A new study has shown revealing insights into how plastic materials used in electronics are formed – and how hidden flaws in their structure could be affecting their performance.
Conjugated polymers are a kind of plastic that conduct electricity and is used in optoelectronics, computing, biosensors, and power generation. The materials are lightweight, low-cost, and can be printed in thin layers onto flexible substrates.
An international team of scientists investigated a popular method for making the polymers known as aldol condensation, which is recognised for being versatile, metal-free, environmentally friendly, and scalable.
Supported by funding from the Leverhulme Trust, the Royal Society, and the European Research Council, the scientists have published their results in Nature Communications – revealing that this method of synthesis introduces structural defects that could affect how well the polymer conducts electricity or converts heat into electrical energy in thermoelectric devices.
“The aldol condensation process can create defects in the polymer sequences, like missteps in a molecular dance, which can disrupt the flow of electrons through the material, reducing efficiency and reliability in devices. Our findings could have wide-reaching implications for the development of high-performance, flexible, low-cost electronics and help reduce reliance on rare or toxic metals in manufacturing,” said Professor Giovanni Constantini, from the University of Birmingham, lead author of the paper.
These defects, and the secondary reaction pathways that produce them, have not been primarily considered because conventional analytical techniques are unable to detect them.
The researchers used a powerful imaging technique called scanning tunnelling microscopy (STM) combined with electrospray deposition, enabling them to examine polymers at the molecular level; zooming in to see how the building blocks were connected, one molecule at a time.
They studied four different polymers created using aldol condensation, and discovered two main types of defects:
• Coupling defects – these are like kinks or bends in the polymer chain, caused by the building blocks connecting in the wrong orientation or position
• Sequence defects – these occur when the order of the building blocks is incorrect, like having two of the same blocks in a row when they’re supposed to alternate
By adjusting the chemical design and purifying the building blocks before polymerisation, however, the team was able to significantly reduce the number of defects.
One approach involved using aldol condensation to create small, well-defined molecules, which were then linked using a different method, producing much cleaner polymer chains.
“This is a major step forward in understanding how to make better-performing, more sustainable materials for electronics,” said Professor Costantini. “It shows that even green chemistry needs careful control to deliver the best results.”
