Low Roll-Off and High Efficiency Orange Organic Light Emitting Diodes with Controlled Co-Doping of Green and Red Phosphorescent Dopants in an Exciplex Forming Co-Host

An exciplex forming co-host is introduced in order to fabricate orange organic light-emitting diodes (OLEDs) with high efficiency, low driving voltage and an extremely low efficiency roll-off, by the co-doping of green and red emitting phosphorescence dyes in the host. The orange OLEDs achieves a low turn-on voltage of 2.4 V, which is equivalent to the triplet energy gap of the phosphorescent-green emitting dopant, and a very high external quantum efficiency (EQE) of 25.0%. Moreover, the OLEDs show low efficiency roll-off with an EQE of over 21% at 10 000 cdm(-2). The device displays a very good orange color (CIE of (0.501, 0.478) at 1000 cdm(-2)) with very little color shift with increasing luminance. The transient electroluminescence of the OLEDs indicate that both energy transfer and direct charge trapping takes place in the devices.