Low Optical Transmittance Research Articles

Hybrid Functional ITO/Silver Nanowire Transparent Conductive Electrodes for Enhanced Output Efficiency of Ultraviolet GaN-Based Light-Emitting Diodes.

We investigated hybrid functional transparent conductive electrodes (HFTCEs) composed of indium-tin-oxide (ITO) and silver nanowires (AgNWs) for the enhancement of output efficiency in GaN-based ultraviolet light-emitting diodes (UVLEDs). The HFTCEs demonstrated an optical transmittance of 69.5% at a wavelength of 380 nm and a sheet resistance of 16.4 Ω/sq, while the reference ITO TCE exhibited a transmittance of 76.4% and a sheet resistance of 18.7 Ω/sq. Despite the 8.9% lower optical transmittance, the UVLEDs fabricated with HFTCEs achieved a 25% increase in output efficiency compared to reference UVLEDs. This improvement is attributed to the HFTCE's twofold longer current spreading length under operating forward voltages, and more significantly, the enhanced out-coupling of localized surface plasmon (LSP) resonance with the trapped wave-guided light modes.

Multicoated Flexible Indium Tin Oxide Electrodes Fabricated Using Magnetron Sputtering and Arc Plasma Ion Plating for Flexible Perovskite Solar Cells.

High-performance flexible Sn-doped In2O3 (indium tin oxide, ITO) electrodes were fabricated using a multicoating process on colorless polyimide (CPI) substrates for flexible perovskite solar cells (FPSCs). The effects of different coating sequences on the electrical, optical, and mechanical properties of the flexible ITO electrodes were thoroughly investigated after preparing them with direct-current magnetron sputtering (DMS) and arc plasma ion plating (APIP). Although both the sputtered ITO (SITO)/arc ion-plated ITO (AITO) film and the AITO/SITO film showed similarly low sheet resistance (18.69-25.29 Ω/sq) and high optical transmittance (94.96-96.85%), the coating sequence significantly affected the mechanical flexibility of the multicoated ITO films. The 120 nm-thick SITO/AITO electrode exhibited small outer and inner critical bending radii (3 mm and 3 mm, respectively) compared to the AITO/SITO electrode (4 and 5 mm, respectively). Owing to better adhesion of the arc-ion-plated ITO bottom layer and the amorphous structure of the top SITO layer, the SITO/AITO electrode exhibited excellent mechanical flexibility and durability. In addition, an FPSC using the SITO/AITO electrode achieved a higher power conversion efficiency (15.09%) than that with the AITO/SITO electrode (13.22%). This improvement was attributed to its high transmittance, low sheet resistance, smooth surface morphology, and enhanced hole collection efficiency. These findings highlight the efficacy of the combined DMS and APIP multicoating process for fabricating high-quality flexible ITO electrodes for high-performance FPSCs.

Excellent low-E energy storage and fluorescence temperature sensing features in Bi0.5Na0.5TiO3-based transparent ceramics

Transparent dielectric ceramics with ultrafast discharge rates and gigantic power densities are ideal candidates for transparent pulse capacitors (TPCs). However, the requirement of a high external electric field and inferior temperature stability hinder practical applications. (Bi0.5Na0.5)TiO3-based ceramics exhibit large polarization and two characteristic dielectric peaks, easy to obtain high energy-storage density under low electric fields (low-E) and maintain stable energy-storage performance (ESP) within a wide temperature range. However, their low optical transmittance (T%) limits their development into TPCs. In this work, to concurrently obtain high T% and excellent ESP and stability under low-E conditions, we propose a collaborative optimization strategy for determining the regulations of grain size, bandgap energy and domain structure. The results show that the pellucidity and energy-storage characteristics improve with decreasing grain and domain sizes. A relatively high T% of 45.6 % (at 710 nm) and recoverable energy-storage density (Wrec ∼ 3.46 J cm−3 at 197 kV cm−1) are obtained for the (1-x)[0.85(Bi0.5-3yNa0.5-yYb3yHoyTiO3)-0.15SrZrO3]-xBaHfO3 ceramics. Additionally, the dielectric temperature stability also results in splendid storage temperature stability (ΔWrec/Wrec < 3.1 % in the range of 0–200 °C). Importantly, codoping Ho/Yb in the ceramics induces excellent fluorescence temperature sensing feature. The multifunctional TPCs have application potential in the field of search and rescue signal transmission, providing ideas for developing novel optoelectronic devices.

