Flexible PET Substrate Research Articles

Mechanical flexibility of transparent PEDOT:PSS electrodes prepared by gravure printing for flexible organic solar cells

The mechanical flexibility of transparent poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films printed onto a flexible PET substrate using a gravure printing method was investigated using a lab-made bending test system. Gravure-printed PEDOT:PSS electrodes with a sheet resistance of 359 Ω/square and a transparency of 88.92% showed outstanding flexibility in several types of flexibility tests, including outer/inner bending, twisting and stretching. Notably, the PEDOT:PSS electrode had a constant resistance change (Δ R/ R 0) within an outer and inner bending radius of 10 mm. In addition the stretched PEDOT:PSS electrode showed a fairly constant resistance change (Δ R/ R 0) up to 4%, which is more stable than the resistance change of conventional amorphous ITO electrode. The twisting test revealed that the resistance of the PEDOT:PSS electrode began to increase at an angle of 36° due to delamination of the film from the PET substrate. Despite the high sheet resistance of the PEDOT:PSS electrode the flexible organic solar cells fabricated on the PEDOT:PSS electrode showed a power conversion efficiency of ∼2% (FF: 44.9%, V o: 0.495 V and J sc: 9.1 mA/cm 2), indicating the possibility of using gravure printed PEDOT:PSS as a flexible and transparent electrode for printing-based flexible organic solar cells.

Inkjet Printing of Low-Temperature Cured Silver Patterns by Using AgNO3/1-Dimethylamino-2-propanol Inks on Polymer Substrates

1-Dimethylamino-2-propanol (DP) was added to silver nitrate to fabricate silver conductive lines by inkjet printing at low sintering temperatures on flexible PET substrates. Using an optimal ratio of a mixed solvent (ethanol and ethylene glycol), the morphology of the pattern surface and the formation of coffee-rings could be controlled. X-ray diffraction (XRD) analysis indicated that the AgNO3/DP inks were converted to silver completely at low temperatures. Using the AgNO3/DP inks, continuous and smooth silver conductive lines with a resistivity of 1.37 ± 0.44 × 10–5 Ω cm were fabricated at 100 °C by an inkjet printing system. This resistivity was close to the resistivity of bulk silver.

Fabrication of high-resolution conductive line via inkjet printing of nano-palladium catalyst onto PET substrate

In this paper, a method to fabricate high-resolution conductive metal line on a flexible PET substrate is described. This method involves inkjet printing of a thermo-sensitive St-co-NIPAAm/Pd nanoparticle-based ink on an untreated polymer to create the catalytic site, onto which nickel is subsequently deposited by an electroless plating method, to obtain the desired width and conductivity of the metal line. The Pd nanoparticles reduced and stabilized by styrene-N-isopropylacrylamide co-oligomer showed their well dispersion in the water without surfactant and reductant in the mixture and these nanoparticles adhered well to untreated PET surface. Through a systematic study with a variety of inkjet variables such as firing voltage and droplet spacing, the optimum inkjet parameters were obtained. The adhesion of the deposited Ni–P coating to the substrate was ascertained by the scotch tape test method. The line width and electrical resistivity were examined as function of electroless plating time. The procedure was successfully applied for manufacturing high-resolution conductive metal line.

Growth of Cu/Zn Alloy Films Sputtered on Flexible Acrylic Resin-Coated PET Substrates

Cu/Zn alloy films were DC-sputtered on flexible acrylic resin-coated PET substrates and the effect of sputtering condition on the morphology and growth rate of Cu/Zn alloy films were investigated. It is found that long sputtering time, low voltage and large target-to-substrate distance can lead to smooth and uniform films. Chamber pressure must be well controlled at several Pascal. High voltage, short target-to-substrate distance and media chamber pressure can improve the growth rate of Cu/Zn alloy films. The suitable DC sputtering condition is 1.6 kV of voltage, 25 mm of target-to-substrate distance, 10 Pa of chamber pressure and 20 min of sputtering time, under which the as-prepared Cu/Zn alloy films possess of smooth surface and 41 nm of thickness.

Solution processed non-volatile top-gate polymer field-effect transistors

This communication describes development of a top gate solution processable organic memory solution. Transistor memories (p-type and ambipolar) operating at voltages between 20 and 30 V with memory on–off ratios close to 103 at programming speeds of 1 ms were fabricated on glass and flexible PET substrates. Successful retention of the stored state for 1 week is also demonstrated.

