electrochemically exfoliated graphene hybrid films for transparent electrothermal heaters

Accepted Manuscript Title: Large-area self-assembled reduced graphene oxide/electrochemically exfoliated graphene hybrid films for transparent electrothermal heaters Authors: Hongyan Sun, Ding Chen, Chen Ye, Xinming Li, Dan Dai, Qilong Yuan, Kuan W.A. Chee, Pei Zhao, Nan Jiang, Cheng-Te Lin PII: DOI: Reference:

S0169-4332(17)33475-X https://doi.org/10.1016/j.apsusc.2017.11.182 APSUSC 37764

To appear in:

APSUSC

Received date: Revised date: Accepted date:

21-8-2017 12-11-2017 21-11-2017

Please cite this article as: Sun H, Chen D, Ye C, Li X, Dai D, Yuan Q, Chee KWA, Zhao P, Jiang N, Lin C-T, Large-area self-assembled reduced graphene oxide/electrochemically exfoliated graphene hybrid films for transparent electrothermal heaters, Applied Surface Science (2010), https://doi.org/10.1016/j.apsusc.2017.11.182 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Large-area self-assembled reduced graphene oxide/electrochemically exfoliated graphene hybrid films for transparent electrothermal heaters Hongyan Suna,b, Ding Chena,*, Chen Yeb,c, Xinming Lid, Dan Daib, Qilong Yuanb,e, Kuan W. A. Cheeb,e, Pei Zhaof, Nan Jiangb, Cheng-Te Linb,c,* a

A

N

U

SC R

IP T

College of Materials Science and Engineering, Hunan University, Changsha 410082, P. R. China. E-mail: [email protected] b Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, China 315201. E-mail: [email protected] c University of Chinese Academy of Sciences, 19 A Yuquan Rd., Shijingshan District, Beijing 100049, China d National Center for Nanoscience and Technology, Beijing, 100190, P. R. China. e Department of Electrical and Electronic Engineering, University of Nottingham, Ningbo 315100, China. f Institute of Applied Mechanics and Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province, Zhejiang University, Hangzhou 310012, P. R. China. *

M

Corresponding author: Fax: +86 158-6736-2138

A

CC E

PT

ED

Graphical Abstract

Highlights 

A high-performance and cost-effective self-assembly method to successful fabricate large-area reduced graphene oxide/electrochemically exfoliated graphene hybrid films for heaters.



The self-assembled graphene hybrid films with the area of 20 × 20 cm2 could

IP T

be transferred onto arbitrary substrates with nonplanar surfaces and simply patterned with the hard mask. 

The reduced graphene hybrid films can reach a saturated temperature of up to



SC R

127.5 °C at 40 V for 60 s.

It can completely remove fog within 11 s when supplied a safe voltage of 30 V.

U

ABSTRACT

N

Graphene shows great promise as a high-efficiency electrothermal film for flexible

A

transparent defoggers/defrosters. However, it remains a great challenge to achieve a

M

good balance between the production cost and the properties of graphene films. Here, we proposed a cost-effective self-assembly method to fabricate high-performance,

ED

large-area graphene oxide/electrochemically exfoliated graphene hybrid films for heater applications. The self-assembled graphene hybrid films with the area of 20 × 20

PT

cm2 could be transferred onto arbitrary substrates with nonplanar surfaces and simply patterned with the hard mask. After reduction by hydrogen iodide vapor followed by

CC E

800 °C thermal treatment, the hybrid films with the transmittance of 76.2 % exhibit good heating characteristics and defogging performance, which reach a saturation

A

temperature of up to 127.5 °C when 40 V was applied for 60 s.

Keywords Graphene, self-assembly, nonplanar surface, heater, defogging

1. Introduction Transparent electrothermal film heaters have attracted growing interest for a wide

range of applications including defogging windows [1], vehicle window defrosters [2], heating retaining windows [3], outdoor displays [4], the heating source of sensors [5], and even heating of microchannel chips [6]. Generally, transparent electrothermal film heaters have been made using an optically transparent substrate which is coated with a transparent and conductive layer. To date, indium tin oxide (ITO) has been widely used to prepare transparent electrothermal films as it is optical transparency and has high

IP T

electrical conductivity. However, the limitations of ITO material, such as the growing cost of indium, harsh processing conditions and the brittleness seriously limit the use

SC R

of ITO in transparent electrothermal film heaters [7-9]. As a consequence, to address these issues, recent work has devised strategies based on new materials. Such as carbon

nanotubes (CNTs) [10, 11], chemical vapor deposition (CVD) grown graphene [12-14]

U

and reduced graphene oxide (rGO) [2] have been explored to improve the performance

N

of transparent electrothermal film heaters.

