Flexible Polyethylene Terephthalate Substrate Research Articles

Fabrication of Fast Responsive and Insensitive-Humidity Sensor Based on Polyaniline-WO3-CuCl2 for Hydrogen Sulfide Detection

Simple and low-cost hydrogen sulfide gas sensors based on polyaniline-copper chloride and polyaniline- tungsten trioxide- copper chloride composites were developed. The sensing film was produced by drop cast of the dispersed composite on top of screen-printed carbon electrodes on a flexible polyethylene terephthalate substrate. A fast onset time of detection of 10 s and 20 s towards 0.1 ppm of hydrogen sulfide were obtained for polyaniline-tungsten trioxide-copper chloride and polyaniline-copper chloride sensors, respectively. The calibration curve displays a good working range between 0.1 and 1 ppm with a limit of detection and limit of quantification of 155 and 512 ppb, respectively. The polyaniline-CuCl2 sensor presented a high response to humidity change. In contrast, the incorporation of tungsten oxide into the polyaniline-CuCl2 composite exhibited significantly improved the response time to target gas from 15 min to 4 min and make it nearly insensitive to humidity changes up to 40 %. Gas-sensing tests show that polyaniline- tungsten trioxide-copper chloride composites exhibit a high and fast response as well as an excellent selectivity to hydrogen sulfide at ppm level in room temperature. The proposed sensors could be used for different industrial applications.

All-Solution-Processed Molybdenum Oxide-Encapsulated Silver Nanowire Flexible Transparent Conductors with Improved Conductivity and Adhesion.

A novel transparent conductive conductor composed of a silver nanowire (AgNW) network and MoOx on a flexible polyethylene terephthalate (PET) substrate, with contemporaneously improved adhesion and reduced resistivity, is prepared using the full-solution process without high-temperature annealing. Under the optimized conditions, a MoOx/AgNW/MoOx multilayer is achieved, which shows much superior optoelectronic performance to that obtained from ITO with a high optical transmittance of 89.2% and a low sheet resistance of ∼12.5 Ω/sq. Unlike pure AgNW films, the sheet resistance is little changed after the tape and ultrasonication tests, illustrating a very strong adhesion to the PET substrate after the encapsulation of MoOx. Moreover, the multilayer film exhibits excellent stability to resist mechanical bending and acid damage. In addition, the successful implementation of the flexible transparent heater demonstrates the practical application value of the electrode.

Flexible M-Tooth Hybrid Micro-Structure-Based Capacitive Pressure Sensor With High Sensitivity and Wide Sensing Range

A novel flexible capacitive pressure sensor based on hybrid micro-structured (HM) polydimethylsiloxane (PDMS) dielectric layer was developed. The HM-PDMS with M-tooth structured patterns was fabricated using a laser engraved acrylic master mold. The top and bottom electrodes were fabricated by depositing silver (Ag) on flexible polyethylene terephthalate (PET) substrate using additive screen-printing process. The pressure sensor was assembled by sandwiching two HM-PDMS based dielectric layers between the top and bottom electrodes. The capability of the developed pressure sensor to detect a wide range of pressure was investigated by applying varying pressure from 0 to 1 kPa, 1 to 10 kPa, and 10 kPa to 40 kPa. A sensitivity of 51.36% kPa-1, 8.37% kPa-1, and 2.46% kPa-1 was obtained for the pressure ranges of 0 to 1 kPa, 1 to 10 kPa, and 10 to 40 kPa, respectively. The capacitive pressure sensor response, hysteresis, and repeatability of the fabricated pressure sensor is investigated and presented in this paper. To demonstrate the wide sensing range of the pressure sensor, the sensor was attached to face mask for breath monitoring applications that require low pressure sensing of ~20 Pa, and to the hand glove for fingertip pressure monitoring applications that require relatively high pressure sensing of ~3 kPa.