Droplet-on-a-wristband: Chip-to-chip digital microfluidic interfaces between replaceable and flexible electrowetting modules

We present a long (204 mm), curved (curvature of 0.04 mm(-1)), and closed droplet pathway in "droplet-on-a-wristband" (DOW) with the designed digital microfluidic modular interfaces for electric signal and droplet connections based on the study of electrowetting-on-dielectric (EWOD) in inclined and curved devices. Instead of using sealed and leakage-proof pipes to transmit liquid and pumping pressure, the demonstrated modular interface for electrowetting-driven digital microfluidics provides simply electric and fluidic connections between two adjacent parallel-plate modules which are easy-to-attach/detach, showing the advantages of using droplets for microfluidic connections between modules. With the previously reported digital-to-channel interfaces (Abdelgawad et al., Lab Chip, 2009, 9, 1046-1051), the chip-to-chip interface presented here would be further applied to continuous microfluidics. Droplet pumping across a single top plate gap and through a modular interface with two gaps between overlapping plates are investigated. To ensure the droplet transportation in the DOW, we actuate droplets against gravity in an inclined or curved device fabricated on flexible PET substrates prepared by a special razor blade cutter and low temperature processes. Pumping a 2.5 μl droplet at a speed above 105 mm s(-1) is achieved by sequentially switching the entire 136 driving electrodes (1.5 mm × 1.5 mm) along the four flexible modules of the DOW fabricated by 4-inch wafer facilities.

Design of a Label-Typed UHF RFID Tag Antenna for Metallic Objects

In this letter, we present a label-typed UHF RFID tag antenna for metallic objects. The antenna is fabricated on a thin flexible PET substrate with a thickness of 0.07 mm. In order to achieve good performance on metallic objects as well as in free space, the design of the proposed antenna is mainly considered for two factors; gain and impedance matching. To increase the gain of the proposed antenna, we place an additional loop, which has a line width of 2.5 mm and surrounds the original meandered folded dipole antenna. Also, the design is achieved by matching in frequency region where minimum impedance variation occurs on metallic objects, so that the change of the input impedance is small compared to free space case. The experimental results show that the maximum reading range of the proposed antenna is about 7.5 m in free space, and 3 m for 1-mm separation from the metallic surface. Furthermore, reading range has been compared among commercial and the proposed label-typed RFID tags, revealing about 3 times longer reading range than Alien M-tag when it is placed 1 mm above a metal surface.

On physical properties of undoped and Al and In doped zinc oxide films deposited on PET substrates by reactive pulsed laser deposition

Undoped and Al and In doped ZnO films were deposited on flexible PET substrates by Reactive Pulsed Laser Deposition (R-PLD). The morphological and structural characteristics of the obtained structures were investigated by AFM, SEM and XRD respectively. The transmittance spectra were recorded in the 300–1200 nm wavelength range and the electrical conductivity was measured. The samples appeared as granular and polycrystalline with high transparency and had a good electrical conductivity. The crystallinity of the undoped ZnO films improved with increasing pressure of the reactive oxygen gas. Doping of ZnO with Al or In modified the energy band gap and the resistivity of the material. The possibility for the application of such structures for the development of hybrid photovoltaic cells on flexible substrates will be demonstrated.

Fabrication of Polyaniline-Based Gas Sensors Using Piezoelectric Inkjet and Screen Printing for the Detection of Hydrogen Sulfide

This work describes a fully printable polyaniline-copper (II) chloride sensor for the detection of hydrogen sulfide gas. The sensing device is composed of screen printed silver interdigitated electrode (IDE) on a flexible PET substrate with inkjet printed layers of polyaniline and copper (II) chloride. The sensor is employed as a chemiresistor with changes in measured current being correlated with concentration. On exposure to hydrogen sulfide, 2.5 ppmv (parts per million by volume) is clearly detectable with a linear relationship between measured current and concentration over the 10-100 ppmv region. The detection mechanism is discussed with respect to the hydrogen sulfide response, the choice of electrode materials in addition to UV-vis and surface enhanced Raman spectroscopy (SERS) characterization.

Improvement of organic solar cells by flexible substrate and ITO surface treatments

In this paper, surface treatments on polyethylene terephthalate with polymeric hard coating (PET-HC) substrates are described. The effect of the contact angle on the treatment is first investigated. It has been observed that detergent is quite effective in removing organic contamination on the flexible PET-HC substrates. Next, using a DC-reactive magnetron sputter, indium tin oxide (ITO) thin films of 90 nm are grown on a substrate treated by detergent. Then, various ITO surface treatments are made for improving the performance of the finally developed organic solar cells with structure Al/P3HT:PCBM/PEDOT:PSS/ITO/PET. It is found that the parameters of the ITO including resistivity, carrier concentration, transmittance, surface morphology, and work function depended on the surface treatments and significantly influence the solar cell performance. With the optimal conditions for detergent treatment on flexible PET substrates, the ITO film with a resistivity of 5.6 × 10 −4 Ω cm and average optical transmittance of 84.1% in the visible region are obtained. The optimal ITO surface treated by detergent for 5 min and then by UV ozone for 20 min exhibits the best WF value of 5.22 eV. This improves about 8.30% in the WF compared with that of the untreated ITO film. In the case of optimal treatment with the organic photovoltaic device, meanwhile, 36.6% enhancement in short circuit current density ( J sc) and 92.7% enhancement in conversion efficiency ( η) over the untreated solar cell are obtained.