Hierarchical Networks Composed of Silver Micromeshes and Silver Nanowires for Optoelectronic Devices

Metal based networks are expected to be promising candidates to replace transparent conducting oxides such as indium tin oxide and doped zinc oxide in many kinds of optoelectronic devices such as displays and thin-film solar cells because they have lower sheet resistance, higher optical transmittance, and better mechanical flexibility than transparent conducting oxides. However, carrier transport in the empty spaces present in the metal networks has to be considered for the metal networks to be successfully integrated to real electronic devices. Therefore, it is still questionable for them to be appropriately implemented in real optoelectronic devices even though they have such advantages over transparent conducting oxides. Here, hierarchical networks composed of silver micromeshes and silver nanowires are presented. The hierarchical networks are successfully integrated to thin-film solar cells as transparent conducting electrodes by replacing transparent conducting oxides while they show low sheet resistance of ~2 ohm/sq, high optical transmittance of 88%. The silver micromeshes provides such low sheet resistance and high optical transmittance and the silver nanowires have role of ensuring carrier transport between empty spaces in the hierarchical network. In addition, they have excellent mechanical flexibility of no degradation of optoelectronic properties at a mechanical bending of radius of curvature of 5 mm.

Highly flexible and transparent electrodes for high-performance thin-film heaters with nanostructured micromesh Cu–Ag ultrathin films

Herein, we present a facile method to fabricate transparent, flexible, and high-performance thin-film heaters (TTFHs) based on nanostructured micromesh (NSMM) Cu–Ag/indium tin oxide bilayer transparent thin-film electrodes (TTFEs) with both nano- and microstructures. Our approach combines Ar-assisted thermal evaporation and pulsed laser ablation techniques to fabricate NSMM TTFEs with a low sheet resistance (∼2.1 Ω/sq) and high optical transmittance (∼80.1 %). By adjusting the spacing of microholes, we can achieve excellent figure of merit values (∼51.8 × 10−3 Ω−1) for the NSMM TTFEs. These electrodes also show excellent durability and flexibility, as evidenced by a resistance change of only 4 %–18 % in cyclic bending tests with up to 200,000 cycles. Finally, we demonstrate that the NSMM TTFEs can be used as high-performance TTFHs with short response times (3.97 s at a steady temperature of 87.5 °C under low-voltage operation (5 V)) and infrared shielding properties. Our results suggest that the Cu–Ag-alloy-based NSMM TTFEs are promising transparent electrodes for various applications in flexible electronics, smart windows, and wearable devices.

Active matrix driven electrophoretic display with in-plane switching layout and driving waveform for reflective and transparent modes.

In-plane switching electrophoretic display (IPS-EPD) is an emerging field of display technology which achieves particles moving horizontally through a lateral electric field. Compared to vertically driven electrophoretic display (V-EPD), IPS-EPD exhibits the feasibility of transparent display function. However, most of the previous research was hindered by long response time, low optical transmittance, or complex structures. In this paper, we have proposed a newly developed electrode layout and driving waveform for IPS-EPD, achieving a device with fast response time of 0.32 s, high transmittance of 58.07%, good transmittance-contrast ratio of 11.25, and simple structure, which show a significant improvement over other related research. Additionally, we elucidated the physical mechanism for the device through developing a particles motion simulation. Finally, we presented a prototype of an IPS-EPD with TFT panel, which exhibits excellent performance in various application scenarios, making it a possible application prospect in mobile phone cases, glasses, windows, and so on.

