The recent display revolution has made use of organic light emitting diodes (OLEDs) to generate the RGB colors required to construct all colors. The advantage of OLED materials are lower power consumption, blacker backs, and much better color contrast. While the term OLED suggests the use of organic based molecules, these lack overall quantum efficiency because organic molecules, when excited, only access singlet excited states. This reduces the maximum efficiency to no more than 25%. This loss of efficiency can be recovered by the use of phosphorescent transition-metal complexes that can populate both singlet and triplet excited states through quantum mechanical spin-orbit coupling, yielding a theoretical efficiency of 100%. Additionally, because of this higher efficiency, only about 5% of the emissive layer is the actual emitter complex, which is important for maintaining the display flexibility associated with OLEDs. However, predicting what complexes will give the desired color and high performance in a device architecture is dependent on many variables.

Dr. Morello’s research employs 4-component density-functional theory (DFT) calculations to determine both the expected color of emission, the radiative rates and also radiative lifetimes of organometallic complexes. It has been shown experimentally that shorter radiative lifetimes of excited states correlate with more efficient devices by eliminating the time available for non-radiative pathways. By calculating radiative lifetimes of well-known complexes, his group will first prove the accuracy followed by the development of new complexes for efficient emissive properties through electronic and steric requirements of ligands and metal centers.

Working with program designers in Norway, calculations run on HPC clusters at CCAST/NDSU will help to understand the efficiencies of complexes. Because relativistic calculations are not available in most commercially available software platforms, they aim to lead the charge of OLED emitter development and device property predictions for next-generation OLED displays.