Transparent Plastic Substrates Research Articles

Investigation of Structure and Optical Properties for Copper Oxide Thin Films on Plastic Substrate by Helicon Plasma DC Magnetron Sputtering Technique

As we move towards a decarbonized society, transparent solar cells have recently become an important means of increasing power generation in familiar locations. Copper oxide has been attracting attention as a candidate material for the production of transparent solar cells. In order to further expand the range of applications, it is believed that it will be necessary to develop flexible, transparent plastic substrates. For the purpose of optical applications, copper oxide thin films with CuO, Cu2O, or both phases were fabricated on highly transparent plastics such as poly-methyl methacrylate (PMMA) and polycarbonate (PC), as well as on a glass substrate as a comparable sample. The helicon plasma DC magnetron sputtering method was used to fabricate thin films at a low deposition temperature due to the low heat resistance of plastic substrates. In addition, the helicon plasma DC magnetron sputtering method is capable of depositing films at low vacuum pressure, which enables the preparation of thin films with high crystallinity. The structure, surface shape, and optical properties of fabricated films were investigated using X-ray diffraction (XRD), a laser microscope, and a UV-Vis spectrophotometer, respectively. In this study, the formation of copper oxide thin films on plastic substrates at low temperatures has been verified, as have the crystal structure and optical properties, which is considered a rare study in this field.

Laser-patterned carbon coatings on flexible and optically transparent plastic substrates for advanced biomedical sensing and implant applications

Plasma and laser-based processing for tailoring DLC thin film properties for state-of-the-art wearable sensing applications.

Rapid hybrid microwave cladding of SiO2/TiO2 sol–gel derived composite coatings

UV protection and coatings for plastics are important in many applications. The cladding of low microwave (MW) absorption composite coatings on high MW transparent plastic substrates is a challenge due to their disparate dielectric properties. Moreover, an uneven heat energy conversion within the composite creates an additional hurdle in producing a coating with good surface integrity. In this study, a protocol was developed to overcome these difficulties based on a hybrid approach. The adverse effect of temperature mismatch between the coating and substrate was reduced through a two-way susceptor-aided heating mechanism. Low MW absorbing sol–gel derived composite coatings consisting of silicon dioxide (SiO2) and titanium dioxide (TiO2) were successfully cladded on the surface of MW and visual light transparent polycarbonate to produce a clear protective coating with UV-resistance. Nanoindentation tests were conducted to assess the effectiveness of the proposed protocol. Significant enhancement in the surface elastic modulus and hardness were achieved. Schematic of hybrid MW cladding of sol–gel derived SiO2/TiO2 coating on polycarbonate. The heat energy transferred to the sample is a combination of (1) the heat generated through MW coupling of the SiO2/TiO2 coating and (2) the heat transfer by conduction, convection, and radiation from the heated. This process promotes hydrolysis and condensation reactions, leading to fast densification of the coating. Moreover, the difficulty of processing low microwave absorbing and microwave transparent materials simultaneously has been overcome. As a result, a crack-free SiO2/TiO2 coating with enhanced surface mechanical properties can be produced within a minute.

Three-Terminal Floating-Gate Cell for Threshold-Voltage Control of Organic Thin-Film Transistors

A floating-gate (FG) cell as a circuit-level approach to control the threshold voltage of organic thin-film transistors (TFTs) operated in the transdiode configuration is presented. Charging and discharging of the FG are achieved by controlling the charge leakage through the gate dielectric of one of the organic TFTs that constitute the FG cell. Using programming voltages not exceeding 4 V, systematic tuning of the threshold voltage to values between −0.5 and 2.6 V was achieved. The versatility of the concept is demonstrated by employing organic-TFT-based FG cells as transdiodes with programmable threshold voltage in passive rectifiers and diode-load inverters fabricated on flexible, transparent plastic substrates. Rectifiers with programmable FG cells show flatter frequency response, improved 3-dB point, and reduced ripple compared to conventional rectifiers. Inverters with programmable FG-transdiode load have larger small-signal gain, larger output-voltage swing, and larger noise margins than conventional diode-load inverters.

Ultraviolet Photodetection Based on High-Performance Co-Plus-Ni Doped ZnO Nanorods Grown by Hydrothermal Method on Transparent Plastic Substrate.