An Aluminum-coated sCMOS Sensor for X-Ray Astronomy

In recent years, tremendous progress has been made on scientific Complementary Metal Oxide Semiconductor (sCMOS) sensors, making them a promising device for future space X-ray missions. We have customized a large-format sCMOS sensor, G1516BI, dedicated for X-ray applications. In this work, a 200 nm thick aluminum layer is successfully sputtered on the surface of this sensor. This Al-coated sensor, named EP4K, shows consistent performance with the uncoated version. The readout noise of the EP4K sensor is around 2.5 e− and the dark current is less than 0.01 e− pixel−1 s−1 at −30°C. The maximum frame rate is 20 Hz in the current design. The ratio of single pixel events of the sensor is 45.0%. The energy resolution can reach 153.2 eV at 4.51 keV and 174.2 eV at 5.90 keV at −30°C. The optical transmittance of the aluminum layer is approximately 10−8 to 10−10 for optical lights from 365 to 880 nm, corresponding to an effective aluminum thickness of around 140 to 160 nm. The good X-ray performance and low optical transmittance of this Al-coated sCMOS sensor make it a good choice for space X-ray missions. The Lobster Eye Imager for Astronomy, which has been working in orbit for about one year, is equipped with four EP4K sensors. Furthermore, 48 EP4K sensors are used on the Wide-field X-ray Telescope on the Einstein Probe satellite, which will be launched at the end of 2023.

Metallic Micro-Nano Network-Based Soft Transparent Electrodes: Materials, Processes, and Applications.

Soft transparent electrodes (TEs) have received tremendous interest from academia and industry due to the rapid development of lightweight, transparent soft electronics. Metallic micro-nano networks (MMNNs) are a class of promising soft TEs that exhibit excellent optical and electrical properties, including low sheet resistance and high optical transmittance, as well as superior mechanical properties such as softness, robustness, and desirable stability. They are genuinely interesting alternatives to conventional conductive metal oxides, which are expensive to fabricate and have limited flexibility on soft surfaces. This review summarizes state-of-the-art research developments in MMNN-based soft TEs in terms of performance specifications, fabrication methods, and application areas. The review describes the implementation of MMNN-based soft TEs in optoelectronics, bioelectronics, tactile sensors, energy storage devices, and other applications. Finally, it presents a perspective on the technical difficulties and potential future possibilities for MMNN-based TE development.

Growth of TiO2 single crystals by the Verneuil method at different gas flow ratio

The oxygen-rich atmosphere is a prerequisite for the preparation of high-quality TiO2 single crystals using the Verneuil method. However, too much oxygen will bring down the temperature of the growing chamber, so the key to growing high-quality TiO2 single crystals is to ensure that the temperature distribution is stable and that the heat in the growth chamber is in equilibrium. In this paper, TiO2 single crystals were prepared by the Verneuil method under different gas flow ratio. Due to the inability to obtain a stable temperature field, the crystals produced at the hydrogen-to-oxygen ratios of 1.4 and 1.8 both had substantial dislocation densities and low optical transmittance. The heat in the growth chamber reaches equilibrium and the temperature distribution is steady-state when the hydrogen-to-oxygen ratio is 1.6. The FWHM of the crystal obtained under this condition is 0.02334°, the transmittance is nearly 70 %, and the etch pit density is only 6.21 × 104 cm−2. This work is a major boost to the industrial production of rutile crystals.

Preparation of Zn2+ doped NiCo2O4: Hole transport layer for high performance of perovskite solar cells

Inorganic hole transport materials (HTMs) play an important role for the stability and efficiency of planar perovskite solar cells (PSCs). Among the numerous inorganic HTMs, NiCo2O4 with its excellent performance is the emerging candidate for hole transport layers (HTLs) and is attracting increasing attention. However, the low electrical conductivity and optical transmittance of NiCo2O4 severely limit the device performance. Herein, the Zn2+ was used to dope NiCo2O4 to improve the electrical conductivity and optical transmittance of NiCo2O4. And the effects of the concentration of Zn2+ on the morphology, structure and properties of NiCo2O4 were investigated. The morphology and transparency of ZnxNi1-xCo2O4 would not be affected when the concentration of Zn2+ is below 0.1, but when it is up to 0.15 and 0.2, the morphology of NiCo2O4 clustered together or showed a diamond-shaped block, and the optical transmittance also decreased significantly. Meanwhile, with the increase of doping amount, the conductivity and hole mobility are gradually increased. As a result, the optimal concentration of Zn2+ is 0.1. Besides, the Zn0.1Ni0.9Co2O4 possessed a significant improvement in hole extraction and better band alignment compared to the NiCo2O4. And hence, the power conversion efficiency (PCE) of PSCs fabricated in open air is up to 13.41% by using Zn0.1Ni0.9Co2O4. This work develops a potential strategy for developing highly efficient and stable PSCs, opens up a new horizon for the development of inorganic HTMs.

