Efficient deep blue OLEDs with extremely low efficiency roll-off at high brightness based on phenanthroimidazole derivatives

Phosphorescent and thermally activated delayed fluorescence (TADF) emitters can break through the spin statistics rules and achieve great success in external quantum efficiency (over 5%). However, maintaining high efficiency at high brightness is a tremendous challenge for applications of organic light emitting diodes. Hence, we reported two phenanthroimidazole derivatives PPI-An-CN and PPI-An-TP and achieved extremely low efficiency roll-off with about 99% of the maximum external quantum efficiency (EQE_max) maintained even at a high luminance of 1000 cd/cm² based non-doped devices. When doping the two materials in CBP (4,4′-bis(N-carbazolyl)-1,1′-biphenyl), the doped devices still exhibited excellent stability at high brightness with CIE_y ≈ 0.07 and low turn-on voltage of only 2.8 V. The state-of-the-art low efficiency roll-off makes the new materials attractive for potential applications. It is the first time that the Fragment Contribution Analysis method has been used to analyze the excited state properties of the molecules in the field of OLEDs, which helps us understand the mechanism more intuitively and deeply.