Electrospun Metal Nanofiber Webs as High-Performance Transparent Electrode

Abstract

Transparent electrodes, indespensible in displays and solar cells, are currently dominated by indium tin oxide (ITO) films although the high price of indium, brittleness of films, and high vacuum deposition are limiting their applications. Recently, solution-processed networks of nanostructures such as carbon nanotubes (CNTs), graphene, and silver nanowires have attracted great attention as replacements. A low junction resistance between nanostructures is important for decreasing the sheet resistance. However, the junction resistances between CNTs and boundry resistances between graphene nanostructures are too high. The aspect ratios of silver nanowires are limited to ∼100, and silver is relatively expensive. Here, we show high-performance transparent electrodes with copper nanofiber networks by a low-cost and scalable electrospinning process. Copper nanofibers have ultrahigh aspect ratios of up to 100000 and fused crossing points with ultralow junction resistances, which result in high transmitance at low sheet resistance, e.g., 90% at 50 Ω/sq. The copper nanofiber networks also show great flexibility and stretchabilty. Organic solar cells using copper nanowire networks as transparent electrodes have a power efficiency of 3.0%, comparable to devices made with ITO electrodes.

Performance enhancement of metal nanowire transparent conducting electrodes by mesoscale metal wires

“…In the past decade, it has been also used to produce wires of a variety of inorganic materials 39 . Our group has previously used electrospinning for making Cu nanowires for transparent electrodes 15,16 . Here we extend this method for making larger diameter mesoscale wires.…”

“…Recently, there have been increasing efforts in developing nanomaterial TCEs including carbon nanotubes (CNTs) 1,[6][7][8][9] , graphene 4,[10][11][12][13] , metal nanowires [14][15][16][17][18][19][20][21] and nanoparticles 22,23 to replace conventional indium tin oxide (ITO) films, in order to enable low-cost and mechanical flexibility while maintaining low sheet resistance (R s ) and high transmittance (T). For the active layers of many devices, the lateral surface electrical conductance is sufficient to transport electrons only locally from several 100 nm to a few mm scale without serious ohmic loss, therefore interfacing with external connection requires additional TCEs with good R s -T performance.…”

Solution-Processed Graphene-Based Transparent Conductive Electrodes as Ideal ITO Alternatives for Organic Solar Cells

“…One very promising technique is the employment of a mesh structure with periodic lines on the rGO film [53], with OSC devices based on graphene mesh electrodes (GMEs) already exhibiting performances comparable to those using conventional ITO TCEs [54,55]. Therefore, it is possible to control the films R s and transparency by tailoring the grid width, spacing, and thickness [56].…”

Nanomaterial-based stretchable and transparent electrodes

“…Instead of the metal grid, which has a complicated fabrication process and relatively poor stretchability, several methods of creating stretchable transparent electrodes based on metal nanofibers have been developed [58][59][60][61][62][63][64]. Among them, electrospinning is a method that is optimized to make continuous one-dimensional nanomaterials with polymers, oxides, and carbon [65,66].…”

“…Cui et al demonstrated a random network of Cu nanofibers by electrospinning copper acetate melt in poly(vinyl acetate), as shown in Figure 3(a). After the electrospinning, the fibers were successively annealed at 300°C and 500°C [58]. This increased the aspect ratio of the nanofiber to ∼ 10 6 , and 50 /sq sheet resistance at 90% transmittance was obtained due to the fused junctions within the metal nanofiber networks.…”