Hybrid Transparent Conductive Electrodes Research Articles

Enhanced performance of GaN-based long-wavelength blue light-emitting diodes with graphene-ITO composite film as transparent conductive electrode

Abstract We present enhanced performance of GaN-based long-wavelength blue light emitting diodes (LEDs) with hybrid transparent conductive electrodes (TCE) made of graphene and indium tin oxide (ITO) composite. The nearly 100% transmittance TCE were gained when graphene grown by chemical-vapor-deposition was annealed with ITO on the top of it. Compared to conventional LEDs, the work voltage was reduced to 3.5 V at 5 mA forward current. The light emission power was improved about 190%. The good peformance can be attributed to the improved lateral current spreading over the composite graphene-ITO TCE before p-GaN layer injected by carriers.

Flexible, stripe-patterned organic solar cells and modules based on multilayer-printed Ag fibers for smart textile applications

Rapid advancement in the fabrication technologies of stripe/fiber-shaped optoelectronic devices has driven the performance of smart textile electronics to a new height. In the development of high-performance smart textile electronics, indium tin oxide (ITO)-free flexible transparent conductive electrodes (TCEs) are particularly desirable because they offer superior flexibility and lower manufacturing cost than the brittle ITO-based counterparts. Herein, we innovatively combine spin-coating and three-dimensional direct-ink writing (three-dimensional-DIW) techniques to develop large-area (5 × 5 cm2) PEDOT:PSS/Ag-fibers hybrid TCEs (denoted as DIW-TCEs) for application in flexible organic solar cells (OSCs). Through a multilayer printing strategy, high aspect-ratio Ag-fibers are successfully deposited on top of the planar PEDOT:PSS film. The resulting DIW-TCEs, when fully embedded in a colorless polyimide substrate, exhibit excellent electrical conductivity (sheet resistance ∼ 4 Ω/□), superior optical transmittance, and mechanical flexibility. One-dimensional stripe-patterned OSCs (stripe-OSCs) based on DIW-TCEs achieved power conversion efficiency of 9.3% and 8.2% at an active area of 0.11 cm2 and 0.31 cm2, respectively. For real-life application, a flexible power module was constructed using eight stripe-OSCs. When attached on textile, the module successfully lit up a commercial light-emitting diode upon photocharging. The unique DIW-TCE fabricated herein can be the ITO-free alternative for the production of smart textile electronics.

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.

Hybrid transparent conductive electrode structure for solar cell application

This study draws on our experiences with graphene to perform a hybrid TCO structure composed of AZO and graphene. We first set out to enhance the electrical and optical properties of AZO to enable its use especially in the field of solar cell. Hence, in our study, we deposited various thicknesses of AZO thin films on glass substrates and transferred single layer graphene on them to realize the formation of hybrid TCO structure. Among the various AZO film thicknesses, the optimum one, 300 nm, was determined and then the graphene film was added on top of the AZO film. This hybrid structure was applied to the silicon-based heterojunction solar cell with the idea of improving the cell performance. The cell performance fabricated using AZO film and AZO + graphene structure was analyzed using solar simulator. Our findings highlight the fact that the presence of graphene improved the cell efficiency by about 7%. Our research was further extended using ITO and ITO + graphene hybrid structure as TCO for silicon-based solar cell. We discovered that graphene incorporation increased the cell efficiency by almost 12% based on our results with ITO + graphene hybrid TCO structure on a similar cell.

Silver Nanowire Network Hybridized with Silver Nanoparticle-Anchored Ruthenium Oxide Nanosheets for Foldable Transparent Conductive Electrodes.

Facile strategies in flexible transparent conductive electrode materials that can sustain their electrical conductivities under 1 mm-scale radius of curvature are required for wider applications such as foldable devices. We propose a rational design as well as a fabrication process for a silver nanowire-based transparent conductive electrode with low sheet resistance and high transmittance even after prolonged cyclic bending. The electrode is fabricated on a poly(ethylene terephthalate) film through the hybridization of silver nanowires with silver nanoparticles-anchored RuO2 nanosheets. This hybridization significantly improves the performance of the silver nanowire network under severe bending strain and creates an electrically percolative structure between silver nanowires and RuO2 nanosheets in the presence of anchored silver nanoparticles on the surface of RuO2 nanosheets. The resistance change of this hybrid transparent conductive electrode is 8.8% after 200,000 bending cycles at a curvature radius of 1 mm, making it feasible for use in foldable devices.

