ITO/Ag/ITO Research Articles

Flexible, Transparent, High Mobility Amorphous In–Ga–Zn-O Thin Film Transistors Fabricated on Textile

To implement wearable textile displays (WTDs), it is essential that unique properties such as physical and chemical properties, aesthetics, and flexibility of the textile be maintained. Therefore, thin film transistors (TFTs) for WTDs should exhibit excellent electrical properties to enable 4K and 8K high resolution and high frame-rate (>120 Hz) displays while maintaining the properties of textiles. All layers of TFTs were formed by vacuum deposition and oxide-based transparent materials; amorphous In–Ga–Zn-O (a-IGZO), indium tin oxide (ITO), and Al2O3 were used. A transparent and flexible electrode with an ITO/Ag/ITO (IAI) structure was optimized and applied to the source/drain and gate. All processes were performed below 150 °C, and the wet-step was eliminated to prevent physical and chemical deformation of the substrate. The flexible, transparent, high mobility a-IGZO TFTs (FTH TFTs) for WTDs were fabricated on glass, polyethylene terephthalate (PET) film, and textile substrates, respectively. Their electrical performance, transparency, and flexibility were then compared. The textile-based TFTs showed transmittance of 72.98%, high mobility of 11.5 cm2/(V s), and an on/off ratio of 9.28 × 107 even in a low temperature process (<150 °C). In addition, the electrical properties of the textile-based TFTs were maintained despite testing entailing 1000 cycles of bending with a tensile strain of 0.8%. In particular, the FTH TFTs for WTDs were able to stably drive a red organic light-emitting diode on textile.

Optimization of oxide materials in oxide-metal-oxide(OMO) electrodes for flexible electrochromic devices

The use of the oxide-metal-oxide (OMO) structure is one of the key strategies for enhancing the sheet resistance and flexibility of large-area flexible displays. Various combinations of OMOs with indium-tin oxide (ITO) and zinc-tin oxide (ZTO) for the oxide layer and a metal layer with silver (Ag) are discussed. Four-types of OMO are fabricated and the electrical characteristics of each are confirmed through electrochromic devices. The type of oxide layer affects the electron transfer from the metal layer to the oxide layer. Thus, the position of the oxide layer depends on the band structure and should be considered to achieve better performance. The ITO/Ag/ITO (IAI) type of electrode demonstrated the lowest sheet resistance at an average of 8 Ω sq −1 as well as high transparency above 80% at a wavelength of 650 nm. Electrochromic transparency differences between the bleached and colored states were maintained at 52.1% after 200 cycles, and the times required for coloration and bleaching were 0.5s and 8.1s, respectively. A stable redox reaction was confirmed after storing the devices at −30 °C and 85 °C for 18 h. • Fabrication of various OMO electrodes for flexible electrochromic devices is possible. • Relationship between the top-layer and bottom-layer of OMO electrode are investigated. • Flexible large-area electrochromic devices are tested within long-term cycles and harsh temperature.

Ultra-flexible and transparent electrodes with controllable crack length via metal–polymer hybrid nanostructure

• A method for fabricating a super-flexible transparent electrode. • The flexible electrodes exhibited excellent flexibility. • Under severe cyclic folding fatigue a peak strain of 2.5% was observed. • A folding-cycle count of 100,000 was obtained. • The good performance was due to the metal–polymer hybrid nanostructure. We propose a method for improving the flexibility of transparent electrodes through a mechanism that effectively reduces the crack length under cyclic folding fatigue. Our proposed method is based on the use of a metal–polymer hybrid (MPH) nanostructure composed of indium tin oxide (ITO), Ag, and a fluoropolymer, which are commercially available materials widely used in the display-panel manufacturing industry. For flexible electrodes wherein the MPH nanostructure was adjusted using Ag sputtering powers within the range of 20–50 W, the changes in the resistance after 100,000 folding cycles with a peak strain of 2.5% were 4.57–17.9%, whereas those in the case of the ITO/Ag/ITO (IAI) thin-film electrode, i.e., without the MPH nanostructure, increased dramatically to 11,228%. Through the introduction of the MPH nanostructure, the crack length was significantly reduced to 8.76–88.1 μm compared to that of the IAI thin-film electrode (> 945 μm), and also became controllable through the adjustment of the number density of the MPH nanostructure.

