Overview of OLED Colorization Technology and its Advantages and Disadvantages
Overview of OLED Colorization Technology and its Advantages and Disadvantages
I. Advantages of OLED 1. Thickness can be less than 1 mm, only 1/3 the thickness of an LCD screen, and it is also lighter. 2. Solid-state structure, without liquid substances, therefore better shock resistance and less prone to breakage. 3. Almost no viewing angle issues; the image remains undistorted even when viewed from a wide angle. 4. Response time is one-thousandth that of LCD, eliminating ghosting in motion images. 5. Excellent low-temperature performance; it can still display normally at -40 degrees Celsius, while LCD cannot. 6. Simpler manufacturing process and lower cost. 7. Higher luminous efficiency and lower energy consumption than LCD. 8. Can be manufactured on substrates of different materials, allowing for flexible, bendable displays. II. Disadvantages of OLED 1. Lifespan is typically only 5000 hours, shorter than LCD's at least 10,000 hours. 2. Mass production of large-size screens is not possible, therefore it is currently only suitable for portable digital products. 3. There is a problem with insufficient color purity, making it difficult to display vivid and rich colors. Modification to point 2: The lifespan of current OLEDs far exceeds 5000 hours, and larger-sized OLED panels with very vivid colors have been produced. As of around July 2007, the highest-performing fluorescent materials were those from Idemitsu Kosan of Japan. Red light efficiency reached 11 cd/A with a lifespan of up to 160,000 hours; green light efficiency reached 30 cd/A with a lifespan of 60,000 hours; the high-efficiency, long-lifespan blue light material BD-2 (0.13, 0.22), currently under development, has an efficiency of 8.7 cd/A and a lifespan of 23,000 hours. Regarding phosphorescent materials, UDC's red phosphorescent material has chromaticity coordinates of (0.67, 0.33), achieving an efficiency of 15 cd/A and a lifetime exceeding 150,000 hours at 500 cd/m². Its green phosphorescent material has chromaticity coordinates of (0.34, 0.61), achieving an efficiency of 65 cd/A and a lifetime exceeding 40,000 hours at an initial brightness of 1000 cd/m². The most difficult to obtain is the blue phosphorescent material. The phosphorescent material achieves an efficiency of 30 cd/A and a lifetime of 100,000 hours at an initial brightness of 200 cd/m². Overall, the luminous efficiency and lifetime of the red, green, and blue phosphorescent materials for OLEDs basically meet the requirements for practical application. Based on the above data, current OLEDs have at least 20,000 hours of operating time at 500 cd/m². III. OLED Colorization Technology Full-color display is a crucial indicator of a display's market competitiveness. Therefore, many full-color technologies are applied to OLED displays. Based on panel type, these typically fall into three categories: RGB pixel independent emission, color conversion, and color filter. 1. RGB Pixel Independent Emission Utilizing luminescent materials for independent emission is currently the most widely adopted color mode. It employs precise metal shadow mask and CCD pixel alignment technology to first prepare the red, green, and blue primary color luminescent centers. Then, the mixing ratio of the three colors is adjusted to produce true color, allowing the three-color OLED elements to emit light independently, forming a pixel. The key to this technology lies in improving the color purity and luminous efficiency of the luminescent material; the metal shadow mask etching technology is also crucial. Currently, the organic small-molecule luminescent material AlQ3 is an excellent green light-emitting small-molecule material, exhibiting excellent green light purity, luminous efficiency, and stability. However, the best red-emitting small-molecule materials for OLEDs have a luminous efficiency of only 31mW and a lifespan of 10,000 hours, and the development of blue-emitting small-molecule materials is also slow and difficult. The biggest bottleneck facing organic small-molecule luminescent materials lies in the purity, efficiency, and lifespan of red and blue materials. However, by doping the host luminescent material, researchers have obtained blue and red light with relatively good color purity, luminous efficiency, and stability. The advantage of polymeric luminescent materials is that their emission wavelength can be adjusted through chemical modification, and various colors covering the entire visible light range from blue to green to red have been obtained. However, their lifespan is only one-tenth that of small-molecule luminescent materials. Therefore, the luminous efficiency and lifespan of polymeric luminescent materials need to be improved. Continuously developing high-performance luminescent materials should be a challenging and long-term task for materials scientists. With the increasing colorization, resolution, and size of OLED displays, metal shadow mask etching technology directly affects the quality of the display panel, thus placing more stringent requirements on the dimensional accuracy and positioning accuracy of the metal shadow mask pattern. 2. Color Conversion Color conversion combines a blue OLED with a color conversion film array. First, a blue-emitting OLED device is fabricated. Then, the blue light from the OLED excites a color conversion material to produce red and green light, thus achieving full color. The key to this technology lies in improving the color purity and efficiency of the color conversion material. This technology does not require metal shadow mask alignment; it only requires the deposition of blue OLED elements, making it one of the most promising full-color technologies for future large-size full-color OLED displays. However, its disadvantages include the color conversion material's tendency to absorb ambient blue light, causing a decrease in image contrast, and light guide issues that also reduce image quality. Currently, Idemitsu Kosan of Japan, which possesses this technology, has produced a 10-inch OLED display. 3. Color Filter This technology utilizes a white OLED combined with a color filter. First, a white-emitting OLED device is fabricated. Then, the three primary colors are obtained through a color filter, and these three primary colors are combined to achieve color display. The key to this technology is obtaining high-efficiency and high-purity white light. Its manufacturing process does not require metal shadow mask alignment technology and can utilize the mature color filter fabrication technology of LCD displays. Therefore, it is one of the promising full-color technologies for future large-size full-color OLED displays. However, using this technology results in light loss of up to two-thirds due to the color filter. Currently, TDK Corporation of Japan and Kodak Corporation of the United States use this method to manufacture OLED displays. The three full-color OLED display manufacturing technologies—independent RGB pixel emission, color conversion, and color filter—each have their own advantages and disadvantages. The choice depends on the process structure and organic materials used.
