Conductive Film Applications Research Articles

Flexible Transparent Films of Oriented Silver Nanowires for a Stretchable Strain Sensor.

The potential applications of stretchable strain sensors in wearable electronics have garnered significant attention. However, developing susceptible stretchable strain sensors for practical applications still poses a considerable challenge. The present study introduces a stretchable strain sensor that utilizes silver nanowires (AgNWs) embedded into a polydimethylsiloxane (PDMS) substrate. The AgNWs have high flexibility and electrical conductivity. A stretchable AgNW/Pat-PDMS conductive film was prepared by arranging nanowires on the surface of PDMS using a simple rod coating method. Depending on the orientation angle, the overlap area between nanowires varies, resulting in different levels of separation under a given strain. Due to the separation of the nanowire and the change in current path geometry, the variation in strain resistance of the sensor can be primarily attributed to these factors. Therefore, precision in strain regulation can be adjusted by altering the angle θ (0°, 60°, or 90°) of the nanowire. At the same time, the stability of the AgNW/Pattern-PDMS (AgNW/Pat-PDMS) conductive film application was verified by preparing a sandwich structure PDMS/AgNW/Pat-PDMS stretchable strain sensor. The sensor exhibited high sensitivity within the operating sensing range (gauge factor (GF) of 15 within ~120% strain), superior durability (20,000 bending cycles and 5000 stretching cycles), and excellent response toward bending.

Physical and Electrical Properties of Spray Coating Graphene Films: The Effect of Solution Concentration

Graphene nanofilms were deposited by the spray coating method at different concentrations (0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 g) and prepared at 120°C. The prepared nanofilms were characterized in terms of their structural, morphological, optical, and electrical properties. The results confirm the formation of high-purity and high-crystallinity graphene nanofilms with a layered nanosheet morphology. The X-ray diffraction pattern shows the presence of pure graphene with (002) crystal planes. SEM Images show that the intended graphene films are symmetrical with few wrinkles on their surface. The graphene films show semi-transparent behavior with a maximum transmission of 50%. Raman spectroscopy shows that the relative intensity, position, and shape of the G and 2D Raman peaks change with the number of graphene layers. The electrical conductivity increases with temperature, and the conductivity can be further increased depending on the metal or metal oxide functionalization. The electrical conductivity of the graphene film deposited at a concentration of 0.3 g was significantly higher than the values reported for other concentrations. The results of this study suggest that the physical and electrical properties of spray-coated graphene films can be optimized by controlling the solution concentration, which could have potential applications in transparent conductive films.

Exfoliation of Al-Residual Multilayer MXene Using Tetramethylammonium Bases for Conductive Film Applications.

This study describes the concise exfoliation of multilayer Ti3C2T x MXene containing residual aluminum atoms. Treatment with tetramethylammonium base in a co-solvent of tetrahydrofuran and H2O produced single-layer Ti3C2T x , which was confirmed via atomic force microscopy observations, with an electrical conductivity 100+ times that of Ti3C2T x prepared under previously reported conditions. The scanning electron microscopy and X-ray diffraction measurements showed that the exfoliated single-layer Ti3C2T x MXenes were reconstructed to assembled large-domain layered films, enabling excellent macroscale electric conductivity. X-ray photoelectron spectroscopy confirmed the complete removal of residual Al atoms and the replacement of surface fluorine atoms with hydroxy groups. Using the exfoliated dispersion, a flexible transparent conductive film was formed and demonstrated in an electrical application.

Large‐Diameter Carbon Nanotube Transparent Conductor Overcoming Performance–Yield Tradeoff

AbstractThe floating catalyst chemical vapor deposition (FCCVD) method for producing single‐walled carbon nanotubes (SWNTs) has demonstrated great potential in transparent conductive film (TCF) application. In FCCVD, reducing the concentration of carbon nanotubes (CNTs) is a well‐agreed method of improving the conductivity of SWNT TCF, achieved by producing thinner and longer CNT bundles. However, this method decreases the yield dramatically, which has persisted throughout the TCF development. Here, the production of large‐diameter double‐walled CNT (DWNT) TCFs via FCCVD is reported, which overcomes the tradeoff between performance and yield. These TCFs of DWNTs with an average diameter of ≈4 nm have a low sheet resistance of 35 Ω sq−1 at 90% transmittance. The conductivity here aligns with the best‐performing SWNT TCFs reported to date, showing a production yield greater than two orders of magnitude. The main factor contributing to the high performance and yield is considered to be the large tube diameter, which greatly improves the yield threshold of CNT bundling and leads to long tube length and unique junctions broadening. Moreover, the application of DWNT TCFs in perovskite solar cells exhibits a power conversion efficiency of 17.4%, which has not been reported yet in indium‐free CNT‐based solar cells.

