Transparent Cathode Research Articles

ZnO/Ag/ZnO multilayers as an n-type transparent conducting electrode for transparent organic light-emitting diodes

Alternative transparent conducting electrodes (TCEs) have gained significant attention in recent decades in an effort to replace costly indium-tin oxide (ITO) in organic optoelectronic devices. For example, state-of-the-art top-emitting and transparent organic light-emitting diodes (OLEDs) in the display industry require a transparent or semitransparent cathode for electron injection. Current OLED display technology employs ultrathin metallic (typically Mg:Ag) layers as semitransparent cathodes. However, recent studies have shown that metal oxide/metal/metal oxide multilayers can perform better optically and offer improved stability compared to semitransparent metal cathodes. Deposition of these multilayers with minimal damage to the underlying organic emissive layer is imperative. Here, we investigate a ZnO/Ag/ZnO TCE multilayer TCE deposited under mild sputtering conditions that are safe for the emissive layer. We demonstrate ∼ 85 % transparent electrodes with a sheet resistance of 1.47 Ω/sq, which is more conductive than the industry standard, ITO. We also integrate the multilayer TCE as the cathode in a transparent OLED device built on ITO, demonstrating the compatibility of this TCE with the existing OLED technology.

Innovative Energy Storage Smart Windows Relying on Mild Aqueous Zn/MnO2 Battery Chemistry.

Rechargeable mild aqueous Zn/MnO2 batteries are currently attracting great interest thanks to their appealing performance/cost ratio. Their operating principle relies on two complementary reversible electrodeposition reactions at the anode and cathode. Transposing this operating principle to transparent conductive windows remains an unexplored facet of this battery chemistry, which is proposed here to address with the development of an innovative bifunctional smart window, combining electrochromic and charge storage properties. The proof-of-concept of such bifunctional Zn/MnO2 smart window is provided using a mild buffered aqueous electrolyte and different architectures. To maximize the device's performance, transparent nanostructured ITO cathodes are used to reversibly electrodeposit a high load of MnO2 (up to 555 mAhm-2 with a CE of 99.5% over 200 cycles, allowing to retrieve an energy density as high as 860 mAhm-2 when coupled with a zinc metal frame), while flat transparent FTO anodes are used to reversibly electrodeposit an homogenous coating of zinc metal (up to ≈280 mAhm-2 with a CE > 95% over 50 cycles). The implementation of these two reversible electrodeposition processes in a single smart window has been successfully achieved, leading for the first time to a dual-tinting energy storage smart window with an optimized face-to-face architecture.

Modeling and optimization of a relativistic magnetron with transparent cathode and output mode

Abstract This paper outlines the results of particle-in-cell simulations of a relativistic magnetron with six cavities and a transparent cathode configuration. Excitation of the π mode in the interaction region was attained, which in turn led to $\textrm{TE}_{11}$ mode emission of microwaves to the waveguide. This mode transformation was achieved with a non-symmetric diffraction output, consisting of four large and two small tapered cavities. Simulations were performed with a voltage across the anode-cathode gap varying from 164 to 356 kV, and axial magnetic field strengths between 0.24 and 0.34 T. Maximum efficiency of 37% was obtained with a peak output power of 590 MW, having a voltage of 261 kV and a magnetic field of 0.30 T. Furthermore, a frequency of 2.57 GHz and a rise time of microwaves at the waveguide of 15 ns were demonstrated. The electron leakage current was shown to decrease from ∼10 $\%$ to less than $1\%$ when employing a longer interaction region, while still exhibiting good performance. Additionally, we show that there is an optimal range of voltages given a magnetic field, for which π mode excitation with high efficiency is attained.