A

CNTs possess excellent electrical, thermal, and optical properties, which are key factors that influence the performance of electrothermal films [15]. Yoon et al. first

M

fabricated transparent heating films using single-wall carbon nanotubes (SWCNTs) and

ED

the films exhibit excellent heating performance [16]. However, SWCNTs still have some issues in their separation, purification, and dispersion in an aqueous media or polymer mixture, leading to the limitation of their practical applications [17]. Graphene

PT

also has been the focus of intense research due to its outstanding electrical, optical, mechanical and thermal properties [18-20]. Kang et al. reported that CVD graphene

CC E

films after chemical doping exhibited superior performance as compared to that of conventional ITO film as low-voltage transparent heaters [12, 13]. But, the preparation of CVD graphene and transfer technique is high cost and complexity. In addition, the

A

transfer of CVD graphene is limited to be only available to the flat substrate [14]. Compared to CVD method, chemical exfoliation of graphene oxide (GO) allows for low-cost, large-scale production, and solution processability, which make it a good candidate for flexible electronic applications. Thin GO films with excellent chemical stability and mechanical flexibility can be easily prepared by spin-coating onto various substrates, followed by reduction with chemical and/or high-temperature annealing. Sui

et al. reported that GO films fabricated through spin-coating of GO solution on quartz for a heater, which could reach a saturated temperature of 42 °C at 60 V [2]. Electrochemically exfoliated graphene (EEG) nanosheets have attracted great attention due to their fast, massive and environmentally friendly preparation process [21, 22], In addition, EEG nanosheets preserve most of the defect-free hexagonal carbon lattice and have a relatively low density of oxygen-containing groups, which is distinct from high

IP T

oxygen content of GO nanosheets.

In this work, large-scale GO/EEG hybrid films could be fabricated on quartz and

SC R

nonplanar substrates utilizing a simple and fast interfacial self-assembly route [23], which were then reduced by hydrogen iodide (HI) vapor and then thermal treatment [2, 24]. We demonstrated that the reduced GO/EEG hybrid films have good heater

U

performance, with a transmittance of 76.2 % at 550 nm and reaching a steady state

N

temperature as high as 83.2 °C at an applied voltage of 30 V (and 127.5 °C at 40 V),

A

making them very attractive for a variety of heating fields applications.

2.1 Materials & synthesis

M

2. Experimental

ED

Natural graphite was employed as both electrode and source for producing graphene nanosheets based on electrochemical exfoliation method [25]. Two electrodes were placed in an electrolyte solution (a mixture of H2SO4 and KOH). Then, 1 A current was

PT

applied to the system to start the exfoliation reaction, and the EEG nanosheets were generated from the electrode surface. After the electrochemical exfoliation, the EEG

CC E

nanosheets were collected by filtration and washed with deionized water to remove the residual electrolyte. A graphene ink was made by dispersion of EEG in ethanol solution (Supporting Information, Fig. S1a). GO powder (1-5 layer, Fig. S1b) was purchased

A

from Qingdao Huagao Graphene Technology Corp., LTD. 45 wt % hydroiodic acid (HI) was purchased from Sinopharm Chemical Reagent Co., Ltd. 2.2 Preparation of reduced GO/EEG hybrid films The single-step Marangoni self-assembly for the preparation of EEG film was adopted in our experiment [23, 25]. 5 ml EEG nanosheets dispersions in ethanol with 0.1 mg/ml concentration was injected onto the surface of 50 mL of DI water at a speed

of 1 mL/10 s by virtue of a syringe, and the nanosheets moved from low surface tension regions (ethanol-rich) to high surface tension regions (DI water-rich) derived by Marangoni effect. EEG nanosheets would collide and bind with each other via π-π interactions [23]. Then EEG nanosheets temporarily suspended on aqueous media and formed a large area uniform film in a few seconds (Fig. 1a). After stabilized for about 1 min, the uniform EEG films could be easily transferred to the insulating substrates.