Isolation and characterization of regenerated cellulose films using microcrystalline cellulose from oil palm empty fruit bunch with an ionic liquid

There is increasing interest in regenerated cellulose (RC) films for advanced manufacturing applications using natural polymers and renewable materials. In this study, RC films were isolated via solution casting process using microcrystalline cellulose (MCC) and the ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl). Initially, MCC was synthesized from oil palm empty fruit bunch using total chlorine-free (TCF) pulping and acid hydrolysis. Effects of MCC on the structures and physicochemical properties of the isolated RC films were determined for 4 wt%, 6.5 wt%, and 9 wt% of MCC at 80 °C. Several analytical methods were employed to evaluate degree of crystallinity, chemical stability, mechanical properties, morphology, opacity, water vapor permeability, and thermal stability of the RC films. The results showed that the addition of 6.5 wt% of MCC yielded the greatest tensile strength. Compared with the RC films with 6.5 wt% of MCC, thermal stability and water vapor permeability slightly increased when the MCC content was 9 wt%. According to the analytic hierarchy process (AHP), 6.5 wt% of MCC was the optimum MCC concentration to mix with [BMIM]Cl to manufacture RC films for packaging applications, while 9 wt% of MCC was ideal for photocatalytic and electrically conductive thin film applications.

The Effects of Size and Shape Dispersity on the Phase Behavior of Nanomesogen Lyotropic Liquid Crystals

Self-assembly of anisotropic nanomaterials into fluids is a key step in producing bulk, solid materials with controlled architecture and properties. In particular, the ordering of anisotropic nanomaterials in lyotropic liquid crystalline phases facilitates the production of films, fibers, and devices with anisotropic mechanical, thermal, electrical, and photonic properties. While often considered a new area of research, experimental and theoretical studies of nanoscale mesogens date back to the 1920s. Through modern computational, synthesis, and characterization tools, there are new opportunities to design liquid crystalline phases to achieve complex architectures and enable new applications in opto-electronics, multifunctional textiles, and conductive films. This review article provides a brief review of the liquid crystal phase behavior of one dimensional nanocylinders and two dimensional nanoplatelets, a discussion of investigations on the effects of size and shape dispersity on phase behavior, and outlook for exploiting size and shape dispersity in designing materials with controlled architectures.

Electrochemical enhancement of optoelectronic performance of transparent and conducting single-walled carbon nanotube films

We propose a novel approach to enhance optoelectronic performance of single-walled carbon nanotubes (SWCNTs) for transparent conducting film applications. The method provides fine and reversible tuning of optoelectrical properties of SWCNT films over a wide range of parameters. Using imidazolium-based ionic liquid with a wide electrochemical window (BMIM-PF6), we achieved the film sheet resistance as low as 53 Ω/sq at the 90% transmittance, thereby shifting the SWCNT Fermi level up to 1.4 eV. We believe the results to promote collateral research of adjustable tuning of the electronic structure of carbon nanomaterials as promising components for future electronics, electrochromic devices, and ionotronics.

Laser-induced growth of large-area epitaxial graphene with low sheet resistance on 4H-SiC(0001)

Multilayer graphene on SiC is a promising material due to its compatibility with modern electronics technology. Herein, we demonstrate the growth of large-area (~10 × 5 mm2), high-quality (D/G area ratio: ~0.03) epitaxial graphene on 4H-SiC(0001) using a high-power continuous laser with an extremely fast heating rate of 500 °C/s. As the growth temperature rises from 1550 °C to 1780 °C, the number of graphene layers increases from three to more than ten. The obtained graphene/SiC samples are highly conductive, with a sheet resistance of as low as ~0.43 Ω/sq. The high power and fast heating rate of the laser contribute to the formation of large-area and low-sheet-resistance graphene. The high conductivity makes graphene/SiC a very promising material for applications in conductive films. The growth mechanism of graphene and the influence of the structural properties of graphene on the conductivity are also discussed.

Facile synthesis of battery waste-derived graphene for transparent and conductive film application by an electrochemical exfoliation method.

