Humidity assisted annealing technique for transparent conductive silver nanowire networks

Abstract

The surfactant polyvinylpyrrolidone (PVP) commonly used to synthesize silver nanowires (AgNW) in solution is known to negatively affect the performance of nanowire-based thin film electrodes. An insulating shell of the polymer hinders tight contact between the nanowires themselves and between the nanowires and substrate, resulting in high sheet resistance of the freshly prepared nanowire films. Here, we develop a simple low-temperature method allowing us to reduce the sheet resistance of AgNW networks and simultaneously improving the optical transmittance. The method is based on the capacity of PVP to absorb moisture which results in a strong decrease in the glass transition temperature of the polymer.The latter leads to softening effects, causing a reduced wire contact resistance already at 60 C for 90 nm thick AgNWs and even at 45 C for 35 nm thick AgNWs. As a result, the sheet resistances of the thin film electrodes treated by our method are near to the values conventionally obtained after thermal annealing at temperatures between 140-250 C. Our humidity assisted low temperature approach is especially advantageous for organic electronics and fabricating devices on thermally sensitive transparent flexible foils. † Electronic supplementary information (ESI) available: Changes in total transmittance DT vs. initial total transmittance; transmittance spectra of NW-35 electrode vs. annealing time; SEM images of a NW-35 electrode on glass; sheet resistance vs. annealing time at a constant temperature of 60 C and different RH values; SEM image, transmittance and reectance spectra of NW-90 electrode on PEN foil. See

Electrical limit of silver nanowire electrodes: Direct measurement of the nanowire junction resistance

“…According to Chung et al, 16 we assumed that this surface coverage is equal to T spec . In corresponding measurements published recently by our group, 17 we have seen a slight increase in the total transmittance of annealed AgNWs. This transmittance increase in annealed networks may originate from a closer and tighter alignment of NWs on the substrate.…”

Reinventing Butyl Rubber for Stretchable Electronics

“…To stress test T‐IIR encapsulation layers, we formed AgNW films onto glass substrates by simply drop casting AgNW suspensions in ethanol. These AgNW films consist of a uniform distribution of AgNWs on the surface, exhibit a signature absorbance peak at 365 nm, and have a sheet resistance of 10.8 ± 2.4 Ω sq −1 ( Figure a,b). We laminated T‐IIR and PDMS over these films to create T‐IIR/AgNW/glass and PDMS/AgNW/glass structures, which we then exposed to the corrosive vapor of nitric acid in a closed container for 12 h. AgNW films encapsulated with PDMS were no better than unprotected films after the vapor treatment: Neither unprotected nor PDMS‐protected films exhibited the characteristic absorption at 365 nm (Figure a), and the films were no longer conductive.…”

Efficient flexible organic photovoltaics using silver nanowires and polymer based transparent electrodes

“…A sheet resistance (R S ) of 30 U/▫ and a total transmittance of 86% are achieved for both NW35 and NW90. This performance is comparable to a NW90 electrode with 85% total transmittance and R s of 28.6 U/▫ [19] and significantly better than that of a 120 nm PEDOT: PSS electrode, which has an Rs of 100 U/▫, insufficient for large size devices. OPV devices were deposited on these electrodes with glass and PET substrates.…”

“…Secondly, overlapping wires cause roughness, often resulting in electrical shorting of devices deposited on top of these electrodes. To create a smooth and well connected network, post-treatment techniques such as mechanical pressure [16], plasmonic welding [17,18], thermal treatment [12], and humidity assisted low temperature treatments [19] have been applied. Thirdly, open spaces between wires can be in the range of square micrometers.…”