High-performance Transparent Conductive Films Research Articles

Large area AZO/Ag NWs/AZO transparent conductive film based on the Dip-coating method

Metal nanowires have received much attention when considering new promising transparent conductors to replace the cost rising tin-doped indium oxide (ITO). Here, we successfully obtained AZO/Ag NWs/AZO transparent conductive films (TCFs) with a large area (∼150 cm2) by dip-coating. It is found that the resistance and the transmittance of TCFs decrease with increasing Ag NWs immersion-coating time. A maximum figure of merit (ΦTC) value was achieved when the Ag NWs 5 cycles: ΦTC ∼ 3.05 × 10−3 Ω−1 (T:75.6 %, R: 20 Ω). The TCFs prepared by simple solution dip-coating method has superior optical and electric properties. This work provides a simple and effective way to develop large area, low-cost, and high-performance TCFs, and is expected to be applied to various optoelectronic devices (such as solar cells and photodetectors) as an alternative electrode.

One-pot multi-step synthesis of high-aspect-ratio Cu nanowires based on an environment-friendly manner for low-cost and high-performance transparent conductive films

High-aspect-ratio Cu nanowires (NWs) were synthesized based on an environment-friendly synthesis method in which aqueous Cu–Cl complexes were reduced to Cu atoms in a weak ascorbic acid solution. Constant reaction temperatures led to many reduced Cu atoms relative to NWs and then the synthesized Cu atoms were deposited on the end and side faces of Cu NWs, resulting in low aspect ratios. Two-step temperature synthesis was suggested to suppress Cu atoms during the Cu NW growth. High temperatures during the early reaction stage maximized NW seeds and low temperatures in the late stage decreased the number of Cu atoms under precisely controlled temperature and temperature drop time, leading to Cu deposition on the end faces rather than side faces. Additionally, optimum Cu-source additions continuously facilitated the preferential growth in length of Cu NWs. The one-pot multi-step synthesis controlled the reduction rate of Cu complexes and substantially increased the aspect ratio of Cu NW from 313 to 760, showing that the precise control was suitable for changing the NW sizes. Finally, transparent conductive films comprising the NWs showed high performances (transmittance = 90.8 %, sheet resistance = 94 Ω/sq).

High-performance transparent conductive film by using ultra-thin metal grids

Transparent conductive films (TCFs) are indispensable for many optoelectronic devices. Films with high transmittance and low sheet resistance at low cost are ideal for people to pursue. In this paper, ultra-thin Au grid TCFs with thickness less than 0.32 μm are developed and fabricated by ultraviolet lithography. Nanoscale thick metal grid and simple experimental steps can greatly reduce their cost. The influence of grid shape (square, hexagon, ring), thickness and duty ratio on the transmittance and sheet resistance has been investigated systematically. The TCF with square shape Au grid has excellent properties with transmittance of 96.9%, sheet resistance of 11.5 Ω sq−1, and corresponding figure of merit of 1016. It is a good transparent heater with heating speed 100% faster and heating temperature 3.3% higher than indium tin oxide. It can also be fabricated on flexible substrates and exhibit good mechanical property, which have wide practical applications.

Transparent conductive films based on Ag nanowires and alginate hydrogel

In this study, we report that the high-performance transparent conductive films based on silver nanowires (AgNWs) can be fabricated in a single-step spin-coating process by simply introducing a biocompatible polymer (alginate, Alg) into an aqueous suspension of AgNWs. The presence of Alg in the aqueous suspension enables AgNWs to be deposited on the substrate at a higher density, and AgNWs are uniformly distributed on the substrate without aggregation. In addition, through the treatment process using CaCl2 aqueous solution, the conductivity of the AgNWs films can be further improved and their adhesion to the substrate is also enhanced.