One of the emerging challenges in tackling environmental issues is to treat electronic waste, with fast-growing battery waste as a notable threat to the environment. Proper recycling processes, particularly the conversion of waste to useful & value-added materials, are of great importance but not readily available. In this work, we report a facile and fast production of graphene from graphite extracted from spent Zn–C batteries. The graphene flakes are produced by electrochemically exfoliating graphite under varying DC voltages in poly(sodium 4-styrenesulfonate) (PSS) solution of different concentrations. The exfoliation takes place via the insertion of PSS into the interlayers of graphite to form C–S bonds as confirmed by FTIR and XPS studies. Under an applied voltage of 5 V and in 0.5 M PSS, high quality graphene flakes are obtained in a good yield, giving an ID/IG ratio of about 0.86 in Raman spectroscopy. The transparent conductive film prepared from the dispersion of high quality graphene flakes shows great promise due to its low sheet resistance (Rs) of 1.1 kΩ sq−1 and high transmittance of 89%. This work illustrates an effective and low-cost method to realize large scale production of graphene from electronic waste.

Synthesis and Characterization of Nickel-Coated Copper Nanowires for Flexible Conductive Thin Film Applications

Abstract In this work, Cu-Ni nanowires were prepared by a single and two-step coating process. For the two-step method, as-prepared Cu nanowires with mean diameter of about 75 nm were coated with Ni, resulting in a Ni layer 35 nm thick. On the other hand, the single-step process resulted in Cu-Ni nanowires with mean diameter and length of about 100 nm and 120 µm, respectively. Cu-Ni nanowire flexible conducting electrode achieved a sheet resistance of about 304 ohm/sq. This is slightly higher than the sheet resistance Cu nanowire electrode of about 197 ohm/sq

NaCl and oxalic acid–assisted solvothermal exfoliation of edge-oxidized graphite to produce organic graphene dispersion for transparent conductive film application

Here, we demonstrate a facile method to prepare dispersible few-layer graphene sheets (GSs) by NaCl and oxalic acid–assisted solvothermal exfoliation of edge-oxidized graphite (EOG) in presence of polyvinylpyrrolidone under the synergetic effect of short-time ultrasonication. During solvothermal heating process, NaCl, oxalic acid, and PVP adsorbed on the edge/surface of EOG, and oxalic acid decomposed into CO2, CO, and H2O steam weakening the Van der Waals force between sheet layers of EOG. The solvothermal process results in the exfoliation and reduction of EOG to GSs which can be dispersed in various organic solvents with high concentrations (0.10–2.68 mg/mL) and remained stable for 6 months except dimethyl sulfoxide and acetonitrile. The GS film prepared by vacuum filtration method using EtOH phase GS dispersion had a sheet resistance of 28.0 kΩ/□ at a transparency of 81.2%. This method shows great promise for mass synthesis of few-layer graphene dispersions for thin film applications.

Roles of sulfur in floating-catalyst CVD growth of single-walled carbon nanotubes for transparent conductive film applications

Sulfur is an effective promoter for growing single-walled carbon nanotubes (SWCNTs) and tuning their structural properties. In particular, sulfur has been utilized in the floating-catalyst chemical vapor deposition (FC-CVD) process to fabricate SWCNT-based transparent conductive films (TCFs). However, in-situ catalyst nucleation process in conventional FC-CVD, hinders to correlate the substantial role of sulfur in tuning SWCNTs synthesis and enhancing the performance of SWCNT-based TCFs. Herein, we have for the first time, systematically studied the roles of sulfur on yield, morphology, and structure of SWCNTs grown by FC-CVD, using ex-situ Fe and Co catalyst particles. We found that SWCNT yield is largely dependent on the amount of sulfur introduced into the FC-CVD reactor and on catalyst composition. More importantly, the addition of an optimized amount of sulfur resulted in a three-fold enhancement of the opto-electronic performance of SWCNT-TCFs, by increasing diameter and bundle length along with improving the quality of SWCNTs. Surprisingly, electron diffraction analysis revealed that SWCNTs grown from both Fe and Co display wide chirality distributions spanning from zig-zag to armchair edges, indicating that the sulfur promoter has little influence on the chirality modulating of SWCNTs.

