Polymers for Printed Electronics
In the area of research on n-type conductive polymers for printed electronics, scientist at the Fraunhofer IWS institute for material and beam technology have made a large step forward. Situated in Dresden, Germany, the institute has been successful in modifying an n-type polymer synthesized in 2015. The polymer can now be processed as a paste and used for 3-dimensional printing.
At first sight, conductive polymers may seem paradoxical to many, in particular, if thinking of those plastics that surround us in everyday life. However, conductive polymers are in fact used in many technical applications, e.g. batteries, LCD screens, transistors and solar cells. And it has been a known fact since the eighties that the electrical conductivities of polymers may well be comparable to those of metals.
The main difference between polymers and metals is the fact that in metals, electrons, i.e. negatively charged carriers, enable the electrical conduction process, whereas, in commercially available polymers (e.g. PEDOT: PSS), charge carriers with a positive elementary charge are responsible for electrical conductivity. This is therefore referred to as p-type conductivity.
Seeking the n-Type Polymer
However, to design complete electronic components, both p-type as well as n-type conductive materials are required, with n-type polymers being the bottleneck in many technical applications. Their electrical conductivities are frequently poor. Structural integrity as well as electrical properties severely suffer from degradation due to environmental impact. In 2015, however, the IWS group “Printing” had successfully synthesized an n-type polymer with its conductivity enhanced by one order of magnitude.
The scientist had to master another obstacle on the way to application of the n-type conductive polymer, though. Similar to its p-type PEDOT archetype, the IWS polymer was almost insoluble in all known solutions. The Institute has recently mastered this challenge, too. For the first time a thermoelectric generator (a device which is able to generate electrical power out of temperature differences) was designed and tested, consisting of p- and n-type conductive polymers.