High-contrast tandem organic light-emitting devices employing semitransparent intermediate layers of LiF/Al/C60

摘要

The use of a black cathode with a metal-organic-metal structure is an attractive approach to achieving a high-contrast organic light-emitting device (OLED) for future-generation flat panel displays. However, the large reduction in OLED power efficiency is currently restricting the use of the black cathode for industrial applications. In this paper, a high-contrast, high-efficiency tandem OLED employing a black cathode is proposed and experimentally demonstrated. The OLED is implemented by stacking two organic phase tuning layers between a composite intermediate layer of LiF/Al/C60 and LiF/Al and optimizing their thicknesses. Electroluminescence spectra and brightness-current measurement reveal that the phase tuning layer emits photons. Such a tandem device can increase the current efficiency by 110% and reduce the operating voltage by 1.3 V, in comparison to the conventional high-contrast OLED. Measured reflection spectra validate the high-contrast capability of the OLED and demonstrate experimentally an average reflectance of 5.9% in the visible range from 400 to 750 nm, which is much lower than 20.3% for the conventional high-contrast OLED.