The outstanding electrical, mechanical and chemical properties of graphene make it attractive for applications in flexible electronics. However, efforts to make transparent conducting films from graphene have been hampered by the lack of efficient methods for the synthesis, transfer and doping of graphene at the scale and quality required for applications. Here, we report the roll-to-roll production and wet-chemical doping of predominantly monolayer 30-inch graphene films grown by chemical vapour deposition onto flexible copper substrates. The films have sheet resistances as low as approximately 125 ohms square(-1) with 97.4% optical transmittance, and exhibit the half-integer quantum Hall effect, indicating their high quality. We further use layer-by-layer stacking to fabricate a doped four-layer film and measure its sheet resistance at values as low as approximately 30 ohms square(-1) at approximately 90% transparency, which is superior to commercial transparent electrodes such as indium tin oxides. Graphene electrodes were incorporated into a fully functional touch-screen panel device capable of withstanding high strain.

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Roll-to-roll production of 30-inch graphene films for transparent electrodes

We report a comprehensive study of transparent and conductive silver nanowire (Ag NW) electrodes, including a scalable fabrication process, morphologies, and optical, mechanical adhesion, and flexibility properties, and various routes to improve the performance. We utilized a synthesis specifically designed for long and thin wires for improved performance in terms of sheet resistance and optical transmittance. Twenty Ω/sq and ∼80% specular transmittance, and 8 ohms/sq and 80% diffusive transmittance in the visible range are achieved, which fall in the same range as the best indium tin oxide (ITO) samples on plastic substrates for flexible electronics and solar cells. The Ag NW electrodes show optical transparencies superior to ITO for near-infrared wavelengths (2-fold higher transmission). Owing to light scattering effects, the Ag NW network has the largest difference between diffusive transmittance and specular transmittance when compared with ITO and carbon nanotube electrodes, a property which could gr...

/pdf/scalable-coating-and-properties-of-transparent-flexible-83mkmpnvqi.pdf

Scalable Coating and Properties of Transparent, Flexible, Silver Nanowire Electrodes

Transparent electrodes are a necessary component in many modern devices such as touch screens, LCDs, OLEDs, and solar cells, all of which are growing in demand. Traditionally, this role has been well served by doped metal oxides, the most common of which is indium tin oxide, or ITO. Recently, advances in nano-materials research have opened the door for other transparent conductive materials, each with unique properties. These include CNTs, graphene, metal nanowires, and printable metal grids. This review will explore the materials properties of transparent conductors, covering traditional metal oxides and conductive polymers initially, but with a focus on current developments in nano-material coatings. Electronic, optical, and mechanical properties of each material will be discussed, as well as suitability for various applications.

Emerging Transparent Electrodes Based on Thin Films of Carbon Nanotubes, Graphene, and Metallic Nanostructures

We report a comprehensive study of transparent and conductive silver nanowire (Ag NW) electrodes,includingascalablefabricationprocess,morphologies,andoptical,mechanicaladhesion,andflexibility properties, and various routes to improve the performance. We utilized a synthesis specifically designed for long andthinwiresforimprovedperformanceintermsofsheetresistanceandopticaltransmittance.Twenty/sqand 80% specular transmittance, and 8 ohms/sq and 80% diffusive transmittance in the visible range are achieved, whichfallinthesamerangeasthebestindiumtinoxide(ITO)samplesonplasticsubstratesforflexibleelectronics andsolarcells.TheAgNWelectrodesshowopticaltransparenciessuperiortoITOfornear-infraredwavelengths(2- foldhighertransmission).Owingtolightscatteringeffects,theAgNWnetworkhasthelargestdifferencebetween diffusive transmittance and specular transmittance when compared with ITO and carbon nanotube electrodes, a propertywhichcouldgreatlyenhancesolarcellperformance.AmechanicalstudyshowsthatAgNWelectrodeson flexiblesubstratesshowexcellentrobustnesswhensubjectedtobending.Wealsostudytheelectricalconductance ofAgnanowiresandtheirjunctionsandreportafacileelectrochemicalmethodforaAucoatingtoreducethewire- to-wire junction resistance for better overallfilm conductance. Simple mechanical pressing was also found to increasetheNWfilmconductanceduetothereductionofjunctionresistance.Theoverallpropertiesoftransparent Ag NW electrodes meet the requirements of transparent electrodes for many applications and could be an immediate ITO replacement forflexible electronics and solar cells.