IP T

When EEG nanosheets/ethanol solution was injected onto the surface of 0.05 mg/ml

aqueous GO dispersions, GO/EEG hybrid films could be made (Fig. 1b). The obtained

SC R

films were dried in air and then they were reduced by hydrogen iodide (HI) vapor at

90 °C for 10 min, and further reduced by thermal annealing at 800 °C for 1 h under Ar atmosphere in a quartz tube furnace.

U

The surface morphologies of self-assembled graphene films were examined by

N

scanning electron microscopy (SEM, QUANTA FEG250) and atomic force microscopy

A

(AFM, Vecco Dimension 3100). The GO and EEG nanosheets were characterized using Raman spectrometer with a laser wavelength of 532 nm (Renishaw plc, Wotton-under-

M

Edge), X-ray photoelectron spectroscopy (XPS, Kratos AXIS ULTR DLD

ED

spectrometer), contact angle analysis (CA, OCA20 Data physics), UV-Vis Spectroscopy (Lambda 950 Perkin-Elmer), Hall effect measurement system (Swin Hall 8800), and IR-photos were captured by infrared camera (Fluke, Ti400).

PT

3. Results and discussion

The GO/EEG hybrid films could be transferred to arbitrary substrates with good

CC E

uniformity and strong adhesion. As shown in Fig. 2a, the self-assembled graphene films were well coated on the nonplanar surfaces (75 mm in diameter). GO/EEG hybrid films also can be simply patterned on quartz substrates through a hard mask based on stencil

A

printing method, and a patterned graphene with letter “SHY” has been directly prepared on the quartz, as presented in Fig. 2b. In comparison with other solution processes (e.g., spin coating and drop casting), the unique feature of the self-assembled method is the high morphological uniformity of graphene films [25]. Especially, this simple fabrication technique could be scaled up to a large area (20×20 cm2) for preparing GO/EEG hybrid films on the glass substrate (Fig. 2c). The surface morphology of self-

assembled graphene films deposited on SiO2/Si substrates was observed using SEM. Fig. 2d shows the morphology of EEG films prepared using 5 ml of 0.1 mg/ml dispersions injected DI water, and many spaces between nanosheets can be seen. When the EEG nanosheets dispersions with the same concentration were injected on the surface of 0.05 mg/ml GO solution will be formed GO/EEG hybrid films (Fig. 2e), the spaces between adjacent EEG nanosheets could be filled up by GO nanosheets. After

IP T

being reduced by HI vapor and then 800 °C thermal treatment, both reduced GO and

EEG nanosheets were interconnected with spatial uniformity over a large area, leading

SC R

to the formation of a continuous and monolithic conductive film (Fig. 2f).

More detailed information about the chemical composition of the surface of GO/EEG and reduced GO/EEG films were obtained by XPS spectra (Fig. 3a). The C1s

U

signal mainly consisted of four different chemical components, containing a mixture of

N

sp2- (C=C, 284.6 eV) and sp3-hybridized bonds with epoxide/hydroxyls (C–O, 285.3

A

eV), carbonyl (C=O, 286.8 eV) and carboxyl (O–C=O, 288.7 eV) groups [22, 26]. The C–O, C=O and O–C=O oxygen-containing functional groups accounted for 52.1 % in

M

the GO/EEG hybrid films, which were subsequently reduced to 30.9 %, after the

ED

reduction. The Raman spectra of the GO and the EEG directly reflect the degree of disorder and the stacking structure. The restoration of the conjugated C=C bonds during the GO/EEG to reduced GO/EEG was shown in Raman spectra (Fig. S2). A slight

PT

increase of the ID/IG ratio for the reduced GO and EEG with reduction was observed, and the reduced GO and EEG show much narrower Raman peaks than the GO and EEG,