Systematic investigations on morphological properties of aluminum-doped zinc oxide transparent electrode prepared from pulsed laser deposition and its electrochromic application

Transparent electrode (TE) is considered as one of the fundamental components in the optoelectronics. The surface of TE layer plays a crucial role in the charge-transport characteristics. Herein, a systematic investigation on the morphological properties of the laser-ablated aluminum-doped zinc oxide (AZO) films as a TE material prepared from various laser fluences is demonstrated. It is revealed that the electrical properties of AZO films are strongly associated with their surface properties rather than that of the bulk film. As the laser fluence increased, the concentration of Al-dopant in AZO films is decreased which directly impacts on the electrical properties. Such vanishment is originated from the bombardment of the incident particles/ions with excessive kinetic energy on film's surface during the deposition. Moreover, the optimized AZO film with low resistivity (1.13 × 10−3 Ω cm) and high optical transmittance (over 90%) achieved from controlling the laser fluence at 0.7 J/cm2 is employed as TE layer in the electrochromic device. Our results highlight that the surface properties of TE layer are very critical for electronic performance.

Perovskite solar cells on Sn-doped In2O3 electrodes with artificially controlled (222) preferred orientation

Despite the rapid advancements in transparent conductive electrodes (TCEs), most planar-type perovskite solar cells (PSCs) are still fabricated on commercial polycrystalline Sn-doped In2O3 (ITO) electrodes, due to their resulting high conductivity, transmittance, and technological mutuality. However, artificially controlling the preferred orientation of a sputtered ITO electrode through O2 partial pressure can lead to differences in the conductivity, transmittance, and surface morphology of the ITO electrode, as well as in the growth behavior of the NiOx hole transport layer and methylammonium lead iodide (MAPbI3) active layer on the ITO for high-performance planar-type PSCs. Here, we comprehensively compared the electrical, optical, structural, and morphological properties of (222) and (400) artificially preferred ITO electrodes, and we correlated the performances of the PSCs with these differently preferred ITO electrodes. The higher power conversion efficiency (17.82%) of PSCs on (222) preferred ITO electrode than that (7.98%) of PSCs on the (400) preferred ITO electrode could be attributed to the larger grain size of the MAPbI3 active layer on the (222) preferred ITO electrode with low sheet resistance (2.66 Ohm/square) and high optical transmittance (93.47%). This suggests that artificial control of the (222) preferred orientation of sputtered ITO electrode represents a simple method for improving the performance of PSCs with identical perovskite photoactive layer.

Optical performance of Tin doped Indium Oxide (ITO) thin films prepared by sol gel dip coating techniques using acrylamide route

At present various oxide of metal semiconductors play a significant role in the field of electronics. Most of the semiconductor devices exploit the special characteristics of the junction between a p-type and n-type semiconductor. These devices can be made extremely small in size and they are incredibly fast in their response. Generally metal have good reflectivity in the electromagnetic region of infrared and visible radiation. Indium oxide material doped with tin (ITO) is recently used in the substrate material for various applications, because it has special properties of low resistivity and high optical transmittance in the visible region. In this paper, we prepare ITO films with different tin concentration (5%, 10%, 15%, 20%, 30%, 40%, 50%, 60% and 70%) using acrylamide sol gel dip coated method and its results were reported. TCO materials have good electrical conductivity and optical transparency, and also it has n-type semiconductor with a band gap between 3.5 and 4.3 eV. An X-ray study indicates all the prepared samples had bixbyte structure. Optical behaviour of materials can be understood in the near infrared and visible spectrum. Some optical parameters of refractive index, extinction coefficient and dielectric constant of ITO films are calculated from the data received from the UV transmission studies. Using W-D model the dispersion of refractive index was calculated. The optical band gap, oscillator energy, dispersion energy and optical conductivity and N/m* ratio were estimated and this material is well suitable for dye sensitized solar cell and sensor application.

