A dual-scale metal nanowire network transparent conductor for highly efficient and flexible organic light emitting diodes

Adv Materials Technologies

Xiao

Rao

et al. 2018

deposition temperature (≈300 °C) limit their applications in large-area/flexible/ curved optoelectronic devices. Therefore, several candidates, including carbon nanotubes, [4,10] graphene, [11,12] conductive polymers, [13,14] and metal-network electrodes (MNEs) [15,16] were investigated to replace ITO films. Due to the relatively low electrical conductivity of large-scale graphene and high contact resistance of carbon nanotubes, the applications of these carbon-based nanomaterials are highly limited. And further on the poor conductivity and instability of conducting polymers, MNEs are a strong candidate due to their superior electrical and optical performance. [17][18][19] The solution-processed metal nanowires such as Ag NWs [20,21] and Cu NWs [22][23][24] are excellent materials to structure high-property electrodes by a coating process. [25] However, the contact resistance at the nanogap junctions between these nanowires results in much lower conductivity compared to the evaporated metal electrodes. Moreover, the poor adhesion [26] and protrusions [27] limit the applications of these solution-processed electrodes. The continuous metal nanowires could be fabricated by the using of a electrospun nonwoven masks [28][29][30][31][32] before the metal evaporation process and avoids the influence of contact resistance. But the disorderly arrangement of metal nanowires makes the inhomogeneity of film conductivity and results in the inferior quality of electrodes. Screen printing or inkjet printing can construct and arrange metal nanowires networks by using the metal precursor solution [33,34] or metal nanoparticle pastes, [35][36][37] but usually requiring a high temperature annealing (>200 °C) process. The high temperature heavily limits the selection of polymeric/elastomeric substrates. Therefore, in addition to transparency and resistance, low preparation temperature is very important in flexible MNEs.In this work, we reported highly transparent, ultrathin/ curved MNEs fabricated by programmable electrohydrodynamic (EHD) lithography, which directly generates high-resolution pattern of photoresist on ultrathin and curved substrates. The EHD lithography technique is a simple, data-driven, and inexpensive process, avoiding exposure or development process of conventional photolithography. [38] Moreover, it does not require high-temperature heat treatment and complicated transferring, Metal-network electrodes (MNEs) are excellent substitutes to the brittle and expensive indium tin oxide (ITO) films for flexible and transparent electronic devices. For a high transmittance and low resistivity, highly ordered metal wire arrays with suitable gap and width are essential. Here, high-orderly and dimension-controllable ultrathin/conformal MNEs are fabricated on µm thick/curved substrate via programmable electrohydrodynamic (EHD) lithography. By employing EHD direct-writing, large-scale high-resolution photoresist micro/nano-pattern can be digitally printed on ultrathin/curved substrates, as the digital mask in chemical etching ...

Section: Introductionmentioning

confidence: 99%

High‐Performance, Micrometer Thick/Conformal, Transparent Metal‐Network Electrodes for Flexible and Curved Electronic Devices

Adv Materials Technologies

Xiao

Rao

et al. 2018

“…Metal nanowire network electrode, particular silver nanowires (AgNWs) as a solution processable material have been developed for FOLEDs because of their superior optical, electrical, and mechanical properties . Excellent sheet resistance and transparency can be obtained via the use of high aspect ratio AgNWs.…”

Section: Fundamental Elements Of Foledsmentioning

confidence: 99%

“…Moreover, the surface morphology also could be improved due to without high temperature fused junctions which are adverse to obtain a smooth surface. Also, Lee et al reported a film with dual‐scale AgNWs percolation networks, which showed superior electrical and optical characteristics to demonstrate a high efficiency FOLED ( Figure ) . The secondary AgNWs networks can be formed on the voids between longer AgNWs percolation networks and fill the large fluctuation of longer AgNWs networks.…”

