Laser induced forward transfer (LIFT) and laser sintering of metal nanoparticle inks constitute a two-step digital fabrication technique which has been proven a key enabling technology for the fabrication of flexible microelectronic devices. In this work we will present the investigation of the laser printing and sintering process of Ag nanoparticle inks for the production of a conductive grid comprised of parallel lines as replacement for the bottom Indium Tin Oxide (ITO) electrode in organic photovoltaics (OPVs). We study the effect of a range of laser parameters and their impact on the morphological characteristics and the electrical performance of the laser printed conductive grid. The electrical conductivity of the laser printed lines is calculated by means of electrical measurements in a 4-point probe IV station while their morphological characteristics are assessed with profilometry measurements. As a result, flexible ITO-free OPVs incorporating laser-printed Ag grids as a bottom electrode on PET substrates will be presented. The results confirm that the laser printing and sintering combination is an advantageous technique, which can offer a distinguishing solution for applications in highly efficient ITO-free OPVs.
In this work, we report on the conformal laser printing and sintering of Ag nanoparticle inks applied on particularly sensitive substrates and structures. The latter involve challenging patterns with periodicity and aspect ratio in the nano to 100-micron scale. We investigate the effect of a number of essential to the laser sintering technique parameters, such as the laser wavelength, repetition rate, pulse duration and the pulse to pulse spatial and temporal overlap. The demonstrated results show that laser printing and sintering can offer specific solutions to particularly challenging use cases and applications in flexible electronics.
The recent developments in the field of large area, flexible and printed electronics have fueled substantial advancements in Laser Printing and Laser Sintering, which have been attracting interest over the past decade. Resulting applications, ranging from flexible displays and sensors, to biometric devices and healthcare, have already showcased transformational advantages in terms of form factor, weight and durability. In HiperLAM project, Laser-Induced Forward Transfer (LIFT), combined with high speed laser micro-sintering are employed, as digital microfabrication tools for the demonstration of fully functional RFID antennas and fingerprint sensors based on highly viscous Ag and Cu nanoparticle inks. Having previously successfully demonstrated complex structures, this work’s focus is on increasing the process throughput and yield by increasing the laser repetition rate (up to 40 kHz) and scanning speed (up to 2 m/s), without compromising reliability and resolution. In order to gain insight into the effects of the incremented repetition rate on the printing procedure, the latter was monitored in real time via a high-speed camera, able to acquire up to 540.000 fps, coupled to the setup. Examples of resulting structures comprise well-defined interdigitated and spiral micro-electrodes with post-sintering electrical resistivity lower than 5 x bulk Ag and 3 x bulk Cu. The aforementioned results validate the compatibility of laser based processing with the field of flexible RFID tags and OTFT based fingerprint sensors and foster the wider adoption of LIFT and laser micro-sintering technology for laboratory and industrial use.
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