- You are here:About
- Research and Development
- Introduction of OLED Technology
- Konica Minolta' s Spirit of Innovation
- Vol. 01 - White OLED Combining High Efficiency With Long Life
- Target of Power Efficiency
Research and Development
About
Development of Phosphorescent White OLED
with Extremely High Power Efficiency and Long Lifetime
Tomoyuki Nakayama, Kunimasa Hiyama, Keiichi Furukawa, and Hirofumi Ohtani
Konica Minolta Technology Center, Inc., Display Technology R&D Laboratories,
2. Target of Power Efficiency
To replace a conventional light source with a OLED device, it is important to raise power efficiency of OLED to the level that can compete with the level of conventional light sources. Generally, power efficiency is about 10 - 20lm/W for electric bulbs and 60 - 90lm/W for fluorescent lamps. Therefore, we aimed at 60lm/W as the first step of development of white OLED.
It is well known that considerable amount of the emitted light of OLED is confined in the device. Therefore various light out-coupling techniques have been developed to take out the confined light to the outside of the device. The confined light exists as glass mode or waveguide mode, and it is comparatively easy to take out the glass mode. Using light out-coupling technique to take out the glass mode light, 1.6 times increase of the external quantum efficiency could be achieved.
Assuming the 1.6 times of the efficiency of light out-coupling, 38lm/W without light out-coupling is necessary to obtain 60lm/W. Then how much EQE and drive voltage of device are necessary to get this power efficiency?
Fig.1 shows the relations with power efficiency and drive voltage, and the dependence on EQE in a case of the OLED device which emits warm white color.
For example, it is shown that the drive voltage less than 3.8V with 20% EQE is necessary to obtain 38lm/W, although these values change to some extent depending on the emission spectrum. If the EQE is 12.5%, the voltage less than 2.5V is necessary, and the voltage less than 1V if it is 5%. The voltage less than 2.5V is less than emission energy of the blue emissive material so that it is impossible to make a device. That is to say, the achievement of EQE of around 20% is required to get 38lm/W.
By the way, because the maximum of EQE in fluorescent OLED is generally around 5%, power efficiency of 38lm/W cannot be obtained. It is the reason that we wrestle with the development of phosphorescent OLED.
Based on such consideration, we developed organic materials and designed organic layer structure paying attention to achieve 20% EQE and the drive voltage less than 4V.
Previous Page
