Discussion on the application of OLED in lighting field

Yao Qi Chen Dahua Lin Yandan Institute of Electric Light Sources, Fudan University, 200433

Abstract: Due to the low cost of OLED technology, large color adjustable range, thin and light, etc., it has developed rapidly in the display field in recent years. With the improvement of OLED light efficiency and the development of white OLED technology, OLED has appeared in the trend of lighting. Based on the current efficacy and power of white OLEDs, this paper attempts to simulate the OLED lighting devices from software simulation and design the lighting. By comparing with the theoretical analysis of fluorescent lamps, the advantages and disadvantages of OLEDs applied to general illumination are discussed. The results show that the prospect of white OLED application in the field of lighting is promising, but its efficiency and longevity still need to be further improved.

Key words: OLED lighting; surface light source; lighting design

The Investigations of OLED's Application on Lighting

Yao Qi, Chen Dahua, Lin Yandan
(Institute for Electric Light Sources, Fudan University, 200433)

Abstract: In recent years, OLED technology has been rapidly developed because of its lower cost, broad adjustable color range and lightness. With the improvement of the luminous efficacy and white light technology, OLEDs gradually find their application in the field of lighting. Based on Current white OLED's efficiency, power, etc, the author simulates the OLED light source by virtue of software. Through theoretical analysis and the comparison with fluorescent lamps, the author discuss the strength and weakness of OLED's application in the general lighting. Results show that white OLED has the opportunity to be used for general lighting, while its efficiency and lifetime need further improvements.

Key words: OLED lighting; surface light source; lighting design

1 Introduction

OLED (Organic Light Emitting Diode) refers to the phenomenon that organic semiconductor materials and luminescent materials are driven by electric field to cause luminescence by carrier injection and recombination. The principle is to use ITO transparent electrode and metal electrode as the anode and cathode of the device respectively. Under a certain voltage, electrons and holes are injected from the cathode and the anode to the electron and hole transport layers, respectively. The electrons and holes pass through the electron and the hole respectively. The hole transport layer migrates to the light-emitting layer and meets in the light-emitting layer to form excitons and excite the light-emitting molecules, and the light-emitting molecules emit visible light through the radiation. Radiation light can be observed from the ITO side, and the metal electrode film also functions as a reflective layer. From the current technological development of organic electroluminescent components, green light, blue light, and red light have related material development, among which green light technology is the most mature, and red light technology is stepping up research and development. The OLED structure is shown in Figure 1. [1] [2]

The earliest discovery of OLED was in 1979. Dr. Deng Qingyun, a scientist who was engaged in scientific research at Kodak Company, discovered that an experimental organic battery was emitting light, and began research on OLED. [2] In 1987, Deng Qingyun and others used ultra-thin film technology and two-layer structure to successfully prepare low-voltage-driven small-molecule OLEDs with a luminance of 1000 cd/m2 and a luminous efficacy of 1.5 lm/W. In 1997, Japan's Pioneer Company used monochrome OLEDs on car audio panels, and OLEDs began to gradually become industrialized. [3] OLED development from hard screen to soft screen, panel size from small to medium to large, color rendering color from monochrome, multi-color to full color. OLED is mainly used on display screens, and with the development of white OLEDs, it will gradually be applied to lighting.

OLED and LED are both solid-state lighting, which has the advantages of low heat generation, low power consumption, fast response, small size, shock and wear resistance, and easy development into light, short and short products. The key technologies for OLED application in lighting are high efficiency and long life. [4]

At the same time, OLED has the characteristics of light and thin, surface illuminating, softness and ductility. By adopting a combination of different light colors, various modules with soft illuminance are formed, which brings a new concept to future lighting design. In lighting applications, the industry goal is to achieve an efficiency of 50-80 lm/W at 1,000 cd/m2. [5] At present, the white light OLED products used for illumination have a luminous efficacy of more than 60 lm/W and a color rendering index of about 80. [6] has been able to meet the needs of some places lighting.

2 white light OLED

There are two main ways to implement white OLEDs for illumination: [7]

1) Wavelength conversion method is to use white light-emitting OLEDs to excite yellow, orange, red fluorescent or phosphorescent powder to achieve white light;

2) The color mixing method is a method of realizing white light by doping or multi-layering by using two kinds of blue and orange light compensation light or red, green and blue primary colors.

The two methods of implementing white light are different in principle. However, the implementation is either by mixing two light colors into white light or by mixing three light colors into white light. Figure 2 shows the mixing of two light colors (blue light and yellow light) into white light. The distribution ratio of blue light and yellow light is different. The OLED light color will be at a certain point on the black line between the two points shown. Figure 3 is a mixture of three light colors to form white light. The red, green, and blue primary colors have different light ratios, and the OLED light color can be changed within a triangle composed of three points. The two light colors are mixed into white light, and the selectivity is small, but the light color consistency is relatively good; the three light color white light has a wide selection range, but the light color consistency is poor. Either way, as long as the ratio is appropriate, you can get a more comfortable white light, the color temperature can be selected in a wide range, and the color rendering can reach 80 or so.

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