A systematic approach to the modelling and comparison of the geometries of spherical electrodes in inertial electrostatic confinement fusion devices

Inertial electrostatic confinement fusion (IECF) devices often use two concentric spherical electrodes to converge ions in a plasma electrostatically. Using a highly transparent inner cathode, the ions can move through the cathode and collide at the center to undergo fusion reactions. This is a simple method to build a neutron source. Past research has focused chiefly on cathode “grids” manufactured by joining metal wire loops or disc-shaped elements via spot welding. There are two common geometries: “Globe” grids with a distinct latitude-longitude structure and “symmetric” grids with even-sized triangular-shaped apertures. Recent advances in additive manufacturing have opened the way to manufacturing a third class of grids in which the apertures are evenly distributed over the grid surface and have either circular or polygonal shaped apertures - here called “regular” grids. These three types are analyzed and compared based on a set of metrics, including transparency, homogeneity of aperture size, and the regularity of aperture distribution. It is shown that every type of grid comes with different advantages and disadvantages. The analysis focuses on grid geometries with 6 to 120 apertures.

Ultrathin transparent carbon nanotube/LiMn2O4 and carbon nanotube/MoS2 film electrodes for Li-ion full batteries

The increasing demands for wearable devices have significantly facilitated the development of transparent electronics. Serving as key components of fully integrated transparent devices, transparent batteries are urgently needed yet their development is largely hindered by the difficulties of fabricating transparent electrode materials. Here, we successfully designed the transparent cathodes and anodes through combining transparent single-walled carbon nanotubes (SWNTs) films with lithium manganate (CNT/LMO) and molybdenum disulfide (CNT/MoS2), respectively. We found that the fabricated cathode and anode composite films exhibit excellent transmittances of 75% and 80%, respectively. Also, the interconnected SWNT networks in the composite films provide an efficient channel for fast electron transport that significantly contribute to their electrochemical performance. Specifically, when employed as battery electrodes, the highly transparent CNT/LMO cathode and CNT/MoS2 anode show initial areal capacities of 13 and 66 μAh cm−2 at current densities of 0.05 and 0.2 mA cm−2, respectively. More impressively, a full cell, which is constructed with transparent CNT/LMO and CNT/MoS2 composite films as electrodes, shows the capacity retention up to 90% after 100 cycles. The demonstration of transparent electrodes in this study provides a promising strategy to realize the fabrication of fully transparent wearable devices.

Semitransparent organic solar cells based on low temperature processed PEIE as electron transport layer with enhanced charge transfer ability

In inverted structure-based semitransparent organic solar cells (OSCs), the electron transport layer (ETL) plays a crucial role in the improvement of the transparent cathode efficiency in collecting and extracting negative charge carriers. Zinc oxide (ZnO) thin film prepared by zinc acetate dihydrate precursor with various benefits is generally used as ETL. However, high temperature, less charge transfer ability, and irregular film surface due to fiber-like domain formation limit the device performance. In this work, a new approach is presented by using low-temperature processed polyethylenimine ethoxylated (PEIE) as ETL in semitransparent OSCs fabricated in an ambient environment with a blend of low-bandgap donor polymer PTB7-Th, and fullerene acceptor, PC71BM, based active layer. For semitransparent OSCs, the thickness of the silver electrode has been varied from 55 nm to 25 nm to investigate its effect on the electrical and optical properties of the devices. The power conversion efficiencies (PCE) of 5.1% and 4.6% were achieved for semitransparent devices (25 nm thickness of silver electrode) for PEIE and ZnO ETLs, respectively. Similarly, PCE of 7% and 6.7% have been achieved for opaque devices (85 nm thickness of silver electrode) using PEIE and ZnO ETLs, respectively. PEIE based devices with 25 nm Ag demonstrate about 25%–30% transparency. The impedance spectroscopy measurements indicate low interfacial contact resistance and fast charge transfer capability for PEIE interlayer-based devices compared to the ZnO based devices. The encapsulated semitransparent devices processed and stored in ambient conditions with PEIE and ZnO ETLs were found to retain ≈80% performance for up to 45 days.