Preparation and property optimization of silver-embedded FTO transparent conductive thin films by laser etching and coating AZO layer

Preparation and property optimization of silver (Ag)-embedded fluorine-doped tin oxide (FTO) films were achieved based on laser etching, sputtering Ag layers, furnace annealing, sputtering aluminum-doped zinc oxide (AZO) layers and laser annealing. Specifically, a nanosecond pulsed laser (λ = 532 nm) was used to etch grooves on FTO films before sputtering 5-nm-thick Ag layers, with an aim for enabling the Ag nanoparticles from the furnace-annealed Ag layers to be intensively embedded in the grooves under the thermal-induced dewetting effect. The optimal laser fluence for laser etching and temperature for furnace annealing were found to be 0.4 J/cm2 and 300 °C, respectively. The as-obtained Ag-embedded FTO film exhibited significantly improved optical and electrical properties, being attributed mainly to the decreased coverage area of the Ag nanoparticles on the FTO film surface and the furnace annealing effect. The subsequently sputtered 10-nm-thick AZO layer suppressed the internal light reflection from the Ag nanoparticles, and laser annealing further facilitated grain growth in the film. Therefore, the resulting film had the best comprehensive property with the highest figure of merit of 20.94 × 10–3 Ω–1, which was much higher than that of the original FTO film (7.65 × 10–3 Ω–1). This work may provide a new combined processing method for high-performance transparent conductive films.

Photoelectric property enhancement of Ag/FTO thin films by fabricating antireflection grating structures using ultrasonic-vibration-assisted laser irradiation

This work focuses on the fabrication of antireflection grating structures on Ag/F-doped SnO2 (FTO) films by ultrasonic-vibration-assisted laser irradiation to compensate the optical transmittance loss due to coating the Ag layers. The effects of laser fluence and ultrasonic vibration on formation of laser-induced grating structures are investigated. The results indicate that ultrasonic-vibration-assisted laser irradiation can not only contribute to generating a complete and uniform periodic grating structure, it can also bring about a laser annealing effect to the film. Ultrasonic vibration is considered to play an important role in generating the grating structure by changing the defocusing amount of the film surface, inputting energy and providing mechanical vibration. Moreover, under the favorable influence of ultrasonic vibration, the laser parameter values can be lowered, and the interference of the laser-excited surface plasmons (SPs) with the incident laser can be facilitated. In this present work, the optimal grating-structured Ag/FTO film has the highest figure of merit of 3.26 × 10−2 Ω−1, showing significant increases compared to the untreated FTO (1.13 × 10−2 Ω−1) and the ultrasonic-vibration-free laser-irradiated Ag/FTO (2.34 × 10−2 Ω−1) films. This work may be of important enlightening and reference significance for preparing high-performance transparent conductive films.

Facile synthesis of Ag nanowires enhanced PVB for transparent conductive film

Transparent conductive films (TCFs) are highly desirable for making full use of solar energy. However, the production and application of TCFs are seriously restricted by two obvious weaknesses: complex processes and poor properties. In this research, simple and direct approaches including condensation reflux and hot-pressing are selected to gain a cheap TCF with good properties. The polyvinyl butyral enhanced by 6 spray layers of Ag nanowires (AgNWs/PVB) TCF is found to achieve an optical transmittance of 80.1% and a sheet resistance of 86.4 Ω/sq, and meanwhile, withstand bending cycles over 150 and an extensile rate of 15%. Additionally, the AgNWs/PVB TCF has a deep potential to be further improved by hot-pressing treatment and its sheet resistance can be reduced to 19.7 Ω/sq. Our findings may show a facile way to produce low-cost and high-performance TCFs.

Fabrication of embedded metal-mesh flexible transparent conductive film via electric-field-driven jet microscale 3D printing and roller-assisted thermal imprinting