A growth scheme at a low processing temperature for high crystalline-quality of ZnO nanostructures can be a prime stepping stone for the future of various optoelectronic devices manufactured on transparent plastic substrates. In this study, ZnO nanorods (NRs) grown by the hydrothermal method at 150 °C through doping of transition metals (TMs), such as Co, Ni, or Co-plus-Ni, on polyethylene terephthalate substrates were investigated by various surface analysis methods. The TM dopants in ZnO NRs suppressed the density of various native defect-states as revealed by our photoluminescence and X-ray photoelectron spectroscopy analysis. Further investigation also showed the doping into ZnO NRs brought about a clear improvement in carrier mobility from 0.81 to 3.95 cm2/V-s as well as significant recovery in stoichiometric contents of oxygen. Ultra-violet photodetectors fabricated with Co-plus-Ni codoped NRs grown on an interdigitated electrode structure exhibited a high spectral response of ~137 A/W, on/off current ratio of ~135, and an improvement in transient response speed with rise-up and fall-down times of ~2.2 and ~3.1 s, respectively.

Growth of MWCNTs on Plasma Ion-Bombarded Thin Gold Films and Their Enhancements of Ammonia-Sensing Properties Using Inkjet Printing

Multiwalled carbon nanotubes (MWCNTs) have been synthesized on thin gold (Au) films using thermal chemical vapor deposition (CVD). The films were evolved to catalytic Au nanoparticles (Au NPs) by plasma argon (Ar) ion bombardment with a direct current (DC) power of 216 W. The characteristics of the MWCNTs grown on Au catalysts are strongly dependent on the growth temperature in thermal CVD process. The MWCNTs were then purified by oxidation (550°C) and acid treatments (3 : 1 H2SO4/HNO3). After purifying the MWCNTs, they were dispersed in deionized water (DI water) under continuous sonication. The MWCNT solution was then ultrasonically dissolved in a conducting polymer mixture of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to prepare for an electronic ink. The ink was deposited onto the flexible and transparent plastic substrates such as polyethylene terephthalate (PET) with fabricated silver interdigitated electrode using two methods such as drop-casting and inkjet printing to compare in the detection of ammonia (NH3) and other volatile organic compounds (VOCs) at room temperature. Based on the results, the gas response, sensitivity, and selectivity properties of MWCNT-PEDOT:PSS gas sensor for NH3 detection are significantly enhanced by using inkjet printing technique. The sensing mechanism of fabricated gas sensor exposed to NH3 has been also proposed based on the swelling behaviour of polymer due to the diffusion of NH3 molecules into the polymer matrix. For the MWCNTs, they were mentioned as the conductive pathways for the enhancement of gas-sensing signals.

Highly Thermal‐Resilient AgNW Transparent Electrode and Optical Device on Thermomechanically Superstable Cellulose Nanorod‐Reinforced Nanocomposites

AbstractTransparent plastics coated with a nanonetwork of metal nanowires or carbon nanomaterials are promising future electrodes for large‐area, lightweight, and flexible optoelectronic devices. However, plastics are generally thermal‐ dimensionally instable, meaning that they expand and shrink in response to temperature change. This behavior may severe the ultrathin nanonetwork of the conducting nanomaterials, resulting in reduced performance of the electrodes and resulting optoelectronic devices. Herein, an incredibly thermal‐dimensionally stable (3.26–4.68 ppm K−1) transparent and flexible plastic substrate is presented that results in high thermal performance of the resulting silver nanowire (AgNW) electrode and smart optical device. The high thermal‐dimensional stability is achieved through the generation of a hierarchical network of cellulose nanorods (a highly regarded biobased reinforcing material) in the plastic via a water‐based process. The improved nanocomposite electrode exhibits good electro‐optical performance (12.4–15.6 Ω sq−1 vs 84%); high flexibility; good mechanics even at 150 °C; and the capability to withstand repeated extreme heating and cooling at 150 and −196 °C, respectively. The findings of this study combined with those reported in the literature can show a pathway for further performance improvement of transparent electrodes for future advanced devices.

Recent Trends on Transparent Colorless Polyimides with Balanced Thermal and Optical Properties: Design and Synthesis

AbstractRecently, colorless and transparent plastic substrates with high glass transition temperature and suitable thermo‐mechanical properties are in high demand in optoelectronic device industries, due to their various optical applications. Colorless polyimides (CPIs) exhibit both high thermo‐mechanical stability as well as high transparency that are suitable for optoelectronic applications. The most recent (2010–2018) developments on CPIs, in terms of design and synthesis of new monomers and their effects on the thermo‐optical properties of the obtained CPIs, are reviewed in this article.