Characterization of the material and electrical properties depending on the Mg:Ag ratio as a cathode for TEOLED

In this study, Mg:Ag mixed alloy films were comprehensively analyzed as a potential transparent cathode, depending on the deposition ratio of Mg:Ag atoms. It was determined that the work function, refractive index, and film formation characteristics varied depending on the deposition ratio of Mg:Ag, and affected electro-optical characteristics such as transmittance and sheet resistance. In addition, the applicability of the proposed transparent cathode for top emitting organic light-emitting diodes (TEOLEDs) was analyzed by comprehensively considering the TEOLED performance in relation to the Mg:Ag deposition ratio. The TEOLED performance was optimized by adjusting the Mg:Ag transmittance, sheet resistance and appropriate work function, and the emission spectrum could be controlled by localized surface plasmon resonance (LSPR) and cavity mode coupling effect.

Plasma damage control via adjusting the target to substrate distance used to prepare semi-transparent perovskite solar cells

To realize semi-transparent perovskite solar cells (ST-PSCs), a high-quality amorphous transparent cathode must be deposited on the perovskite active layer without plasma damage at room temperature. In this study, we have investigated the effect of the target-to-substrate distance (TSD) on the performance of ST-PSCs during linear facing target sputtering (LFTS) to achieve the plasma damage-free sputtering of Ga and Ti co-doped In2O3 (IGTO) upper cathodes on planar ST-PSCs. We comprehensively compare the electrical, optical, structural, and morphological properties of IGTO cathodes grown using different TSDs and correlate them to performances of the ST-PSCs to determine the optimal TSD. We demonstrate the importance of optimal TSD and deposition mechanism at different TSDs based on the properties of the resulting IGTO films and ST-PSC performance. At an optimal TSD of 6 cm, the amorphous IGTO film demonstrate a sheet resistance of 9.22 Ω/sq. and optical transmittance of 87.74%. The ST-PSC constructed using the optimized IGTO upper cathode exhibit an open-circuit voltage of 1.12 V, short circuit current of 20.23 mA/cm2, fill factor of 83.73%, power conversion efficiency of 18.91%, and average transmittance of 19.31%. Consequently, the choice of the TSD is crucial in LFTS process for the fabrication of high-performance ST-PSCs without plasma damage.

Charting Ba-Based Double Perovskite Oxides for Visible-Light-Driven Photocatalytic Water Splitting

Realizing green hydrogen generation is contingent on developing low-cost, ecofriendly, and viable photocatalysts for water splitting. Using first-principles screening, we filtered out several Ba-based double perovskites (i.e., Ba2BB′O6) that are desired for such applications. Detailed chemical and electronic structure analyses reveal that all of the studied double perovskites, despite their disparate compositions, fall into five classes, depending on the orbital occupancy of the B and B′ cations. Of the five different classes, class I with the B = B′ = d10s0 electronic configuration has proper band gap ranges (1.4–2.8 eV) and significant optical absorption coefficients, making them viable photocatalysts for visible-light-driven one- and two-photon water-splitting reactions. Among the materials examined, Ba2AgIO6, Ba2CdTeO6, Ba2InSbO6, and Ba2BiSbO6, the only class V materials, stand out for their favorable optical absorptions and low exciton binding energies. The other classes include perovskites with large band gaps (>3 eV) that are suggested as transparent anode and cathode shields to protect photocatalysts from corrosion. Our findings provide valuable insights into exploring a rich family of nontoxic, highly effective Ba-based double perovskites for photocatalytic water-splitting applications.

Robust method for uniform coating of carbon nanotubes with V2O5 for next-generation transparent electrodes and Li-ion batteries.

Composites comprising vanadium-pentoxide (V2O5) and single-walled carbon nanotubes (SWCNTs) are promising components for emerging applications in optoelectronics, solar cells, chemical and electrochemical sensors, etc. We propose a novel, simple, and facile approach for SWCNT covering with V2O5 by spin coating under ambient conditions. With the hydrolysis-polycondensation of the precursor (vanadyl triisopropoxide) directly on the surface of SWCNTs, the nm-thick layer of oxide is amorphous with a work function of 4.8 eV. The material recrystallizes after thermal treatment at 600 °C, achieving the work function of 5.8 eV. The key advantages of the method are that the obtained coating is uniform with a tunable thickness and does not require vacuuming or heating during processing. We demonstrate the groundbreaking results for two V2O5/SWCNT applications: transparent electrode and cathode for Li-ion batteries. As a transparent electrode, the composite shows stable sheet resistance of 160 Ω sq-1 at a 90% transmittance (550 nm) - the best performance reported for SWCNTs doped by metal oxides. As a cathode material, the obtained specific capacity (330 mA h g-1) is the highest among all the other V2O5/SWCNT cathodes reported so far. This approach opens new horizons for the creation of the next generation of metal oxide composites for various applications, including optoelectronics and electrochemistry.

