Thermally activated delayed fluorescence materials for nondoped organic light-emitting diodes with nearly 100%exciton harvest

High-performance nondoped organic light-emitting diodes(OLEDs)are promising technologies for future commercial applications.Herein,we synthesized two new thermally activated delayed fluorescence(TADF)emitters that enable us,for the first time,to combine three effective approaches for enhancing the efficiency of nondoped OLEDs.First,the two emitters are designed to have high steric hindrances such that their emitting cores will be suitably isolated from those of their neighbors to minimize concentration quenching.On the other hand,each of the two emitters has two stable conformations in solid films.In their neat films,molecules with the minority conformation behave effectively as dopants in the matrix composing of the majority conformation.One hundred percent exciton harvesting is thus theoretically feasible in this unique architecture of“self-doped”neat films.Furthermore,both emitters have relatively high aspect ratios in terms of their molecular shapes.This leads to films with preferred molecular orientations enabling high populations of horizontal dipoles beneficial for optical outcoupling.With these three factors,OLEDs with nondoped emitting layers of the respective emitters both achieve nearly 100%exciton utilization and deliver over 30%external quantum efficiencies and ultralow efficiency roll-off at high brightness,which have not been observed in reported nondoped OLEDs.

Efficient solution-processable OLEDs near BT.2020 red standard enabled by a multiresonant emitter

Organic light-emitting diodes(OLEDs)are a highly competitive technology for high-quality displays,but they face considerable challenges in satisfying the BT.2020 standard for ultrahighdefinition displays,mainly due to the ubiquitous weakness of poor color purity for organic systems[1,2].

Improving performance of thermally activated delayed fluorescence emitter by extending its LUMO distribution

An optimized compound 9-(9,9-dimethylacridin-10(9 H)-yl)-6 H-benzo[c]ch-romen-6-one(MAB) was designed and synthesized based on our previously reported TADF emitter 6-(9,9-dimethylacridin-10(9 H)-yl)-3-methyl-1 H-isochromen-1-one(MAC) to further improve the performance of thermally activated delayed fluorescence(TADF)emitters. With the additional phenyl in coumarin-contained plane, MAB possesses an extended distribution of the lowest unoccupied molecular orbitals(LUMO), and thus realizes reduced electron exchange between the frontier molecular orbitals and a stretched molecular dipole moment compared with MAC. MAB based organic light-emitting diode(OLED)exhibits a remarkable maximum external quantum efficiency(EQE) of 21.7%, which is much better than the maximum EQE of MAC-based OLED with a value of 12.8%. Our work proves that extending the distribution of LUMO is a simple but effective method to improve the efficiency of TADF emitter.