A research team led by Professor Lee Yeon-jin in the Department of Physics at Yonsei University, together with LG Display, has become the first in the world to reveal why the key material widely used in mass production of large organic light-emitting diode (OLED) TVs, "magnesium fluoride," actually boosts performance.
Magnesium fluoride is a compound in which magnesium and fluorine atoms are bonded. Because it is relatively inexpensive and stable in production, it has long been used as a hole injection layer material in OLED panels. The hole injection layer is the layer that helps charges enter smoothly.
The issue, however, is that magnesium fluoride has been known as an "insulator" that does not conduct electricity well. Neither academia nor industry had a clear explanation for why an insulator helps improve performance in a hole injection layer where charges must move. As a result, manufacturing sites faced the limitation of having to tune processes through experience and trial and error without understanding the principle.
To solve this long-standing question, the team tracked the changes that occur when magnesium fluoride mixes with organic semiconductors. They confirmed for the first time that magnesium fluoride, long regarded only as an insulator, pulls electrons from organic molecules. Simply put, even without external stimuli, electron transfer occurs naturally the moment organic materials and magnesium fluoride are mixed.
In this process, magnesium fluoride increased holes, that is, "positive charge carriers." In fact, it increased the hole concentration by more than 50 times compared to before. When there are more holes, charge flow becomes smoother, allowing the process by which OLEDs emit light to proceed more efficiently.
The team also identified another important change. When magnesium fluoride is mixed with organic materials, it does not form its usual crystal structure but changes into a glass-like disordered "amorphous state." This structural change lowers the energy barrier that tends to form at the interfaces where different materials meet, helping charges move more easily even at lower voltages.
Song Ki-uk, a doctoral candidate at Yonsei University and first author of the paper (employed at LG Display), said, "Magnesium fluoride is essential in mass production of large OLEDs, but parts of why it is effective had not been clearly laid out," adding, "Now that the mechanism is clear, we expect it will genuinely help develop high-efficiency, long-lifespan panels."
Professor Lee said, "There is great significance in the virtuous cycle of scientifically interpreting a technology first used in industry to identify its principles and then linking the results back to industrial competitiveness."
The results were published on the 30th (local time) in Advanced Functional Materials, an international journal in the field of materials.
References
Advanced Functional Materials (2025), DOI: https://doi.org/10.1002/adfm.202525568