LG announces blue PHOLEDs: Will mobile devices now become more efficient?

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The significantly more efficient emission variant phosphorescence generates three times as many light quanta with the same excitation energy as the fluorescent emission previously used for blue. In other words, PHOLEDs only need a quarter of the electrical energy for the same amount of light.

As panel specialist LG Display explained in a press release, it has already been able to test phosphorescent light generation on a mass production line. The test was successful and commercialization appears to be within reach.

Efficient blue emitters

While red and green light is already generated using phosphorescence, it has not yet been possible to use efficient light generation for blue light in organic displays for mobile devices, televisions or monitors.

Purely fluorescent OLED emitters only use the singlet excitons, which means that all triplets and therefore three quarters of the excitons are lost during light generation – the internal quantum efficiency (IQE) is only 25 percent. The blue pixels therefore require much more energy or shine less brightly. However, the service life of blue phosphorescent emitters, known as PHOLEDs, has so far only been a few hundred hours at high luminance levels.

Cooperation with UDC

The US company Universal Display Corporation (UDC) has been working on phosphorescent organic phosphors for a long time and is said to have already achieved emitters with a slightly longer service life in the laboratory. However, UDC has also required special dopants such as iridium, osmium or platinum for PHOLEDs to date: the rare metals (iridium is the second rarest metal on earth) drive up costs and hinder a permanent – and sustainable – material supply. Every year, the company announces that it will achieve a breakthrough by the end of the year, but so far this has not happened.

Now the cooperation between UDC and LG Display, which was launched in late summer 2024, appears to be more successful. LG has used its recently unveiled hybrid tandem OLED structure, layering a layer of blue phosphorescent emitters on top of the blue stack of fluorescent emitters. By combining the long-lasting fluorescent emitters with the more efficient phosphorescent emitters, the tandem stack is said to require 15 percent less power overall and at the same time be as stable as previous OLED panels. Although this is less than expected or possible, it is still an important step, especially for mobile devices.

Secured with patents

LG Display has already applied for patents for its new technology in South Korea and the USA, the company explained. This is likely to be a safeguard against Korean OLED competitor Samsung Display. The latter acquired all 700 patents of the German start-up Cynora from Bruchsal for 300 million dollars in 2022. At the time, Cynora had failed with the development of TADF technology (Thermally Activated Delayed Fluorescence), which was intended to produce PHOLED emitters.

LG plans to demonstrate the first hybrid tandem OLEDs next week at Display Week in San José on a small smartphone panel and a medium-sized tablet panel. (uk)