Section: Efficiency Improvement Of Flexible Organic Light‐emitting Dementioning

confidence: 99%

See 1 more Smart Citation

Recent Developments in Flexible Organic Light‐Emitting Devices

Adv Materials Technologies

Feng

et al. 2018

116

wearable displays, and conceptual lighting panels. In addition, besides the excellent designs, a flexible OLED (FOLED) [7, has several other advantages, the displays and lighting panels are thinner, lighter, more cost effective, shatterproof, and durable compared to glass or silicon based OLEDs. They are impact resistance and less prone to break than glass. At present, both flexible displays and lighting panels are being mass produced (Samsung and LG on displays, LG and Konica Minolta on lighting). FOLEDs are becoming most promising and popular next-generation display technology in consumer electronics and lighting panels.In order to develop the FOLEDs and realize their practical application, many great efforts have been conducted. The key components of the FOLEDs are flexible substrate, bottom and top electrode, organic functional layers, encapsulation layer, and optional light extraction layers. Differed from conventional OLEDs on rigid glass or silicon substrate, FOLEDs are fabricated on flexible substrates. Up to now, metal foil, flexible glass, and plastic film have been commonly used as flexible substrates for FOLEDs. On the other hand, actual fabric materials, natural silk fibroin films, bacterial cellulose, and rubbery poly (urethane acrylate) have also been developed to achieve the requirements of wearable and stretchable displays. The electrode is also very important for FOLEDs. Compared with the top electrode, more research has been conducted on the bottom electrode because its surface roughness, conductivity, and transmittance for bottom emitting OLEDs play a key role in the performance of FOLEDs. As conventional indiumtin-oxide (ITO) is not suitable for flexible devices as it is brittle, many great alternatives such as thin metal film, conducting polymer, dielectric-metal-dielectric (DMD) multilayers, metal nanowires, graphene, carbon nanotubes (CNTs), and their compound have been studied. It should be mentioned that the performance of organic layers has almost no difference with rigid OLEDs because of their inherent excellent ductility and identical working mechanism. Moreover, for practical and commercial applications, stability and efficiency are two factors of crucial importance. As a consequence, the encapsulation technique and light extraction of FOLEDs are also two research hotspots in recent years. This review will summarize the key components, discuss the method of implementation, highlight the recent research progresses, and conclude the challenges and prospects of FOLEDs. demand for display technology in consumer electronics and lighting panels increases, thin, light, high-quality, and more cost-effective light-emitting devices are required. Organic light-emitting devices (OLEDs), satisfying the criteria exactly, have been considered the most promising next-generation display and lighting technique. In particular, an OLED based on flexible substrate enables the device to be applied to curved displays, electronic newspapers, wearable displays, and conceptual lighting panels, has been alwa...

“…Meanwhile, silver nanowire (AgNW) electrodes with high electrical conductivity, good optical transparency, high mechanical flexibility, and low cost have been widely used to replace indium tin oxide (ITO) electrodes in OLED devices . By controlling the aspect ratio of AgNWs and applying postprocessing treatments, the AgNW electrodes can simultaneously possess high transmittance, superior mechanical flexibility, and good electrical conductivity .…”

Section: Introductionmentioning

confidence: 99%

A Solution Processed Flexible Nanocomposite Substrate with Efficient Light Extraction via Periodic Wrinkles for White Organic Light‐Emitting Diodes

Huang

Advanced Optical Materials

Youssef

et al. 2018

A new flexible nanocomposite substrate is reported to enhance the light outcoupling efficiency of white organic light‐emitting diodes (OLEDs). The substrate comprises silver nanowires as electrode and periodic wrinkles as external structures for light extraction. It can outcouple both the waveguide and substrate modes. With the optimized external light extraction structures, white OLEDs based on the nanocomposite substrates show external quantum efficiency (EQE) enhancement factor of 2.34 compared to control devices on indium tin oxide (ITO)/glass, with an EQE of (38.4 ± 2.7)%, a power efficiency of 85.8 ± 2.9 lm W−1, and a current efficiency of 100.3 ± 7.1 cd A−1 at luminance of 1000 cd m−2. Moreover, the external wrinkles improve the spectral uniformity over a wide range of viewing angles, which is an important feature for lighting applications. The nanocomposite substrate is fully solution‐processed and thus can potentially lower the manufacturing cost of high‐efficiency flexible OLEDs.