This is a high performance semiconducting polymer with an amorphous structure. Highlighted in yellow is a single chain demonstrating negligible backbone torsion. Credit: Deepak Venkateshvaran/Mark Nikolka
A team of researchers led by Professor Henning Sirringhaus at the University of Cambridge, have discovered a new class of semiconducting polymers that can efficiently transport electrons despite their disorganised internal structure. Semiconducting polymers are used in flexible LED displays, solar cells and in printed electronic circuits.
In conventional polymers, less than 50% of the electrons can travel freely, whereas in the new semiconducting polymer approximately 70% of the electrons can travel freely.
Researchers have been trying to find out cheap semiconducting polymers that could be solution processed and also printed, while retaining their electronic properties. Most electronic devices have an ordered crystal lattice structure. However, semiconducting polymers have a spaghetti-like internal structure that traps the electrons that carry charge, affecting their performance.
What is most surprising about these materials is that they appear very disordered at the microstructural level, while at the electronic level they allow electrons to move nearly as freely as in crystalline inorganic semiconductors.
Mark Nikolka, a PhD student at the University’s Cavendish Laboratory
Generally, polymer molecules are made up of one long backbone chain with shorter side chains. These side chains enhance the disorder, causing more electrons to get trapped, leading to an inferior performance.
The newly discovered conjugated polymers at Cambridge can tolerate disorder created due to the side chains. At the microstructural level, they are amorphous and very disordered. However, at the electronic level, it allows electron flow in about the same manner as crystalline inorganic semiconductors. The researchers found that the materials approached disorder-free limits electronically, and that all the molecular units in the polymer chain participated in the charge transportation.
These materials resemble graphene where electrons can move fast. However, the electron movement is not as fast as in graphene. These semiconducting polymers can be easily processed, that makes them cheaper than graphene.
The results of this study could help provide guidelines for developing disorder-free conjugated polymers that could be used for flexible electronic applications.
This study has been published in the Nature journal.
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