Ultra-efficient organic light-emitting diode developed successfully

German scientists have developed a new type of organic light-emitting diode (OLED), which produces white light with a quality comparable to incandescent bulbs, and its energy efficiency is even much better than fluorescent lamps. The leader of the study, Sebastian Renéco of the German Institute of Applied Optics, said that the OLED prototype may be an ultra-efficient light source for displays and general lighting. Their long-term goal is to use traditional Low cost tape and reel printing to assemble these devices.

In recent years, many countries have sought to convert incandescent lighting to compact fluorescent lamps because the latter can save more energy. For the same reason, the use of light-emitting diodes (LEDs) in displays and general lighting has also gained popularity. However, whether it is a fluorescent lamp or LED lighting, the quality of the white light it produces has yet to be improved. Fluorescent lamps make people feel uncomfortable due to the lack of red light, and most white LEDs currently on the market will bring some blue, which makes people feel a little cold.

In contrast, OLED manufacturing materials come from a wide range of sources, and it is relatively easy to obtain high-quality white light. As far as OLED is concerned, the problem it faces has not been white light quality, but its energy efficiency. The energy efficiency of fluorescent lamps is about 60 lumens to 70 lumens per watt, the energy efficiency of incandescent lamps is about 10 lumens to 17 lumens per watt, and so far, the largest reported energy efficiency of OLED is 44 lumens per watt.

In the newly published "Nature" magazine, Reneco and colleagues reported an OLED structure design with an energy efficiency of up to 90 lumens per watt, and the highest energy efficiency even reached 124 lumens per watt.

Researchers have improved and perfected the OLED design process. On the one hand, they doped organic materials connected to the luminescent material to its metal contacts, thereby reducing its operating voltage. On the other hand, they use glass with optical properties that better match the device substrate to make the outer surface of the device. In the traditional structure, about 80% of the light will be lost.

The most novel aspect of this OLED is the organization of different light-emitting materials inside the device. The three materials are used to emit blue, green, and red light, respectively, with the main matrix material in between. The trick is to choose a matrix material with a high "spin state" that matches the blue light and is interposed between the green and red materials as if it were part of a separate main matrix material. This means that any electron-hole pairs (excitons) that escape from the red or green light material will pass through the blue light material, thereby increasing the chance of conversion into photons.

However, the main drawback of this new type of OLED is still its longevity. Although companies such as Philips have been able to produce OLEDs that have the same lifespan as fluorescent lamps (more than 10,000 hours), materials with higher performance often have a lifespan that cannot last that long. At present, the lifetime of Renéco's OLED devices can only reach a few hours.