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Material and Structure Problem Facing OLED High Light Efficiency
alexyang   1/29/2013 4:43:08 AM

In order to reach the level of fluorescent lamp in efficiency, OLED lighting should have power efficiency of at least 70lm / W; despite the reported 100lm/W OLED lighting, which is manufactured in a very extreme condition. The efficiency of generally-made OLED lighting device is only 30~50lm/W, which is significantly far from requirements.

On the material side, to reach such a high efficiency, the phosphorescent material with luminous efficiency up to 100% is the only choice; currently the green and red phosphorescent material is of no problem, the urgent problem lies in blue phosphorescent material which can plays an important role. At present, there is very lack of high-efficiency and high-stability blue phosphorescent material, the major technical difficulty currently hindering the efficiency increase of OLED lighting devices, so develop the production technology of practical, high-efficiency, high-stability blue phosphorescent material has become the main research direction of the field.

From the device structure point of view, the effective device structure design is also the key to improve the efficiency of the device. The currently good device structure includes the structure of the multiple light emitting layers, a single light emitting layer structure, the laminated structure, and a top emission structure. The multiple light emitting layer structure is used most to make the white OLED device with mature technology and the best device performance, but the complex process may have an impact on its yield and production costs in the future OLED lighting devices; in addition, this structure device sometimes would show disadvantage of spectrum and chromaticity coordinates changing with the drive voltage. However, due to the good performance of the device and that the problem of spectrum and chromaticity coordinates changing with the drive voltage can be solved through the device structure design, so if the yield can be controlled and improved, this structure is still a mass production technology that has been used by Philips, UDC, Novaled.

Although the single light emitting structure can avoid chromaticity coordinates changing with the drive voltage at some extent, and also enable streamline process, the disappointing efficiency and stability problems prevent this structure from being adopted in practical application.

The laminate structure, with the characteristics of a single light emitting layer and the light emitting layer structure, is a device structure cascading multiple light emitting cells through the charge generation layer. Laminated device has a very good spectral stability, and high light-emitting efficiency, high luminance and excellent stability and other characteristics, enabling it very competitive; if the complex process of laminated structure can be further improved; laminate structure is projected to become the mainstream technology of the white OLED production.

Top emission structure, owing to its advantage in effective emitting area and improving efficiency, is also possible to become an important technology development direction of white OLED lighting; besides, the combination of other  structures and top emission structure can develop more high-performance white OLED.

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