A team of Korean researchers has developed a deep blue-emitting phosphorescent OLED which is four times more efficient than OLEDs that use fluorescent materials.
The Korea Research Foundation announced on June 14 that a research team led by Jin Sung-ho, a professor at Busan National University, has developed a deep-blue phosphorescent material and device that has superior external quantum efficiency and field lighting characteristics compared to fluorescent materials.
OLEDs are receiving much attention as a next-generation light-emitting device as they have an excellent wide optical night angle, fast response speed, and highly luminous characteristics. OLEDs are divided into the fluorescent and phosphorescent types. The former has a 25 percent internal quantum efficiency, while the latter can achieve 100 percent internal quantum efficiency. Accordingly, fluorescent OLEDs are being replaced by phosphorescent ones. However, blue phosphorescent OLEDs still have their limitations — they are difficult to apply to actual displays because they do not satisfy color TV standards due to very low efficiency and luminance.
The research team solved low luminance and efficiency problems by adjusting doping concentration to optimize concentration imbalance between electrons and pores inside an OLED luminous layer. Although the external quantum efficiency (the ratio of actual light emitted outside the material) of current dark blue phosphorescent OLEDs is only 15 percent, the researchers achieved 24 percent efficiency by controlling the concentration of electrons and pores in the light emitting layer.
“While resolving the problem of low external quantum efficiency, we can satisfy NTSC’s blue standards that establish luminous characteristics and color TVs’ color representation standards, so we can use them for future QLED rear lights and next-generation displays,” said Prof. Jin.
The research results were published in the June 9 edition of the international journal “Advanced Materials.”
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