Temperature dependence of the piezotronic effect in CdS nanospheres

We used simple graphene transfer and microwave synthesis to deposite wurtzite-structured CdS nanospheres with gold nanoparticles (AuNPs) on a flexible polyethylene terephthalate (PET) substrate. The temperature dependence of the piezotronic effect of the CdS nanospheres was studied in the temperature range 240–320 K under tensile strains of 0.00–0.40%, the effect was found to significantly depend on the device temperature. Moreover, the piezotronic effect was enhanced by over 590% at a strain of 0.40% by cooling temperature owing to the improved efficiency of piezoelectric potential charges. This is a result of the decreased screening effect by reduced carrier generation in the CdS. In addition, the consistent charge transfer mechanism in the investigated piezotronic device is explained by the possible energy band diagrams. The results of this analysis provide a comprehensive understanding of the piezotronic effect and provide a direction for future device applications in fields such as health monitoring, human-machine communication, surgical robotics, and artificial intelligence.

Towards high performance flexible planar supercapacitors: In-situ laser scribing doping and reduction of graphene oxide films

A novel, scalable, single-step and low-synthesis temperature fabrication approach is proposed for real-time doping, reduction, and patterning of graphene oxide-based films supported on flexible polyethylene terephthalate (PET) substrate using a CO2 Laser system. Laser reduced graphene oxide (LrGO), nitrogen-doped laser reduced graphene oxide (N-LrGO), and sulfur-nitrogen co-doped laser reduced graphene oxide (SN-LrGO) planar supercapacitors (PSCs) are readily fabricated with the proposed approach. Structural and elemental characterizations prove the successful integration of nitrogen and sulfur atoms into the graphene framework with high contents up to 3.71 at% N and 1.82 at% S, and at a low density of structural defects. An areal capacitance as high as 13.8 mF cm−2 at 10 mV s−1 and a maximum power density of 151.7 mW cm−3 at an energy density of 0.152 mWh cm−3 is achieved by SN-LrGO PSC composed of 10 interdigitated fingers with an excellent retention rate after 2000 charging/discharging cycles at 0.125 mA cm−2. Furthermore, higher operating voltage window and current ratings are easily achieved via series and parallel combinations of SN-LrGO PSCs directly on the same substrate. This manifests the versatility of the proposed approach for producing flexible and high-performance graphene-based electrochemical storage devices.

Pattern Visibility Enhancement by the Hybrimer Index-Matching Inter Layer in Oxide/Metal/Oxide-Structured Transparent Conductive Electrode on Flexible Polyethylene Terephthalate Substrates

For this study, we fabricated transparent Mn-doped tin oxide (MTO)/Ag/MTO films with refractive index-matching layer on a polyethylene terephthalate (PET) substrate. The hybrimer indexmatching layer containing TIP (Titanium isopropoxide) in hydroxy terminated PDMS (PDMS-OH) matrix was placed between the MTO/Ag/MTO multilayer and PET substrate. MTO and Ag were deposited by using RF/DC magnetron sputtering at room temperature, whereas a hybrimer mixture was spin-coated on the PET substrate after adjusting the molar ratios between the TIP and PDMS-OH. Pattern visibility was examined by comparing the differences in the reflectance and transmittance of MTO/Ag/MTO multilayer films before and after placing the hybrimer index-matching layer. As the PDMS-OH concentration increased, the reflectance difference at the wavelength of 550 nm (ΔR550nm) showed a tendency of decreasing from 0.66% to 0.53%. The index-matched MTO/Ag/MTO multilayer films showed the highest transmittance (>86% at 550 nm) at a molar ratio of 1:4.

