Roll-to-roll encapsulation of metal nanowires between graphene and plastic substrate for high-performance flexible transparent electrodes

Transcription

1 Supplementary Information for Roll-to-roll encapsulation of metal nanowires between graphene and plastic substrate for high-performance flexible transparent electrodes Bing Deng 1,, Po-Chun Hsu 2,, Guanchu Chen 1, B. N. Chandrashekar 1, Lei Liao 1, Zhawulie Ayitimuda 3, Jinxiong Wu 1, Yunfan Guo 1, Li Lin 1, Yu Zhou 1, Mahaya Aisijiang 3, Qin Xie 1, Yi Cui 2,4,*, Zhongfan Liu 1,*, and Hailin Peng 1,* 1 Center for Nanochemistry, Beijing Science and Engineering Center for Nanocarbons, Beijing National Laboratory for Molecular Sciences (BNLMS), College of Chemistry and Molecular Engineering, Peking University, Beijing , P.R. China. 2 Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, US 3 College of Chemistry and Biological Sciences, Yili Normal University, Yining, Xinjiang 83500, P. R. China 4 Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA. These authors contributed equally to this work. *To whom correspondence should be addressed. hlpeng@pku.edu.cn; yicui@stanford.edu; zfliu@pku.edu.cn 1

2 Experimental Section: Roll-to-roll CVD growth of graphene. The copper foil used in the growth was industrial electrolytic copper foil (99.9% purity, 18-µm thickness, 1-µm roughness, ~100 RMB/kg) purchased from Suzhou Fukuda Metal Co. Ltd. The schematic and photograph of the R2R low-pressure CVD system was shown in Supplementary Figure S1. The home-made roll-to-roll CVD system was composed of four components: the vacuum system (ultimate vacuum of ~5 Pa), the operating system (running rate of 0 ~ 50 cm/min), the gas supplying system (CH 4 gas flow of 0 ~ 36 s.c.c.m, H 2 gas flow of 0 ~ 50 s.c.c.m), the high-temperature tube furnace (temperature programming up to 1060 o C). The 100-mm diameter and 1.4-m length quartz tube furnace (the effective heating length is 60 cm) was equipped with two winder roller to supply and receive the copper strip simultaneously controlled by a stepping motor to accurately adjust the speed of operation. Growing conditions were well optimized. For a typical growth, copper strip with the size of 5 m long and 5 cm wide was inserted in the furnace and heated up to 1000 with gas flow of 50 s.c.c.m H 2 at 90 Pa. After reaching 1000, copper strip was annealed at a speed of 5 cm/min to increase the grain size of copper and remove contaminants and oxidation layer on the surface of copper. After annealing, the copper strip was switched back to the supplying roller. The gas mixture of 36 s.c.c.m CH 4 and 5 s.c.c.m H 2 was then flowed at 80 Pa. The post-annealed copper strip was then operated from the supplying roller to the receiving roller at a speed of 5 cm/min. Finally, the graphene/cu strip was rapidly cooled down by the circulating cooling water built in the receiving roller. 2

3 Coating or transfer of NWs to EVA/PET substrate. The EVA/PET (50 µm/75 µm thickness) substrate was purchased from Deli Stationery Co. Ltd. The AgNWs suspension (30-nm diameter, 20-µm length, dispersed in isopropanol, concentration of 10 mg/ml, purchased from Suzhou Coldstones Tech Co. Ltd) was diluted to the specific concentration using methane and underwent ultrasonic treatment at 90 W power for 2 min before Mayer rod coating. The coated AgNW film was washed in DI water for 10 seconds to remove surfactant and dried up immediately using nitrogen gas gun. The CuNWs suspension (10 to 100-nm diameter, 1 to 10-µm length, dispersed in ethanol, concentration of 5 mg/ml, purchased from Nanjing XFNANO Materials Tech Co. Ltd) was diluted to 1 mg/ml using ethanol and underwent ultrasonic treatment at 90 W power for 2 min before Mayer rod coating. The coated CuNWs film was washed in 1M HCl (aq) for 30 seconds to remove surface oxide layer and surfactant and dried immediately using a nitrogen gas gun. The CuNTs were made by electrospinning polyvinylpyrrolidone (PVP) nanofibers onto a metallic ring collector, followed by Cu thermal evaporation to coat Cu onto one side of the PVP nanofibers. The PVP@Cu nanofibers were then scooped and transferred onto EVA/PET substrates. The polymer was dissolved by ethanol, leaving CuNTs on the substrate. Hot press lamination of NWs/EVA/PET film and graphene/cu film. The lamination process was realized using an SG 330-SCL lamination machine purchased 3

