Spirobifluorene-based hole-transporting materials for RGB OLEDs with high efficiency and low efficiency roll-off.

In this work, we designed and synthesized three spirobifluorene (SBF)-based hole-transporting materials (HTMs) by incorporating the di-4-tolylamino group at different positions of the SBF skeleton. These materials demonstrate excellent thermal stability with thermal decomposition temperatures ( T d ) up to 506 °C and outstanding morphological stability with a glass transition temperature ( T g ) exceeding 145 °C. The meta -linkage mode between the conjugated skeleton and functional groups in the molecular structure results in electronic decoupling, giving these 3,6-substituted SBFs higher triplet energies ( E T ) compared to 2,7-substituted SBFs. This makes the 3,6-substituted SBFs suitable as universal HTMs for red, green, and blue (RGB) organic light emitting diodes (OLEDs). Among the three HTMs, 3,3',6,6'-tetra( N , N -ditolylamino)-9,9'-spirobifluorene (3,3',6,6'-TDTA-SBF) exhibits the best device performance, achieving maximum external quantum efficiencies (EQE max ) of 26.1%, 26.4%, and 25.4% for RGB phosphorescent OLEDs, with extremely low efficiency roll-off in both green and blue devices. Utilizing 3,3',6,6'-TDTA-SBF as the HTM, we have also fabricated narrowband blue OLEDs based on the widely used multiple resonance emitter BCz-BN, which exhibits a EQE max of 29.8% and low efficiency roll-off.