Dendritic Silica Particles with Well-Dispersed Ag Nanoparticles for Robust Antireflective and Antibacterial Nanocoatings on Polymeric Glass

Robust nanocoatings with both antireflective (AR) and antibacterial properties for transparent plastic substrates are not only significantly attractive in science but also urgently needed in wide applications. However, it is still a great challenge to realize the fabrication of this kind of multifunctional nanocoatings on plastic/polymer substrates. In this work, a series of single-particle-layered nanocoatings were prepared by partially embedding dendritic fibrous nanosilica (DFNS) with well-dispersed Ag nanoparticles (NPs) onto the surface of poly(methyl methacrylate) (PMMA) polymeric glass via organic vapor treatment. The optimal coated PMMA slide not only exhibits the enhanced transmittance with the highest one of 94.5% but also shows excellent antibacterial activity (at least killing 80% bacteria) toward both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. Moreover, both long-term ultrasonic processing and pencil hardness tests proved strong adhesion of particles on PMMA subst...

Poly(vinylpyrrolidone)-modification of sol-gel films for flexible piezoelectric energy harvesting systems

A crack-free and dense, yet thick lead lanthanum zirconium titanate (PLZT; P0.92L0.08Z0.65T0.35) film was achieved by single-step, non-repetitive spin-coating of PLZT sol-gel chemically modified with poly(vinylpyrrolidone) (PVP). Incorporation of PVP into the precursor solution could be highly beneficial for prohibiting cracks during the condensation reaction of spin-cast gel film and controlling the film thickness. Close examination by using optical microscopy, X-ray diffraction, Raman spectroscopy, and scanning electron microscopy enabled compositional and structural characterization of PLZT films on both transparent sapphire and flexible plastic substrates before and after the laser lift-off process. Such dense and crack-free PLZT film with thickness ranging from 2.5 to 3.4 μm was successfully applied for fabricating flexible piezoelectric energy harvester. This study can be further extended to prepare other crack-free, dense piezoelectric films, thus offering a facile and robust pathway to the fabrication of the piezoelectric energy harvesting devices.

Back-irradiation photonic sintering for defect-free high-conductivity metal patterns on transparent plastic

Photonic sintering has attracted considerable attention for printed electronics. It irradiates high-intensity light onto the front surface of metal nanoparticle patterns, which often causes defects such as delamination, cavities, and cracks in the patterns. Here, a back-irradiation photonic sintering method is developed for obtaining defect-free high-conductivity metal patterns on a transparent plastic substrate, through which high-intensity light is irradiated onto the back surface of the patterns for a few milliseconds. Ag patterns back-irradiated with ∼10.0 J cm−2 are defect-free in contrast to front-irradiated patterns and exhibited an electrical conductivity of ∼2.3 × 107 S m−1. Furthermore, real-time high-speed observation reveals that the mechanisms that generate defects in the front-irradiated patterns and prevent defects in the back-irradiated patterns are closely related to vapor trapping. In contrast to the latter, in the former, vapor is trapped and delaminates the patterns from the substrate because the front of the patterns acts as a barrier to vapor venting.

A strain induced subwavelength-structure for a haze-free and highly transparent flexible plastic substrate.

This paper presents a method to produce subwavelength-scale (<250 nm) AgCl nanostructures on a flexible plastic film, which is indispensable for highly efficient flexible displays. Using Cl2 plasma treatment on an Ag-coated plastic film, AgCl nanostructures were produced through the reaction of Ag atoms with Cl radicals. During the reaction, the volume of AgCl expands, leading to drastically changed surface morphology from a two-dimensional (2D) flat Ag surface to a 3D subwavelength-scale AgCl nanostructure. The optical properties of AgCl on the plastic film were remarkably enhanced from 89.6% to 93.4% and the average transmittance ranged between 400 and 800 nm, while the average haze was retained below 0.3%. Consequently, OLEDs based on the subwavelength-scale AgCl nanostructure had an enhanced luminance efficiency (88.6 cd A-1 at 1000 cd m-2) of up to 10.7% without modifying the angular emission pattern, superior to that of the as-received PI film (efficiency of 80.0 cd A-1). The nanostructure enhances the transmission of electromagnetic (EM) waves as well as prohibits the scattering of EM waves, which was confirmed by finite-difference time-domain simulation and rigorous coupled wave analysis.

Versatile Antireflection Coating for Plastics: Partial Embedding of Mesoporous Silica Nanoparticles onto Substrate Surface.