CC E

which indicate that an increase in the number of smaller sp2 domains [27, 28]. Hence, the above observation based on the Raman analysis is consistent with the XPS results. The degree of reduction of GO/EEG films were also determined using water contact

A

angle analysis. As shown in Fig. 3b, the contact angle EEG, GO/EEG films were 38° and 32°, respectively. After reduced by HI vapor and then 800 °C thermal treatment, the contact angle of reduced GO/EEG films then increased to 53° and 86°, respectively. The optical and electrical properties of the hybrid films are presented in Fig. 4. It is well known that both sheet resistance and transmittance of graphene films are significantly influenced by reduction methods [2, 29]. GO and EEG nanosheets, which

were with varying degrees damaged of conjugated aromatic structure due to their preparation process. As shown in Table 1, after reduced by HI vapor followed by 800 °C thermal treatment, the reduced GO/EEG films have the transmittance of 76.2 % and a sheet resistance of 3 kΩ/sq. The decrease of transmittance after reduction can be attributed to the restoration of the π-electron system in the graphene structure, corresponding with the observations in previous works [29].

IP T

To demonstrate its potential as an electrode for transparent heaters, we constructed a transparent electrothermal film heater with dimensions of 1×1 cm2 under a two-

SC R

terminal side contact configuration (Fig. 5a). Direct current power was applied to the graphene films and their electrothermal performances were investigated under ambient

conditions, as demonstrated in Fig. 5b. Among different graphene films, the reduced GO/EEG-HI-800 °C, which has a relatively lower sheet resistance, displays the highest

M

A

N

U

steady-state temperature (83.6 °C) at the same applied voltage of 30 V for 60 s. Fig. 5c presents an infrared thermal image of the surface of reduced GO/EEG-HI-800 °C films, which was supplied by a 10 V ~ 40 V input voltage at different heating times. When the power was supplied to the films, the surface temperature of the film monotonically increases until the surface temperature reached a steady state after 60 s, and the steady state temperature increases with the increase of applied voltage (Fig. 5d). The surface temperatures were 35.7 °C (10 V), 52.8 °C (20 V), 83.2 °C (30 V) and 127.5 °C (40 V) in the central region, respectively, excluding the edge areas with silver paste electrode

CC E

PT

ED

deposition, demonstrating the excellent electrothermal uniformity of reduced GO/EEG films. Compared to the film heater based on chemically doped CVD graphene, which just reached 55 °C at 30 V input voltage [12]. Moreover, compared with the reduced GO films by spin coating method with a saturated temperature of 42 °C at 60 V for 2 min [2], our reduced GO/EEG films heater exhibited a better heating performance (up to 127.5 °C at 40 V for 60 s). To further demonstrate its potential as an efficient transparent defogger, a defogging test was performed using reduced GO/EEG-HI-800 °C hybrid films on quartz (1×1 cm2)

A

with an input voltage of 30 V (below the safe voltage of 36 V). Fig. 6 shows the defogging screenshots taken from the defogging video at different times (Supporting Information, Movie S1). The top (left) photo represents the defogger was covered by the water (~ 95 °C) vapor before applied voltage. In the anticlockwise direction, the second photo showed the starting point of the defogging after applied voltage for 3 s. The fog started to disappear on the edge of the reduced GO/EEG-HI-800 °C hybrid films defogger. And fog disappears completely until 11 s. In terms of real application in daily life, our experiments were the safe voltage of 30 V and the complete defogging time was 11 s, which is superior to that of other graphene-based defoggers (e.g.,

need >30 s under 20 ~ 60 V) [2, 30-32].

SC R

IP T

4. Conclusion In summary, a rapid interfacial self-assembly of large-area GO/EEG hybrid films as a cost-effective and high yield route has been demonstrated, which can be easily transferred onto the nonplanar substrates and patterned. As a transparent conductive heater reduced GO/EEG hybrid films shows high performance in heating, the heater can reach a saturated temperature of up to 35.7 °C, 52.8 °C, 83.2 °C and 127.5 °C when 10 V ~ 40 V were applied for 60 s, respectively. As an efficient defogger, it can completely remove fog within 11 s when supplied a safe voltage of 30 V. Therefore, we conclude that our reduced GO/EEG hybrid films can serve as glass tinting and various defoggers/defrosters such as anti-fog glasses, mirror and auto window defogging/defrosting.