Temperature measurement and simulation analysis of heaterless hollow cathode during start-up process

Monochromatic radiation thermometry is used to quantify temperature distribution during the start-up process for a heaterless hollow cathode. A transparent cathode is designed to facilitate the transmission of thermally and spontaneously radiated photons from the interior of the structure and their reception by the detection equipment. The relative radiation intensities can be obtained by the developed measurement equipment, which consists of an scientific complementary metal oxide semiconductor camera and a 780 nm narrow-band filter, and then transformed into temperature distributions calibrated by a two-color pyrometer. The current and voltage characteristics of the anode and keeper and plasma image captured by the high-speed camera are used to analyze the thermal evolution mechanism. A 2D extended fluid model coupling with a thermal model is also developed and used to help clarify the thermal deposition variation at different locations. These results provide further support for the hypothesis that thermal deposition of ions and electrons, thermal conduction, and thermal radiation all affect the rate of change in temperature of various components.

Charge Transfer Dynamics of Doped Graphene Electrodes for Organic Light-Emitting Diodes.

Atomically thin graphene has attracted immense attention as a future transparent electrode for flat-panel displays owing to its excellent conductivity, optical transparency, and flexibility. In particular, a graphene doping process is essential for implementing graphene-based high-performance devices, and the development of a transparent cathode with a low work function is required to simplify the integration process of thin-film transistors and organic light-emitting diodes (OLEDs) into active matrix displays. In this study, a transparent n-doped graphene cathode is proposed for implementing inverted OLEDs through two types of cesium (Cs)-based doping techniques: a dipping method using wet chemicals and an evaporation method under a vacuum atmosphere. The changes in the chemical structures and work functions of the n-doped graphene electrodes, as well as their surface morphologies and transmittances, were systematically investigated. The n-type doping mechanism of graphene was investigated, and a close relationship between the electrical charge transfer characteristics of graphene transistors and the formation of C-O-Cs complexes was revealed. Finally, an effective Cs-doped graphene electrode was developed, exhibiting a dramatically decreased work function while maintaining high transmittance; therefore, the Cs-doped graphene cathode was successfully integrated with inverted OLEDs with a bottom-light emission structure that exhibited enhanced external quantum efficiency of graphene cathode-based OLEDs. Thus, our findings provide a better understanding of the doping strategies and potential of n-doped graphene as a transparent cathode for developing high-performance future displays.

Robust Laminated Anode with an Ultrathin Titanium Nitride Layer for High-Efficiency Top-Emitting Organic Light-Emitting Diodes.

The effective reflective anode remains a highly desirable component for the fabrication of reliable top-emitting organic light-emitting diodes (TE-OLEDs) which have the potential to be integrated with complementary metal-oxide-semiconductor (CMOS) circuits for microdisplays. This work demonstrates a novel laminated anode consisting of a Cr/Al/Cr multilayer stack. Furthermore, we implement an ultra-thin titanium nitride (TiN) layer as a protective layer on the top of the Cr/Al/Cr composite anode, which creates a considerably reflective surface in the visible range, and meanwhile improves the chemical stability of the electrode against the atmosphere or alkali environment. Based on [2-(2-pyridinyl-N)phenyl-C](acetylacetonate)iridium(III) as green emitter and Mg/Ag as transparent cathode, our TE-OLED using the TiN-coated anode achieves the maximum current efficiency of 71.2 cd/A and the maximum power efficiency of 66.7 lm/W, which are 81% and 90% higher than those of the reference device without TiN, respectively. The good device performance shows that the Cr/Al/Cr/TiN could function as a promising reflective anode for the high-resolution microdisplays on CMOS circuits.

