, T. Pustelny, M. Kotyczka-Moran
M. Setkiewicz, Studies of reduced graphene oxide and graphite oxide in the
aspect of their possible application in gas sensors, Sensors 16 (1) (2016).
/>[32] T.D. Nguyen, L.P. Yeo, T.C. Kei, D. Mandler, S. Magdassi, A.I.Y. Tok, Efficient
near infrared modulation with high visible transparency using SnO2eWO3
nanostructure for advanced smart windows, Adv Opt Mater 0 (0) (2019)
1801389. />[33] H. Ling, L.P. Yeo, Z. Wang, X. Li, D. Mandler, S. Magdassi, A.I.Y. Tok, TiO2eWO3
coreeshell inverse opal structure with enhanced electrochromic performance

259

in NIR region, J. Mater. Chem. C 6 (31) (2018) 8488e8494. />1039/c8tc01954a.
[34] 3M. 3M™ Sun Control Window Films, Prestige Series for Residential, 2019.
/>N¼5002385þ3292716662&preselect¼3293786499&rt¼rud.
[35] Eastman Chemical Company, iQUETM BY V-KOOL Architecture Window Films,
2018. />[36] G. Lian, C.-C. Tuan, L. Li, S. Jiao, Q. Wang, K.-S. Moon, D. Cui, C.-P. Wong,
Vertically aligned and interconnected graphene networks for high thermal
conductivity of epoxy composites with ultralow loading, Chem. Mater. 28 (17)
(2016) 6096e6104. />