Spiro-annulated triarylamine-based hosts incorporating dibenzothiophene for highly efficient single-emitting layer white phosphorescent organic light-emitting diodes

Abstract

Four novel host materials were designed and synthesized, incorporating fluorene-spiro-annulated triphenylamine–carbazole (ST–SCz) and dibenzothiophene (DBT) blocks. A meta-linking strategy was applied by introducing DBT moieties to ST–SCz skeletons at the C3 position of the fluorene backbones. As expected, high triplet energies (over 2.80 eV) were achieved in all four materials despite the different linking positions on the DBT. All four materials show a high T_g from 149 to 163 °C, which benefits from their spiro-structure. Their thermal, electrochemical and photo-physical properties were fully characterized. Highly efficient blue and white PHOLEDs were fabricated using these four materials as the hosts. Triphenylamine-containing STDBT4 and STDBT2 demonstrate better device performance due to their relatively high-lying HOMO compared to carbazole-containing SCzDBT4 and SCzDBT2. Maximum η_ext of 19.6% and 18.4% (STDBT4 and STDBT2) were achieved for FIrpic-based devices, and 23.7% and 22.2% (STDBT4 and STDBT2) were achieved for two color-based white PHOLEDs with double emitting layers, using PO-01 as a yellow dopant. Finally, a highly efficient single-emitting layer white PHOLED with maximum efficiencies of 24.0%, 77.0 cd A⁻¹ and 63.2 lm W⁻¹ and CIE coordinates of (0.38, 0.48) was realized using the device configuration of ITO/HAT–CN/TAPC/STDBT4: 8 wt% FIrpic: 0.8 wt% PO-01/TmPyPB/Liq/Al. The device shows good color stability and low efficiency roll-off. Even at a high luminance of 10 000 cd m⁻², it still maintains very high efficiencies of 17.9%, 56.4 cd A⁻¹ and 26 lm W⁻¹.