Benefits of organic light emitting diodes (OLED) go beyond simple static image quality and the responsiveness and smoothness of the display itself. These are capable of refresh rates a 1000 times faster than standard LED-backlit liquid crystal display (LCD) panels. So these can easily catch a blur that might have been lost in traditional displays. But are we happy with such blazing-fast displays?
No, we definitely are not. Numerous researches are underway to further improve OLED efficiency and illumination at a lower cost. After all, a reduced price point sells. It helps boost displays for televisions, phones, tablets and more to an entire new level.
Like LCDs, OLEDs produce colour through green, red and blue sub-pixels on screen. However, there is a catch.
Blue emitters are hard to find
Organic molecules emitting blue light have been rare to find. Dr Mark Thompson, who is Ray R. Irani chair of chemistry, department of chemistry, chemical engineering and materials science, University of South California, USA, explains, “Blue phosphorescence remains a central challenge and has been so for the last ten years.”
Manufacturers have created organometallic molecules to overcome this problem. The problem here lies with expensive transition metals like iridium. These are used to enhance the molecule through phosphorescence, in order to improve efficiency. This solution, though expensive, does not produce stable blue colour.
Advanced matrix OLED (AMOLED) and super AMOLED has been one of the interesting application areas. Some of the best displays in the recent past have been the super-AMOLED ones like that of Samsung Galaxy Note 7.
Towards the new blue
Molecular Space Shuttle, a large-scale computer-driven screening process, was developed by a research team from Harvard University, USA, in collaboration with Massachusetts Institute of Technology, and Samsung. It identifies new OLED molecules that perform at par with industry standards through machine learning, cheminformatics, theoretical and experimental chemistry.
Kyulux, an advanced materials startup working in the field of OLED displays and lighting technology, has also announced securing Molecular Space Shuttle deep-learning system license for the discovery of materials for display and lighting applications. However, this process is more suited for finding dopants and not base materials.
An interdisciplinary team led by Dr Alan Aspuru-Guzik, professor of chemistry and chemical biology, Harvard University, has been working on replacing these organometallic systems with entirely organic molecules. Some algorithms were developed to compute the likelihood of efficient outcomes on a candidate pool of about 1.6 million. This helped prioritise molecules to be virtually tested and significantly reduce computational costs. Hopefully, these could help bring the prices down for hi-end devices like a MacBook Pro or Galaxy.
Successful reduction in the candidate pool.
Machine-learning tools have helped predict the colour and brightness of molecules using simple quantum chemical calculations. Finally, these were left with hundreds of blue molecules with performance improvement over organometallic molecules.
Harvard’s Office of Technology Development has a pending patent application on the molecules while they consider commercialisation opportunities. Further research in the field is expected to lead to molecules that could be used in flow batteries, solar cells, organic lasers and more.
Thompson says, “We are now looking at an approach that can capture high energy before the molecules disintegrate.” If we could stabilise reactive states, it could open up a lot of possibilities. Let us find out what is degrading the blue molecules, and what could possibly lead to some very interesting displays in the future.
TADF could hold another answer.
According to experts, thermally-activated delayed fluorescence (TADF) could solve the challenge of efficient and stable blue emission. Initial TADF devices, however, lost five per cent of their brightness in just 85 hours, which fuelled further research into the process.
Claims have been made regarding extending this time by eight times since then. In the newly-developed modification, two extremely thin (1nm to 3nm) layers of lithium-containing molecule, Liq, are placed on each side of the hole-blocking layer. This brings electrons to TADF material and prevents holes from leaving before contributing to emission.
A team led by Prof. Tae-Woo Lee, department of materials science and engineering, Pohang University of Science and Technology, South Korea, used pure organic TADF emitters that show very high internal quantum efficiency of nearly 100 per cent without precious metals. Easy synthesis due to use of pure organic molecules reduces synthesis cost. This is a big leap towards the development of inexpensive and solution-processed OLED displays and solid-state lighting.
Pinning together different refractive indices of titanium oxide and a conductive polymer, composite electrodes were developed by a collaboration of Korea Advanced Institute of Science and Technology, South Korea, and Pohang University of Science and Technology researchers. This increased the optical efficiency to about 1.5 times.
Usually, increasing the efficiency leads to a drop in flexibility. However, due to the involvement of a composite electrode, it endured strains four times stronger than convention. Even after 1000 bending cycles at a radius of curvature as small as 2.3mm, OLEDs remained intact and operational.