Improvement of electrical properties of ITO thin films by melt-free ultra-short laser crystallization

We describe a novel solid state crystallisation method for optimising a thin film transparent conductive oxide when deposited on flexible polymer substrates. The method is based on ultra-short non-thermal laser sintering of indium tin oxide (ITO) thin films. In this study, we used commercial ITO thin films deposited on a flexible polyethylene terephthalate substrate with a relatively low melting temperature compared with ITO on glass. We demonstrate the use of laser scanning with high pulse overlapping at fluences seven times less than the threshold required for melting/damage of ITO. The results confirm greater than four times enhancement in the mobility of charge carriers of ITO thin films after laser scanning and sheet resistance can be reduced up to 25%. There is no reduction in optical transparency observed in laser treated samples. Surface morphology and x-ray diffraction analyses confirm the improvement in crystallite sizes by laser sintering, resulting in a greater than 37% increase in grain size due to enhanced crystallization. Comparison of experimental and simulation based on a delayed two temperature model confirms that ITO thin film crystallization occurred at about one-third of the melting temperature of ITO.

Transparent water-based UV-curable urethane acrylate ink-jet ink

Attention has recently been paid to ink-jet printing inks to more environmentally friendly types and faster methods with lower energy consumption. The ink-jet printing industry has a preference to use ultraviolet-curable inks for packaging and labeling applications. This research reports a simple approach to prepare a water-based UV-curable ink-jet ink based on urethane acrylate to print onto the transparent flexible polyethylene terephthalate substrate. Isophorone diisocyanate, dimethylolpropionic acid, a low molecular weight polyester resin, and 2-hydroxyethyl methacrylate used to synthesize the urethane acrylate resin. Then, the prepared resin was neutralized with triethylamine and emulsified in deionized water. Fourier transformed infrared spectroscopy spectra characterized the chemical structure of synthesized resin. The gel permeation chromatography was used to determine the synthesized resin's molecular weight. The hydroxyl value, acid value, conversion percentage under UV radiation, transparency, haze, and surface tension results of the emulsified resin were measured. The physical properties of prepared ink-jet ink, such as rheology, surface tension, and dynamic light scattering, were measured. The ink-jet ink could fabricate uniform patterns by a general ink-jet printer onto the transparent polyethylene terephthalate flexible substrate. Eventually, the acceptable appearance was achieved due to the transparency and clarity of the printed polyethylene terephthalate.

Label free, electric field mediated ultrasensitive electrochemical point-of-care device for CEA detection

Developing point-of-care (PoC) diagnostic platforms for carcinoembryonic antigen detection is essential. However, thefew implementations of transferring the signal amplification strategies in electrochemical sensing on paper-based platforms are not satisfactory in terms of detection limit (LOD). In the quest for pushing down LOD, majority of the research has been targeted towards development of improved nanostructured substrates for entrapping more analyte molecules and augmenting the electron transfer rate to the working electrode. But, such approaches have reached saturation. This paper focuses on enhancing the mass transport of the analyte towards the sensor surface through the application of an electric field, in graphene-ZnO nanorods heterostructure. These hybrid nanostructures have been deposited on flexible polyethylene terephthalate substrates with screen printed electrodes for PoC application. The ZnO nanorods have been functionalized with aptamers and the working sensor has been integrated with smartphone interfaced indigenously developed low cost potentiostat. The performance of the system, requiring only 50 µl analyte has been evaluated using electrochemical impedance spectroscopy and validated against commercially available ELISA kit. Limit of detection of 1 fg/ml in human serum with 6.5% coefficient of variation has been demonstrated, which is more than three orders of magnitude lower than the existing attempts on PoC device.

Optical and electrical characterization of WS2 multilayer on flexible PET substrate

WS2 is two-dimensional layered material which the electronic band gap is dependent on the number of layers. From application point of view, the WS2 few layers are good candidate for nano scale flexible electronics . In this study, the WS2 number of layers is modified using liquid phase exfoliation method. The blue shift of WS2 supernatant absorption peaks suggested the change of layer thickness compare to the non-exfoliated one. This supernatant is further deposited on Polyethylene terephthalate (PET) to create a flexible multilayer WS2 thin films. The morphology and the content of the thin film are confirmed by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS), respectively. The Raman and photoluminescence spectroscopy show typical characteristics of WS2 multilayers which are dominated by W-S vibrations, exciton contributions, as well as the local defect and strain effects. Furthermore, the electrical characterization reveals the robustness of the WS2 electronic properties again the mechanical stretching. This study highlights the abundant optical and electrical characterization of WS2 multilayer which are applicable for flexible electronic devices.

