Reverse‐Offset Printed Ultrathin Ag Mesh for Robust Conformal Transparent Electrodes for High‐Performance Organic Photovoltaics

Mechanically durable transparent electrodes are needed in flexible optoelectronic devices to realize their long‐term stable functioning, for applications in various fields such as energy, healthcare, and soft robotics. Several promising transparent electrodes based on nanomaterials have been previously reported to replace the conventional and fragile indium‐tin oxide (ITO); however, obtaining feasible printed transparent electrodes for ultraflexible devices with a multistack structure is still a great challenge. Here, a printed ultrathin (uniform thickness of 100 nm) Ag mesh transparent electrode is demonstrated, simultaneously achieving high conductance, high transparency, and good mechanical properties. It shows a 17 Ω sq^?1 sheet resistance (R_sh) with 93.2% transmittance, which surpasses the performance of sputtered ITO electrodes and other ultrathin Ag mesh transparent electrodes. The conductance is stable after 500 cycles of 100% stretch/release deformation, with an insignificant increase (10.6%) in R_sh by adopting a buckling structure. Furthermore, organic photovoltaics (OPVs) using our Ag mesh transparent electrodes achieve a power conversion efficiency of 8.3%, which is comparable to the performance of ITO‐based OPVs.     

Pressure Welding of Silver Nanowires Networks at Room Temperature as Transparent Electrodes for Efficient Organic Light‐Emitting Diodes

In this work, polymethylmethacrylate (PMMA) as a superior mediate for the pressure welding of silver nanowires (Ag NWs) networks as transparent electrodes without any thermal treatment is demonstrated. After a pressing of 200 kg cm^?2, not only the sheet resistance but also the surface roughness of the PMMA‐mediated Ag NWs networks decreases from 2.6 kΩ sq^?1 to 34.3 Ω sq^?1 and from 76.1 to 12.6 nm, respectively. On the other hand, high transparency of an average transmittance in the visible wavelengths of 93.5% together with a low haze value of 2.58% can be achieved. In terms of optoelectronic applications, the promising potential of the PMMA‐mediated pressure‐welded Ag NWs networks used as a transparent electrode in a green organic light‐emitting diode (OLED) device is also demonstrated. In comparison with the OLED based on commercial tin‐doped indium oxide electrode, the increments of power efficiency and external quantum efficiency (EQE) from 80.1 to 85.9 lm w^?1 and 19.2% to 19.9% are demonstrated. In addition, the PMMA‐mediated pressure welding succeeds in transferring Ag NWs networks to flexible polyethylene naphthalate and polyimide substrates with the sheet resistance of 42 and 91 Ω sq^?1 after 10 000 times of bending, respectively.     

Transparent conductive film having sandwich structure of gallium-indium-oxide/silver/gallium-indium-oxide

New transparent conductive films having the sandwich structure of gallium-indium-oxide/silver/gallium-indium-oxide (GIO/Ag/GIO) were prepared by conventional magnetron sputtering method at ambient substrate temperature. The electrical and optical properties of the films were compared with those of conventional indium-tin-oxide (ITO) films and ITO/Ag/ITO sandwich films. The GIO/Ag/GIO (40 nm/8 nm/40 nm) sandwich films, in which the GIO film was deposited using a GIO ceramic target with In content [In/(Ga + In)] of 10 at.%, exhibited a low sheet resistance of 11.3 Ω/sq and a large average transmittance of over 92.9% in the visible region (400-800 nm). This GIO/Ag/GIO films also exhibited a novel characteristic of transparency in the ultraviolet region; they showed high transmittance of 82.2% at the wavelength of 330 nm and 40.8% at the wavelength of 280 nm, which was not shown in the ITO films and the ITO/Ag/ITO sandwich films. The GIO/Ag/GIO sandwich films are useful as transparent electrode for emitting devices of ultraviolet radiation because of both their high conductivity and high transparency in the ultraviolet region.     