M

A

N

U

Acknowledgements The authors are grateful for the financial support by the National Natural Science Foundation of China (51402060, 51573201, 51501209 and 201675165), Program for International S&T Cooperation Projects of the Ministry of Science and Technology of China (2015DFA50760), Public Welfare Project of Zhejiang Province (2016C31026), Science and Technology Major Project of Ningbo (2014S10001, 2016B10038 and 2016S1002), International S&T Cooperation Program of Ningbo (2015D10003 and 2017D10016) for financial support. We also thank the Chinese Academy of Science for

A

CC E

PT

ED

Hundred Talents Program, Chinese Central Government for Thousand Young Talents Program and 3315 Program of Ningbo, the open fund of Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province, and The Key Technology of Nuclear Energy (CAS Interdisciplinary Innovation Team, 2014).

References [1] L. Tan, M. Zeng, Q. Wu, L. Chen, J. Wang, T. Zhang, J. Eckert, M.H. Rümmeli, L. Fu, Direct Growth of Ultrafast Transparent Single-Layer Graphene Defoggers, Small 11 (2015) 1840-1846. [2] D. Sui, Y. Huang, L. Huang, J. Liang, Y. Ma, Y. Chen, Flexible and transparent electrothermal film heaters based on graphene materials, Small 7 (2011) 3186-3192.

IP T

[3] Z. Wu, Z. Chen, X. Du, J.M. Logan, J. Sippel, M. Nikolou, K. Kamaras, J.R. Reynolds, D.B. Tanner, A.F. Hebard, Transparent, conductive carbon nanotube films,

SC R

Science 305 (2004) 1273-1276.

[4] C. Celle, C. Mayousse, E. Moreau, H. Basti, A. Carella, J.-P. Simonato, Highly flexible transparent film heaters based on random networks of silver nanowires, Nano

U

Res. 5 (2012) 427-433.

N

[5] Y. Mo, Y. Okawa, M. Tajima, T. Nakai, N. Yoshiike, K. Natukawa, Micro-machined

A

gas sensor array based on metal film micro-heater, Sens. Actuator B-Chem. 79 (2001) 175-181.

M

[6] J. Yeon Woo, S. Kumar Tripathy, K. Kim, C.-S. Han, Thermal and structural

ED

dependence of the band gap of quantum dots measured by a transparent film heater, Appl. Phys. Lett. 100 (2012) 063105. [7] D.R. Cairns, R.P. Witte, D.K. Sparacin, S.M. Sachsman, D.C. Paine, G.P. Crawford,

PT

R.R. Newton, Strain-dependent electrical resistance of tin-doped indium oxide on polymer substrates, Appl. Phys. Lett. 76 (2000) 1425-1427.

CC E

[8] J. Liu, D. Wu, S. Zeng, Influence of temperature and layers on the characterization of ITO films, J. Mater. Process. Technol. 209 (2009) 3943-3948. [9] K.S. Kim, Y. Zhao, H. Jang, Y.L. Sang, J.M. Kim, K.S. Kim, J.H. Ahn, P. Kim, J.Y.

A

Choi, B.H. Hong, Large-scale pattern growth of graphene films for stretchable transparent electrodes, Nature 457 (2009) 706-710. [10] H.-S. Jang, S.K. Jeon, S.H. Nahm, The manufacture of a transparent film heater by spinning multi-walled carbon nanotubes, Carbon 49 (2011) 111-116. [11] T.J. Kang, T. Kim, S.M. Seo, Y.J. Park, Y.H. Kim, Thickness-dependent thermal resistance of a transparent glass heater with a single-walled carbon nanotube coating,

Carbon 49 (2011) 1087-1093. [12] J. Kang, H. Kim, K.S. Kim, S.-K. Lee, S. Bae, J.-H. Ahn, Y.-J. Kim, J.-B. Choi, B.H. Hong, High-performance graphene-based transparent flexible heaters, Nano Lett. 11 (2011) 5154-5158. [13] J.J. Bae, S.C. Lim, G.H. Han, Y.W. Jo, D.L. Doung, E.S. Kim, S.J. Chae, T.Q. Huy, N. Van Luan, Y.H. Lee, Heat dissipation of transparent graphene defoggers, Adv. Funct.