PIC simulations of a frequency agile multicavity relativistic magnetron using irregular ring metamaterials driven by a transparent cathode

The design of an agile 5° irregular ring metamaterial for a 24-cavity relativistic magnetron with diffraction output (MDO) using single-stepped cavities for frequency switching is presented. By inserting six pieces of 5° irregular ring metamaterials in place of the traditional 5° vanes of a slow wave structure, the operating frequency can be tuned. When U = 400 kV high voltage is applied, with an applied magnetic field B = 0.36 T, the operating mode can be switched from the TE41 mode with a frequency of 2.585 GHz to the TE31 mode with a frequency of 2.282 GHz. The 24-cavity anode block is an electromagnetic medium which can support the operating mode working under its cutoff frequency, and the insertion of the irregular ring metamaterials alters its dispersion relation. The results suggest a new technique to achieve frequency agility by changing the dispersion relation of the electromagnetic system using a metamaterial unit cell. This work seeks to design a compact high power microwave source for a narrowband directed microwave wave beam that is suitable for frequency agility.

Performance of Dye-Sensitized Solar Cell using Hamelia Patens leaves as natural dye

Dye-Sensitized Solar Cells (DSSC), a 3rd generation solar cell has gained huge attention in the field of solar photovoltaics as a substitute for the silicon solar cell. The performance of the DSSC mainly depends on all the important components such as transparent conductive oxide substrate, cathode, photo-anode, dye, and electrolyte. Additionally, sensitizing dyes also perform a vital role in the absorption of light and the conversion of solar energy into electrical energy in DSSC. However, its efficiency is low and it consumes good amount of energy in manufacturing. In this respect scientists and researcher are more focus on how to improve its efficacy and production cost to make it economically viable. For this purpose, in this present work we have the natural dyes from Hamelia patens plant’s leaf which is available throughout the year for the fabrication of DSSC at low temperature. Semiconductor film electrode, ZnO has been synthesized via. chemical bath deposition process, which is anchored on the FTO glass substrate. Various characterizations techniques such as UV-vis absorption, FTIR were done for the extracted natural dye. XRD and FE-SEM were also performed for crystallinity and morphological analysis of ZnO material. XRD data reveals the formation of hexagonal ZnO (JCPDS card no. 01-082-9744 where 2θ° at 31.799, 34.454, 36.289, 47.586 corresponds to (100), (002), (011), (012) respectively). Using the ZnO and natural dyes, a sandwiched type DSSC has been fabricated and various parameter such as power conversion efficiency, Voc (open circuit voltage), Isc (short circuit current) has also been measured for continuous 3 days. DSSCs which is fabricated by using natural dye extracted from Hamelia patens leaves (sample 1) shows Voc = 132.2 and Isc = .065 mA.

Particle-In-Cell Simulations on Long Pulse Large Current Behavior of Magnetron With Diffraction Output

Relativistic magnetron is an important choice for high power microwave (HPM) source because it is relatively small compared with other HPM sources; in this respect, magnetron with diffraction output (MDO) is particularly attractive because its output port is already a horn. Previous experimental studies on MDO were conducted using a short pulse (~25 ns) SINUS-6 accelerator; here, we investigate the dynamical properties of an MDO under long pulse (~100 ns) and high monitored current (25–30 kA) conditions using a commercial particle-in-cell (PIC) code. The results show that MDO operation can be divided into two stages, and both are capable of HPM generation. At 450-kV applied voltage, the first stage happens between 0 and 35 ns when the transparent cathode rods emit electrons and they form spoke motion, and the dominant frequency is 4 GHz. The second stage happens after 35 ns, the spoke rotation in conventional magnetron region continues, but massive particles begin to flow toward the extended vanes region, and the dominant frequency is 2 GHz. If the applied voltage is higher, the stage transition happens sooner. Particle phase space plots show particle propagation toward the output port direction, which is a natural consequence of the pulsed power system and Lorentz force. Placing a cathode endcap on top of the cathode rods cannot stop the particles. The output power is well in the gigawatt (GW) realm and no pulse shortening is observed despite considerable particles are lost through contact with the anode wall in 100-ns pulse. The peak beam to microwave conversion efficiency is not as high as reported experimental value, but still a decent number close to 60%. Overall, the MDO is a suitable choice for certain applications that requires 100-ns pulse in GW range with high energy efficiency.