Fabrication and Characterization of Zinc Oxide Nanowire Based Two‐electrode Capacitive Biosensors on Flexible Substrates for Estimating Glucose Content in a Sample

AbstractThe present work deals with fabrication and characterization of the zinc oxide (ZnO) nanowire based novel two‐electrode capacitive biosensors on flexible Polyethylene terephthalate (PET) substrates for accurate estimation of glucose by analyzing the fundamental dielectric nature of the relevant sample. The morphology and crystalline quality of grown nanowires are analyzed by using field‐emission scanning electron microscope (FESEM) and X‐ray diffractometer (XRD), respectively. Current and capacitance values of the device have been studied for ten different glucose concentrations relevant to the physiological standards. The analytical performance of the devices in terms of enzyme activity, reliability and flexibility has also been evaluated.

Amorphous ZnSn x O y Fabricated at Room-Temperature for Flexible pH-EGFET Sensor

In this article, the zinc-tin oxide (ZnSn x O y ) based sensing membrane fabricated on a flexible polyethylene terephthalate substrate at room temperature as an extended-gate field-effect transistor (EGFET) is investigated for pH-sensing applications. The ZnSn x O y -based EGFET sensor showed a super-Nernstian pH response (70.79 mV/pH) with very good linearity (0.997), a low hysteresis voltage (6 mV), and a low drift rate (0.25 mV/h). The high pH sensing behavior is attributed to the redox reaction of amphoteric zinc oxide (ZnO) in different pH solutions. Furthermore, good flexibility and bendability were shown by the ZnSn x O y -based EGFET sensor after 400 bending cycles.

High performing flexible optoelectronic devices using thin films of topological insulator

Topological insulators (TIs) possess exciting nonlinear optical properties due to presence of metallic surface states with the Dirac fermions and are predicted as a promising material for broadspectral phodotection ranging from UV (ultraviolet) to deep IR (infrared) or terahertz range. The recent experimental reports demonstrating nonlinear optical properties are mostly carried out on non-flexible substrates and there is a huge demand for the fabrication of high performing flexible optoelectronic devices using new exotic materials due to their potential applications in wearable devices, communications, sensors, imaging etc. Here first time we integrate the thin films of TIs (Bi2Te3) with the flexible PET (polyethylene terephthalate) substrate and report the strong light absorption properties in these devices. Owing to small band gap material, evolving bulk and gapless surface state conduction, we observe high responsivity and detectivity at NIR (near infrared) wavelengths (39 A/W, 6.1 × 108 Jones for 1064 nm and 58 A/W, 6.1 × 108 Jones for 1550 nm). TIs based flexible devices show that photocurrent is linearly dependent on the incident laser power and applied bias voltage. Devices also show very fast response and decay times. Thus we believe that the superior optoelectronic properties reported here pave the way for making TIs based flexible optoelectronic devices.

Highly efficient and stable flexible perovskite solar cells enabled by using plasma-polymerized-fluorocarbon antireflection layer