IP T

Mater. 22 (2012) 4819-4826.

[14] H. Sun, D. Chen, Y. Wu, Q. Yuan, L. Guo, D. Dai, Y. Xu, P. Zhao, N. Jiang, C.-T.

transfer process, J. Mater. Chem. C 5 (2017) 1880-1884.

SC R

Lin, High quality graphene films with a clean surface prepared by an UV/ozone assisted

[15] D. Kim, H.-C. Lee, J.Y. Woo, C.-S. Han, Thermal behavior of transparent film

U

heaters made of single-walled carbon nanotubes, J. Phys. Chem. C 114(13) (2010)

N

5817-5821.

A

[16] Y.H. Yoon, J.W. Song, D. Kim, J. Kim, J.K. Park, S.K. Oh, C.S. Han, Transparent Film Heater Using Single‐Walled Carbon Nanotubes, Adv. Mater. 19 (2007) 4284-

M

4287.

ED

[17] S. Manivannan, J.H. Ryu, J. Jang, K.C. Park, Fabrication and effect of post treatment on flexible single-walled carbon nanotube films, J. Mater. Sci.-Mater. Electron. 21 (2010) 595-602.

PT

[18] X. Li, H. Zhu, K. Wang, A. Cao, J. Wei, C. Li, Y. Jia, Z. Li, D. Wu. Graphene-onsilicon Schottky junction solar cells. Adv. Mater. 22 (2010) 2743-2748.

A

CC E

[19] Z. Chen, Z. Wang, X. Li, Y. Lin, N. Luo, M. Long, N. Zhao, J. Xu. Flexible piezoelectric-induced pressure sensors for static measurements based on nanowires/graphene heterostructures. ACS Nano 11 (2017) 4507-4513. [20] X. Li, L. Tao, Z. Chen, H. Fang, X. Li, X. Wang, J.-B. Xu, H. Zhu, Graphene and related two-dimensional materials: Structure-property relationships for electronics and optoelectronics, Appl. Phys. Rev. 4 (2017) 021306. [21] C.-Y. Su, A.-Y. Lu, Y. Xu, F.-R. Chen, A.N. Khlobystov, L.-J. Li, High-quality thin graphene films from fast electrochemical exfoliation, ACS Nano 5 (2011) 2332-2339. [22] L. Li, X. Li, M. Du, Y. Guo, Y. Li, H. Li, Y. Yang, F.E. Alam, C.T. Lin, Y. Fang, Solid-Phase Coalescence of Electrochemically Exfoliated Graphene Flakes into a Continuous Film on Copper, Chem. Mater. 28 (2016) 3360-3366.

[23] H. Sun, X. Li, Y. Li, G. Chen, Z. Liu, F.E. Alam, D. Dai, L. Li, L. Tao, J.B. Xu, High-Quality Monolithic Graphene Films via Laterally Stitched Growth and Structural Repair of Isolated Flakes for Transparent Electronics, Chem. Mater. 29 (2017) 7808– 7815. [24] S. Pei, J. Zhao, J. Du, W. Ren, H.-M. Cheng, Direct reduction of graphene oxide films into highly conductive and flexible graphene films by hydrohalic acids, Carbon 48 (2010) 4466-4474. [25] X. Li, T. Yang, Y. Yang, J. Zhu, L. Li, F.E. Alam, X. Li, K. Wang, H. Cheng, C.T.

SC R

IP T

Lin, Large ‐ Area Ultrathin Graphene Films by Single ‐ Step Marangoni Self ‐ Assembly for Highly Sensitive Strain Sensing Application, Adv. Funct. Mater. 26 (2016) 1322-1329. [26] C. Mattevi, G. Eda, S. Agnoli, S. Miller, K.A. Mkhoyan, O. Celik, D.

