Graduate Student (Cavagnero) & Department of Communications
Organic light emitting diodes (OLEDs) are non-metallic layers situated between charged surfaces that will emit light in response to electrical currents. Most everyone interacts with organic light emitting diodes on a daily basis, maybe without even realizing it. In fact— you might be using one right now!
Numerous devices, such as: television screens, computer monitors, cell phones and gaming consoles all use OLEDs in their display screens. Understanding how to make more efficient OLEDs can impact the battery life of these devices and contribute to their longevity.
Professor Mark Ediger’s group at the University of Wisconsin-Madison Department of Chemistry doesn’t make OLED displays, but they are interested in understanding fundamental questions about these organic layers that will be the framework for OLED development and enhancement moving forward.
Graduate student and lead researcher on the project, Marie Fiori believes that, “… There
is a value to fundamental research, because it allows us to learn what we don’t know.”
The layers of material that make up OLED devices are created using a process called physical vapor deposition. This is when thin films of material can be produced by vaporizing organic materials and then condensing the material in a thin layer on top of a surface. Deposition conditions alter the way molecules pack together to form the glassy layers of OLED.
Interfaces between glassy layers are prevalent throughout all OLED devices and vital for device performance; however, little is known about how the molecular packing that can affect the packing in the layer next to it.
Fiori and her collaborators set out to understand the structure of these glassy films by using two different techniques. They could compare the results that they obtained with thin layers to thicker layers of the same molecules.
First, Fiori used Grazing-incidence wide-angle X-ray scattering (GIWAXS). This technique can provide a profile of the wide-angle x-ray scattering (i.e. how x-ray waves, like at the doctors office, interact with a material) that is collected from a thin film to be compared to thicker layers of film. Similarities in the scattering indicate that the overall packing of a material hasn’t changed, and differences suggest that the packing has changed. Measurements via spectroscopic ellipsometry (VASE), show how the direction of light waves changes once it interacts with a material. VASE can also discern differences in the optical properties that give information about molecular packing in the film.
Ultimately, Fiori and her collaborators found that an underlying layer does not change the overall structure of an organic material, even for layers as thin as 5 nanometers, which is about 1/1,000,000 of the width of a strand of hair! Ediger mentioned that they kept looking at the results more and more closely, but ended up with the same conclusion.
Fiori believes that these findings will help develop better OLED devices in the future because these results indicate that physical vapor deposition can be used to finely tune the layers that make up OLED devices, no matter how thin the layers are, or the materials with which they are interacting.
Fundamental research that answers important questions about OLED devices will not only enhance their functionality and longevity, but will influence how we interact with screens and devices on a daily basis.