Cyclic nanoindentation of ITO/Ag/ITO multilayer films: Hysteresis behavior and cyclic deformation response

The poor evaluation of the cyclic deformation response has been a main challenge for extensive applications and developments of ITO/Ag/ITO (IAI) multilayer films. In this paper, the effects of tri-layer film structure on hysteresis behavior and cyclic deformation response were investigated for IAI multilayer films via nanoindentation. The results indicate that the decreased density of picture-frame cracks and the enhanced mechanical performances for 300°C-IAI multilayer films are compared with those of ITO single-layer films under cyclic nanoindentation. Additionally, according to the energy-based method, the values of fracture toughness for 300°C-IAI multilayer films and ITO single-layer films are 3.49–4.17 MPa m0.5 and 3.04–3.18 MPa m0.5, respectively. Consequently, the structural design of ceramic/metal/ceramic tri-layer films are expected to be a potential method to enhance the resistance of cyclic deformation damage for transparent conducting films.

Perovskite/InGaAs tandem cell exceeding 29% efficiency via optimizing spectral splitter based on RF sputtered ITO/Ag/ITO ultra-thin structure

In this paper, the optimization, elaboration and characterization of an efficient spectral beam splitter based on a simple RF sputtered ITO/Ag/ITO (IAI) ultra-thin multilayer structure are presented. An experimental investigation assisted by Genetic Algorithm (GA) metaheuristic optimization was carried out to achieve high-performance spectral splitter for tandem solar cell applications. The RF magnetron sputtering method was used to elaborate the optimized IAI structure. The optical and structural properties of the sputtered splitter were also analyzed using UV–Vis-IR spectroscopy and X-ray diffraction (XRD) measurements. It is found that the elaborated splitter structure offers 84% of transparency and a high reflectance of 87% with an optimum cut-off wavelength of 800 nm. This is attributed to the design approach, which leads to promote spectral splitting mechanism by inducing efficient optical modulation. Interestingly, a new Figure of Merit (FoM) parameter, which evaluates the optical splitting performances is proposed. Moreover, a new Perovskite/InGaAs tandem cell is proposed and analyzed to show the impact of the elaborated spectrum splitter on the solar cell efficiency. It is revealed that the investigated solar cell exhibits an improved efficiency approaching 30%. The latter value far surpasses that provided by Perovskite tandem cells. These results indicate that our spectrum splitting approach can open a new pathway towards designing high-performance tandem photovoltaic devices.

Improvement in the Figure of Merit of ITO-Metal-ITO Sandwiched Films on Poly Substrate by High-Power Impulse Magnetron Sputtering

High-power impulse magnetron sputtering (HiPIMS) was used to deposit ITO/Ag/ITO (IAgI) and ITO/Cu/ITO (ICuI) sandwiched films on polyethylene naphthalate substrate at room temperature as flexible transparent conductive materials. The hybrid layers were constructed with 40 nm ITO bottom and top layers, and a 5–20 nm Ag or Cu interlayer. The microstructure and optoelectrical properties were estimated for these films with various thicknesses of the metal interlayer. Thanks to the high-power density and highly ionized plasma in the HiPIMS process, the IAgI and ICuI sandwich structures exhibited good crystallinity and smooth surfaces with high optical transmittance and low sheet resistance. The optimal figure of merit was obtained as 101.16 × 10−3·Ω−1 for the IAgI film and 4.83 × 10−3·Ω−1 for the ICuI film with the metal interlayer thickness of 10 nm, both of which are higher than that from a similar structure reported via sputtering at room temperature. These results indicate that HiPIMS is a promising technique to deposit transparent conductive films onto soft substrates for applications in flexible optoelectronic devices.