Improved electrical and optical properties of ITO/Ag/ITO films by using electron beam irradiation and their application to ultraviolet light-emitting diode as highly transparent p-type electrodes

We have investigated the effect of insertion of a Ag layer in ITO film as well as electron beam irradiation to the multilayer films on the electrical and optical properties of the ITO-based multilayer deposited by magnetron sputtering method at room temperature. Inserting a very thin Ag layer between ITO layers resulted in a significant decrease in sheet resistance and increased the optical band gap of the ITO/Ag/ITO multilayer to 4.35 eV, followed by a high transparency of approximately 80% at a wavelength of 375 nm. We have also fabricated ultraviolet light-emitting diodes (LED) by using the ITO/Ag/ITO p-type electrode with/without electron beam irradiation. The results show that the UV-LEDs having ITO/Ag/ITO p-electrode with electron beam irradiation produced 19% higher optical output power due to the low absorption of light in the p-type electrode.     

Solution-processed flexible polymer solar cells with silver nanowire electrodes

The conventional anode for organic photovoltaics (OPVs), indium tin oxide (ITO), is expensive and brittle, and thus is not suitable for use in roll-to-roll manufacturing of OPVs. In this study, fully solution-processed polymer bulk heterojunction (BHJ) solar cells with anodes made from silver nanowires (Ag NWs) have been successfully fabricated with a configuration of Ag NWs/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/polymer:phenyl-C(61)-butyric acid methyl ester (PCBM)/Ca/Al. Efficiencies of 2.8 and 2.5% are obtained for devices with Ag NW network on glass and on poly(ethylene terephthalate) (PET), respectively. The efficiency of the devices is limited by the low work function of the Ag NWs/PEDOT:PSS film and the non-ideal ohmic contact between the Ag NW anode and the active layer. Compared with devices based on the ITO anode, the open-circuit voltage (V(oc)) of solar cells based on the Ag NW anode is lower by ~0.3 V. More importantly, highly flexible BHJ solar cells have been firstly fabricated on Ag NWs/PET anode with recoverable efficiency of 2.5% under large deformation up to 120°. This study indicates that, with improved engineering of the nanowires/polymer interface, Ag NW electrodes can serve as a low-cost, flexible alternative to ITO, and thereby improve the economic viability and mechanical stability of OPVs.     

Electrochromic modulation of near-infrared light by WO<Subscript>3</Subscript> films deposited on silver nanowire substrates

Silver nanowire (Ag NW) transparent conductive electrodes with high conductivity and optical transmittance are fabricated. Then, WO₃ films are deposited on Ag NW electrodes by an electrochemical deposition method. The WO₃/Ag NW films act as obvious optical modulators in the visible region. More importantly, the WO₃/Ag NW films have distinct advantage on NIR modulation over conventional WO₃/ITO electrode. Meanwhile, the WO₃/Ag NW films own high electrochromic efficiency of 86.9 cm² C^?1 at NIR region of 1100 nm. Furthermore, electrochromic devices (ECDs) based on Ag NW substrates are fabricated in this study, which exhibit excellent cycling stability and distinct modulation of near-infrared light compared with ITO-based ECDs. This work is the first study that reports the application of Ag NW-based electrochromic films and electrochromic devices in modulation of NIR light. It exhibits bright prospects that the electrochromic materials deposited on Ag NW electrodes may find potential application in thermal control and emission detectors for spacecraft.     

Transparent organic bistable memory devices using a low resistance transparent electrode

Pure polymer-based transparent organic bistable memory devices (TOBDs) were developed using transparent WO₃/Ag/WO₃(WAW) as a low resistance electrode. A device structure of indium tin oxide/polyphenylenevinylene/Al/WAW was used for the fabrication of TOBDs. PPV, as an active organic material without metal nanoparticles, was spin coated on a WAW electrode, which was followed by the deposition of an Al/WAW layer on PPV for bistability in PPV OBDs. PPV based transparent OBDs showed a high transparency and on/off ratio of 53% and 1000, respectively.     

Influence of Ag thickness on electrical, optical and structural properties of nanocrystalline MoO3/Ag/ITO multilayer for optoelectronic applications