Despite of enormous potential in niche applications, flexible perovskite solar cells (F-PSCs) still suffer from low power conversion efficiency (PCE) compared to rigid PSCs largely because of the reduced photocurrent driven by low transmittance of their flexible substrate and transparent electrode. This paper presents a plasma-polymerized-fluorocarbon (PPFC) thin film as an antireflection (AR) coating material for enhancing the efficiency of F-PSCs. The PPFC, which are deposited on flexible polyethylene terephthalate (PET) substrates at low temperature by a mid-range frequency sputtering process, are highly transparent because of their amorphous structure. Due to the very low refractive index (~ 1.38) of PPFC over a wide wavelength range, these thin films decrease the average reflectance by 2.22% and increase the average transmittance in the visible light region by 1.40%. As a result, the AR films increase the PCE of F-PSCs from 18.6% to 20.4%. The thin films have a self-cleaning effect due to their hydrophobic surface, excellent mechanical flexibility (bending radius: 4 mm), and high chemical stability. Accordingly, the thin films improve the long-term stability of F-PSCs in humid environments. Finally, these AR PPFC thin films can be manufactured by a roll-to-roll process, making them suitable for future use in highly efficient F-PSCs. The plasma-polymerized-fluorocarbon (PPFC) films have an antireflection (AR) effect due to low refractive index (~ 1.38), self-cleaning effect due to their hydrophobic surface, excellent mechanical flexibility, and chemical stability. As a result, the AR PPFC films increase the power conversion efficiency of flexible perovskite solar cells (F-PSCs) from 18.6% to 20.4%, and improve the long-term stability of F-PSCs in humid environments. • The plasma-polymerized-fluorocarbon (PPFC) thin film is introduced as an antireflection (AR) film on the flexible substrate. • PPFC AR coating effectively improves transmittance due to its low refractive index (~1.38) over a wide wavelength range. • The AR PPFC thin film enhances the efficiency of flexible perovskite solar cells (F-PSCs) from 18.6% to 20.4%. • The PPFC film exhibits self-cleaning effect due to its hydrophobic surface. • The hydrophobic nature of PPFC film aids to improve the long-term stability of F-PSCs under high humidity. • The PPFC thin films shows excellent stability under humidity, heat, and chemicals, and retains its form after bending test.

Flexible electrochromic devices based on tungsten oxide and Prussian blue nanoparticles for automobile applications.

Smart windows, which control the amount of light entering buildings, houses, and automobiles, are promising in terms of energy conservation and their low environmental impact. Particularly, a next-generation smart window for automobiles will require high optical modulation, along with flexibility to adapt to various intelligent designs. We have previously fabricated electrochromic devices (ECDs) by wet coating glass substrates with nanoparticles (NPs), such as water-dispersive ink containing tungsten oxide (WO3), and Prussian blue (PB), and have evaluated and confirmed the various electrochromic (EC) properties, such as optical modulation, cyclic durability, and colouration efficiency, of the ECDs. However, glass substrates are heavy and difficult to adapt by deformation to meet the demand of next-generation automobiles. In this study, we aim to prepare complementary ECDs by wet coating WO3 and PB thin films on indium tin oxide (ITO)-coated flexible polyethylene terephthalate (PET) substrates. Chromaticity and haze of ECDs were investigated in detail as evaluation indexes to verify specifications for practical use in automotive applications. Repeated switching, bending, and twisting did not degrade the ECD properties, thereby demonstrating its durability and mechanical robustness. These excellent electrochromic properties of the flexible ECDs suggest that they are promising materials for application in next-generation smart windows for automobiles.

Optical and Electrical characterization of Silver nanowire -reduced graphene oxide hybrid thin film on PET for transparent electronics

Graphene is an excellent nanoscale allotrope of carbon in which carbon atoms are bonded through sp2 hybridization. Graphene itself or its thin film exhibits excellent transparency to visible light. Silver nanowires are also being used for making transparent electrodes. Herein, we prepared a thin film of reduced graphene oxide and silver nanowires on flexible PET (polyethylene terephthalate) substrate. Characterization of graphene oxide/reduced graphene oxide has been carried out through X-ray diffractometry, FTIR (Fourier transformed infrared spectroscopy). Ultraviolet-visible spectroscopy and I-V measurements demonstrated high conductivity and transmittance of the above prepared film.

Electrowetting-on-Dielectric Based Economical Digital Microfluidic Chip on Flexible Substrate by Inkjet Printing.

