Researchers from National Taiwan University, led by Prof. Chung-Chih Wu, have developed a 3D pixel configuration for OLED devices, which can improve the light extraction. The new design can improve the external quantum efficiency of a top-emitting OLED device by up to 30%.
The new design uses a 3D reflective pixel structure filled with a patterned high-index material. The researchers created several pixels with difference sizes, and found that the smaller the pixel, the higher the efficiency boost.
To create the device, the researchers took advantage of the concave bank structure on conventional AMOLED pixels and modified the integration processes so that the reflective bottom anode was extended onto the pixel bank slope to form the optically reflective (but electrically isolated) slope surface surrounding the pixel emission area. The high-index filler material was further selectively filled in the concave pixel region by vacuum evaporation through tiny openings in the aligned fine metal mask (FMM), completing the reflective 3D pixel configuration.
The researchers say that even greater efficiency enhancements may be achieved with further improvement in 3D pixel structures, such as reducing the optical loss with adoption of transparent top electrodes.