Researchers from Korea's Advanced Institute of Science and Technology and Samsung are reporting that they have increased the efficiency of an organic light-emitting diode (OLED) by texturing the glass substrate with a photonic-crystal (PC) pattern. They are reporting an increase of 50% over a wide viewing angle but believe they can make up to an 80% improvement.
In order to enhance the extraction, a 200-nm thick layer of SiO2 was deposited on the glass substrate of the OLED. Next a square array of 200nm diameter rods with a 600nm lattice constant was created by holographic lithography and reactive ion etching. Finally this was topped with an 800-nm SiNx buffer layer and the OLED electrode and light-emitting active layer.
Emitted photons from an OLED come from one of three modes:
- 20% go to direct transmission into the air
- 30% are totally internally reflected
- 50% go to a high index guided mode
The research team maximised the extraction of photons from the high-index guided mode close to the light-emitting region for reasons of maintaining image quality for in display devices.