Research and Development

Development of Phosphorescent White OLED
with Extremely High Power Efficiency and Long Lifetime

• Abstract
• Introduction
• Target of Power Efficiency
• Experimental
• Performance of Efficiency and Lifetime
• Performance of Color Stability
• Performance of Thermal Stability
• Summary and Conclusion Remarks
• References

1. Introduction

From a recent environmental problem and energy supply circumstances, light sources of low energy consumption and eco-friendly are demanded. An enormous amount of research effort goes into the field. And inorganic and organic light-emitting diodes attract attention as candidates of this new light source for these past several years.

Organic light-emitting diode (OLED) is regarded as a powerful candidate because it is an area light source, can be driven at low voltage such as several voltage, and does not include a material which is harmful to the human body and environment like mercury. As a light source for illumination or backlight, a white light is usually required. To realize a white OLED device, plural light emissive materials such as blue, green, red are used　generally.

OLED is classified roughly into two types by a difference of mechanism of emission, namely the fluorescent OLED or phosphorescent OLED. It is well known that the phosphorescent OLED is advantageous from an aspect of emission quantum efficiency [1]. For example, Y. Tung et al. reported a phosphorescent white OLED with power efficiency of 18.4lm/W and 16% external emission quantum efficiency (EQE) [2]. However it has been difficult to make a phosphorescent white OLED of a practical performance level because blue phosphorescent materials didn’t have enough performance, especially operating stability. Recently, remarkable improvement was achieved about the operating stability of blue phosphorescent material. M. S. Weaver et al. reported blue phosphorescent OLEDs with improved operating stability [3]. And B. W. D’Andrade et al. reported a phosphorescent white OLED with 14% EQE and a long Lifetime [4].

Konica Minolta Technology Center, Inc. also pushes forward development of blue phosphorescent materials, and recently succeeded to develop blue phosphorescent dopant and host materials which have superior durability. These materials have 16000 hours of Lifetime from initial luminance to a half at initial luminance of 300cd/m². By using these materials and technology of organic layer design, we developed phosphorescent white OLED of performance, such as power efficiency, operating stability and storage stability, at a level of practical use. In this paper, we discuss outline of the technology and major performances of the white OLED developed.

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