The effect of nanowire length and diameter on the properties of transparent, conducting nanowire films

Abstract

This article describes how the dimensions of nanowires affect the transmittance and sheet resistance of a random nanowire network. Silver nanowires with independently controlled lengths and diameters were synthesized with a gram-scale polyol synthesis by controlling the reaction temperature and time. Characterization of films composed of nanowires of different lengths but the same diameter enabled the quantification of the effect of length on the conductance and transmittance of silver nanowire films. Finite-difference time-domain calculations were used to determine the effect of nanowire diameter, overlap, and hole size on the transmittance of a nanowire network. For individual nanowires with diameters greater than 50 nm, increasing diameter increases the electrical conductance to optical extinction ratio, but the opposite is true for nanowires with diameters less than this size. Calculations and experimental data show that for a random network of nanowires, decreasing nanowire diameter increases the number density of nanowires at a given transmittance, leading to improved connectivity and conductivity at high transmittance (>90%). This information will facilitate the design of transparent, conducting nanowire films for flexible displays, organic light emitting diodes and thin-film solar cells.Indium tin oxide (ITO) is the material of choice for transparent conducting films in flat-panel displays, organic solar cells, and organic light emitting diodes because, with a sheet resistance of 10 U sq À1 at a transmittance of 90% (l ¼ 550 nm), it is highly conductive and transparent. However, indium is a scarce element, ITO is brittle, and ITO film is expensive because it is produced with a vapor-phase coating process that is 1000 times slower than newspaper printing.1,2 These problems have motivated a search for alternatives to ITO that are flexible and can be deposited from liquids at high coating rates.3-9 As discussed in recent reviews, promising solution-processed alternatives to ITO include poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate), carbon nanotubes, graphene, ITO nanowires, and metal nanowires.10-15 Of these alternatives, films of silver nanowires currently have the highest conductance and transmittance. 4,16-18For example, Leem et al. have recently reported obtaining silver nanowire films with a sheet resistance of 10 U sq À1 at a transmittance of 89.3% (l ¼ 550 nm), nearly matching ITO. Although silver ($1000 kg À1) is more expensive than indium ($800 kg À1 ), the fact that silver nanowire films can be produced with highthroughput wet-coating processes allows them to achieve lower costs. 19,20Here we report a simple polyol synthesis that enables control over the length and diameter of silver nanowires, as well as their production on the gram scale. By measuring the properties of films composed of nanowires with distinct ranges of dimensions, we have obtained the first quantitative confirmation of theoretical predictions for the effect of nanowire length and number density on the conductance of 2D...

High Stable, Transparent and Conductive ZnO/Ag/ZnO Nanofilm Electrodes on Rigid/Flexible Substrates

“…Φ TC was calculated as shown in Figure 6e, as was as high as 4.53ˆ10´2 Ω´1 when the f(O 2 ) was 2.0%, matching well the foregoing results. The Φ TC of ZnO/Ag/ZnO is higher than the reported value (0.88ˆ10´2) of ITO [29]. The result indicates that highly transparent and conductive ZnO/Ag/ZnO can be prepared by the inclusion of a remarkably small amount of oxygen while the Ag films are deposited.…”

Resistance of Single Ag Nanowire Junctions and Their Role in the Conductivity of Nanowire Networks

“…In this regard many factors have been examined, including the impact of nanowire geometry, [18][19] the methods used to fabricate the network, 5,[20][21][22][23] and the postfabrication processing techniques employed to remove/modify the insulating polymer shell on the nanowires. The widely used polyol method for Ag nanowire fabrication results in a nanoscale coating of insulting polyvinylpyrrolidone (PVP).…”

Fully Solution-Processed Semitransparent Organic Solar Cells with a Silver Nanowire Cathode and a Conducting Polymer Anode

“…14,[18][19][20] Several groups have tested solution-deposited AgNW films in OSCs, using them as a bottom or a top electrode, and frequently achieving comparable PCEs to equivalent ITO-based devices. [21][22][23][24][25][26][27] Virtually all devices reported to date, however, have used ITO or a thermally evaporated metal as the counter electrode, with a consequent need for vacuum processing during fabrication.…”