Antireflection (AR) coating for transparent plastic substrates is constructed by partially embedding mesoporous silica nanoparticles (MSNs) onto the surface of the substrates. Simulation of optical properties of polymer substrates coated with a single-particle MSN layer indicates that the surface has a low and graded refractive index in the direction of the thickness and effectively decreases the reflectance of visible light. The MSN-coated surfaces can be prepared by exposure of the MSN-painted substrates to a solvent vapor, irrespective of the shape of the polymer substrates. The plastic substrates with a single-particle layer of MSNs with diameters of 145-165 nm exhibit high transparency and good AR behavior as simulated. The mesoporous structures of MSNs play important roles not only in decreasing the refractive index but also in strengthening the adhesion between MSNs and substrate surfaces. Moreover, fixation of MSNs onto a thermosetting epoxy resin is successfully achieved by transfer of a single layer of MSNs from flexible films for which MSNs are weakly bonded. The present simple AR coating is applicable to a wide range of substrates with various materials and shapes, and useful for various applications such as optical devices, displays, and solar cells.

Flexible Hybrid Organic-Inorganic Perovskite Memory.

Active research has been done on hybrid organic-inorganic perovskite materials for application to solar cells with high power conversion efficiency. However, this material often shows hysteresis, which is undesirable, shift in the current-voltage curve. The hysteresis may come from formation of defects and their movement in perovskite materials. Here, we utilize the defects in perovskite materials to be used in memory operations. We demonstrate flexible nonvolatile memory devices based on hybrid organic-inorganic perovskite as the resistive switching layer on a plastic substrate. A uniform perovskite layer is formed on a transparent electrode-coated plastic substrate by solvent engineering. Flexible nonvolatile memory based on the perovskite layer shows reproducible and reliable memory characteristics in terms of program/erase operations, data retention, and endurance properties. The memory devices also show good mechanical flexibility. It is suggested that resistive switching is done by migration of vacancy defects and formation of conducting filaments under the electric field in the perovskite layer. It is believed that organic-inorganic perovskite materials have great potential to be used in high-performance, flexible memory devices.

Light management in flexible thin‐film solar cells on transparent plastic substrates

Maintaining efficient light management is an essential part for obtaining high efficiency flexible thin‐film solar cells. Transparent plastic films like polyethylene terephthalate (PET) are a cost efficient substrate alternative but also impose additional constraints on the light management approaches available. In this study, we investigate and compare two approaches to prepare substrates with light scattering characteristics. We have developed low temperature ZnO:Al layers, which are fully compatible with PET substrates, and are textured by wet‐chemical methods. These low temperature textured ZnO:Al layers implemented in amorphous silicon solar cells on glass substrates result in similar efficiencies as highly optimized high temperature‐etched ZnO:Al layers. Nanoimprint lithography was used as an alternative light management approach and we show that an improved solar cell performance can be achieved on flexible PET substrates with both methods. Besides the effect on solar cell performance, pros and cons of both approaches with respect to flexibility in choice of materials and textures, fabrication process, stress evolution, and reproducibility are discussed.

Kinetic study of low‐temperature imidization of poly(amic acid)s and preparation of colorless, transparent polyimide films

ABSTRACTConventional synthesis of polyimides includes high‐temperature (160–350 °C) imidization of poly(amic acid)s. In the present work, imidization has been carried out at much lower temperatures (40–160 °C). 1,2,4,5,‐cyclohexanetetracarboxylic dianhydride (HPMDA) or pyromellitic dianhydride (PMDA) was polymerized with an aromatic diamine, 4,4′‐diaminodiphenylmethane (DDPM), to give poly(amic acid)s, which were then imidized chemically. Imidization was more than 90% complete even at the very low imidization temperature of 40 °C. It was found that the imidization occurs in two steps: an initial rapid cyclization and a subsequent slower cyclization. The activation energy for the rapid process was determined to be 4.3 kJ/mol, and that of the slower process, 4.8 kJ/mol. As the imidization temperature decreases, the transmittance of the resulting polyimides tends to gradually increase, the cutoff wavelength decreases and the color becomes pale. A partially aliphatic polyimide based on HPMDA and DDPM prepared at 40 °C yielded thin films that were highly transparent and colorless, and had good flexibility, solubility and thermal stability. The polyimide films prepared in this study may be good candidates for flexible, transparent plastic substrates in the display industry. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1593–1602

Photolithographic Synthesis of High-Density DNA and RNA Arrays on Flexible, Transparent, and Easily Subdivided Plastic Substrates.

