Conductive polymer films for plastic electronics

Singaporean scientists have developed conducting polymer films that provide high performance in plastic electronics, including organic LEDs, solar cells and transistors.

To create devices with better functionality and efficiency, researchers are constantly looking for better ways to make them, in particular from earth-abundant materials using eco-friendly processes. A lot of attention has been placed on plastic or organic electronics, made from organic carbon-based semiconductors, which can potentially provide flexible, lightweight, large-area and additively manufactured devices.

To make high-performance devices, however, good ohmic contacts with low electrical resistances are required to allow the maximum current to flow both ways between the electrode and the semiconductor layers. That is what the scientists from the National University of Singapore (NUS) have achieved, creating conducting polymer films with apparently unprecedented ohmic contacts.

Writing in the journal Nature, the researchers explained that they sought to design polymer films with the desired extreme work functions — ie, the minimum amount of energy needed to liberate an electron from the film surface into vacuum — needed to generally make ohmic contacts. As noted by research leader Dr Png Rui-Qi, “The lack of a general approach to make ohmic contacts has been a key bottleneck in flexible electronics.”

To design polymer films with high work functions, the researchers “developed the concept of doped conducting polymers with bonded ionic groups, in which the doped mobile charges — electrons and holes — cannot dissipate away because their counter-balancing ions are chemically bonded”, said Dr Rui-Qi. Work functions as high as 5.8 eV and as low as 3 eV could now be attained.

“As a result, these conducting polymers can remain stable despite their extreme work functions and provide the desired ohmic contacts,” said Dr Rui-Qi, claiming that his team’s research will open a path to “better performance in a wide range of organic semiconductor devices”.

The work was a result of collaboration between the departments of chemistry and physics at NUS, as well as technology company Cambridge Display Technology (CDT). The researchers are now looking to further develop the technology.

Pictured: Dr Png Rui-Qi, Mervin Ang and Cindy Tang. Image credit: Seah Zong Long.