Electrolessly deposited electrospun metal nanowire transparent ...
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Electrolessly deposited electrospun metal nanowire transparent electrodes Po-Chun Hsu1, Desheng Kong1, Shuang Wang2, Haotian Wang3, Alex J. Welch1, Hui Wu1, §, Yi Cui1,4,* 1
Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA,
2
Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA,
3
Department of Applied Physics, Stanford University, Stanford, CA 94305, USA,
4
Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA,
1. Experimental 1.1 Electrospinning The solution for electrospinning consists of 8 wt% of polyvinyl butyral (PVB, Butvar B-98, Santa Cruz Biotechnology, Inc.) and 9 wt% of anhydrous tin(II) chloride (Fisher Scientific) in n-butanol (99.4%, EMD Millipore Chemicals). The solution was loaded in a 1-mL syringe with a needle tip which is connected to a voltage supply (ES30P-5W, Gamma High Voltage Research). The applied potential onto the needle was +8 kV. The collector was grounded aluminum foil, and the substrate (glass slide/ polyethylene terephthalate film/ polystyrene plate) spin-coated with PVB was placed on the foil to collect PVB/SnCl2 NWs. The distance between the syringe needle tip and the collector was 20 cm, and the pump rate was 0.08 ml/h. High electrical field and surface charges pulled PVB/SnCl2 NWs out of the droplet, and the NWs were attracted onto the collector and the glass slides due to electrical force. S1
1.2 Ag electroless deposition PVB/SnCl2 NWs and the substrate were immersed into 25g/L of AgNO3 aqueous solution (99.9995%, Alfa Aesar) to deposit Ag seed layers for 30 min. The sample was then thoroughly rinsed with deionized water before immersed into 5g/L of glucose aqueous solution (anhydrous, EMD Millipore Chemicals), which is the reducing agent. The Ag precursor, Ag(NH3)2+ solution, was made by adding NH4OH (14.8M, EMD Millipore Chemicals) into 5g/L Ag(NO)3 aqueous solution dropwisely until the solution became clear again. The Ag(NH3)2+ solution was then added dropwisely into the vigorously stirred glucose solution until AgNWs reached desired thickness. 1.3 Cu electroless deposition The Ag seed layer synthesis is the same as Ag electroless deposition. The aqueous solution for Cu electroless deposition contained 0.0258 M CuSO4 (99%, Alfa Aesar), 0.0413 M tetrasodium ethylenediaminetetraacetate dihydrate (Na4EDTA, 99%, Fisher Scientific), 0.09M H2SO4 (95~98%, EMD Millipore Chemicals), 0.3M triethanol amine (99.4%, J.T.Baker), 0.1 wt% triton x-100 (Alfa Aesar), and 0.1 M dimethylamine borane (DMAB, 97%, Alfa Aesar). The Ag seed/PVB NWs were immersed into the stirred Cu electroless deposition solution capped in a N2 purging bottle. Different thickness of CuNWs could be achieved by changing the immersion time period. 1.4 Optical and electrical measurement The transmittance measurement used a quartz tungsten halogen lamp as the light source, coupled with a monochromator (Newport 70528) to control the wavelength. An iris and a convex lens were used to focus the beam size to about 1mm × 2mm, and a
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beam splitter split the light beam into an integrating sphere (Newport) for transmittance measurement and a photodiode (Newport, 818-UV-L). The photodiode is connected to an electrometer (Keithley 6517A) for light intensity calibration. The samples were placed in front of the integrating sphere, so both specular transmittance and diffuse transmittance were included. An identical glass slide was used for reference. A source-measure unit (Keithley 236) was used to measure the photocurrent from the integrating sphere, and the transmittance spectrum was thus calculated based on the reference plain glass slide. The transmittance spectrum was then weighted by solar spectrum from 400 nm to 800 nm to obtain the average transmittance TAM1.5. For the sheet resistance measurement, two contacts were drawn by a silver pen (CircuitWorks, ITW Chemtronics), separated by a square area of transparent electrode, and then the resistance was measure by a calibrated multimeter. 1.5 Bending tests To perform bending test, PET substrates (Ridout Plastics Company) were used to conduct electroless deposition. ITO thin films on PET with Rs of 20 Ω/sq were bought from Sigma-Aldrich for comparison. The samples were bent to a mandrel with radius of 4 mm up to 1000 times, and their sheet resistances were recorded after certain cycles to track the performance degradation. 1.6 Characterization All the scanning electron microscope (SEM) images were taken by FEI XL30 Sirion SEM equipped with an energy dispersive spectrometer. The PVB/SnCl2 NWs sample was sputtered with ~3nm of gold to prevent electron charging. X-ray photoelectron spectra (XPS) were collected by SSI SProbe XPS spectrometer with Al Kα source. S3
2. Figures
Figure S1. (a) SEM images of electrospun PVB/SnCl2 nanowires. (b) High-magnification image. The sample was sputter with ~3 nm of gold for imaging. The scale bars are 1 µm and 200 nm respectively.
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Figure S2. Time-series SEM images of electrolessly deposited CuNWs. (a) 0 min, (b) 30 min, (c) 45 min, (d) 60 min, (e) 80 min. The scale bars are 200 nm.
Figure S3. AgNWs on a bare glass slide. Without hydrophobic coating, Ag nanoparticles can electrolessly deposit on the glass substrate and reduce the optical transmittance. The scale bar is 500 nm.