The photolithographic fabrication of high-density DNA and RNA arrays on flexible and transparent plastic substrates is reported. The substrates are thin sheets of poly(ethylene terephthalate) (PET) coated with cross-linked polymer multilayers that present hydroxyl groups suitable for conventional phosphoramidite-based nucleic acid synthesis. We demonstrate that by modifying array synthesis procedures to accommodate the physical and chemical properties of these materials, it is possible to synthesize plastic-backed oligonucleotide arrays with feature sizes as small as 14 μm × 14 μm and feature densities in excess of 125 000/cm(2), similar to specifications attainable using rigid substrates such as glass or glassy carbon. These plastic-backed arrays are tolerant to a wide range of hybridization temperatures, and improved synthetic procedures are described that enable the fabrication of arrays with sequences up to 50 nucleotides in length. These arrays hybridize with S/N ratios comparable to those fabricated on otherwise identical arrays prepared on glass or glassy carbon. This platform supports the enzymatic synthesis of RNA arrays and proof-of-concept experiments are presented showing that the arrays can be readily subdivided into smaller arrays (or "millichips") using common laboratory-scale laser cutting tools. These results expand the utility of oligonucleotide arrays fabricated on plastic substrates and open the door to new applications for these important bioanalytical tools.

An approach for transparent and electrically conducting coatings: A transparent plastic varnish with nanoparticulate magnetic additives

For the purpose of preparing TCCs (=transparent and electrical conducting coatings), metallic and ferromagnetic nano-additives were dispersed into a transparent varnish and the obtained dispersions were coated on transparent plastic substrates. During hardening of the dispersion the magnetic nano-additives were aligned by a magnetic field. The resulting coatings have electrical pathways along lines of nano-additive chains and are highly transparent in the areas between the lines. Therefore, the electrical conductivity is anisotropic, and it depends on the alignment of the nano-additives (i.e. on the distance between the nano-additives within the chains and the length of the lines) as well as on the thickness of an oxide and/or solvent shell around the nano-additives. The transparency depends also on the alignment and here especially on the thickness and the distance between the formed lines. The quality of the alignment in turn, depends on the magnetic properties and on the size of the particles. We used commercial plastic varnishes, which form electrically isolating (≥10−12S/m) and transparent (about 90% transparency) coatings, and the following magnetic additives: Co-, Fe-, CoPt3, CoPt3@Au- and Fe@Au-nanoparticles as well as CoNi-nanowires. Coatings with Fe@Au-nanoparticles show the best results in terms of the electrical conductivity (10−5S/m–10−6S/m) at transparencies above 70%. Furthermore, in addition to the magnetic nano-additives, transparent additives (Al2O3-particles) and non-magnetic, but better conducting additives (carbon-nanotubes) were added to the varnish to increase the transparency and the electrical conductivity, respectively.

High mobility transparent flexible nickel‐doped zinc oxide thin‐film transistors with small subthreshold swing

High-mobility nickel (Ni)-doped zinc oxide thin-film transistors (NZO TFTs) have been successfully fabricated on flexible transparent plastic substrates at a low temperature. The devices all exhibited good electrical properties with small subthreshold swing (SS) and high saturation mobility fabricated under different sputtering pressure (0.4, 0.8, 1.2, 1.6 Pa) during channel deposition by RF magnetron sputtering were found. The electrical properties of NZO TFTs reached the best when the sputtering pressure was 1.6 Pa, with an SS of 89 mV/decade, a saturation mobility of 172 cm2·V−1·s−1, a drain current on/off ratio of 108, and a positive threshold voltage of 2.36 V. The results show that Ni-doped ZnO is a promising candidate for flexible fully transparent displays.

Optically transparent frequency selective surfaces on flexible thin plastic substrates

A novel 2D simple low cost frequency selective surface was screen printed on thin (0.21 mm), flexible transparent plastic substrate (relative permittivity 3.2). It was designed, fabricated and tested in the frequency range 10-20 GHz. The plane wave transmission and reflection coefficients agreed with numerical modelling. The effective permittivity and thickness of the backing sheet has a significant effect on the frequency characteristics. The stop band frequency reduced from 15GHz (no backing) to 12.5GHz with polycarbonate. The plastic substrate thickness beyond 1.8mm has minimal effect on the resonant frequency. While the inner element spacing controls the stop-band frequency, the substrate thickness controls the bandwidth. The screen printing technique provided a simple, low cost FSS fabrication method to produce flexible, conformal, optically transparent and bio-degradable FSS structures which can find their use in electromagnetic shielding and filtering applications in radomes, reflector antennas, beam splitters and polarizers.