Transparent conductive films play a pivotal role in advanced optoelectronic devices, especially the flexible optoelectronic devices. The next-generation transparent conductive films require not only an optimal trade-off between the sheet resistance and optical transparency, but also an excellent flexibility. Although indium tin oxide (ITO) has been widely used in conventional transparent conductive films, the scarcity of indium, the brittleness and high sheet resistance of ITO hinder the further application in the emerging flexible optoelectronic devices. Among all the ITO substitutes, metal-mesh flexible transparent conductive film could be an ideal candidate due to its good flexibility and excellent photoelectric properties. However, the metal-mesh usually forms on the surface of the film, leading to high surface roughness, poor adhesion of the metal-mesh to the flexible substrate, and potential electrical short-circuits between the metal-mesh and a top electrode, which limits its applications for highly flexible electronic devices and optoelectronic devices. All these defects can be mitigated or optimized with embedded metal-mesh flexible transparent conductive films to achieve higher performance. Additionally, the embedded nature of the metal-mesh can make it have favorable resistance against moisture, oxygen, and chemicals. But the fabrication of embedded metal-mesh flexible transparent conductive film is more challenging. Despite some recent efforts to address these challenges, existing fabrication methods are still complex, with long cycles, high production costs and waste generation, especially they are difficult to realize the fabrication of large-area transparent conductive film. Therefore, new technologies to achieve high-efficiency, low-cost fabrication of large-area, high-performance embedded metal-mesh flexible transparent conductive film are needed. This paper proposes a new method for fabricating embedded metal-mesh flexible transparent conductive film based on electric-field-driven jet microscale 3D printing and roller-assisted thermal imprinting technology. First, the basic principle and process flow of the fabrication process are explained. Then, the effects and rules of the main process parameters (printing voltage, printing speed, printing pressure, imprinting temperature and imprinting force) on the precision and quality of the embedded metal-mesh flexible transparent conductive film are revealed via experiments for optimization of the process window. Finally, by using the optimized parameters on the electric-field-driven jet deposition micro-nano 3D printer and composite nanoimprint lithography machine independently developed by the research group, an embedded square metal-mesh flexible transparent conductive film with a pattern area of 70 mm ×70 mm, a line width of 20 μm and a pitch of 1000 μm is fabricated. It has a sheet resistance of 3.62 Ω/sq and a transmittance of 92.3% at a wavelength of 550 nm. In addition, the contact level of the metal-mesh to the substrate is up to 5B, the surface roughness value is 18.81 nm, and the change rate of the sheet resistance of the fabricated embedded metal-mesh flexible transparent conductive film after 1000 bending tests is less than 8%. The research shows that the proposed new method for fabricating embedded metal-mesh flexible transparent conductive film requires simple process steps and low production cost. The transparent conductive film produced has excellent photoelectric performance, low surface roughness and good mechanical flexibility. It provides a promising solution for high-efficiency mass production of high-performance transparent conductive films.

Surface treatment of Cu nanowires using hydroxy acids to form oxide-free Cu junctions for high-performance transparent conductive films

Copper nanowires (Cu NWs) are promising materials for fabricating low-cost, flexible, transparent, and conductive films. However, their synthesis typically requires capping agents and their surfaces are easily oxidized, hindering NW performance. In this study, the surfaces of polyvinylpyrrolidone (PVP)-stabilized Cu NWs were treated with hydroxy acids to create impurity-free Cu junctions between the NWs. The PVP on the NW surfaces was removed in hydroxy acid solutions under neutral conditions, followed by surface oxidation. The oxides were more stable than the adsorbed PVP; therefore, this treatment completely converted PVP-stabilized surfaces into oxide-covered surfaces. The oxides were then eliminated and their surfaces were stabilized by hydroxy acids under acidic conditions. Among the tested acids, citric acid completely removed the surface oxides and best protected the NW surfaces, resulting in oxide-free Cu NWs. This treatment was then applied in combination with vacuum filtration to fabricate transparent conductive films comprised of Cu NWs. The surface treatment substantially improved the sheet resistance and transmittance of the film from 583.3 Ω/sq and 84% (at 550 nm) to 81.7 Ω/sq and 86%, respectively. The simple treatment process developed herein is expected to be widely applied to improve Cu NW performance.

Synthesis of uniform silver nanowires from AgCl seeds for transparent conductive films via spin-coating at variable spin-speed

Uniform silver nanowires (AgNWs) with high aspect ratio are significant to fabricate high-performance transparent conductive films (TCFs). In this work, AgNWs were synthesized through polyol method using AgCl as seeds. The growth mechanism of AgNWs upon AgCl particles was demonstrated, which provided a clear understanding of heterogeneous nucleation for synthesizing crystal. The amounts and the reaction time of AgCl were discussed to probe the effect on morphology of final AgNWs. Apart from that, the temperature was also tuned to provide appropriate thermal energy for synthesis of AgNWs. Uniform AgNWs with thin diameter about 52 nm and aspect ratio above 1000 were synthesized by optimizing the amounts, reaction time of AgCl and the temperature. These AgNWs were utilized to fabricate TCFs firstly through spin-coating at a variable speed. The resulting films coated at variable spin-speed largely improved the performance of films compared with those of films coated at constant spin-speed, exhibiting a low sheet resistance of 54 Ω sq−1 and high transmittance of 92% at 550 nm with haze of 5.4%.

