At the Paul Scherrer Institute (PSI), researchers have discovered a green luminescent substance that could enable OLEDs to deliver high light yields inexpensively and on a large scale. Many of the materials that have been considered for OLEDs contain expensive additives such as iridium, making their large-scale application impractical. The researchers at PSI turned to the copper-containing compound CuPCP. Copper is a relatively inexpensive metal, and the compound CuPCP can be easily produced in large quantities. CuPCP gives off an intense green glow not only when current is applied, but also under UV light. Courtesy of University of Bremen/Matthias Vogt. At the Swiss Light Source (SLS) and the x-ray free-electron laser (SwissFEL) facilities at PSI and the European Synchrotron Radiation facility in France, the researchers investigated the short-lived excited states of CuPCP. They examined how the structure of the compound changed when it absorbed energy, and how the charge was distributed over individual atoms after excitation. “We wanted to understand what the excited state of the compound looks like,” physicist Grigory Smolentsev said. “This reveals how high the losses of energy that will not be released as light are likely to be, and it shows us how we can possibly minimize these losses.” The measurements taken by the researchers confirmed that the CuPCP substance could potentially be a light-emitter for OLEDs. The CuPCP compound’s chemical properties make it possible to achieve a high light yield, the researchers said. One reason for this is that the molecule is relatively stiff, and its 3D structure changes only slightly when excited. Grigory Smolentsev in front of SwissFEL. Courtesy of Paul Scherrer Institute/Mahir Dzambegovic. In addition to ascertaining the suitability of CuPCP as an OLED luminophore, the experimental data obtained at the three research facilities could help improve theoretical calculations regarding the suitability of other molecules as OLED light emitters. “So in the future it will be possible to better predict which compounds are more suitable for OLEDs and which less,” Smolentsev said. “The measurement data will help the chemists understand which part of the molecule stands in the way of high efficiency. And of course, how the compound can be improved to increase its light output.” The CuPCP substance is a yellow solid that gives off a luminescent green glow when it is dissolved in a liquid or when a layer of it is placed on an electrode. The researchers plan to further optimize the compound for use in OLEDs. The research was published in Nature Communications (www.doi.org/10.1038/s41467-020-15998-z).