Suppressed Interdiffusion and Degradation in Flexible and Transparent Metal Electrode-Based Perovskite Solar Cells with a Graphene Interlayer.

Metal-based transparent conductive electrodes (TCEs) are attractive candidates for application in indium tin oxide (ITO)-free solar cells due to their excellent electrical conductivity and cost effectiveness. In perovskite solar cells (PSCs), metal-induced degradation with the perovskite layer leads to various detrimental effects, deteriorating the device performance and stability. Here, we introduce a novel flexible hybrid TCE consisting of a Cu grid-embedded polyimide film and a graphene capping layer, named GCEP, which exhibits excellent mechanical and chemical stability as well as desirable optoelectrical properties. We demonstrated the critical role of graphene as a protection layer to prevent metal-induced degradation and halide diffusion between the electrode and perovskite layer; the performance of the flexible PSCs fabricated with GCEP was comparable to that of their rigid ITO-based counterparts and also exhibited outstanding mechanical and chemical stability. This work provides an effective strategy to design mechanically and chemically robust ITO-free metal-assisted TCE platforms in PSCs.

Facile preparation of flexible and highly stable graphene oxide-silver nanowire hybrid transparent conductive electrode

The flexible and highly stable graphene oxide (GO)/silver nanowires (AgNWs) hybrid transparent conductive electrode (TCE) was fabricated by coating AgNWs and GO inks on the surface of polyethylene terephthalate (PET) using a Meyer rod. The as-prepared GO/AgNWs hybrid TCE with a GO concentration of 0.75 mg·ml−1 exhibits excellent optoelectronic performances with a sheet resistance of 25 Ω·sq−1, a transmittance of 87.6% at 550 nm, and a lower surface roughness with a root mean square (RMS) roughness value of 4.86 nm. The existence of protective GO layer endows excellent thermal oxidation resistance and outperforming mechanical stabilities for GO/AgNWs hybrid TCE even at the conditions of temperature 80 °C, relative humidity (RH) 75% for 16 days, at room temperature in ambient air for 3 months, and mechanical bending of 2200 times, respectively. The GO/AgNWs hybrid TCE is a promising candidate for ITO used in optical devices such as organic light-emitting diodes (OLEDs), solar cells and flat panel displays.

Hybrid film of single-layer graphene and carbon nanotube as transparent conductive electrode for organic light emitting diode

Single layer graphene as a transparent conductive electrode (TCE) suffers from high sheet resistance, low work function, and hydrophobicity. In this work, a hybrid TCE of single-layer graphene, carbon nanotube (CNT) and gold nanoparticles (Au NP) decoration is proposed. The hybridization of graphene with CNT enhances the electrical conductivity while maintaining its high transmittance. The Au NP decorated TCE shows a sheet resistance of ∼100 Ω/sq and transmittance of 96%. The potential of TCE is demonstrated in a solution-processed yellow organic light emitting diode (OLED). By introducing a thin layer of Al-doped zinc oxide between the Au NPs and graphene-carbon nanotube networks which increases the hydrophilicity of the surface, OLED with a current efficiency of ∼2.1 cd/A and a turn-on voltage of ∼5 V is obtained suggesting that this TCE can be a viable option for OLED-anode.

Screen printed silver nanowire and graphene oxide hybrid transparent electrodes for long-term electrocardiography monitoring

Silver nanowires (AgNWs) have attracted considerable attention as the material for emerging flexible, high conductive, and transparent wearable healthcare monitoring. However, due to the high possibility of AgNWs being oxidized in air and the discomfort caused by direct contact between silver nanowires and human skin, there are still some concerns to be taken into account in the direct application of AgNWs to ECG electrodes. Here, we combined AgNWs with graphene oxide (GO), and adopted the screen-printing technology for the fabrication of AgNWs/GO hybrid transparent conductive electrodes. Using the screen-printing technology throughout the whole fabrication process gives the ability to fabricate patterned films easily, and has the advantages of simple control and low cost, which makes it superior in mass production compared to previous studies. By encapsulating the AgNW with the GO layer, the electrodes obtained exhibit excellent optical and electrical properties (transmittance of 83.5% at 550 nm and sheet resistance of 11.9 Ohm/sq). Apart from optical and electrical properties, with GO as a protective layer, the reliability, bio-friendliness and long-term stability of AgNWs/GO hybrid electrodes have been greatly improved. In addition, AgNWs/GO electrodes fabricated on PET substrate also show excellent mechanical flexibility. We anticipate that AgNWs/GO electrodes will be promising materials for the implementation of emerging portable healthcare electronics such as wearable ECG monitoring.

