Stable and efficient phosphorescent organic light-emitting device utilizing a δ-carboline-containing host displaying thermally activated delayed fluorescence†
Materials displaying thermally activated delayed fluorescence (TADF) can when used as hosts alleviate the serious efficiency roll-off of phosphorescent organic light-emitting devices (PHOLEDs). However, the stability of the device remains challenging due to the unstable moiety in the TADF molecule. Here, a stable and efficient yellow PHOLED based on a δ-carboline-containing TADF host and bis(4-phenyl-thieno[3,2-c]pyridinato-C2′) (acetylacetonato) iridium(III) (PO-01) guest was demonstrated. Compared to the lifetime of the PHOLED with a 4,4′-bis(N-carbazolyl)-2,2′-biphenyl host, a greater than twenty times enhancement of the lifetime of the PO-01-based device was achieved. The LT50 lifetime (time to 50% of initial luminance of 1000 cd m−2) of an unpackaged DCb-BPP-based PHOLED reached 424 h, and was accompanied by a maximum external quantum efficiency of 21.5% and an impressive low efficiency roll-off of 17.7% at a high luminance of 10 000 cd m−2. These values are among the best of those reported for PO-01-based yellow PHOLEDs.