Design of monoalcohol – Copolymer system for high quality silver nanowires

Research to improve the dimensional properties of silver nanowires (Ag NWs) for transparent conductive film (TCF) applications are being carried out intensively. However, the protocol for the designed synthesis of high-quality Ag NWs is yet to be developed due to the inadequacy of knowledge on the role of parameters. Here, we attempt to elucidate the role played by the parameters and propose a monoalcohol-copolymer based system for the designed synthesis of Ag NWs superior in quality to the one synthesized using conventional ethylene glycol (EG)-polyvinylpyrrolidone (PVP) system. The key findings of the study are as follows: (1) the solubility of Ag source and the partially formed AgCl particles in monoalcohols was found to play an important role not only in the reduction to metallic Ag but also on the uniaxial growth, (2) the adsorption of capping agents on Ag NWs was carried through O and N atoms in the base molecule and their binding energies indicated that the strength is the key parameter to obtain Ag NWs with high aspect ratio, (3) the properties of nanowire could be enhanced through copolymerization of VP and base molecules that have O- and N-based ligands, and (4) the influence of copolymerization on the physical and chemical properties of the surface active agent has been theoretically and experimentally verified. Consequently, we succeeded in the development of a new technique to synthesize high yield of Ag NWs with improved aspect ratio than EG-PVP system by using benzyl alcohol as reducing solvent and N-vinylpyrrolidone/N,N-diethylaminoethyl metacrylate copolymer as a capping agent. The optical transmittance and electrical resistivity of TCFs prepared using the Ag NWs with an average diameter of 43 nm, and an average length of 13 μm were 98.6% and R: 49.1 Ω/□, respectively.

Preparation of Graphene Sheets by Electrochemical Exfoliation of Graphite in Confined Space and Their Application in Transparent Conductive Films.

A novel electrochemical exfoliation mode was established to prepare graphene sheets efficiently with potential applications in transparent conductive films. The graphite electrode was coated with paraffin to keep the electrochemical exfoliation in confined space in the presence of concentrated sodium hydroxide as the electrolyte, yielding ∼100% low-defect (the D band to G band intensity ratio, ID/IG = 0.26) graphene sheets. Furthermore, ozone was first detected with ozone test strips, and the effect of ozone on the exfoliation of graphite foil and the microstructure of the as-prepared graphene sheets was investigated. Findings indicate that upon applying a low voltage (3 V) on the graphite foil partially coated with paraffin wax that the coating can prevent the insufficiently intercalated graphite sheets from prematurely peeling off from the graphite electrode thereby affording few-layer (<5 layers) holey graphene sheets in a yield of as much as 60%. Besides, the ozone generated during the electrochemical exfoliation process plays a crucial role in the exfoliation of graphite, and the amount of defect in the as-prepared graphene sheets is dependent on electrolytic potential and electrode distance. Moreover, the graphene-based transparent conductive films prepared by simple modified vacuum filtration exhibit an excellent transparency and a low sheet resistance after being treated with NH4NO3 and annealing (∼1.21 kΩ/□ at ∼72.4% transmittance).

Effects of silver nanowire concentration on resistivity and flexibility in hybrid conducting films

Silver nanowires (AgNWs) are attracting much attention for their potential use in flexible or stretchable conducting film applications and in printed and wearable electronics devices. In this study, we fabricated flexible hybrid conducting films using different concentrations of composite silver ink prepared by mixing AgNW and silver nanoparticle (AgNP) materials, which we synthesized, for flexible interconnects and electrodes. These films had low resistivities at low sintering temperatures. Furthermore, they were also stable to tensile bending in comparison with a pure AgNP film. We found that there is an optimum concentration of AgNWs in the composite silver ink for the hybrid conducting film to have a lower resistivity even with sintering below 100 °C. We also found that the reason why hybrid conducting films are stable to repeated tensile bending is that AgNWs maintain functional conducting paths by making bridges that compensate for cracks between AgNPs during film bending.

Formulation of concentrated and stable ink of silver nanowires with applications in transparent conductive films

Concentrated and long-term stable Ag nanowire ink is formulated to coat transparent conductive films with superior comprehensive performance after simple cleaning.

