Researchers at the University of Michigan have developed a new electrode that can increase the light output of OLEDs by 20%. It is assumed that the development will help increase the battery life of smartphones and laptops or make TVs and monitors of the next generation more energy efficient.
Significantly, the fabrication of the new electrode fits well with the existing OLED display and lighting production process.
The problem with OLED is that a lot of the light can’t get out. Rays that do not reach the working surface at an angle close to a straight line are reflected back from the electrode and scattered inside due to multiple reflections. There is a waveguide effect. According to the source, without special measures, 80% of the light would remain inside the OLED.
The main contribution to the formation of modes is made by a transparent electrode located between the light-emitting material and glass. It is typically made from Indium Tin Oxide (ITO). The researchers replaced it with a layer of silver just five nanometers thick, deposited on a seed copper layer. At the same time, it was possible to preserve the electrode function, completely eliminating the problem of the waveguide. This simple yet effective technique has significantly increased the external quantum efficiency of OLEDs.
According to scientists, their proposed approach can be extended to other solid-state light-emitting diodes, since they are all sensitive to the waveguide problem.
The situation can be further improved by a special treatment of the glass, which reduces the reflection of light from it. In the experimental setup, the glass was replaced with a liquid. By “matching the parameters”, it was possible to prevent reflection at the interface between two media: glass with a high refractive index and air with a low index. As a result, the brightness of the LED has increased by about 20%.
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