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Electrolessly deposited electrospun metal nanowire transparent electrodes Po-Chun Hsu1, Desheng Kong1, Shuang Wang2, Haotian Wang3, Alex J. Welch1, Hui Wu1, §, Yi Cui1,4,* 1
Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA,
2
Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA,
3
Department of Applied Physics, Stanford University, Stanford, CA 94305, USA,
4
Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA,
1. Experimental 1.1 Electrospinning The solution for electrospinning consists of 8 wt% of polyvinyl butyral (PVB, Butvar B-98, Santa Cruz Biotechnology, Inc.) and 9 wt% of anhydrous tin(II) chloride (Fisher Scientific) in n-butanol (99.4%, EMD Millipore Chemicals). The solution was loaded in a 1-mL syringe with a needle tip which is connected to a voltage supply (ES30P-5W, Gamma High Voltage Research). The applied potential onto the needle was +8 kV. The collector was grounded aluminum foil, and the substrate (glass slide/ polyethylene terephthalate film/ polystyrene plate) spin-coated with PVB was placed on the foil to collect PVB/SnCl2 NWs. The distance between the syringe needle tip and the collector was 20 cm, and the pump rate was 0.08 ml/h. High electrical field and surface charges pulled PVB/SnCl2 NWs out of the droplet, and the NWs were attracted onto the collector and the glass slides due to electrical force. S1
1.2 Ag electroless deposition PVB/SnCl2 NWs and the substrate were immersed into 25g/L of AgNO3 aqueous solution (99.9995%, Alfa Aesar) to deposit Ag seed layers for 30 min. The sample was then thoroughly rinsed with deionized water before immersed into 5g/L of glucose aqueous solution (anhydrous, EMD Millipore Chemicals), which is the reducing agent. The Ag precursor, Ag(NH3)2+ solution, was made by adding NH4OH (14.8M, EMD Millipore Chemicals) into 5g/L Ag(NO)3 aqueous solution dropwisely until the solution became clear again. The Ag(NH3)2+ solution was then added dropwisely into the vigorously stirred glucose solution until AgNWs reached desired thickness. 1.3 Cu electroless deposition The Ag seed layer synthesis is the same as Ag electroless deposition. The aqueous solution for Cu electroless deposition contained 0.0258 M CuSO4 (99%, Alfa Aesar), 0.0413 M tetrasodium ethylenediaminetetraacetate dihydrate (Na4EDTA, 99%, Fisher Scientific), 0.09M H2SO4 (95~98%, EMD Millipore Chemicals), 0.3M triethanol amine (99.4%, J.T.Baker), 0.1 wt% triton x-100 (Alfa Aesar), and 0.1 M dimethylamine borane (DMAB, 97%, Alfa Aesar). The Ag seed/PVB NWs were immersed into the stirred Cu electroless deposition solution capped in a N2 purging bottle. Different thickness of CuNWs could be achieved by changing the immersion time period. 1.4 Optical and electrical measurement The transmittance measurement used a quartz tungsten halogen lamp as the light source, coupled with a monochromator (Newport 70528) to control the wavelength. An iris and a convex lens were used to focus the beam size to about 1mm × 2mm, and a
S2
beam splitter split the light beam into an integrating sphere (Newport) for transmittance measurement and a photodiode (Newport, 818-UV-L). The photodiode is connected to an electrometer (Keithley 6517A) for light intensity calibration. The samples were placed in front of the integrating sphere, so both specular transmittance and diffuse transmittance were included. An identical glass slide was used for reference. A source-measure unit (Keithley 236) was used to measure the photocurrent from the integrating sphere, and the transmittance spectrum was thus calculated based on the reference plain glass slide. The transmittance spectrum was then weighted by solar spectrum from 400 nm to 800 nm to obtain the average transmittance TAM1.5. For the sheet resistance measurement, two contacts were drawn by a silver pen (CircuitWorks, ITW Chemtronics), separated by a square area of transparent electrode, and then the resistance was measure by a calibrated multimeter. 1.5 Bending tests To perform bending test, PET substrates (Ridout Plastics Company) were used to conduct electroless deposition. ITO thin films on PET with Rs of 20 Ω/sq were bought from Sigma-Aldrich for comparison. The samples were bent to a mandrel with radius of 4 mm up to 1000 times, and their sheet resistances were recorded after certain cycles to track the performance degradation. 1.6 Characterization All the scanning electron microscope (SEM) images were taken by FEI XL30 Sirion SEM equipped with an energy dispersive spectrometer. The PVB/SnCl2 NWs sample was sputtered with ~3nm of gold to prevent electron charging. X-ray photoelectron spectra (XPS) were collected by SSI SProbe XPS spectrometer with Al Kα source. S3
2. Figures
Figure S1. (a) SEM images of electrospun PVB/SnCl2 nanowires. (b) High-magnification image. The sample was sputter with ~3 nm of gold for imaging. The scale bars are 1 µm and 200 nm respectively.
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Figure S2. Time-series SEM images of electrolessly deposited CuNWs. (a) 0 min, (b) 30 min, (c) 45 min, (d) 60 min, (e) 80 min. The scale bars are 200 nm.
Figure S3. AgNWs on a bare glass slide. Without hydrophobic coating, Ag nanoparticles can electrolessly deposit on the glass substrate and reduce the optical transmittance. The scale bar is 500 nm.
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