A Dielectric Polymer/Metal Oxide Nanowire Composite for Self-Adaptive Charge Release.

Electrostatic discharge is a fatal threat to a variety of electronic products. Here we report on a polymer nanocomposite composed of a dielectric polymer embedded with aligned core-shell structured nanowires for highly efficient distributed electrostatic discharge protection. The dielectric nanocomposite is capable of self-adaptive charge release, stemming from the nonlinear interface built in the Bi/Co oxide coated ZnO nanowires that leads to a "hand-in-hand" double-Schottky barrier. The ultralow filler concentration (e.g., 0.5 vol %) endows the nanocomposite with low permittivity (close to the pristine polymer matrix) and high optical transmittance (75%) in the visible light wavelength range, which is desirable in packaging materials and display coatings for portable electronics. The effectiveness for electrostatic discharge protection was validated with an organic light-emitting diode screen protected by the nanocomposite that survived multiple rounds of electrostatic discharge.

Mg-doped Cu2O thin films with enhanced functional properties grown by magnetron sputtering under optimized pressure conditions

Cu2O appears as a promising material for synthesizing p-type transparent semiconducting oxides with low electrical resistivity and high optical transmittance. We report on an exhaustive study of magnesium-doped cuprous oxide layers deposited by radio frequency magnetron sputtering. We present the characterization of the structural and optoelectronic properties of Mg:Cu2O thin films deposited at room temperature with varied argon plasma pressure. As a result, we found that by adjusting the Ar plasma pressure, Mg-doped Cu2O layers with high crystallinity combined with optimal electrical and optical properties can be synthesized. Using a plasma pressure of 13 mTorr, we obtained a transparent p-type material with crystallite size of 15 nm, electrical resistivity of 10.2 Ωcm, and optical band gap of 2.55 eV.

Thermal optimization of defected Cu2O photon-absorbing layer and the steady p-Cu2O/n-Si photovoltaic application

Cuprous oxide (Cu2O), a far-reaching photon-absorption layer, is active in the field of solar cells and sensors. In this work, the Cu2O films prepared at low temperature by radio frequency (RF) magnetron sputtering holds a branch-like crystalline morphology, low optical transmittance and unsatisfactory carrier mobility. However, peroxidation will occur when thermal is excessive. By optimizing, the (111)-oriented monocrystal Cu2O films with trapping light structure are obtained through the rapid thermal annealing (RTA) process in N2 atmosphere, and the carrier mobility is escalated by five times to 11.75 cm2/v·s. On this basis, we construct an Au/p-Cu2O/n-Si/Al device and keep the leakage current standing at 1.81 × 10−9 A and the rectification ratio (IF/IR) reaching 177. Surprisingly, the unpackaged device still maintains a rectification ratio of 44 and a considerable leakage current even operating at 120 °C. Finally, we have measured the photovoltaic characteristic and provided some optimization strategies for power conversion efficiency.

Recent Applications of Carbon Nanotubes in Organic Solar Cells.

In recent years, carbon-based materials, particularly carbon nanotubes (CNTs), have gained intensive research attention in the fabrication of organic solar cells (OSCs) due to their outstanding physicochemical properties, low-cost, environmental friendliness and the natural abundance of carbon. In this regard, the low sheet resistance and high optical transmittance of CNTs enables their application as alternative anodes to the widely used indium tin oxide (ITO), which is toxic, expensive and scarce. Also, the synergy between the large specific surface area and high electrical conductivity of CNTs provides both large donor-acceptor interfaces and conductive interpenetrating networks for exciton dissociation and charge carrier transport. Furthermore, the facile tunability of the energy levels of CNTs provides proper energy level alignment between the active layer and electrodes for effective extraction and transportation of charge carriers. In addition, the hydrophobic nature and high thermal conductivity of CNTs enables them to form protective layers that improve the moisture and thermal stability of OSCs, thereby prolonging the devices’ lifetime. Recently, the introduction of CNTs into OSCs produced a substantial increase in efficiency from ∼0.68 to above 14.00%. Thus, further optimization of the optoelectronic properties of CNTs can conceivably help OSCs to compete with silicon solar cells that have been commercialized. Therefore, this study presents the recent breakthroughs in efficiency and stability of OSCs, achieved mainly over 2018–2021 by incorporating CNTs into electrodes, active layers and charge transport layers. The challenges, advantages and recommendations for the fabrication of low-cost, highly efficient and sustainable next-generation OSCs are also discussed, to open up avenues for commercialization.

