Mixed-Polymer Ink Holds Promise for Improving Electronic Device Performance and Conductivity

To improve the conductivity of polymers and obtain higher efficiency in organic solar cells, LEDs, and other electronic applications, a process called “doping”, which uses various substances to modulate electrical properties, is used. 

Doping may soon become a thing of the past, however, as scientists from Linköping University have managed to create a non-dopable organic ink that boasts excellent conductivity.

 

Polymers in Electronic Applications

Polymers are typically used in electrical and electronic applications as insulators. In contrast, conducting polymers become electrically conductive via a process known as doping—where electrons are removed (via oxidation) or introduced (via reduction). 

Doping has been used in practical applications for a long time, and engineers can exercise a high degree of control over a device’s performance and conductivity by increasing the number of charges in a semiconductor with the dopant molecule. 

 

The polymer ink developed by Fabiano's team. The blue solution is the donor polymer solution and the red one is the accepter polymer solution. While both are non-conducting on their own, electrons from the donor polymer automatically transfer to the acceptor polymer when the solutions meet. Image used courtesy of Thor Balkhed of Linköping University.

 

 

Combining Two Polymers to Produce Conductive Ink

Doping, however, is an imperfect solution that is inherently unstable over time and is prone to degeneration–causing doping agents to leach out.  

“This is something that we want to avoid at any cost in, for example, bioelectronic applications, where the organic electronic components can give huge benefits in wearable electronics and as implants in the body,” said Associate Professor Simone Fabiano, head of the Organic Nanoelectronics group within the Laboratory of Organic Electronics at Linköping University.

To make the mixed-polymer conducting ink, the research group, in conjunction with scientists from five different countries, combined two polymers with energy levels that perfectly match, meaning that charges are able to spontaneously transfer between them.

“The phenomenon of spontaneous charge transfer has been demonstrated before, but only for single crystals on a laboratory scale. No one has shown anything that could be used at an industrial scale,” added Fabiano. 

 

Potential Applications

During testing, no leaching was found to be taking place and the ink appeared to remain stable for a long period of time, even when exposed to high temperatures. This is according to the research team’s findings as published in Nature Materials. It is also thought that the new mixed-polymer ink can remain stable over longer periods of time and be used in demanding applications on account of it being free from doping agents. 

While the mixed-polymer ink may find potential applications in several more “popular” consumer products such as wearable electronics, the Linköping University research team is particularly hopeful that their mixed-polymer ink will bring forth new possibilities for improving the performance of solar cells and LEDs specifically.