Advanced X-ray techniques have revealed new structural details about the specific arrangement of atoms in conjugated polymers, an important class of materials that are used in LEDs, organic solar cells, transistors, sensors and thermoelectric power devices.
Conjugated polymers are organic macromolecules with an unusual electronic structure, a backbone with alternating single and double bonds, which produces interesting, useful optical and electrical properties. Because of a level of disorder in the arrangement of atoms in conjugated polymers, the use of direct methods, such as conventional X-ray diffraction, reveals only limited information.
Researchers from Monash University led by Prof Christopher McNeill, in association with American collaborators at Brookhaven National Laboratory, have demonstrated that resonant X-ray diffraction performed at X-ray energies that resonate with sulphur atoms in the polymer can discriminate between different types of packing structures in conjugated polymers. The research was published in the Journal of the American Chemical Society and earned an inside back cover of the publication (pictured above).
Instrument scientist Dr Lars Thomsen said near-edge absorption fine structure (NEXAFS) spectroscopy performed on the Soft X-ray spectroscopy beamline at the Australian Synchrotron provided spectroscopic information that was necessary for the analysis of the resonant diffraction data.
Thomsen has collaborated on the structural investigation of conjugated polymers using synchrotron techniques with McNeill, Professor of Materials Science and Engineering at Monash University for many years. The resonant diffraction measurements were undertaken at NSLS-II at Brookhaven National Lab in the United States by first author Guillaume Freychet.
Conjugated polymers have a ring structure, like benzene, with orbitals coming out above and below the rings. The electrons move through the orbitals, Dr Thomsen explained. “If you have a device that has a couple of electrodes on either side and a conjugated polymer layer in between, you want all the polymers orientated in the same direction, so the electrons can move through freely from one electrode to the other,” he added.
NEXAFS can provide information regarding the alignment of the polymers with respect to the surface, he said. When using organic polymers in a device, it is important to align the molecules in a certain way to get the best performance.
Thomsen said the energy range for the experiment was a little beyond what is usually used on the instrument, but they were able to acquire data with good results. Elliot Gann of The National Institute of Standards and Technology in the United States, who previously worked at the Australian Synchrotron, also contributed to the research.
Thomsen said a new Medium energy X-ray absorption spectroscopy beamline under construction at the Australian Synchrotron as part of Project bright, will be ideally suited for these experiments in the future.
Australia developing next-gen solar tech
According to another press release, The US government announced, on 26 March 2021, that it will fund a pilot-scale test facility to demonstrate a next-generation concentrated solar thermal (CST) technology that Australia helped develop.
The falling particle CST technology is 100 per cent renewable and can store multiple hours of thermal energy for firm, fully dispatchable power generation. It is a simple, thermally stable and relatively low-cost system with applications for power generation and heat processing across mining, mineral processing, chemical processing and other high-temperature industrial processes.
Australia’s involvement was managed through the Australian Solar Thermal Research Institute (ASTRI), a ten-year, $100 million international research collaboration funded (50 per cent) by the Australian Renewable Energy Agency (ARENA).
Australia’s national science agency, CSIRO, has been one of the main external contributors to the falling particle technology being developed by US-based Sandia Laboratories, which will receive US$25 million from the US Department of Environment to aid in the construction of a demonstration plant in Albuquerque New Mexico.
The technology involves a falling curtain of small particles which is heated by concentrated sunlight.
The particles are heated to well over 700 °C and then stored as thermal energy for use day or night, to generate electricity or to provide high-temperature industrial process heat. Temperatures over 1,000°C are possible depending on the process.
This next phase of the US project will design and test a megawatt-scale thermal falling particle CST system. As a demonstration project, it will have the potential to operate for thousands of hours and has been designed for over six hours of energy storage at temperatures well over 700 °C.
