Consolidation and performance gains in plasma-sintered printed nanoelectrodes

Abstract

We report on the unusual, advantageous ageing of flexible transparent electrodes (FTEs) that were self-assembled from oleylamine-capped gold nanospheres (AuNPs) by direct nanoimprinting of inks with different particle concentrations (cAu = 3 mg mL−1 to 30 mg mL−1 ). The resulting lines were less than 2.5 mm wide and consisted of disordered particle assemblies. Small-Angle X-ray Scattering confirmed that particle packing did not change with ink concentration. Plasma sintering converted the printed structures into lines with a thin, electrically conductive metal shell and a less conductive hybrid core. We studied the opto-electronic performance directly after plasma sintering and after fourteen days of storage at 22 °C and 55% rH in the dark. The mean optical transmittance T 400–800 in the range from 400 nm to 800 nm increased by up to z 3%, while the sheet resistance Rsh strongly decreased by up to z 82% at all concentrations. We correlated the changes with morphological changes visible in scanning and transmission electron microscopy and identified two sequential ageing stages: (I) post-plasma relaxation effects in and consolidation of the shell, and (II) particle re-organization, de-mixing, coarsening, and densification of the core with plating of Au from the core onto the shell, followed by solid-state de-wetting (ink concentrations cAu < 15 mg mL−1 ) or stability (cAu $ 15 mg mL−1 ). The plating of Au from the hybrid core improved the FTEs' Figure of Merit FOM = T 400–800$Rsh−1 by up to z 5.8 times and explains the stable value of z 3.3%$Usq−1 reached after 7 days of ageing at cAu = 30 mg mL−1.