High performing AgNW transparent conducting electrodes with a sheet resistance of 2.5 Ω Sq-1 based upon a roll-to-roll compatible post-processing technique.

D Kumar,J Kettle,G C Smith,V Stoichkov,E Brousseau

doi:10.1039/c8nr07974a

Abstract

A report of transparent and conducting silver nanowires (AgNWs) that produce remarkable electrical performance, surface planarity and environmental stability is given. This research presents an innovative process that relies on three sequential steps, which are roll-to-roll (R2R) compatible: thermal embossing, infrared sintering and plasma treatment. This process leads to the demonstration of a conductive film with a sheet resistance of 2.5 Ω sq-1 and high transmittance, thus demonstrating the highest reported figure-of-merit in AgNWs to date (FoM = 933). A further benefit of the process is that the surface roughness is substantially reduced compared to traditional AgNW processing techniques. The consideration of the long-term stability is given by developing an accelerated life test process that simultaneously stresses the applied bias and temperature. Regression line fitting shows that a ∼150-times improvement in stability is achieved under 'normal operational conditions' when compared to traditionally deposited AgNW films. X-ray photoelectron spectroscopy (XPS) is used to understand the root cause of the improvement in long-term stability, which is related to reduced chemical changes in the AgNWs.

Highlights

The global market in flexible displays, solar energy and large area electronics is expected to boom in the 5–10 years
One of the primary current issues to be addressed in this field is that the incumbent technology indium tin oxide (ITO) is not flexible; upon repeated bending, the films are known to crack and lose conductivity, which is prohibitive for future product emergence of flexible displays, electronics and PVs.[2,3,4]
It can be seen that the optimised individual processes of thermal embossing, sintering and N2 plasma treatment have a similar effect upon the reduction in RSH, leading to a reduction of ∼50%, when compared to the control samples

Summary

Introduction

The global market in flexible displays, solar energy and large area electronics is expected to boom in the 5–10 years. To benchmark the AgNW TCEs, PSC devices were made using ITO coated PET substrates (Rsh = 60 Ω square−1, transmittance = 84%, purchased from Sigma Aldrich) which were first cleaned using deionised water, acetone and isopropanol in an ultrasonic cleaner, and treated in a UV-ozone reactor with oxygen plasma for 10 minutes. In order to evaluate the long-term effect of post-processing upon the AgNW stability, a bespoke accelerated life testing (ALT) system was constructed This enabled high current biasing of the AgNW electrodes and repeated sheet resistance calculations every 30 minutes, during which the bias was momentarily switched off (∼5 seconds). Data were analysed using CasaXPS software version 3.16, with quantification using Scofield cross-sections corrected for the energy-dependence of the analyser transmission and the electron effective mean free paths

Results and discussion

A I n eÀVB ð3Þ

Conclusion