Experts have found a new technique to simplify the structure of high-efficiency blue organic light-emitting diodes (OLEDs). This could lead to longer-lasting and higher definition TV and smartphone screens.
What are OLEDs?
OLEDs refer to a class of organic electronic materials which glow when electricity is applied. They are already commercially present in smartphones, with the potential to be more efficient than competing technologies such as liquid crystal display (LCD).
OLED displays include screen pixels which are made of three different colored subpixels: red, green and blue. These subpixels light up at various intensities to create different colors. OLED screens work in a very specific way. When a pixel is off, it creates true blacks. If no light is emitted, it results in deeper blacks and more vibrant colors compared to LCD screens.
While OLED TV screens have vivid picture quality, they also have some drawbacks like high cost and short lifespans. Additionally, the subpixels that emit blue light are not stable and could be susceptible to burn-in, a permanent discoloration left by a fixed image on the screen for a long period of time.
Creating More Stable Blue Light
Overcoming these issues has been the goal of experts from Cambridge, Northumbria, Imperial, and Loughborough universities. In the paper "Suppression of Dexter transfer by covalent encapsulation for efficient matrix-free narrowband deep blue hyperfluorescent OLEDs", the researchers describe a new design which could lead to simpler, less expensive systems with purer and more stable blue light.
Led by Hwan-Hee Cho, the research team built an OLED like a sandwich, with organic semiconductor layers between two electrodes. An emissive layer is placed in the middle of the stack where it lights up when powered with electricity. As a result, the electrical energy goes into the molecules, which release the extra energy as light.
Ideally, OLED should turn most of the electrical energy into light, but the energy can sometimes get diverted and degrade the OLED structure. This is particularly observed with blue light where OLED efficiency and lifetime is reduced.
To gain understanding of how this energy transfer works, the team collaborated with Dr. Marc Etherington from Northumbria University's Department of Mathematics, Physics and Electrical Engineering. Using his knowledge on the properties of organic semiconductors, he led a spectroscopic analysis of the triplet energies of the molecules.
Dr. Etherington's findings helped the research team create a complete picture of the energy level arrangement. From this, the researchers designed a new light-emitting molecule with added shields to block the destructive energy pathways and manage the way molecules interact. Understanding how efficient a molecule in an OLED can be provides insights into the design and use of the material in the future, unlocking the path towards higher device performance.
According to Dr. Etherington, the newly created molecule created a channel to develop more efficient OLEDs which can drive down the energy consumption of electronic devices. As modern society works towards net zero targets, this innovation can have a significant impact for both device manufacturers and consumers.
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