M

A

N

U

Mastrogiovanni, G. Granozzi, E. Garfunkel, M. Chhowalla, Evolution of electrical, chemical, and structural properties of transparent and conducting chemically derived graphene thin films, Adv. Funct. Mater. 19 (2009) 2577-2583. [27] S. Park, J. An, I. Jung, R.D. Piner, S.J. An, X. Li, A. Velamakanni, R.S. Ruoff, Colloidal suspensions of highly reduced graphene oxide in a wide variety of organic solvents, Nano Lett. 9 (2009) 1593-1597. [28] H. Feng, R. Cheng, X. Zhao, X. Duan, J. Li, Corrigendum: A low-temperature method to produce highly reduced graphene oxide, Nat. Commun. 4 (2013) 1539-1545. [29] H.A. Becerril, J. Mao, Z. Liu, R.M. Stoltenberg, Z. Bao, Y. Chen, Evaluation of solution-processed reduced graphene oxide films as transparent conductors, ACS Nano

CC E

PT

ED

2 (2008) 463-470. [30] J. Wang, Z. Fang, H. Zhu, B. Gao, S. Garner, P. Cimo, Z. Barcikowski, A. Mignerey, L. Hu, Flexible, transparent, and conductive defrosting glass, Thin Solid Films 556 (2014) 13-17. [31] J. Sun, Y. Chen, M.K. Priydarshi, Z. Chen, A. Bachmatiuk, Z. Zou, Z. Chen, X. Song, Y. Gao, M.H. Rümmeli, Direct chemical vapor deposition-derived graphene glasses targeting wide ranged applications, Nano Lett. 15 (2015) 5846-5854. [32] Z. Wang, Z. Xue, M. Zhang, Y. Wang, X. Xie, P.K. Chu, P. Zhou, Z. Di, X. Wang,

A

Germanium‐Assisted Direct Growth of Graphene on Arbitrary Dielectric Substrates for Heating Devices, Small (2017) 1700929.

SC R

IP T

Figure 1-6

U

Fig. 1. The image of the self-assembly process of EEG nanosheets. EEG nanosheets

A

CC E

PT

ED

M

A

N

were temporarily suspended on the surface of the water (a) and GO solution (b).

Fig. 2. (a) Large-area GO/EEG hybrid films transferred onto nonplanar glass surfaces. (b) A patterned graphene on quartz through a hard mask process. (c) Large-area (20×20 cm2) GO/EEG hybrid films on the glass substrate. SEM images of (d) EEG, (e) GO/EEG and (f) reduced GO/EEG films by HI vapor and then 800 °C thermal treatment.

IP T SC R

Fig. 3. (a) XPS spectra of the as-prepared GO/EEG and reduced GO/EEG films, (b) the change in water contact angle in the quartz, EEG, GO/EEG films and reduced GO/EEG

PT

ED

M

A

N

U

films by HI followed by 800 °C thermal treatment (or only HI treatment).

Fig. 4. (a) Transmittance curves and (b) sheet resistance of EEG and GO/EEG hybrid

A

CC E

films before and after reduction treatment.

IP T SC R

U

Fig. 5. (a) Schematic illustration of the transparent film heater. (b) Infrared thermal

N

images for the reduced EEG and GO/EEG films on quartz (1×1 cm2) at an applied

A

voltage of 30 V for 60 s. (c) Infrared thermal images on the surface of GO/EEG-HI-

M

800 °C films at 10 V ~ 40 V for different heating times. (d) Time-dependent temperature

A

CC E

PT

ED

profile of the GO/EEG-HI-800 °C film heater with different input voltages.

Fig. 6. Real-time defogging screenshots taken from the defogging video at an applied voltage of 30 V for different times.

Table 1. Characterization of the EEG and GO/EEG hybrid films before and after reduction treatment.

A

CC E

PT

ED

M

A

N

U

SC R

EEG GO/EEG EEG-HI GO/EEG-HI EEG-HI-800 °C GO/EEG-HI-800 °C

Sheet resistance [kΩ/sq] --89.8 ± 4.5 48.9 ± 2.7 5.3 ± 0.5 3 ± 0.3

IP T

Transmittance [%, at 550 nm] 85.9 ± 0.7 84.6 ± 0.8 81.4 ± 0.9 76.5 ± 0.5 79.7 ± 0.8 76.2 ± 0.7

Graphene films