High-Responsivity MSM Solar-Blind UV Photodetector Based on Annealed ITO/Ag/ITO Structure Using RF Sputtering

In this paper, a novel ITO/Ag/ITO (IAI) multilayer UV photodetector was successfully prepared via RF magnetron sputtering technique to achieve the dual-benefit of improved photoresponse and outstanding visible blindness properties. The influence of the annealing process on the performance of the elaborated IAI UV photodetector was carried out. Moreover, the structural and photoelectrical properties of the sputtered tri-layered structures with and without annealing effects were also analyzed. It was found that the elaborated UV -photodetector provides near perfect UV absorbance of 96%. This achievement is attributed to the improved light trapping capability and tunable plasmonic resonance effects induced by the efficient optical coupling between free-space UV photons and Ag plasmons. It was also revealed that the heat treatment paves a new path toward preparing efficient visible-blind UV photodetectors, where the annealed sample demonstrated a superior rejection ratio of 225 as compared to that of the unannealed counterpart. Besides, electrical characterization underlined the ability of the annealed IAI UV photodetector at 500°C for offering exciting opportunities, where it exhibits a high responsivity of 3.8mA/W at self-powered condition. Therefore, by well optimizing both IAI multilayer geometry and annealing conditions, we were able to elaborate an ultrathin photodetector suitable for high-performance and flexible UV sensing applications.

Effects of high temperature annealing in enhancing the optoelectronic performance of sputtered ITO/Ag/ITO transparent electrodes

Abstract In this paper, a transparent conductive ITO/Ag/ITO (IAI) multilayer structure with a high Haacke Figure of Merit (FoM) far surpassing those found up to now is experimentally demonstrated. An optimized IAI multilayer electrode was elaborated by means of RF magnetron sputtering technique. The structural and electrical characteristics of the prepared tri-layered design were investigated. The influence of the annealing process on the IAI electrode performance was also carried out. Unlike the IAI structure as-deposited, it was revealed that the annealed samples maintained an average transparency superior than 89%. This behavior indicates the effectiveness of the thermal treatment for ensuring favorable light management. In addition, it was found that the annealing process paves a new path toward improving the electrode conductivity, where the heat treated electrode at 600°C yielded a very low sheet resistance of 2.95Ω × sq−1. Therefore, by well optimizing both IAI geometry and annealing conditions, we were able to elaborate high-quality coating with a superior FoM of 120.8 × 10−3Ω−1. This makes the sputtered IAI multilayer design a suitable alternative to the conventional ITO-based electrodes for optoelectronic and photovoltaic applications.

Optical and electrical studies of sputter-deposited transparent and conducting ITO/Ag/ITO multilayer on Kapton® substrate for transparent flexible electronic applications

Transparent and conducting thin films on flexible substrates have enormous applications in the areas of space, solar, displays, etc. We hereby report the sputter deposition of transparent and conducting ITO/Ag/ITO (IAI) thin films on commercially available flexible Kapton® substrate at a lower substrate temperature. IAI multilayer has been deposited by magnetron sputtering system using an alloy In:Sn (90%:10%) and Ag targets at room temperature without breaking the vacuum. The optimized IAI coating shows high transmittance (∼81.3% at λ = 650 nm) along with very low resistance (8.36 Ω/□). Optical haze value of IAI on Kapton was measured and found to be <7%. The figure of merit of IAI coating on Kapton® has been calculated using the Haacke’s formula ϕ=T10Rs. At λ = 650 nm ϕ=15×10-3Ω-1 was observed. Our findings give worthful insight into the sputter deposition of transparent conducting IAI coating on flexible Kapton® substrate for flexible electronics applications.

Highly transparent and conducting ITO/Ag/ITO multilayer thin films on FEP substrates for flexible electronics applications