Etching processes of transparent carbon nanotube thin films using laser technologies

Carbon nanotubes (CNTs) have potential as a transparent conductive material with good mechanical and electrical properties. However, carbon nanotube thin film deposition and etching processes are very difficult to pattern the electrode. In this study, transparent CNT film with a binder is coated on a PET flexible substrate. The transmittance and sheet resistance of carbon nanotube film are 84% and 1000 Ω/□, respectively. The etching process of carbon nanotube film on flexible substrates was investigated using 355 nm and 1064 nm laser sources. Experimental results show that carbon nanotube film can be ablated using laser technology. With the 355 nm UV laser, the minimum etched line width was 20 μm with a low amount of recast material of the ablated sections. The optimal conditions of laser ablation were determined for carbon nanotube film.

Flexible photonic-crystal Fano filters based on transferred semiconductor nanomembranes

Crystalline semiconductor nanomembranes (NMs), which are transferable, stackable, bondable and manufacturable, offer unprecedented opportunities for unique and novel device applications. We report and review here nanophotonic devices based on stacked semiconductor NMs that were built on Si, glass and flexible PET substrates. Photonic-crystal Fano resonance based surface-normal optical filters and broadband reflectors have been demonstrated with unique angle and polarization properties. Such a low temperature NM stacking process can lead to a paradigm shift on silicon photonic integration and inorganic flexible photonics.

Preparation of ZnMgO:Ga thin films on flexible substrates by pulsed laser deposition

Transparent conducting ZnMgO:Ga films were deposited on flexible PET substrates by pulsed laser deposition (PLD). Effects of deposition pressure and time on the structural, electrical and optical properties of ZnMgO:Ga films were investigated. The films showed a low resistivity about 7.68 × 10 −4 Ω cm when deposited at the pressure of 0.03 Pa for 40 min. All the films exhibited a high transmittance over 80% in the visible and near-ultraviolet region. The band gap of as-grown films was about 3.50 eV.

A flexible drug delivery chip for the magnetically-controlled release of anti-epileptic drugs

A flexible drug delivery device was designed and fabricated using electrophoretic deposition of drug-carrying magnetic core-shell Fe 3O 4 at SiO 2 nanoparticles onto an electrically conductive flexible PET substrate. The PET substrate was first patterned to a desired layout and subjected to deposition. In doing so, a uniform and nanoporous membrane could be produced. After lamination of the patterned membranes, a final chip-like device of thickness less than 0.5 mm is formed that is used for controlled delivery of an anti-epileptic drug, i.e., ethosuximide (ESM). The release of useful drugs can be controlled by directly modulating the magnetic field, and the chip is capable of demonstrating a variety of release profiles (i.e., slow release, sustained release, step-wise release and burst release profiles). These profiles can follow a wide spectrum of patterns ranging from zero to pulsatile release kinetics depending on the mode of magnetic operation. When the magnetic field was removed, the release behavior was instantly ceased, and vice versa. A preliminary in-vivo study using Long–Evans rat model has demonstrated a significant reduction in spike-wave discharge after the ESM was burst released from the chip under the same magnetic induction as in-vitro, indicating the potential application of the drug delivery chip. The flexible and membrane-like drug delivery chip utilizes drug-carrying magnetic nanoparticles as the building blocks that ensure a rapid and precise response to magnetic stimulus. Moreover, the flexible chip may offer advantages over conventional drug delivery devices by improvement of dosing precision, ease of operation, wider versatility of elution pattern, and better compliance.

Replication of high ordered nano-sphere array by nanoimprint lithography

High ordered nano-sphere array patterns on Si substrate were fabricated using nanoimprint lithography. First, using hot embossing method, poly vinyl chloride (PVC) based polymer replica template was duplicated from original high ordered nano-sphere array patterns, which was fabricated by evaporation method. The monolayer transferring condition can be achieved by varying hot embossing pressure. Then, through UV nanoimprint lithography with the replicated polymer template, imprinted patterns, which has high ordered nano-sphere array patterns, was successfully fabricated on Si and flexible PET substrate.