In this study, MoO₃/Ag/ITO/glass (MAI) nano-multilayer films were deposited by the thermal evaporation technique and then were annealed in air atmosphere at 200 °C for 1 h. The effects of Ag layer thickness on electrical, optical and structural properties of the MoO₃(45 nm)/Ag(5-20 nm)/ITO(45 nm)/glass nano-multilayer films were investigated. The sheet resistance decreased rapidly with increasing Ag thickness. Above a thickness of 10 nm, the sheet resistances became somewhat saturated to a value of 3(Ω/□). The highest transparency over the visible wavelength region of spectrum (85%) was obtained for 10 nm Ag layer thickness. Carrier mobility, carrier concentrations, transmittance and reflectance of the layers were measured. The allowed direct band-gap for an Ag thickness range 5-20 nm was estimated to be in the range 3.58-3.71 eV. The XRD pattern showed that the films were polycrystalline. X-ray diffraction has shown that Ag layer has a (111) predominant orientation when deposited. The figure of merit was calculated for MAI multilayer films. It has been found that the Ag layer thickness is a very important factor in controlling the electrical and optical properties of MAI multilayer films. The optimum thickness of the Ag layer for these films was determined. The results exhibit that the MAI transparent electrode is a good structure for use as the anode of optoelectronic devices.     

One step synthesis of silver nanowires used in preparation of conductive silver paste

For mass preparation of conductive silver paste, a convenient approach to synthesize silver nanowires (Ag NWs) is presented. Monodisperse Ag NWs with ca. 40 nm in diameter and over 10 μm in length were successfully obtained in high yield only by heating a mixture of AgNO₃, poly(vinyl pyrrolidone), ethylene glycol and HCl prepared previously. This method not only simplifies the conventional polyol process but also extremely improves its repeatability. More important, the patterns fabricated with the Ag NWs naturally have a high conductivity, up to ca. 13 % of bulk silver, due to the cross-linked network structure formed by accumulation of nanowires. The conductivity even can be improved to 41 % of bulk silver conductivity through a chemical sintering at room temperature, which makes us believe that the Ag NWs could be broadly applied in preparation of conductive paste.     

Improving efficiency of organic light-emitting diodes fabricated utilizing AZO/Ag/AZO multilayer electrode

Multilayer transparent electrode based on Al-doped zinc oxide (AZO)/Ag/Al-doped zinc oxide (AZO) was fabricated by sputtering, and a green organic light-emitting diode (OLED) device utilizing AZO/Ag/AZO as anode was fabricated. The AZO/Ag/AZO multilayer film exhibited superior square resistance and optical transmittance to those of commercial indium tin oxide (ITO). In comparison with the green OLEDs based on ITO and pure AZO anode, the green OLED based on AZO/Ag/AZO showed the highest light-emitting efficiency. The results indicate that AZO/Ag/AZO multilayer electrodes are a promising low-cost, low-toxic and low-temperature processing electrode scheme for OLED application.     

电极材料对聚合物太阳能电池光学性能的影响

利用基于传输矩阵法(Transfer matrix method,TMM)的光学模型系统地研究了金属电极材料(Ag、Al、Au)对聚合物太阳能电池光学性能的影响.研究表明,与传统铟锡化合物(Indium tin oxide,ITO)透明电极相比,以合适厚度的金属Ag膜作透明电极,可提高活性层对入射光子的吸收效率;同时,以Ag膜作背电极时,其相应的聚合物太阳能电池的效率优于以Al或者Au为背电极的电池的效率.     

Selective, electrochemically activated biofunctionalization of In2O3 nanowires using an air-stable surface modifier

Selective electrochemically activated biofunctionalization of In(2)O(3) nanowires (NWs) has been achieved, using monolayer coatings of p-dimethoxybenzene derivatives. Monolayer coatings of 4-(2,5-dimethoxyphenyl)butyl-phosphonic acid (DMP-PA) were deposited on planar indium-tin oxide (ITO) electrodes and In(2)O(3) NWs. The electrochemical behavior of the monolayer coating was first studied using ITO electrodes, as a model system for In(2)O(3) nanowires. When a potential of 950 mV vs a Ag/AgCl reference electrode is applied to an ITO electrode coated with DMP-PA in PBS buffer, the p-dimethoxyphenyl groups are converted to p-benzoquinone (BQ). The electrochemically formed benzoquinone groups react readily with alkyl thiol groups via a Michael addition. The reaction strategy optimized on ITO was applied to an In(2)O(3) NW mat sample coated with DMP-PA. Applying a potential of 950 mV to metal electrodes deposited on NWs converts the DMP-PA NW coating to BQ-PA, which reacts with a thiol-terminated 20-base oligonucleotide. These NWs showed strong fluorescence response after paring with the dye labeled compliment, demonstrating that the probe was bound to the NW surface and that it remained active toward hybridization with its compliment. The unactivated DMP-PA coated NWs showed no response, demonstrating the selective electrochemical functionalization of NWs and the potential of using them in multiplex sensing. We also compared the p-dimethoxybenzene derivative to the conventional hydroquinone analog. The results show that the former can largely enhance the selectivity during the functionalization of both ITO and In(2)O(3) NWs.     

