Dr. Png Rui-Qi (left), Mervin Ang (middle) and Cindy Tang (right) working on conducting polymers that can provide unprecedented ohmic contacts for better performance in a wide range of organic semiconductor devices. Credit: Seah Zong Long
Semiconductors, which are the very basic components of electronic devices, have improved our lives in many ways. They can be found in lighting, displays, solar modules and microprocessors that are installed in almost all modern day devices, from mobile phones, washing machines, and cars, to the emerging Internet of Things. To innovate devices with better functionality and energy efficiency, researchers are constantly looking for better ways to make them, in particular from earth-abundant materials using eco-friendly processes. Plastic or organic electronics, which is made from organic carbon-based semiconductors, is one such group of technologies that can potentially provide flexible, light-weight, large-area and additively-manufactured devices, which are attractive for some types of applications.
Schematic of the preparation of self-compensated heavily doped polymer organic semiconductors.
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. Recently, a team from the National University of Singapore (NUS) successfully developed conducting polymer films that can provide unprecedented ohmic contacts to give superior performance in plastic electronics, including organic light-emitting diodes, OLED, solar cells and transistors.
The key these researchers discovered is to be able to design polymer films with the desired extreme work functions needed to generally make ohmic contacts. Work function is the minimum amount of energy needed to liberate an electron from the film surface into vacuum. Work functions as high as 5.8 electron-volts and as low as 3.0 electron-volts can now be attained for films that can be processed from solutions at low cost.
Stabilization of the doping profile by counter-ion immobilization in self-compensated doped polymer organic semiconductors.
“To design such materials, we 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,” explained Dr Png Rui-Qi. “As a result, these conducting polymers can remain stable despite their extreme work functions and provide the desired ohmic contacts.”
Facile electrode differentiation by self-aligned assembly of ultrahigh- and ultralow-work-function interlayers on Ag.
“The lack of a general approach to make ohmic contacts has been a key bottleneck in flexible electronics. Our work overcomes this challenge to open a path to better performance in a wide range of organic semiconductor devices,” explained Dr Png Rui-Qi. “We are particularly thrilled about this Singapore-led innovation,” she added.
Commenting on the significance of the work, Assoc Prof Chua said, “The close partnership of the chemists and physicists has made this innovation possible. We are now working with our industrial partner to further develop this technology.”
https://www.eurekalert.org/pub_releases/2017-01/nuos-nra011317.php
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