Coating-free, air-stable silver nanowires for high-performance transparent conductive film

Silver nanowire (Ag NW) based films are considered as a promising alternative for traditional indium tin oxide but still suffer from some limitations, including insufficient conductivity, transparency and environmental instability. We here report a novel etching synthesis strategy to improve the performance of Ag NW films. Different from the traditional methods to synthesize high aspect ratios of NWs or employ electrically conductive coatings, we find it effective to reduce the high-reactivity defects of NWs for optimizing the comprehensive performance of Ag NW films. In this strategy etching can suppress the generation of high-reactivity defects and meanwhile the etching growth of NWs can be accomplished in an uneven ligand distribution environment. The resulting Ag NWs are uniformly straight with a sharp-edged structure. The transparent conductive film obtained exhibits simultaneous improvements in electrical conductivity, transparency and air stability. Even after exposure in air for 200 days and no protective coatings, the film can still meet the highest requirement of practical applications, with a figure of merit 361 (i.e., FoM > 350). These results not only demonstrate the importance of defect control in the synthesis of Ag NWs, but also pave a way for further optimizing the performance of Ag NW-based films.

Silver Nanowires with Pristine Graphene Oxidation Barriers for Stable and High Performance Transparent Conductive Films

One-dimensional (1D) silver nanowires (AgNWs) have emerged as a leading candidate for the development of next-generation optoelectronic and wearable electronic devices. However, a key limitation of AgNW electrodes is that they are readily oxidized, resulting in a shift in properties leading to devices becoming erratic over time. To address this problem, we report a facile method to improve both the stability and performance of AgNW films. The AgNWs were combined with pristine graphene (pG) using an optimal (30/70 wt %) with the goals to prove that the pG sheets can provide a barrier shielding to protect against AgNW oxidation and have the additional benefit of improving the connections between wires and stability of the films. The fabrication of these films was demonstrated on wide range of substrates including glass, plastic, textile, and paper. A surface resistance of 18.23 Ω/sq and an optical transparency of 89% were obtained on the glass substrates, 50 Ω/sq and 88% transparency for poly(ethylene terep...

Examination of Treatment Methods for a PEDOT:PSS Transparent Conductive Film Produced Using an Inkjet Method

Flexible devices manufactured using printed electronics have attracted the attention of many researchers. A high-performance transparent conductive film exhibiting high flexibility and elasticity is expected to be developed because of its need for the creation of flexible devices. An indium tin oxide (ITO) thin film, which has generally been used, has weaknesses such as fragility to bending stress and depletion of the resource. This study focused on poly (3, 4-ethy-lenedioxythiophene)/poly (styrenesulfonate) (PEDOT:PSS), a conductive polymer material, and examined improvement in the resistivity and transmittance of the transparent conductive film produced using an inkjet method. The present study improved the electrical and optical characteristics of the thin film by examining the annealing temperature between printing operations and the application method of a polar solvent. As a result, the resistivity and transmittance of a PEDOT:PSS thin film were 1.49 × 10-3 Ω·cm and 89.2%, respectively. This film was obtained by annealing at 90°C for 30 min and applying a polar solvent, using an inkjet printer, between printing operations. The printing was performed three times.

A novel strategy for high-performance transparent conductive films based on double-walled carbon nanotubes.

A high concentration of double-walled carbon nanotubes was dispersed by a carbazole-based conjugated polymer. And a transparent conductive film was fabricated via simple dip-coating using this dispersion, which showed simultaneously a low sheet resistance (average 134 Ω □-1, minimal 86 Ω □-1) and an ultrahigh transmittance (99% at 550 nm). This high-performance transparent conductive film has potential applications in future optoelectronic devices demanding ultrahigh transparency and flexibility.

A one-step route to Ag nanowires with a diameter below 40 nm and an aspect ratio above 1000.

The synthesis of long and thin Ag nanowires is important to achieve high performance transparent conductive films. We report a one-step route to synthesizing Ag nanowires with an average diameter of ∼25 nm and an aspect ratio larger than 1000 by utilizing a mixture of poly(vinylpyrrolidone) with different molecular weights as the capping agent in a polyol reduction reaction.