Influence of ITO patterning on reliability of organic light emitting devices

Indium tin oxide (ITO) films are widely used for a transparent electrode of organic light emitting devices (OLEDs) because of its excellent conductivity and transparency. Two types of ITO substrates with different surface roughness were selected to use as anode of OLEDs. In addition, two types of etching process of ITO substrate, particularly the etching time, were also carried out. It was found that the surface roughness and/or the etching process of ITO substrate strongly influenced on an edge of ITO surface, further affected the operating characteristics and reliability of devices.     

Effects of silver nanowire concentration and annealing temperature on the optoelectronic properties of hybrid transparent electrodes

In this study, Ag nanowire (AgNW) was used to fabricate ITO/AgNW/ITO (IAI) and ZnO/AgNW/ZnO (ZAZ) hybrid transparent electrodes. The covered area ratio of AgNW showed that when AgNW concentration n _AgNW ≥ 2.0 mg/mL, AgNW easily agglomerated during the spin-coating. Meanwhile, Haacke index and haziness measurements also indicated that for application with high optical demands, the AgNW concentration should be ≤2.0 mg/mL for both ZnO or ITO systems. In this study, when n _AgNW = 2.0 mg/mL, the sheet resistant of ZAZ electrodes was 10.5 Ω/sq while the transmittance (including glass) was 72.7% in the visible region. For IAI electrodes, the sheet resistant was 18.8 Ω/sq and transmittance (including glass) was 78.2% in the visible region. Further analysis implied that the sheet resistance of hybrid electrodes could be as low as 10 Ω/sq by optimizing AgNW distribution as well as using suitable annealing techniques.     

Large scale, highly conductive and patterned transparent films of silver nanowires on arbitrary substrates and their application in touch screens

The application of silver nanowire films as transparent conductive electrodes has shown promising results recently. In this paper, we demonstrate the application of a simple spray coating technique to obtain large scale, highly uniform and conductive silver nanowire films on arbitrary substrates. We also integrated a polydimethylsiloxane (PDMS)-assisted contact transfer technique with spray coating, which allowed us to obtain large scale high quality patterned films of silver nanowires. The transparency and conductivity of the films was controlled by the volume of the dispersion used in spraying and the substrate area. We note that the optoelectrical property, σ(DC)/σ(Op), for various films fabricated was in the range 75-350, which is extremely high for transparent thin film compared to other candidate alternatives to doped metal oxide film. Using this method, we obtain silver nanowire films on a flexible polyethylene terephthalate (PET) substrate with a transparency of 85% and sheet resistance of 33 Ω/sq, which is comparable to that of tin-doped indium oxide (ITO) on flexible substrates. In-depth analysis of the film shows a high performance using another commonly used figure-of-merit, Φ(TE). Also, Ag nanowire film/PET shows good mechanical flexibility and the application of such a conductive silver nanowire film as an electrode in a touch panel has been demonstrated.     

Uniform,highly conductive,and patterned transparent films of a percolating silver nanowire network on rigid and flexible substrates using a dry transfer technique

Silver nanowire films are promising alternatives to tin-doped indium oxide (ITO) films as transparent conductive electrodes. In this paper, we report the use of vacuum filtration and a polydimethylsiloxane (PDMS)-assisted transfer printing technique to fabricate silver nanowire films on both rigid and flexible substrates, bringing advantages such as the capability of patterned transfer, the best performance among various ITO alternatives (10 Ω/sq at 85% transparency), and good adhesion to the underlying substrate, thus eliminating the previously reported adhesion problem. In addition, our method also allows the preparation of high quality patterned films of silver nanowires with different line widths and shapes in a matter of few minutes, making it a scalable process. Furthermore, use of an anodized aluminum oxide (AAO) membrane in the transfer process allows annealing of nanowire films at moderately high temperature to obtain films with extremely high conductivity and good transparency. Using this transfer technique, we obtained silver nanowire films on a flexible polyethylene terephthalate (PET) substrate with a transparency of 85%, a sheet resistance of 10 Ω/sq, with good mechanical flexibility. Detailed analysis revealed that the Ag nanowire network exhibits two-dimensional percolation behavior with good agreement between experimentally observed and theoretically predicted values of critical volume.      

