A team of scientists from the National University of Singapore (NUS) claim to have developed conducting polymer films which provide more ohmic contacts and therefore better performance in plastic electronics, including organic light-emitting diodes, solar cells and transistors.
To make high performance devices, 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.
“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,” commented senior research fellow Dr Png Rui-Qi.
The key, these researchers discovered, is to design polymer films with the desired extreme work functions needed to make ohmic contacts.
Work function is the minimum amount of energy needed to liberate an electron from the film surface into vacuum. The researchers showed that work functions as high as 5.8eV and as low as 3.0eV can now be attained for films that can be processed from low cost solutions.
“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 Rui-Qi.
“As a result, the polymers can remain stable despite their extreme work functions and therefore provide the desired ohmic contacts.”