Highly Stable Graphene‐Based Flexible Hybrid Transparent Conductive Electrodes for Organic Solar Cells

AbstractFlexible transparent conductive electrodes (TCEs) are an essential part of flexible electronic and energy devices. As a promising alternative to ITO (In2O3:Sn), silver nanowire has poor environmental stability and adhesion, which limits its development. Herein, transition metal carbides and carbonitrides called MXene are inserted between silver nanowires and graphene grown by chemical vapor deposition to improve the conductivity, adhesion, roughness, and stability of the electrode. Nanosheets fill the voids of the network and connect the nanowires with graphene to provide more conductive channels. In addition, due to the solvent evaporation effect and thermal effect in the preparation process, the nanowire junctions are welded together. Based on the unique structure, the proposed composite TCE shows low sheet resistance (18.1 Ω sq−1) and high optical transmittance (88.1% at 550 nm). Furthermore, compared to the reference samples, the composite TCEs demonstrate stable electrical performances under different environmental conditions, including thermal environment, exposures to air for 80 days, and bending for 2000 cycles. Finally, flexible organic solar cells (OSCs) are prepared using the composite TCEs, which show comparable efficiency to that of ITO‐based OSCs. Therefore, the flexible transparent electrodes are expected to be applied in solar cells, organic light‐emitting diodes, and a broader range.

Prediction of powder bed thickness by spatter detection from coaxial optical images in selective laser melting of 316L stainless steel

The uniformity of a recoated powder layer affects the performance of parts manufactured by SLM directly, while it is related to the characteristics of spatters. The small spatter moves pretty fast, while the low optical transmittance in the spectrum of a hot spatter in the coaxial optical path of SLM equipment prevents clear imaging of this target with high contrast. In this study, a coaxial optical path with an enhanced optical transmittance is used for imaging the melt pool and its surrounding phenomena simultaneously. An experimental system was developed using a high-speed camera for coaxial observation of hot spatters in the SLM process. The problems of limited field of view and high measurement uncertainty of an off-axis process monitoring system are solved. For defocused and distorted spatter images, both a segmentation algorithm and an object detection method have been proposed and proved to be effective. It was found that the direction and strength of the local airflow field could be estimated via the curvature of the spatter trajectory. More importantly, the quantity of spatters detected is positively related to the amount of powder locally distributed on the baseplate, which is useful to estimate the powder bed thickness at this position.

Environmentally Friendly Graphene Inks for Touch Screen Sensors

AbstractGraphene‐based materials have attracted significant attention in many technological fields, but scaling up graphene‐based technologies still faces substantial challenges. High‐throughput top‐down methods generally require hazardous, toxic, and high‐boiling‐point solvents. Here, an efficient and inexpensive strategy is proposed to produce graphene dispersions by liquid‐phase exfoliation (LPE) through a combination of shear‐mixing (SM) and tip sonication (TS) techniques, yielding highly concentrated graphene inks compatible with spray coating. The quality of graphene flakes (e.g., lateral size and thickness) and their concentration in the dispersions are compared using different spectroscopic and microscopy techniques. Several approaches (individual SM and TS, and their combination) are tested in three solvents (N‐methyl‐2‐pyrrolidone, dimethylformamide, and cyrene). Interestingly, the combination of SM and TS in cyrene yields high‐quality graphene dispersions, overcoming the environmental issues linked to the other two solvents. Starting from the cyrene dispersion, a graphene‐based ink is prepared to spray‐coat flexible electrodes and assemble a touch screen prototype. The electrodes feature a low sheet resistance (290 Ω □−1) and high optical transmittance (78%), which provide the prototype with a high signal‐to‐noise ratio (14 dB) and multi‐touch functionality (up to four simultaneous touches). These results illustrate a potential pathway toward the integration of LPE‐graphene in commercial flexible electronics.