Highly Transparent Conductive Sheet by Self-assembled Silver Network Electrodes with Antireflective Coating via Roll-to-Roll Process

A highly transparent conductive film was fabricated using self-assembled silver electrodes with anti-reflection (AR) film. The micro pore diameter of sliver nanoparticles (ca 50～60nm in diameter) network electrodes expanded to size of 200-300 μm by the increase of air voids with evaporated water. The transmittance of the silver network electrode increased was drastically increased by the optical interference from the AR film on the surface and it showed a maximal value 84％ (sheet resistance: 8.0 Ω/□). The surface resistance of silver network electrodes films did not change even after coating with the AR films because thickness of AR films (ca 100～200 nm) are extremely thin compared with the diameter of the silver wire (ca 3 μm). High performance transparent conductive film for electric and optical devic was successfully fabricated by roll to roll layer-by-layer (LBL) process.

Synthesis of Silver Nanofibers Via an Electrospinning Process and Two-Step Sequential Thermal Treatment and Their Application to Transparent Conductive Electrodes

Metal nanowires can be coated on various substrates to create transparent conducting films that can potentially replace the dominant transparent conductor, indium tin oxide, in displays, solar cells, organic light-emitting diodes, and electrochromic windows. One issue with these metal nanowire based transparent conductive films is that the resistance between the nanowires is still high because of their low aspect ratio. Here, we demonstrate high-performance transparent conductive films with silver nanofiber networks synthesized by a low-cost and scalable electrospinning process followed by two-step sequential thermal treatments. First, the PVP/<TEX>$AgNO_3$</TEX> precursor nanofibers, which have an average diameter of 208 nm and are several thousands of micrometers in length, were synthesized by the electrospinning process. The thermal behavior and the phase and morphology evolution in the thermal treatment processes were systematically investigated to determine the thermal treatment atmosphere and temperature. PVP/<TEX>$AgNO_3$</TEX> nanofibers were transformed stepwise into PVP/Ag and Ag nanofibers by two-step sequential thermal treatments (i.e., <TEX>$150^{\circ}C$</TEX> in <TEX>$H_2$</TEX> for 0.5 h and <TEX>$300^{\circ}C$</TEX> in Ar for 3 h); however, the fibrous shape was perfectly maintained. The silver nanofibers have ultrahigh aspect ratios of up to 10000 and a small average diameter of 142 nm; they also have fused crossing points with ultra-low junction resistances, which result in high transmittance at low sheet resistance.

High-Performance Transparent Conductive Films Using Rheologically Derived Reduced Graphene Oxide

In this work, we produced large-area graphene oxide (GO) sheets with fewer defects on the basal plane by application of shear stress in solution to obtain high-quality reduced graphene oxide (RGO) sheets without the need for post-annealing processes. This is described as rheologically derived RGO. The large-area GO sheets were generated using a homogenizer in aqueous solution, which induced slippage of the GO in the in-plane direction during the exfoliation process, in contrast with the conventional sonication method. The effects of chemical reduction under mild conditions demonstrated that the formation of structural defects during the exfoliation process affected the RGO properties. In the Raman spectra, the I(D)/I(G) ratio of the homogenized RGO (HRGO) increased more than that of the sonicated RGO (SRGO) due to the large number of ordered six-fold rings on the basal plane. The enhanced sheet resistance of the HRGO thin film was found to be 2.2 kΩ/sq at 80% transmittance. The effective exfoliation method has great potential for application to high-performance RGO-transparent conducting films.

Influence of post-annealing on the properties of Sc-doped ZnO transparent conductive films deposited by radio-frequency sputtering

Sc-doped ZnO transparent conductive films are deposited on glass substrates by radio-frequency sputtering. The influence of post-annealing on the structural, morphologic, electrical, and optical properties of the films is investigated by energy dispersion X-ray spectroscopy, X-ray diffraction, Hall measurement, and optical transmission spectroscopy. The experimental results show that these films are polycrystalline with a preferred [0 0 1] orientation. The lowest resistivity of 2.6 × 10 −4 Ω cm is obtained from the film annealed at 500 °C. The average optical transmittance of the films is over 90%. These results suggest that Sc-doped ZnO is a good candidate for fabricating high performance transparent conductive films.