Protecting Benzylic CH Bonds by Deuteration Doubles the Operational Lifetime of Deep‐Blue Ir‐Phenylimidazole Dopants in Phosphorescent OLEDs

Abstract

Much effort has been dedicated to increase the operational lifetime of blue phosphorescent materials in organic light-emitting diodes (OLEDs), but the reported device lifetimes are still too short for the industrial applications. An attractive method for increasing the lifetime of a given emitter without making any chemical change is exploiting the kinetic isotope effect, where key C-H bonds are deuterated. A computer model identi ed that the most vulnerable molecular site in an Ir-phenylimidazole dopant is the benzylic C-H bond and predicted that deuteration may lower the deactivation pathway involving C-H/D cleavage notably. Experiments showed that the device lifetime (T 70 ) of a prototype phosphorescent OLED device could be doubled to 355 hours with a maximum external quantum e ciency of 25.1% at 1000 cd/m 2 . This is one of the best operational performances of blue phosphorescent OLEDs observed to date in a single stacked cell.

Effects of Charge Dynamics in the Emission Layer on the Operational Lifetimes of Blue Phosphorescent Organic Light‐Emitting Diodes

“…Specifically, in order to account for the low occupation probability of the defects, f t = p t /Q tot = 1-2% versus 100% from the previous studies, Q tot and thus the defect-generation rate (k TPA ) should be increased by two orders of magnitude. Accordingly, the exciton quenching rate (k QN ), which governs the loss of excitons and hence the luminance reduction, as expressed in Equations ( 7) and (19), should be decreased by two orders of magnitude to compensate for an increased in Q tot by the same order of magnitude.…”

“…Note that the deuterated dopant is chosen over its undeuterated counterpart because the former is found to be more chemically stable and hence ena-bles the longer lifetimes of blue PHOLEDs. [19] The energies of frontier orbitals of the molecules in the blue PHOLEDs were calculated by B3LYP functionals with the 6-31 G** basis set in the density functional theory formalism in the Gaussian09 package.…”

Boosting the Efficiency and Stability of Blue TADF Emitters by Deuteration

“…Highly 31 And Adachi's group also studied the isotope effect of the host material and found a positive effect on the device stability, 21 which was assigned to the enhanced stable amorphous nature and balanced carrier transport properties. The mechanism disclosed here also works well for previous studies.…”

High Efficiency of over 25% and Long Device Lifetime of over 500 h at 1000 nit in Blue Fluorescent Organic Light‐Emitting Diodes

“…Currently, phosphorescent materials are being used as green and red emitters in full color organic light-emitting diodes (OLEDs) display, but in the case of blue, a fluorescence material with low internal quantum efficiency (IQE) is still being used because the device lifetime of the blue phosphorescent emitter is rather poor. [1][2][3][4][5][6][7][8] As the blue emitter has a higher emission energy than red and green emitters, the large electrical stress applied to the blue material during driving damages the emitter and results in the relatively short lifetime. Therefore, various emitters and device structures have been developed to improve the device efficiency and lifetime of blue OLEDs suitable for (t-DABNA) materials demonstrated potential as the blue fluorescent dopant in our previous work by achieving good color purity and high EQE.…”