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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 identifies that the most vulnerable molecular site in an Ir‐phenylimidazole dopant is the benzylic CH bond and predicts that deuteration may hamper the deactivation pathway involving CH/D bond cleavage notably. Experiments show that the device lifetime until the initial luminance diminishes to 70% (LT70) of a prototype phosphorescent OLED device can be doubled to 355 hours with a maximum external quantum efficiency 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. [ABSTRACT FROM AUTHOR]

Although the organic light‐emitting diode (OLED) has been successfully commercialized, the development of deep‐blue OLEDs with high efficiency and long lifetime remains a challenge. Here, a novel hyperfluorescent OLED that incorporates the Pt(II) complex (PtON7‐dtb) as a phosphorescent sensitizer and a hydrocarbon‐based and multiple resonance‐based fluorophore as an emitter (TBPDP and ν‐DABNA) in the device emissive layer (EML), is proposed. Such an EML system can promote efficient energy transfer from the triplet excited states of the sensitizer to the singlet excited states of the fluorophore, thus significantly improving the efficiency and lifetime of the device. As a result, a deep‐blue hyperfluorescent OLED using a multiple resonance‐based fluorophore (ν‐DABNA) with Commission Internationale de L'Eclairage chromaticity coordinate y below 0.1 is demonstrated, which attains a narrow full width at half maximum of ≈17 nm, fourfold increased maximum current efficiency of 48.9 cd A−1, and 19‐fold improved half‐lifetime of 253.8 h at 1000 cd m−2 compared to a conventional phosphorescent OLED. The findings can lead to better understanding of the hyperfluorescent OLEDs with high performance. [ABSTRACT FROM AUTHOR]

Novel homoleptic cyclometalated Ir(III) complexes are designed to improve their emission dipole orientations in the emitting layer of blue phosphorescent organic light emitting devices. Biphenyl group is introduced into the imidazole of cyclometalated Ir(III) complexes to simultaneously achieve enhanced efficiency and operation lifetime, resulting in one of the best device performances of single‐stacked organic light emitting diodes with 91% emission dipole orientation, 26.3% maximum external quantum efficiency (maximally calculated as 41%), and 169 h lifetime at 1000 cd m−2 (LT80), color coordinate (0.17, 0.30). To elucidate the physical origin of this significant improvements, the orientational and positional distributions of the homoleptic dopants are analyzed with consideration on intermolecular interactions through atomistic modeling of the emitting layer. With the findings, the phosphorescent dopants could be designed in the future to achieve enhanced performance. [ABSTRACT FROM AUTHOR]

We report blue thermally activated delayed fluorescent (TADF)organic light emitting diodes(OLEDs) with high efficiencies which areattributed toemployingdonor-acceptor type TADF compounds having highreverse intersystem crossing (RISC)rates. Carbazole derivatives and a triphenyltriazine (or a dibenzothiophene) are employed as the donor (D) and the acceptor (A)moieties, respectively. We can achieve four D-A type blue TADF compounds through the combination of the moieties and adjust the energy gap between the lowest excited singlet and triplet statesand accordingly the RISC rate (k RISC) for the compounds. A blue OLED using one of the TADF molecules,9-(9H-carbazol-9-yl)-12-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5-phenyl-5,12-dihydroindolo[3,2- a ]carbazole exhibitshigh maximum external quantum efficiency (22.3%)due to itsshort excitonlifetime (6.1 μs) induced by its high k RISC (1.825 × 106s−1). Image 1 • A simple combinatorial study of D-A compounds is performed which is effective in making a profound impact on their RISC rates. • A compound having the highest RISC rate exhibits the shortest exciton lifetime and the best OLED performance. • The D-A combination impacts on the charge transfer properties and accordingly govern their OLED driving voltages. [ABSTRACT FROM AUTHOR]