Effect of semiconducting nature of ZnO interfacial layer on inverted organic solar cell performance

The light-soaking effect is one of the major drawbacks for inverted organic solar cells (OSCs) if metal oxides are used as the electron transport layer (ETL). The oxide ETL primarily originates the above effect from the energy barrier, deep level defects, and excess carriers tunneling. Here, electron-beam evaporated high-quality pristine and post-treated e-ZnO thin films are utilized to fabricate inverted OSC as the ETL between the transparent cathode and active bulk-heterojunction PBDB-T-2Cl:PC61BM layer to study the influence on device performance. Various experimental techniques, including AFM, XRD, XPS, and UPS, are utilized to identify the surface and semiconducting properties of differently treated interfacial e-ZnO films precisely. XPS results reveal the variation of oxygen vacancies and adsorbed oxygen species on the surface of e-ZnO layers. The semiconducting nature of various e-ZnO thin films for the use of ETL are also probed with the help of UPS results, which accurately locate the valence band maximum and Fermi level position. After correlating the property of e-ZnO systematically with the respective OSC device performance, it is found that the deeper valence band top and higher n-type nature of e-ZnO is desirable to depict the light soaking free highest solar cell efficiency and large open-circuit voltage of about 0.97 V in a single junction. The presence of lesser chemisorbed oxygen species over the e-ZnO surface might be an added advantage to demonstrate the light soaking free operation in inverted OSC devices.

P‐88: Efficiency Improvement of Top‐Emission Green Quantum‐Dot Light‐Emitting Diode with Dielectric‐Metal‐Dielectric Cathode

In this work, we have demonstrated a top‐emission green quantum dot light‐emitting diode (QLED) with dielectric‐metal‐dielectric (DMD) structure as transparent cathode, which consisted of ytterbium (Yb)‐doped molybdenum oxide (MoO3)/Yb:Ag/MoO3. The DMD‐QLED exhibited a reduced operational voltage and higher efficiency by 1.43‐folds enhancement in external quantum efficiency relative to reference QLED due to the improvement of electron injection and transport as well as less exciton quenching.

7‐2: High Transmittance Under‐Display Camera Structure with COE

A novel under‐display camera structure with high transmittance up to 40.8% was proposed to increace transmittance, in which all pixel circuits and metal traces were moved to the transition zone which is right next to the UDC zone, and the circular polarizer was replaced with COE, and then the metal cathode is patterned by self‐assembly method, and the disconnected cathodes are connected together by transparent auxiliary cathode.

Highly Transparent and Flexible Zn-Ti3C2Tx MXene Hybrid Capacitors.

With the development of transparent and wearable electronic devices, energy supply units with high transmittance and flexibility, long cycle life, and high power and energy density are urgently needed. Zinc ion hybrid capacitors (ZIHCs) combined with the advantages of both supercapacitors and zinc ion batteries are promising energy supply components in the abovementioned devices. In addition, the preparation of multifunctional devices has become a trend for the need of space- and resource-saving. Therefore, obtaining ZIHCs with high transmittance and exploring their potential applications are meaningful challenges. Herein, a transparent and flexible ZIHC composed of a patterned zinc foil anode, transparent MXene cathode, and ZnSO4-polyacrylamide (PAM) hydrogel electrolyte is designed and realized. The ZIHC exhibits a superior capacitance of 318 μF cm-2 (5 mV s-1) with 94% transmittance and retains 76% of the initial capacitance after 10,000 charge-discharge cycles. It also shows excellent flexibility, i.e., its capacitance has no obvious attenuation under different bending states. Interestingly, the leakage current of the ZIHC is highly sensitive to electric fields, which shows potential application in electric field detection. This work presents a method to realize the multifunctional ZIHC with electric field sensing function for transparent and flexible wearable devices in the future.