An effective thermally activated delayed fluorescence host material for highly efficient blue phosphorescent organic light-emitting diodes with low doping concentration

Abstract

A thermally activated delayed fluorescence (TADF) material BCz-2SO has been designed and synthesized as host for blue phosphorescent organic light-emitting diodes (OLEDs). Photophysical studies and theoretical calculations show that the molecule has a small singlet-triplet energy gap (ΔEST) of 0.345 eV, which is beneficial to the reverse energy transferring between the singlet and triplet state. Thanks to the TADF property, the triplet energy can be transmitted to the singlet state through reverse intersystem crossing (RISC), and then transmitted to the guest through the Förster energy transfer (FET) to achieve 100% utilization of energy. Thus, the triplet–triplet annihilation (TTA) of the blue phosphor can be avoided by the extremely low doping concentration of 1%. By using BCz-2SO as the host of FIrpic, the solution-processed blue phosphorescent device achieves the maximum current efficiency (CE), power efficiency (PE), external quantum efficiency (EQE) and highest brightness of 16.38 cd A−1, 9.04 lm W−1, 7.8% and 16,537 cd m-2, respectively. It demonstrates that one can employ the solution-processed method to prepare the high performance phosphorescent OLEDs using the TADF host material we have developed.