Dendritic host materials with non-conjugated adamantane cores for efficient solution-processed blue thermally activated delayed fluorescence OLEDs

Abstract

Two dendritic host materials consisting of non-conjugated adamantane cores and four first-/second-generation carbazole dendrons (Ad-4D1 and Ad-4D2) are developed for efficient solution-processed blue thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs). The dendrimers with three-dimensional geometries, which are constructed through facile one-step palladium-catalyzed C–N coupling reactions involving tetra-substituted adamantane and carbazole dendrons, show high thermal stability and excellent solubility in common organic solvents. The dendrimers possess high triplet energies (E_Ts) of 2.83–2.95 eV, making them suitable to host blue TADF emitters. Compared with Ad-4D1 with the first-generation dendrons showing a deep highest occupied molecular orbital (HOMO) level of −5.51 eV, Ad-4D2 with the second-generation ones exhibits an elevated HOMO level of −5.32 eV, favorable for hole injection from anode to the emissive layer. Solution-processed blue TADF OLEDs utilizing Ad-4D2 as a host exhibit promising device performance with a maximum luminous efficiency, power efficiency and external quantum efficiency of 44.2 cd A⁻¹, 34.4 lm W⁻¹ and 18.3%, respectively, among the highest values for solution-processed blue TADF OLEDs. This work sheds light on the development of dendritic host materials, as an alternative to soluble small-molecule hosts and polymer hosts, to realize high-efficiency solution-processed TADF OLEDs.