Silver Nanowires on Carbon Nanotube Aerogel Sheets for Flexible, Transparent Electrodes.

Flexible, free-standing transparent conducting electrodes (TCEs) with simultaneously tunable transmittances up to 98% and sheet resistances down to 11 Ω/sq were prepared by a facile spray-coating method of silver nanowires (AgNWs) onto dry-spun multiwall carbon nanotube (MWNT) aerogels. Counterintuitively, the transmittance of the hybrid electrodes can be increased as the mass density of AgNWs within the MWNT aerogels increases; however, the final achievable transmittance depends on the initial transparency of the MWNT aerogels. Simultaneously, a strong decrease in sheet resistance is obtained when AgNWs form a percolated network along the MWNT aerogel. Additionally, anisotropic reduction in sheet resistance and polarized transmittance of AgNW/MWNT aerogels is achieved with this method. The final AgNW/MWNT hybrid TCEs transmittance and sheet resistance can be fine-tuned by spray-coating mechanisms or by choosing initial MWNT aerogel density. Thus, a wide range of AgNW/MWNT hybrid TCEs with optimized optoelectronic properties can be achieved depending of the requirements needed. Finally, the free-standing AgNW/MWNT hybrid TCEs can be laminated onto a wide range of substrates without the need of a bonding aid.

Draw-spun, photonically annealed Ag fibers as alternative electrodes for flexible CIGS solar cells

ABSTRACT We explore the feasibility of Ag fiber meshes as electron transport layer for high-efficiency flexible Cu(In,Ga)Se2 (CIGS) solar cells. Woven meshes of Ag fibers after UV illumination and millisecond flash-lamp treatment results in a sheet resistance of 17 Ω/sq and a visible transmittance above 85%. Conductive Ag meshes are integrated into flexible CIGS cells as transparent conductive electrode (TCE) alone or together with layers of Al-doped ZnO (AZO) with various thickness of 0…900 nm. The Ag mesh alone is not able to function as a current collector. If used together with a thin AZO layer (50 nm), the Ag mesh markedly improves the fill factor and cell efficiency, in spite of the adverse mesh shadowing. When Ag mesh is combined with thicker (200 nm or 900 nm) AZO layers, no improvements in photovoltaic parameters are obtained. When comparing a hybrid TCE consisting of 50 nm AZO and Ag fiber mesh with a thick 900 nm reference AZO device, an improved charge carrier collection in the near-infrared range is observed. Regardless of the AZO thickness, the presence of Ag mesh slows down cell degradation upon mechanical tensile stress, which could be interesting for implementation into flexible thin film CIGS modules.

High-Performance Bendable Organic Solar Cells With Silver Nanowire-Graphene Hybrid Electrode

We comprehensively studied the electrical, optical, and mechanical properties, and stability of the hybrid transparent conductive electrode (TCE) prepared by transferring graphene onto random silver nanowires (AgNW) on poly(ethylene terephthalate) (PET) substrates. Compared with the pristine AgNW TCE, the AgNW-graphene hybrid TCE was found to exhibit lower surface roughness, better optical and electrical properties, and excellent long-term stability and flexibility. The power conversion efficiency of the inverted organic solar cells (OSCs) with PTB7:PC71BM as the active material built on the PET/AgNW-graphene TCE is 6.47%, which is 8% higher than the OSCs built on AgNW TCE, and much better than the OSC with conventional ITO. Moreover, the flexible OSCs built on the PET/AgNW-graphene exhibit excellent properties under curved conditions, which suggest that it is promising for applications to uneven surfaces.

Highly Transparent Conductive Reduced Graphene Oxide/Silver Nanowires/Silver Grid Electrodes for Low-Voltage Electrochromic Smart Windows.