Transparent and conducting ITO/Ag/ITO (IAI) multilayer coatings were deposited on glass and flexible fluorinated ethylene propylene (FEP) substrates by reactive sputtering using metallic In:Sn (90%:10%) and Ag targets at room temperature. Middle Ag layer thickness was optimized to obtain maximum figure of merit (ϕ) and the optimum Ag layer thickness was found to be ~13nm. The optimized IAI multilayer on glass substrate showed transmittance of ~88.6% and sheet resistance of ~7.1Ω/sq. The transmittance increased to ~91.4% for the IAI multilayer deposited on one side etched glass. The optimized IAI multilayer coating was also deposited on flexible FEP substrates. The electrical, optical, structural and morphological properties of IAI deposited on glass and FEP substrates were compared. IAI deposited on FEP substrate showed transmittance of ~90.2% at λ = 550nm, sheet resistance of ~6.9Ω/sq. and figure of merit of ~52 × 10−3Ω−1. Bending test of IAI deposited FEP proved the high flexibility of IAI multilayer for the flexible transparent electrode applications. Solar selectivity study of IAI on FEP substrate showed it can effectively reflect the higher wavelength region of solar spectrum and can be used as a flexible solar spectrum segregator. Optical haze measurements of IAI coated glass and FEP show that high haze value can be achieved by increasing the roughness on non-coated side of the FEP substrate.

Spreadability of Ag Layer on Oxides and High Performance of AZO/Ag/AZO Sandwiched Transparent Conductive Film

Single layers of indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), and Ag, bilayers of ITO/Ag and AZO/Ag, and sandwiched layers of ITO/Ag/ITO (IAI) and AZO/Ag/AZO (ZAZ) were fabricated on ordinary glass substrates using magnetron sputtering. The surface morphologies of single layers and bilayers were measured. The sheet resistance and transmittance of the sandwiched layers were investigated. The results showed that the spreadability of the Ag on the AZO was significantly better than that on the ITO or bare glass substrate. The spreadability of Ag on underlayers influences obviously the performance of transparent conductive oxide/Ag/transparent conductive oxides (TCO/Ag/TCO or TAT). The sheet resistance and transmittance of the ZAZ sandwiched layer with the matching of 35 nm AZO (35 nm)/Ag (9 nm)/AZO (35 nm) fabricated in this paper were low to 3.84 Ω/sq and up to 85.55% at 550 nm, respectively. Its maximum Haacke figure of merit was 0.05469 Ω−1, higher than that of IAI multilayer.

Effects of the structural properties of metal oxide/Ag/metal oxide multilayer transparent electrodes on their optoelectronic performances

In this study, we prepared metal oxide-metal-metal oxide (OMO) multilayer transparent electrodes based on indium tin oxide (ITO) and ZnO, viz., ITO/Ag/ITO (IAI) and ZnO/Ag/ZnO (ZAZ) by sputtering and investigated the influence of the thickness of the silver layer as well as the thickness and surface roughness of the metal oxide layers on the optoelectronic performance of the electrodes. The surface roughness of the metal oxide layers affect the critical thickness required to transform the low-conductivity semi-continuous silver films into high-conductivity continuous ones. The thicknesses of the metal oxide layers over and underneath the Ag layer can be modulated not only to enhance the transmittance of the electrodes but also to adjust the position of the maximum transmittance. Optimization of the thicknesses of the metal oxide and Ag layers allows the fabrication of high-quality transparent electrodes. The sheet resistance for the best ZAZ sample was 4.16 Ω/sq while the average transmittance (including glass) was 73.09% in the visible region. For IAI electrodes, the sheet resistance and the average transmittance in the visible region were 5.85 Ω/sq and 82.12%, respectively. The Haacke index indicated that for applications with high optical demands, the Ag film thickness should be 8.5 nm and 13.0 nm for ITO and ZnO systems, respectively. Moreover, semi-continuous Ag layers are bluish due to surface plasmon resonance. This study defines a criterion for determining the optimal thickness of Ag layers in OMO films.

Highly transparent conductive ITO/Ag/ITO trilayer films deposited by RF sputtering at room temperature

ITO/Ag/ITO (IAI) trilayer films were deposited on glass substrate by radio frequency magnetron sputtering at room temperature. A high optical transmittance over 94.25% at the wavelength of 550 nm and an average transmittance over the visual region of 88.04% were achieved. The calculated value of figure of merit (FOM) reaches 80.9 10-3 Ω-1 for IAI films with 15-nm-thick Ag interlayer. From the morphology and structural characterization, IAI films could show an excellent correlated electric and optical performance if Ag grains interconnect with each other on the bottom ITO layer. These results indicate that IAI trilayer films, which also exhibit low surface roughness, will be well used in optoelectronic devices.