4 from Shanghai Shenguang Office Equipment Co. Ltd. equipped with a home-made rolling system. The temperature was adjusted by a knob according to the thickness of EVA/PET film. About 100 was appropriate for the EVA/PET film with the thickness of 125 µm in this work. The lamination machine had a set lamination speed of ~1 cm/s. Roll-to-roll efficient electrochemical bubbling delamination. The home-made R2R delamination system was shown in Supplementary Figure S5. A set of roller was controlled by a stepping motor to realize the supplying of Cu/graphene/NWs/EVA/PET film and the receiving of Cu strip and Graphene/NWs/EVA/PET film after delamination simultaneously. The electrochemical bubbling delamination was conducted using 1M NaOH aqueous solution as the electrolyte and graphite rod as the anode. The typical voltage and current were 3 V and 0.5 A, respectively, and can be adjusted to realize different delamination speed. The separation interface of graphene and copper was on the surface of liquid without copper immersing into liquid (Supplementary Fig. S5b), so large amounts of bubbles were generated at the interface, resulting in considerable mechanical force to delaminate graphene and copper. After delamination, the hybrid film and copper strip were rinsed using DI water and finally dried by nitrogen gas gun. Electrical and optical property measurement. The sheet resistances of the films 4

5 were measured using a four-probe resistance measuring meter (Guangzhou 4-probe Tech Co. Ltd., RTS-4) based on four-point probes method to eliminate contact resistance. Four metal probes were aligned in a line at intervals of 1 mm. The outer pair probe was current-carrying electrode and the inner pair probe was voltage-sensing electrode. The transmittance measurement was conducted using UV-Vis-NIR Perkin Elmer Lambda 950 spectrophotometer. The samples were placed in front of the integrating sphere. Both specular transmittance and diffuse transmittance were included. An EVA/PET film (50 µm/75 µm thick) was used for reference. Characterization. Characterization was carried out using optical microscopy (Olympus DX5r1 microscope), AFM (Vecco Nanoscope Ⅲa, tapping mode), SEM (Hitachi S-4800; acceleration voltage, 1-5 KV), Raman spectra (Horiba HR800 system; nm laser excitation, laser spot size about 1 µm), XPS (Kratos Axis Ultra-DLD spectrophotometer, monochromatic Al X-ray at low pressures of to Torr). Electrochromic device fabrication. The electrochromic samples were made by spin coating 1.3% of PEDOT:PSS aqueous solution (Sigma-Aldrich) on the as-fabricated transparent electrodes. Before spin-coating, approximately 3 nm of indium tin oxide (ITO) was sputter onto the graphene/agnw transparent electrode for better hydrophilicity. Note this ITO coating 5

6 is too thin to change the sheet resistance, so it is only for surface treatment. A standard three-electrode setup (BioLogic) was employed on the electrochromic sample to manipulate the potential, with a graphite rod as the counter electrode and Ag/AgCl as the reference electrode (Accumet). The electrolyte was 0.1 M LiClO 4 (Alfa Aesar) in propylene carbonate (EMD Chemicals). The electrochromic electrode was applied with the potential steps of +0.8V and -1.0V for color changing for 15 s. In the meantime, the transmittance at 550 nm was measured and recorded using a spectrophotometer (Shimadzu, UV-1700). 6

7 Supplementary Figures: Figure S1 Roll-to-roll CVD system for large-area continuous growth of graphene. Figure S2 Roll-to-roll CVD growth of graphene. a, Optical microscopy image of graphene on copper, showing the domains of copper. b, SEM image of graphene on copper, showing full-covered almost monolayer with small island of multi-layer graphene. c, Optical microscopy image of graphene transferred on SiO 2 /Si substrate, revealing the large-area complete graphene. d, Raman spectrum of graphene on SiO 2 /Si substrate, showing the high quality of single layer graphene. e, UV-Vis transmittance spectrum of graphene transferred on quartz, showing the high 7

