Developments from DuPont, NPL and Agfa
DuPont is a world leader in the supply of silver flake ink - for heating applications (automotive seats and defoggers) and PV bus bars and fingers. Speaker Dr Patrick O'Callaghan discussed how unstable silver prices - peaking in 2011 at $49/T.O. and today around $25/T.O. - have driven the company to look at lower cost solutions, for when the cost of silver rises again. That includes formulations with less silver content and alloys, as examples.
Recent progress from DuPont include their 5043 silver conductor which has shown ability to stretch 75%. The company has also developed appropriate dielectrics, and is working on stretchable transparent conductors. For wearable electronics DuPont has recently launched PE871 (silver content <47%) and PE771 (no silver content). For UHF RFID antenna applications DuPont is bringing silver concentration down to 28% from 80% to make silver more attractive, where the higher cost of silver due to the high weight count has been an issue when the cost of silver has increased in the past.
DuPont is working on materials with good thermal properties - one is heat dissipation for LED lighting. They also have formulations which are more stable for heating elements over time and temperature wear. In addition, Patrick reported that they have had a lot of interest for bioelectronics applications.
DuPont nano materials are mainly being targeted to OLED lighting, OPV and RFID, with a recent announcement being for a new nano-Ag conductor for OLEDs.
National Physical Laboratory (NPL), UK
NPL is developing fabrics coated with conductors. Fabrics first undergo a surface treatment consisting of a polymer coating followed by a fine layer of silver nanoparticles coating the surface (typically 20nm thick). The silver nanoparticles act as a seed layer for the next step - copper plating. The thickness of the copper layer can be closely controlled in the plating process. Due to the pure copper plating, they achieve good conductivity depending on the substrate used, as follows:
|Fabric Substrate||Resistivity Ohms/square|
|Non woven fabric (fibres brought together by chemical or thermal process)||0.006|
The fabrics have undergone full wash cycling tests. NPL has received a large amount of interest from end users - and are now seeking partners to help with the manufacturing scale-up.
In 2013 AGFA had sales of 2.8 Billion Euros. In Printed Electronics Agfa offer a PEDOT:PSS conductive polymer and, recently, a nano silver ink. The PEDOT:PSS material is produced by AGFA in quantities of 200 million square meters of film each year for anti-static applications - antistatic optical films and device packaging. In this application AGFA coat the substrate themselves. AGFA also has developed a range of screen printed PEDOT:PSS conductive inks. The material is widely used in polymer capacitors. The emerging application is transparent electrodes. However, here PEDOT:PSS provides good short range conductivity but is more resistive over long ranges. Therefore AGFA has developed a nanosilver ink to support high conductivity over a long range with short range conductivity and transparency provided by PEDOT:PSS.
The nanosilver ink from AGFA looks impressive - 53mOhm/sq for a 1.2 micron thick line, compared to 200mOhm/sq for a 5 micron thick flake ink. Comparing their ink to three flake inks, AGFA report 34% bulk conductivity versus the flake inks being 17%, 6% and 5%. Target applications are RFID antennas, membrane switches (enabling finer lines and less material used) and highly transparent electrodes - currently made by micro imprinting the PEDOT:PSS coated substrate and filling the channels with silver.
Additionally, the silver and polymer and being explored as planar layers - the polymer coated on top of the silver to plaanarise the electrode - something Heliatek, an OPV manufacturer, is exploring with AGFA.
For more attend the forthcoming events: