Solution-processed small-molecular white organic light-emitting diodes based on a thermally activated delayed fluorescence dendrimer

Abstract

Thermally activated delayed fluorescence (TADF) dendrimers have received much attention in solution-processed non-doped organic light-emitting diodes. However, the study of their application as self-host materials in white organic light-emitting diodes (WOLEDs) is quite limited. In this contribution, solution-processed small-molecule WOLEDs were obtained by employing a newly designed blue TADF dendrimer bis(4-(3,6-bis(3,6-di-tert-butylcarbazol-N-yl) carbazole)phenyl)sulfone (G2) with a wide bandgap and a high triplet energy (3.0 eV) as the host and the blue-light-emitting material, combined with an orange iridium complex (bis(2-phenylbenzothiazolato) (acetylacetonate)iridium(III)) (Ir(bt)₂(acac)) as the dopant. The devices achieved a maximum external quantum efficiency of 10.1%, a maximum current efficiency of 17.69 cd A⁻¹ and CIE coordinates of (0.32, 0.33). They also exhibited stable electroluminescence spectra and low efficiency roll-off at a relatively high current density. These improved performances benefit from the advantages of the TADF dendrimer used as the host material. More importantly, the fast rate constant of Förster resonance energy transfer (K_ET > 10⁷ s⁻¹) suppressed intersystem crossing (ISC) on the G2 host from singlet to triplet states, leading to a reduced singlet density and suppressed singlet–triplet annihilation on the G2 host. Therefore, these results indicate that TADF dendrimers have a promising prospect in the application of high-performance solution-processed two complementary color WOLEDs.