Ink-Jet Printing and Electrodeposition for the Production of Free Standing and Polymer Supported Micronet Electrodes

Abstract

A study on optimization of Ink-Jet printing parameters, in terms of drop spacing, operative voltage and waveform, metallic line width and spacing is presented, with the aim of producing flexible Transparent Conducting Electrodes (TCEs). Silver micronets were produced by Ink-Jet printing on PET films, to obtain polymer supported transparent electrodes; preliminary studies were also performed on the production of freestanding electrodes, by electrodeposition on the printed micronets. The study reveals that PET supported transparent conductive electrodes can be obtained by ink-jet printing, having improved performances with respect to Indium Tin Oxide (ITO) in terms of resistivity and resistance to bending: no cracking or delamination was observed during bending of the micronets and resistance, measured between two points at 3 cm distance, is one order of magnitude lower for the micronets. Preliminary studies on production of freestanding meshes reveal that this process is promising and allows further reduction in electrode resistance, measured between two points at 3 cm distance, of one order of magnitude. Line width, which is the main limitation of this process, can be conformally reduced by electropolishing without causing collapse of the freestanding micronet. Transparent conductive electrodes (TCEs) are widely used in the growing market of organic and thin film solar cells, liquid crystalline displays and O-LEDs.1-3 A common requirement among these applications is the possibility of producing transparent and conductive electrodes directly on polymeric substrates, which is related to the growing interest in flexible electronics. Indium tin oxide (ITO), the most commonly used material in the display industry, has several limitations when considering the actual needs in this field: it is prone to cracking on flexible substrates, 4,5 it is expensive, due to the presence of Indium, and requires high temperatures during the thin film fabrication process.6 Therefore substitution of ITO is necessary to satisfy the evolution of electronic industry; at the moment attention is mainly focused on conductive polymers, 4,7,8 single-walled carbon nanotubes (SWNTs), 9-11 graphene and metallic nanostructures. 12-15If polymeric transparent electrodes are limited by their intrinsic low conductivity, carbon nanotubes and silver nanowires (AgNW) show promising properties but still need some improvement. Transparent conducting electrodes produced with SWNTs have typical resistance of 200 / at 80% transmission (at a wavelength of 550 nm). 11This resistance value is an order of magnitude higher than that of ITO, therefore it is insufficient for applications in large-area devices. Lower sheet resistance may be obtained with AgNW, due to the intrinsically lower resistivity of silver, but issues are relative to the presence of height variations greater than 100 nm in the deposit. [16][17][18][19] Despite their promising properties as potential replacements for ITO, these materials still suffer from the trade-off between electrical conduc...