Design and development of ITO/Ag/ITO spectral beam splitter coating for photovoltaic-thermoelectric hybrid systems

ITO/Ag/ITO (IAI) multilayer coatings were designed for spectral beam splitter applications and these coatings were deposited on glass substrates by magnetron sputtering method. The thicknesses of the component layers, namely, Ag and ITO were varied to achieve high visible transmittance, high NIR-IR reflectance and optimum cut-off wavelength. The optimized ITO/Ag/ITO exhibits high visible transmittance (∼88%) and high NIR-IR reflectance (>90%) with an optimum cut-off wavelength (∼900nm). A novel chemical etching method was used to improve the transmittance of the plain glass substrate. The optimized IAI multilayer coating deposited on single side etched glass substrate resulted in increase in transmittance (∼91%), which is due to the nano-porous morphology of the etched glass substrate. The angular and polarization dependence studies of IAI multilayer coatings were also studied in detail.

Roll-to-roll sputtered ITO/Ag/ITO multilayers for highly transparent and flexible electrochromic applications

We demonstrate high-performance, flexible, transparent electrochromic (EC) films fabricated on an ITO/Ag/ITO (IAI) multilayer electrode prepared by roll-to-roll (RTR) sputtering. The IAI multilayer RTR sputtered on a polyethylene terephthalate (PET) substrate at room temperature exhibited a high optical transmittance of 82.4% and a very low sheet resistance of 8.93Ω/sq. In addition, bending and cycling fatigue tests demonstrated better flexibility of the IAI multilayer than that of a sputtered ITO film. Poly(3-hexylthiophene) (P3HT) films prepared on IAI multilayers exhibited fast switching response between colored and bleached states, together with high reversibility and long-term stability of the EC behavior, which is comparable to the P3HT on a ITO/glass substrate. Moreover, after bending test, P3HT on IAI multilayer electrode also showed stable EC coloration, Based on the observed EC performance, the RTR sputtered IAI multilayer is proposed as an excellent substitute for conventional ITO film electrodes in order to realize large-area, transparent, flexible EC devices for flexible smart window applications.

Roll-to-Roll Sputtered ITO/Ag/ITO Multilayers for Highly Transparent and Flexible Electrochromic Applications

Electrochromism refers to the phenomenon where optical changes in a material occur during electrochemical reactions under an applied voltage. Because of advantages such as high contrast and low operating voltage, electrochromic (EC) devices have been widely used in smart windows, switchable mirrors, optical shutters, and information displays.Such devices are usually fabricated on a rigid glass substrate to permit their use in automobile and building applications, which require long-term stability under climatic conditions. However, the use of soft polymer or textile substrates has increased the versatility of such technology, allowing the fabrication of novel flexible, stretchable, and wearable EC devices. Since the first flexible EC devices using WO3layers were developed in 1995 a wide variety of inorganic and organic materials has been investigated with respect to their compatibility with flexible substrates. However, most EC devices fabricated using these materials showed poor performances, especially in terms of coloration speed and long-term stability, which was mainly due to the electrical and mechanical properties of the flexible substrate. In addition, the large area and cost-effective roll-to-roll (RTR) coating process for transparent electrodes has been demonstrated for the fabrication of low cost flexible EC devices. To date, the most common transparent electrode for EC devices is indium-tin-oxide (ITO) due to its low resistivity, high transparency, and mature mass production via processes such as sputtering. Amorphous ITO(a -ITO) films can easily be coated on a flexible substrate using conventional DC sputtering at ambient temperatures, but the high sheet resistance and brittleness of thick a-ITO films prevents their use for flexible and transparent EC devices. Oxide-metal-oxide(OMO) multilayer films have been extensively reported in flexible optoelectronic devices as an alternative to a-ITOfilms. However, there are few reports regarding flexible and transparent EC devices fabricated using OMO multilayer electrodes. The development of a conductive layer with high electrical conductivity and stable mechanical flexibility is greatly needed for flexible EC device applications. In this paper, we report the electrochromic properties of poly(3-hexylthiophene) (P3HT) films coated on ITO/Ag/ITO (IAI) multilayers deposited on flexible PET substrates using an ambient temperature RTR sputtering system. By continuous sputtering of ITO/Ag/ITO layers on the flexible PET substrate, we realized highly transparent, flexible, and conductive electrodes for flexible and transparent EC devices. We characterized the coloration efficiency, response time, and long-term stability of the P3HT on the flexible substrate compared to the material prepared on glass substrates.