https://web.stanford.edu/group/cui_group/papers/Transprent%20Ag.pdf

Scalable Coating and Properties of Transparent, Flexible, Silver Nanowire

Graphene has been hailed as a wonderful material in electronics, and recently, it is the rising star in photonics, as well. The wonderful optical properties of graphene afford multiple functions of signal emitting, transmitting, modulating, and detection to be realized in one material. In this paper, the latest progress in graphene photonics, plasmonics, and broadband optoelectronic devices is reviewed. Particular emphasis is placed on the ability to integrate graphene photonics onto the silicon platform to afford broadband operation in light routing and amplification, which involves components like polarizer, modulator, and photodetector. Other functions like saturable absorber and optical limiter are also reviewed.

Graphene photonics, plasmonics, and broadband optoelectronic devices.

We report an industrially scalable, fast, and simple process for the large scale fabrication of optically transparent and electrically conducting thin films of single-walled carbon nanotubes (SWNT). Purified, pristine HiPco SWNTs were dispersed in water at high concentrations with the help of surfactants, rod-coated into uniform thin films, and doped by various acids. We show how to combine different surfactants to make uniform dispersions with high concentration of SWNTs and optimal rheological behavior for coating and drying, including preventing dewetting and film rupture that has plagued earlier attempts. Doping by fuming sulfuric acid yielded the films with best performance (sheet resistance of 100 and 300 Ω/sq for respective transparency of 70% and 90%). We use a figure of merit (FOM) plot for an immediate evaluation and comparison of the performance and microstructure of CNT films produced by different methods. Further scientific engineering will pave the way to the deployment of CNT films in comme...

/pdf/continuous-and-scalable-fabrication-of-transparent-5gjvbgabja.pdf

Continuous and scalable fabrication of transparent conducting carbon nanotube films.

— Carbon-nanotube (CNT) films on plastic are incorporated as the touch electrode in a four-wire resistive touch panel. Single-point actuation tests show superior mechanical performance to ITO touch electrodes, with no loss of device functionality up to 3 million actuations. Sliding-stylus-pen tests reveal no loss of device linearity after 1 million stylus cycles. A CNT refractive index of ∼1.55 leads to CNT touch panels with low reflection (<9% over the visible range) without costly anti-reflective coatings. CNT films on PET currently have 86% total transmission (including the PET) over the visible and 600 Ω/□, with lab scale tests giving 88% at 500 Ω/□. CNT films are neutrally colored (a* ∼ 0, b* ∼ 1.5), low haze (<1%), uniform, and both chemically and environmentally stable. Unidym's solution-based coatings can be printed directly onto both flexible and rigid polycarbonate using solution coating processes. Unidym films can be patterned using subtractive methods such as laser ablation with resolution down to 10 μm, or additive methods such as patterned gravure. CNTs are grown, purified, formulated into inks, and coated using scalable processes, allowing films to be attractive from a cost perspective as well.

Carbon‐nanotube film on plastic as transparent electrode for resistive touch screens

In this work, we reported high performance OLED devices with transparent and conductive carbon nanotube anodes after modification. The modifications include IMRE proprietary PEDOT:PSS composite top coating (PS C ), concentrated HNO3acid soaking, and polymer encapsulation. For PS C -modified nanotube thin film anode, we achieved maximum luminescence of9000 cd/m 2 , close to ITO-based OLED device performance, andhighefficiencyof10cd/A,similarwithITO-basedOLEDdevice.Theperformanceisapproximately30to450 times better than that achieved for OLED devices using CNT anodes by others. In addition, we also investigate the mechanical property, work function, sheet resistance, and surface morphology of modified carbon nanotube thin-film anodes.

Glen Irvin

Papers

Emerging Transparent Electrodes Based on Thin Films of Carbon Nanotubes, Graphene, and Metallic Nanostructures

Emerging Transparent Electrodes Based on Thin Films of Carbon Nanotubes, Graphene, and Metallic Nanostructures

Continuous and scalable fabrication of transparent conducting carbon nanotube films.

Carbon‐nanotube film on plastic as transparent electrode for resistive touch screens

Surface-Modified Nanotube Anodes for High Performance Organic Light-Emitting Diode