Spin coated graphene films as the transparent electrode in organic photovoltaic devices

Many research efforts have been devoted to the replacement of the traditional indium-tin-oxide (ITO) electrode in organic photovoltaics. Solution-based graphene has been identified as a potential replacement, since it has less than two percent absorption per layer, relative high carrier mobility, and it offers the possibility of deposition on large area and flexible substrates, compatible with roll to roll manufacturing methods. In this work, soluble reduced graphene films with high electrical conductivity and transparency were fabricated and incorporated in poly(3-hexylthiophene) [6,6]-phenyl-C₆₁-butyric acid methyl ester photovoltaic devices, as the transparent electrode. The graphene films were spin coated on glass from an aqueous dispersion of functionalized graphene, followed by a reduction process combining hydrazine vapor and annealing under argon, in order to reduce the sheet resistance. The photovoltaic devices obtained from the graphene films showed lower performance than the reference devices with ITO, due to the higher sheet resistance (2 kΩ/sq) and the poor hydrophilicity of the spin coated graphene films.     

Translucent Photodetector with Blended Nanowires–Metal Oxide Transparent Selective Electrode Utilizing Photovoltaic and Pyro‐Phototronic Coupling Effect

ZnO is a potential candidate for photodetection utilizing the pyroelectric effect. Here, a self‐biased and translucent photodetector with the configuration of Cu₄O₃/ZnO/FTO/Glass is designed and fabricated. In addition, the pyroelectric effect is effectively harvested using indium tin oxide (ITO), silver nanowires (AgNWs), and a blend of AgNWs‐coated ITO as the transparent selective contact electrode. The improved rise times are observed from 1400 µs (bare condition; without the selective electrode) to 69, 60, 7 µs, and fall times from 720 µs (bare condition) to 80, 70, 10 µs for corresponding ITO, AgNWs, and AgNWs‐coated ITO contact electrodes, respectively. Similarly, the responsivity and detectivity are enhanced by about 4.39 × 10⁷ and 5.27 × 10⁵%, respectively. An energy band diagram is proposed to explain the underlying working mechanism based on the workfunction of the ITO (4.7 eV) and AgNWs (4.57 eV) as measured by Kelvin probe force microscopy, which confirms the formation of type‐II band alignment resulting in the efficient transport of photogenerated charge carriers. The functional use of the transparent selective contact electrode can effectively harness the pyro‐phototronic effect for next‐generation transparent and flexible optoelectronic applications.     

Evaluation of metal/indium-tin-oxide for transparent low-resistance contacts to p-type GaN

In search of a better transparent contact to p-GaN, we analyze various metal/indium-tin-oxide (ITO) (Ag/ITO, AgCu/ITO, Ni/ITO, and NiZn/ITO) contact schemes and compare to Ni/Au, NiZn/Ag, and ITO. The metal layer boosts conductivity while the ITO thickness can be adjusted to constructive transmission interference on GaN that exceeds extraction from bare GaN. We find a best compromise for an Ag/ITO (3 nm/67 nm) ohmic contact with a relative transmittance of 97% of the bare GaN near 530?nm and a specific contact resistance of 0.03 Ω·cm². The contact proves suitable for green light-emitting diodes in epi-up geometry.     

Ag@Ni Core–Shell Nanowire Network for Robust Transparent Electrodes Against Oxidation and Sulfurization

Silver nanowire (Ag NW) based transparent electrodes are inherently unstable to moist and chemically reactive environment. A remarkable stability improvement of the Ag NW network film against oxidizing and sulfurizing environment by local electrodeposition of Ni along Ag NWs is reported. The optical transmittance and electrical resistance of the Ni deposited Ag NW network film can be easily controlled by adjusting the morphology and thickness of the Ni shell layer. The electrical conductivity of the Ag NW network film is increased by the Ni coating via welding between Ag NWs as well as additional conductive area for the electron transport by electrodeposited Ni layer. Moreover, the chemical resistance of Ag NWs against oxidation and sulfurization can be dramatically enhanced by the Ni shell layer electrodeposited along the Ag NWs, which provides the physical barrier against chemical reaction and diffusion as well as the cathodic protection from galvanic corrosion.