Ultrafast laser ablation of transparent conductive silver nanowire thin film on polyethylene terephthalate substrate

Abstract

In printed electronics, such as organic photovoltaic or organic light-emitting diode display and lighting, a transparent conductive oxide layer has to be designed to delimit the size and shape of the final device. The most commonly used material is indium tin oxide (ITO). ITO has however many downsides such as resource scarcity, expensive processing, and brittleness (especially on flexible substrates). Silver nanowires are a promising alternative to overcome these issues, although optimization is still needed to reach ITO performance in terms of transparency and conductivity. In this study, the laser process has to remove the silver nanowire layer in order to obtain an electrical isolation: no remaining bridges in the scribe due to recast material or incomplete removal can be tolerated. Laser ablation of this transparent conductive thin film deposited on polyethylene terephthalate has been investigated using an ultrafast laser source. Pulse energy and scan speed were varied to determine their influence on depth selectivity and process window. The profiles of the selectively ablated area were studied with optical, confocal, and scanning electron microscopy. Compared to irradiation through the substrate, it was shown that front side irradiation allows a much larger process window. In the latter configuration, a fluence ranging from 0.22 to 15.8 J/cm2 and a scanning speed from 200 to 3000 mm/s, at a fixed frequency of 200 kHz, allowed a clean removal of silver nanowires. Using these parameters, isolated squares were scribed and electrical resistance was measured between the inside and the outside of the squares. A good electrical isolation (>20 MΩ) proved the successful removal of the silver nanowire layer using picosecond laser pulses, at a wavelength of 532 nm.