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

The demand for flexible and wearable electronic devices is increasing due to their facile interaction with human body. Flexible, stretchable and wearable sensors can be easily mounted on clothing or directly attached onto the body. Especially, highly stretchable and sensitive strain sensors are needed for the human motion detection. Here, we report highly flexible, stretchable and sensitive strain sensors based on the nanocomposite of silver nanowire (AgNW) network and PDMS elastomer in the form of the sandwich structure (i.e., AgNW thin film embedded between two layers of PDMS). The AgNW network-elastomer nanocomposite based strain sensors show strong piezoresistivity with tunable gauge factors in the ranges of 2 to 14 and a high stretchability up to 70%. We demonstrate the applicability of our high performance strain sensors by fabricating a glove integrated with five strain sensors for the motion detection of fingers and control of an avatar in the virtual environment.

Highly Stretchable and Sensitive Strain Sensor Based on Silver Nanowire–Elastomer Nanocomposite

Emerging challenges and materials for thermal management of electronics

IO N Materials that are both conductive and stretchable could enable a spectrum of applications such as stretchable displays, [ 1 ] stretchable radiofrequency antennas, [ 2 ] artifi cial muscles [ 3 ] and conformal skin sensors. [ 4–7 ] A variety of such materials have been recently developed, such as wavy thin metals, [ 8 , 9 ] metal-coated net-shaped plastic fi lm, [ 10 ] graphene fi lms [ 11 ] and carbon nanotube (CNT)-based composites. [ 12–19 ] But several limitations typically exist in these materials including low conductivity, [ 13 , 15 , 16 , 19 ]

Highly Conductive and Stretchable Silver Nanowire Conductors

Colloidal synthesis offers a route to nanoparticles (NPs) with controlled composition and structural features. This Perspective describes the use of polyvinylpyrrolidone (PVP) to obtain such nanostructures. PVP can serve as a surface stabilizer, growth modifier, nanoparticle dispersant, and reducing agent. As shown with examples, its role depends on the synthetic conditions. This dependence arises from the amphiphilic nature of PVP along with the molecular weight of the selected PVP. These characteristics can affect nanoparticle growth and morphology by providing solubility in diverse solvents, selective surface stabilization, and even access to kinetically controlled growth conditions. This Perspective includes discussions of the properties of PVP-capped NPs for surface enhanced Raman spectroscopy (SERS), assembly, catalysis, and more. The contribution of PVP to these properties as well as its removal is considered. Ultimately, the NPs accessed through the use of PVP in colloidal syntheses are opening new applications, and the concluding guidelines provided herein should enable new nanostructures to be accessed facilely.

/pdf/polyvinylpyrrolidone-pvp-in-nanoparticle-synthesis-4i444sejw5.pdf

Polyvinylpyrrolidone (PVP) in nanoparticle synthesis

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

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

The removal of bacteria and other organisms from water is an extremely important process, not only for drinking and sanitation but also industrially as biofouling is a commonplace and serious problem. We here present a textile based multiscale device for the high speed electrical sterilization of water using silver nanowires, carbon nanotubes, and cotton. This approach, which combines several materials spanning three very different length scales with simple dying based fabrication, makes a gravity fed device operating at 100000 L/(h m2) which can inactivate >98% of bacteria with only several seconds of total incubation time. This excellent performance is enabled by the use of an electrical mechanism rather than size exclusion, while the very high surface area of the device coupled with large electric field concentrations near the silver nanowire tips allows for effective bacterial inactivation.

http://web.stanford.edu/group/cui_group/papers/81%20david%20water%20sterilization.pdf

High Speed Water Sterilization Using One-Dimensional Nanostructures

Tandem architectures in which multiple energy gaps are combined in a series-connected stack of solar cells are seen as a promising approach to increasing the power conversion efficiency of organic solar cells to commercially relevant values. Even higher efficiencies can be obtained if the photocurrent-matching requirement of such tandem cells is removed by the use of intermediate electrodes in multi-terminal multijunction cells. We demonstrate semi-transparent organic solar cells and multi-terminal multijunction organic photovoltaic cells using a laminated metal nanowire mesh as a low-cost, high-performance intermediate electrode that can be deposited using a lamination process without damaging the fragile organic layers. Photocurrent matching is not required in the multi-terminal architecture. With adequate material combinations, this cell architecture can be used to build organic solar cells with efficiencies ≫10%.

Han Sun Kim

Papers

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

Scalable Coating and Properties of Transparent, Flexible, Silver Nanowire

High Speed Water Sterilization Using One-Dimensional Nanostructures

Transparent and tandem solar cells using solution-processed metal nanowire transparent electrodes