Structural and Electrode Properties of Iodine Molecules Encapsulated in Single-Walled Carbon Nanotubes

Although transparent conductive films such as indium tin oxide (ITO) or fluorine tin oxide (FTO) are in high demand for use in optoelectronic devices, including solar cells, ITO and FTO are expensive and inflexible. On the other hand, we can fabricate transparent, conductive, and flexible films by placing single-walled carbon nanotubes (SWCNTs) on the surface of transparent and flexible polymer films. Such nanotube-based transparent conductive films are expected to replace ITO and FTO. However, the conductivity of pristine SWCNTs is not sufficient for typical transparent conductive film applications. To improve the conductivity, doping alkali metals (K, Rb) or halogen atoms (Br, I) would be an effective technique. Among the doped SWCNTs, iodine-doped SWCNTs are particularly interesting. Iodine doping can lead to a reduction in current resistance of SWCNTs by an order of magnitude, and the iodine-doped SWCNTs are known to be air-stable charge-transfer compounds. However, it is not very easy to control iodine doping level by conventional doping methods. Recently, we found that iodine molecules can be encapsulated (here we write iodine molecule encapsulated in SWCNTs as I@SWCNTs) by an electrochemical method [1]. This method is very easy to control the doping level. We also found that iodine doping improves not only the conductivity but also the dipersibility of SWCNTs. Interestingly, I@SWCNTs were dispersed in water very well at low temperature. In order to investigate the temperature dependence of I@SWCNT dispersion, we measured Raman spectra of SWCNTs encapsulating iodine molecules at low temperatures. Three kinds of SWCNTs having mean tube diameters of 1.0, 1.5 and 2.5 nm were used in this study. For electrochemical iodine doping, we fabricated three-electrode configuration cells: SWCNT working, Pt counter, and Ag/AgCl reference electrodes. Iodine-doping processes were investigated by in situ Raman scattering and synchrotron XRD measurements of SWCNTs under an applied potential. For the in situ measurements, we fabricated special cells. Raman scattering measurements were performed using a micro-Raman spectroscopy system (JASCO) equipped with a temperature control stage (JHT 10036 L). It was found by Raman measurements that G-band peak position of I@SWCNTs shifts toward higher wavenumber side with decreasing temperature. It indicates that charge transfer from SWCNT to iodine molecules increases with decreasing temperature. Raman peaks of polyiodine molecules and their overtone peaks were also observed in the low wavelength region. The peak at around 175 cm-1 and its overtones are assigned to the Raman band of I5 -, while the peak at around 110 cm-1 is assigned to I3 -. The presence of poly iodine molecules was also confirmed by XPS measurements. It is very interesting that the peak intensity ratio of the I5 - Raman band to the G-band of SWCNTs observed at around 1600 cm-1 increased with decreasing temperature. It indicates that I5 - ion formation in SWCNTs by the reaction (5I2+5e→I5 -) is promoted at low temperature. In the conferece, I will discuss the structural changes of iodide ions in SWCNTs having different diameter with decreasing temperature. Reference [1] H. Song, Y. Ishii, A. Al-zubaidi, T. Sakai, S. Kawasaki, Temperature-dependent water solubility of iodine-doped single-walled carbon nanotubes prepared using an electrochemical method, Phys. Chem. Chem. Phys. 15, 5767-5770 (2013).

P‐150L: Late‐News Poster: Exploration of Coating and Alignment Methods for Making High‐Performance Transparent Conductive Films with Silver Nanowire Networks

Silver nanowire (AgNW) is a promising candidate to replace ITO for transparent conductive film applications. We explored the coating methods, and came up with a crossed‐aligned structure to lower the percolation threshold of AgNW conduction. The sheet resistance can thus be lowered to 30% without affecting the optical transmittance (89%).

Indium tin oxide with titanium doping for transparent conductive film application on CIGS solar cells

In this study, Ti-doped indium tin oxide (ITO:Ti) thin films were fabricated using a DC-magnetron sputtering deposition method. The thin films were grown without introducing oxygen or heating the substrate, and no post-growth annealing was performed after fabrication. The thickness of the ITO:Ti thin films (350nm) was controlled while increasing the sputtering power from 50 to 150W. According to the results, the optimal optoelectronic properties were observed in ITO:Ti thin films grown at a sputtering power of 100W, yielding a reduced resistivity of 3.2×10−4Ω-cm and a mean high transmittance of 83% at wavelengths ranging from 400 to 800nm. The optimal ITO:Ti thin films were used to fabricate a Cu(In,Ga)Se2 solar cell that exhibited a photoelectric conversion efficiency of 11.3%, a short-circuit current density of 33.1mA/cm2, an open-circuit voltage of 0.54V, and a fill factor of 0.64.

High electrical conductivity of graphene-based transparent conductive films with silver nanocomposites

Polycrystalline graphene films grown by chemical vapor deposition (CVD) possess outstanding electrical and optical properties, which make them alternative materials for applications in transparent conductive films (TCF).