Simultaneous realization of high-efficiency, low-drive voltage, and long lifetime TADF OLEDs by multifunctional hole-transporters

Although organic light emitting devices (OLEDs) based on thermally activated delayed fluorescence (TADF) have already achieved impressively high external quantum efficiency (ηext) of over 35%, their operation lifetime still needs to be improved for practical applications. In this study, we developed a molecular design for fabricating high triplet energy (ET = 2.7 eV) multifunctional hole-transport layers (HTLs) based on a hexaphenylbenzene skeleton to realize record-breaking efficient and stable TADF OLEDs. By using a dibenzofuran-end-capped HTL named 4DBFHPB, we could successfully develop a highly efficient, low-drive voltage, and stable green TADF OLED exhibiting an ηext of 19.2% and operation lifetime (LT50) of ∼24 000 h at an initial luminance of 1000 cd m−2. The drive voltage at 1000 cd m−2 was recorded to be 4.07 V. We also developed a sky-blue TADF OLED exhibiting an ηext of 21.5% and LT50 of ∼1700 h at an initial luminance of 500 cd m−2. The developed designs demonstrate record-breaking performances among the existing TADF OLEDs.