8 transmittance of graphene on wide-band region. Note that the measured transmittance mentioned does not include the absorption and reflectance from the substrate. f, Sheet resistance distribution of graphene transferred on SiO 2 /Si. Figure S3 The reuse of copper foil. a-b, Picture and optical microscopy image of copper strip before growth, respectively. c-d, Picture and optical microscopy image of copper strip after one-time growth of graphene, respectively. e-f, Picture and optical microscopy image of copper strip after three-time growth of graphene, respectively. 8

9 Figure S4 Pretreatment of the PET/EVA substrate and coating of nanowires. a, Contact angle of EVA/PET before air plasma treatment. b, Contact angle of EVA/PET after air plasma treatment, showing that the hydrophilicity of EVA is enhanced by air plasma treatment. c, Optical microscopy image of silver nanowires on an EVA/PET substrate, showing the uniformity of silver nanowires in a large scale. d-f, SEM images of silver nanowires with different densities (d, low density; e, middle density; f, high density) on an EVA/PET substrate, showing the tunable density of nanowires by the coating condition. Figure S5 Roll-to-roll electrochemical bubbling delamination system for efficient large-area continuous separation of graphene and copper. a, The photograph of the system. b, The photograph shows the delamination interface of graphene and copper beneath the surface of solution, resulting in ultrafast bubbling generation and efficient delamination. 9

10 Figure S6 Graphene films transferred by the efficient roll-to-roll delamination from copper. a, Optical microscopy image of graphene transferred onto an EVA/PET substrate. b, SEM image of graphene on the EVA/PET substrate, showing little broken in a large scale. c, SEM image of graphene on the EVAPET substrate, revealing completeness on a micro level. d, XPS full spectrum of graphene on the EVA/PET substrate, showing carbon and oxygen as the main elements. Note that the signal of oxygen came from the EVA substrate. e, XPS refined spectrum of graphene on the EVA/PET substrate, showing no residual copper on the graphene film. We can conclude that graphene grown on copper can be transferred onto the EVA/PET substrate without break. What s more, the transfer process is ultraclean without residual copper. Figure S7 SEM image (a) and AFM image (b) of pure AgNWs coated on PET substrate, 10

11 respectively. The profile of AFM image show the diameter of individual nanowires is around 35 nm, and the junction of nanowires is around 70 nm. Figure S8 Corrosion resistance of the encapsulated Graphene/CuNT film. a, SEM image of the CuNT film transferred on an EVA/PET substrate. b, SEM image of the encapsulated Graphene/CuNT film on EVA/PET, showing CuNT partly embedded into EVA substrate and covered by graphene. c, Changes in sheet resistance versus baking time at humidity 40%, 80 o C. Figure S9 Corrosion resistance of the encapsulated Graphene/CuNWs film. a, SEM image of the 11

12 CuNWs film coated on an EVA/PET substrate. b, SEM image of the encapsulated Graphene/CuNWs film, showing CuNWs partly embedded into EVA substrate and covered by graphene. c, Changes in sheet resistance versus baking time at humidity 40%, 80 o C. Figure S10 The peeling test of the encapsulated Graphene/AgNWs film by the Scotch tape. a-b, SEM images of the pure AgNWs film just coated on an EVA/PET substrate and after one time of peeling of the tape, respectively. c-d, SEM images of the encapsulated Graphene/AgNWs film just prepared and after 10 times of peeling, respectively. Figure S11 Corrosion resistance test at 85 o C and 85% relative humidity, showing that the 12

13 encapsulated graphene/agnws/eva/pet transparent electrode keeps stable while the uncoated AgNWs electrode degrades drastically in conductivity. Supplementary Movie S1. Roll-to-roll CVD growth of graphene on copper strip in a high-temperature tube furnace. Supplementary Movie S2. Roll-to-roll hot-press lamination process. A roll of graphene/copper and a roll of nanowires pre-coated EVA/PET was stacked and then passed through a hot-press lamination machine. The EVA layer was melt and adhered firmly to graphene to form the copper/graphene/nanowire/eva/pet stacked structure. Supplementary Movie S3. Roll-to-roll electrochemical delamination. A roll of copper/graphene/nanowire/eva/pet film was roll-to-roll delaminated by the electrochemical bubbling delamination process. The separated roll of the copper strip and graphene/nanowire/eva/pet film were then washed in DI water. Supplementary Movie S4. Cycle life of electrochromic device. Electrochromic device with the size of 5 5 cm 2 based on Graphene/AgNW transparent electrode was shown in this movie. The device can function under bending scenario and showed considerable uniformity of color. The bleach state and color state was fast switched. 13