Phosphorus-doped zinc oxide p–n homojunction thin film for flexible piezoelectric nanogenerators

The performance of zinc oxide (ZnO)-based piezoelectric nanogenerators (PENGs) has been largely limited by piezoelectric potential screening effect due to excess electrons in ZnO. To address this problem, we report here a method that can greatly enhance the performance of ZnO PENGs by reducing excess electrons. We formed ZnO p–n homojunction thin film, composed of unintentionally doped n-ZnO and phosphorus-doped p-ZnO, on the ITO/Ag/ITO(IAI) coated flexible substrate with a low sheet resistance of 3.03Ω/sq and a high optical transmittance of 88.16%, where were prepared by roll-to-roll sputtering. The fabricated PENG with a p–n homojunction demonstrates the output power up to ~140μW, which is approximately two orders of magnitude higher than that of the PENG only with ZnO. Besides, the output performance related with the p-ZnO and n-ZnO thickness ratio and the roles of p–n junction formation were also systematically investigated. The results here introduce a new method to further extend performance limit of ZnO-based PENGs.

Direct laser patterning of transparent ITO–Ag–ITO multilayer anodes for organic solar cells

Direct laser patterning of transparent ITO–Ag–ITO (IAI) multilayer anodes is investigated using a femtosecond fiber laser for application in organic solar cells (OSC) fabrication. By adjusting laser fluence and scan speed, we successfully patterned the IAI multilayer anode without changing the electrical or optical properties. At an optimized laser fluence of 0.6J/cm2 and a scan speed of 200mm/s, the patterned IAI multilayer was electrically isolated with a clean edge. The metallic Ag interlayer of the IAI multilayer plays an important role in direct laser patterning because it absorbed the laser and increases the maximum temperature in the IAI multilayer. In addition, the Ag layer could effectively decrease the temperature of the IAI multilayer after irradiation of laser. The OSC fabricated on the laser patterned IAI multilayer showed power conversion efficiencies of 3.12% (Ag 8nm) and 2.85% (Ag 12nm). Successful operation of the OSC indicates that direct laser patterning of IAI multilayer anodes is a promising, simple patterning technology for fabrication of IAI-based OSCs.

ITO/Ag/ITO multilayer-based transparent conductive electrodes for ultraviolet light-emitting diodes

ITO/Ag/ITO (IAI) multilayer-based transparent conductive electrodes for ultraviolet light-emitting diodes are fabricated by reactive sputtering, optimized by annealing, and characterized with respect to electrical and optical properties. Increasing the annealing temperature from 300°C to 500°C decreased the sheet resistance and increased the transmittance. This may result from an observed improvement in the crystallinity of the IAI multilayer and a reduction in the near-UV absorption coefficient of Ag. We observed the lowest sheet resistance (9.21 Ω/sq) and the highest optical transmittance (88%) at 380 nm for the IAI multilayer samples annealed in N₂ gas at 500°C.

Transmission electron microscopy study of degradation in transparent indium tin oxide/Ag/indium tin oxide multilayer films

The degradation mechanism and structural evolution of transparent ITO/Ag/ITO (IAI) multilayer films caused by rapid thermal annealing (RTA) were investigated by high resolution transmission electron microscopy (HRTEM) and synchrotron X-ray scattering analysis. The IAI multilayer with low sheet resistance of 9.51 Ω/square and high transmittance of 88.24% was significantly degraded after 600 °C RTA. Discontinuity, agglomeration of the embedded Ag layer at the interface region of the IAI multilayer, and oxygen diffusion through crystalline ITO grain boundaries into Ag layers led to electrical and optical degradation of the IAI multilayer. Using HRTEM analysis, the microstructures and interfaces of as-deposited and 600 °C annealed IAI multilayer films were compared to explain their electrical and optical degradation mechanisms.