Panasonic Corporation has developed a white Organic Light Emitting Diode (OLED) with record luminous efficiency of 114 lm/W (light-emitting area of 1 cm²). Panasonic also achieved luminous efficiency of 110 lm/W with a device with a larger emitting area of 25 cm². Panasonic has used "light extraction technology" and the "all phosphorescent white OLED technology" (technology for the multilayering of the organic emitting layer) to achieve this.
Panasonic explains: OLEDs are capable of emitting any color including white when a voltage is applied by combining organic materials that emit various colors such as red, green, and blue. The soft surface luminescence makes OLEDs suitable for lighting a wide area, and along with the benefits of being not overly bright when viewed directly and a thin and lightweight structure, they are receiving attention as the next generation light source. Lighting devices equipped with the high efficiency OLEDs are considered to achieve a luminous efficiency comparable to or higher than that of fluorescent lamps (approx. 60-80 lm/W) or LED lighting fixtures (approx. 80 lm/W) currently available in the market. Further, a wide variety of applications are expected for OLED devices, including use in general lighting. White OLED lighting will create new value in people's daily lives and has great potential for realizing a comfortable and ecological lifestyle.
The other improvements and achievements using this technology as per Panasonic includes:
Approximately 2.5 times improvement in the light extraction efficiency (light extraction efficiency of about 50%)
Simultaneous achievement of high efficiency and long lifetime*3 (over 100,000 hours)
The technologies Panasonic has used for this achievement are: Built-up Light Extraction Substrate (BLES) technology by the optimized arrangement of the film, glass and air for the suppression of light confinement in the OLED, and optimal design of stacked organic emitting layers with high-efficiency phosphorescent materials.
Typically, the organic light emitting layers have higher refractive indices than those of a glass used for substrate and air, and only about 20% of the total generated light can be extracted because of the total internal reflection at interfaces. Although a variety of technologies have been developed, including a light extraction film attached onto the substrate and a light-scattering structure placed between organic layers and the substrate, the light extraction efficiency stayed below 40%, describes Panasonic.
Panasonic has also developed a new semiconductor white light source capable of producing light in the range of 10,000-lumens. Applications suggested for these kind of products include data projectors and vehicle headlights.
Panasonic has modularized near-ultraviolet semiconductor laser in this case of light source. The phosphor material used is not subjected to luminance saturation even when irradiated with high-intensity laser light. The use of a laser with a smaller light-emitting area and superior light emission directionality to LEDs has made a compact optical configuration that boasts higher brightness and a smaller form factor possible, says Panasonic.
The achievements using this technology as per Panasonic includes:
- By increasing the output of the near-ultraviolet laser in the light source, to 10-times that of a conventional laser, the industry's highest light output of 60 watts has been achieved. The miniaturized laser module can be incorporated into a wider range of equipment.
- The use of a newly developed phosphor material has increased blue light emissions by 40%, contributing to the realization of a 10,000-lumen class high-luminous flux white light source through the red, green and blue phosphors.
- The generation of red, green and blue lights from only one type of laser light using a rotating phosphor wheel simplifies the optical system and ensures that the laser is projected directly onto the screen.
The technologies Panasonic has used for this achievement are:
- High-output, low-loss laser design technique with wider near-ultraviolet laser optical waveguide and optimized light loss control.
- Phosphor material technology that utilizes the high-density crystalline structure of SMS (Sr3MgSi2O8) phosphor to control the density of the luminescent center and thus prevent luminous saturation.
- Wavelength conversion technology that uses a rotating phosphor wheel that absorbs near-ultraviolet laser light and converts it to red, green and blue luminescent light.
Panasonic further explains: Conventional laser white light sources require multiple visible light semiconductor lasers that emit blue and other colors, which creates a tradeoff between small form factor and high brightness. Some laser wavelengths are even projected directly, without passing through the phosphor material. Conventional phosphors are not suitable for use as high-intensity light sources, as they are subject to significant luminance saturation when laser light is focused on them.