Transparent conductive electrodes (TCEs) based on hybrid structures (silver nanowires) have been compressively reconnoitered in next-generation electronics such as flexible displays, artificial skins, smart windows, and sensors because of their admirable conductivity as well as flexibility, which make them favorable substitutes to replace ITO (indium tin oxide) as a transparent conductor. Nevertheless, silver-based TCEs grieve from poor stability because of the corrosion and oxidation of silver in electrolytes. To overcome these issues, a RGO (reduced graphene oxide) layer on silver was promoted to resolve the difficulties of corrosion and oxidation in the electrolyte. Moreover, we successfully designed and demonstrated low-voltage WO3-based electrochromic devices (ECDs) with fabricated hybrid TCEs. The hybrid electrodes with RGO/silver nanowires/metal grid/PET (RAM) electrode exhibited improvements in the switching stability and optoelectronic properties, such as the sheet resistance (0.714 ohm/sq) as well as optical transparency of 90.9%. The coloration and bleaching behavior of the ECD was observed in an applied low-voltage range of -1.0 to 0.0 V with a maximum optical difference of 72% at 700 nm, which yielded a coloration efficiency (η) of ∼33.4 cm2/C. The highly conductive hybrid TCEs exhibit favorable features for numerous embryonic flexible electronics and optoelectronic devices.

Low diffuse reflection of silver nanowire/ruthenium oxide nanosheet hybrid films for high-performance transparent flexible electrodes

Transparent conducting electrodes (TCEs) based on silver nanowire (AgNW) networks possess high conductance, transmittance, and mechanical flexibility. However, due to the relatively high diffuse reflection of incident light on AgNWs, they cannot be practically implemented in displays requiring low pattern visibility. One promising strategy for solving this problem is to place an optical stack with high refractive index underneath the AgNW layer. In this work, AgNW-RuO2 nanosheet hybrid TCEs with low diffuse reflections are fabricated using metallic RuO2 nanosheets as undercoats. As predicted by theoretical simulations, RuO2 nanosheets with high refractive indices reduce the diffuse reflections of AgNWs by almost 8%. Moreover, after the partial etching of AgNWs, the difference in the diffuse reflections of their etched and non-etched regions becomes equal to about 0.003, leading to the formation of an invisible pattern. The film consisting of micro-sized RuO2 nanosheets is not damaged during etching, but instead forms a current path between different AgNWs broken by cyclic bending, resulting in a tenfold decrease in the resistance of the AgNW TCE after 170 000 cycles. Further, RuO2 nanosheets suppress the diffusion of humid air from the outside, thus improving the environmental stability of the AgNW-RuO2 nanosheet hybrid TCEs.

Low Temperature Fabrication of Transparent Conductive Electrode With High Ultraviolet Transmittance Down to Wavelength of 250 nm

Indium tin oxide (ITO) is a broadly deployed transparent conductive electrode (TCE) with various applications in solar energy harvesting and optoelectronics. However, the low transmittance of ITO in the ultraviolet range has motivated researchers to opt for alternative materials as TCE. In this paper, the fabrication of a hybrid TCE made up of silver nanowire (AgNW) and peroxo‐constructed amorphous strontium stannate (pcaSS) is reported, employing facile spin coating solution‐processed method at 150 °C. The fabricated TCE demonstrated low sheet resistance of 32.8 Ω sq−1 and high transmittance of 88.2% at 550 nm. Furthermore, benefitting from the ultra‐high band gap of as‐synthesized pcaSS (4.5 eV), this TCE maintained its high transmittance (above 80%) inside ultraviolet range down to wavelength of 250 nm. This research contributes to the fabrication of more efficient solar energy and ultraviolet optoelectronic devices.

A novel design of hybrid transparent electrodes for high performance and ultra-flexible bifunctional electrochromic-supercapacitors

In this study, a simple and cost-effective method of fabricating hybrid transparent conductive electrodes (TCEs) based on embedded silver nanowires (Ag NWs)/PEDOT: PSS was developed with the addition of low-temperature synthesis of Ni(OH)2 and polyethylenimine ethoxylated (PEIE) composites as a novel interlayer. The hybrid TCEs with a Ni(OH)2-PEIE interlayer exhibit remarkable volumetric capacitance of 443 F cm−3 with transparency of 86%, which is one of the highest values reported to date in the transparent supercapacitor. The fabricated bifunctional solid-state electrochromic-supercapacitor device with a transparency of 80% shows stable cyclic stability up to 10,000 charge/discharge cycles, extremely high coloration efficiency of 517 cm2 C−1 at 633 nm, and a fast switching speed (<0.6 s). The noted improvement is mainly caused by the Ni(OH)2-PEIE interlayer influence the pore density of PEDOT: PSS which provides high surface area, thus resulting in efficient charge transfer pathways and fast ion diffusion. Moreover, a capacitance retention of 90% is achieved even after 8000 bending cycles at a bending radius of 1 mm and 15 times of crumpling is tolerated without noticeable degradation, implying excellent mechanical robustness and flexibility. The results present the significant potential of transparent hybrid electrodes for efficient energy storage and electrochromicity with stable transmittance changes, even during fast charge/discharge processes, demonstrating their potential as smart wearable energy storage devices.