Characteristics of ITO films deposited on a PET substrate under various deposition conditions

ITO films, with a thickness of 150 nm to 160 nm, were deposited on an unheated hard coated PET substrate or non-alkali glass substrate via dc magnetron sputtering. Depositions were carried out under the following various conditions: total gas pressure (Ptot), dc sputtering power, target — substrate (T-S) distance, and O2 or H2 addition ratio. The ITO coated on the PET substrate showed relatively lower resistivity than that of the ITO coated on a glass substrate. Relatively small changes in the resistance (ΔR/R0=0.4) of the films were obtained for each deposition condition for the ITO/PET deposited under a sputtering power of 70 W, Ptot of 0.5 Pa, and T-S of 50 mm. It has been confirmed that the results of the electrical property showed concurrence with the results of the bending test. Specifically, the films that have a good electrical property showed only a small change in resistance to the increasing cycle number for each deposition condition. Therefore, it can be assumed that the increased resistance of the ITO films could be due to the formation of micro defects such as micro-cracks and the micro detachment of the ITO film from the flexible PET substrate.

Characterization of Self-Assembled Flexible Multilayer Electrode Film by Roll-to-Roll Process

In this paper, we report a self-assembled multilayer flexible electrode fabricated by a roll-to-roll sequential deposition process. We assembled the multilayer thin films consisting of weak polyelectrolyte poly(ethylenimine) (PEI) and conductive polymer polyaniline (PANi) on a poly(ethylene terephthalate) (PET) substrate via a roll-to-roll sequential deposition process. This fabricated multilayer electrode film showed stepwised growth with an agglomerated structure in accordance with the increase in the bilayer number of (PEI/PANi). The conductivity, morphologies, absorbance, and transmittance of electrode films were investigated using the four-terminal probes unit for current–voltage (I–V) characterization, atomic force microscopy (AFM), field-emission scanning electron microscopy (FE-SEM), and ultraviolet–visible (UV–vis) spectrometry. The prepared multilayer flexible electrode film with the coating sequence of (PEI/PANi)30 showed high transmittance in a visible range and low surface roughness of ca. 9 nm. The resistance of the multilayer electrode film was measured to be ca. 10 kΩ. As the bilayer number of (PEI/PANi) increased from 10 to 30, the surface roughness and resistance of the multilayer electrode film decreased. These experimental results showed that the uniform and highly transparent conductive films were successively formed on a flexible PET substrate by a self-assembly roll-to-roll process.

UV nanoimprint using flexible polymer template and substrate

Nano to micro-sized patterns were formed on a flexible polymer substrate using a flexible UV imprint stamp. A 6 in. diameter flexible UV nanoimprint template was fabricated using PVC hot embossing and DLC coating. Using the UV nanoimprint process with the DLC coated PVC template, nano to micro-sized patterns were clearly formed on the flexible PET substrate without a residual layer, due to the antistiction properties and high mechanical hardness of the DLC coating. By depositing a Cr layer on the imprinted resist pattern and lifting it off, Cr metal patterns were fabricated on the PET substrate.

Deposition of Low Resistive Transparent Conducting Zn<SUB>x</SUB>Cd<SUB>1-x</SUB>O Films on Flexible PET Substrate at Low Temperature

Deposition of Low Resistive Transparent Conducting Zn<SUB>x</SUB>Cd<SUB>1-x</SUB>O Films on Flexible PET Substrate at Low Temperature

Characteristics of Indium Tin Oxide Films Grown on PET Substrate Grown by Using Roll-to-Roll (R2R) Sputtering System

【The electrical, optical, structural and surface properties of an indium tin oxide (ITO) film grown on a flexible PET substrate using a specially designed roll-to-roll (R2R) sputtering system as a function of the DC power, $Ar/O_2$ flow ratio, and rolling speed is reported. It was observed that both the electrical and optical properties of the ITO film on the PET substrate were critically dependent on the $Ar/O_2$ flow ratio. In addition, x-ray diffraction examination results showed that the structure of the ITO film on the PET substrate was an amorphous structure regardless of the DC power and the $Ar/O_2$ flow ratio due to a low substrate temperature, which was maintained constant by a main cooling drum. Under optimized conditions, ITO film with resistivity of $6.44{\times}10^{-4}{\Omega}-cm$ and transparency of 86% were obtained, even when prepared at room temperature. Furthermore, bending test results exhibited that R2R-grown ITO film had good flexibility which would be applicable to flexible displays and solar cells.】