In order to get rid of the dependence on expensive photolithography technology and related facilities, an economic and simple design and fabrication technology for digital microfluidics (DMF) is proposed. The electrodes pattern was generated by inkjet printing nanosilver conductive ink on the flexible Polyethylene terephthalate (PET) substrate with a 3D circuit board printer, food wrap film was attached to the electrode array to act as the dielectric layer and Teflon® AF was sprayed to form a hydrophobic layer. The PET substrate and food wrap film are low cost and accessible to general users. The proposed flexible DMF chips can be reused for a long time by replacing the dielectric film coated with hydrophobic layer. The resolution and conductivity of silver traces and the contact angle and velocity of the droplets were evaluated to demonstrate that the proposed technology is comparable to the traditional DMF fabrication process. As far as the rapid prototyping of DMF is concerned, this technology has shown very attractive advantages in many aspects, such as fabrication cost, fabrication time, material selection and mass production capacity, without sacrificing the performance of DMF. The flexible DMF chips have successfully implemented basic droplet operations on a square and hexagon electrode array.

Self-cleaning structural colors by TiO2/Ti nanostructures.

Structural colors are fascinating due to their stability in comparison with dyes and pigments; nevertheless, environmental pollutants contaminate surfaces and redefine structural colors. To overcome this problem, cleaning of the surface is necessary at regular intervals, which is cumbersome and costly. We have circumvented this issue in this article and fabricated scalable self-cleaning structural colors. The structural colors are generated by TiO2 nanorods and thin films on Ti sputtered glass and flexible polyethylene terephthalate substrates employing a glancing angle deposition (GLAD) technique. Theoretical calculations based on thin film interference validate the experimental results and suggest Al, Ni, Co, and Cu as an alternative of Ti for generating structural colors. Structural colors are transformed to a superhydrophilic state, i.e., a self-cleaning state, via UV exposure and annealing at elevated temperatures. In addition to a self-cleaning state, annealing could control the opaqueness and color tunability of the structural colors. A permanent wettability state in between the superhydrophobic and superhydrophilic states of the structural colors is controlled by the GLAD technique. Moreover, the structural colors are demonstrated for information encryption and optical ethanol sensing applications.

Electroforming-free flexible organic resistive random access memory based on a nanocomposite of poly(3-hexylthiophene-2,5-diyl) and orange dye with a low threshold voltage

The charge trapping characteristics of an organic nanocomposite based on two polymers, poly(3-hexylthiophene-2,5-diyl) (P3HT) and orange dye (OD), were investigated by fabricating a sandwiched structure on a flexible polyethylene terephthalate substrate. The fabricated flexible organic device with a configuration of silver (Ag)/P3HT–OD/Ag displayed highly stable results consistent with a bipolar non-volatile resistive random access memory (RRAM) device using simple and controllable fabrication technology. It was observed that by the addition of OD, low threshold voltages (V th) of V set = 1.5 V and V reset = −1.5 V were achieved owing to the values of work function and energy bandgap of the materials used. Electrical rewritable effects of the fabricated memory device were tested for 102 voltage sweeps and 104s without any considerable degradation of its bistable resistive states. The switching mechanism was considered to be space charge limited current and this was verified by plotting the double logarithmic I–V curve. This is the first RRAM device based on P3HT polymer whose mechanical robustness has been tested for its mechanical robustness by bending it for 25 bending cycles at a bending diameter ranging from 15 cm to 5 cm without any considerable change in its properties. This finding offers important guidelines for reproducing next-generation flexible organic nanocomposite-based memory devices that are simple to fabricate and have low operating voltages and highly stable memory behavior.

Flexible PET substrate coated with V2O5 film with porous network prepared by EPLSD method

Flexible polyethylene terephthalate (PET) substrate coated with a V2O5 film with porous network was prepared by developed electroless-plating-like deposition (EPLSD) method. Peroxo-vanadium-complex (PVC) and V2O5 nanosheets prepared by H2O2 and UV treatment were used as the precursors in the network construction. The morphology and crystalline phase of the V2O5 sample were examined by SEM, TEM, and XRD characterization. Many micropores were formed in the interconnection structure of the V2O5 film with a high orientation of lattice plane. Wettability of this film can be repeatedly switched by UV irradiation and O2 storage conditions.