Efficient red organic LEDs via the combination of an exciplex host and micro-cavity

Exploring exciplexes as the host in organic light-emitting diodes (OLEDs) has attracted extensive attention because of the low driving voltage and high efficiency. However, conventional exciplex-host-based bottom-emission still shows undesirable efficiencies, especially in the red emission channels, due to energy gap law. We here propose exciplex-host-based top-emitting devices to achieve breakthrough efficiency in red light-emitting devices. We optimize the exciplex hosts to maximize energy transfer to the emitting dyes and the cavity length and reflective electrodes to achieve efficient red organic LEDs. We report a current efficiency of 99.7 cd A(-1) for a red OLED with an electroluminescence (EL) peak at 604 nm (full width at half maximum of 32 nm); these efficiencies are the best in red OLEDs, especially with a narrow EL spectrum. This work offers a new strategy to achieve high efficiency and high color-purity LEDs simultaneously.