Transient Thermal Response of Hotspots in Graphene–Silver Nanowire Hybrid Transparent Conducting Electrodes

Graphene-nanowire hybrid films have recently shown excellent performance as transparent conducting electrodes. However, due to their fundamental nonhomogeneity (grain boundaries, nanowire–nanowire junctions), self-heating induces hotspots along the co-percolating electrical conduction pathways. Although the steady-state characteristics of the hotspot temperature and location have been reported, the temporal response of the hotspots has not been studied in detail. In this paper, we use transient thermoreflectance imaging with high temporal resolution to quantify the transient characteristics of the hotspots. At local hotspots as well as nearby intermediate temperature regions, the temperature response in both heating and cooling phases exhibits two distinct time constants. We quantitatively determine the thermal time constants and associated amplitudes and show dependence of these parameters on distance from the contact. Based on solutions to heat diffusion equations, the short-time constant is attributed to the local self-heating within the hotspot region, and the long-time constant to diffusion of heat through the channel region. The knowledge of time evolution of hotspots and hence a more detailed understanding of the electrothermal conduction process through co-percolating networks could enable more reliable, advanced transparent conductors as well as one-dimensional/two-dimensional hybrid materials for other applications.

Hybrid Oblique-Angle Deposited ITO/Silver Nanowire Transparent Conductive Electrodes for Brighter Light Emitters

In this paper, hybrid transparent conductive electrodes (TCEs) consisting of oblique-angle deposited indium tin oxide (OAD ITO) and silver nanowires (Ag NWs) were developed forGaN-based light-emitting diodes (LEDs). The 100-nm thick OAD ITO acted as an Ohmic contact to p-GaN with negligible light absorption having optical transmittance as high as approximately 99% at 450 nm, and Ag NWs acted as a favorable current spreader with sheet resistance as low as $19.9~\Omega $ /sq. Consequently, the hybrid TCEs consisting of OAD ITO and Ag NWs yielded an optical transmittance of 93% at 450 nm, a sheet resistance of 18.9 $\Omega $ /sq, and a specific contact resistance of ${2.1} \times {10}^{-2} \Omega \cdot $ cm2. LEDs fabricated with hybrid TCEs demonstrated improved electrical properties and greater optical output powers than the reference LEDs. This was due to the combined effects of the improved optical transparency, the enhanced current spreading, and the surface roughening effect.

Silver nanowire–graphene hybrid transparent conductive electrodes for highly efficient inverted organic solar cells

Silver nanowires (AgNWs) and graphene are both promising candidates as a transparent conductive electrode (TCE) to replace expensive and fragile indium tin oxide (ITO) TCE. A synergistically optimized performance is expected when the advantages of AgNWs and graphene are combined. In this paper, the AgNW–graphene hybrid electrode is constructed by depositing a graphene layer on top of the network of AgNWs. Compared with the pristine AgNWs electrode, the AgNW–graphene TCE exhibits reduced sheet resistance, lower surface roughness, excellent long-term stability, and corrosion resistance in corrosive liquids. The graphene layer covering the AgNWs provides additional conduction pathways for electron transport and collection by the electrode. Benefiting from these advantages of the hybrid electrodes, we achieve a power conversion efficiency of 8.12% of inverted organic solar cells using PTB7:PC71BM as the active layer, which is compared to that of the solar cells based on standard ITO TCE but about 10% higher than that based on AgNWs TCE.

P-160: Silver Nanowire-Transparent Conducting Oxide-Conducting Polymer Hybrids for Flexible and Transparent Conductive Electrodes for Organic Light Emitting Dodes

We investigated various properties of AgNW-transparent conductive oxide (TCO)-conducting polymer (CP) hybrid electrodes for the application in flexible organic light emitting diodes (OLEDs). The hybrid transparent conductive electrodes (TCEs) fabricated on plastic substrates consists of AgNW networks, Indium zinc oxide (TCO) and CP that is deposited on top of the AgNW.