Alkoxy-capped carbazole dendrimers as host materials for highly efficient narrowband electroluminescence by solution process

Abstract

Narrowband electroluminescence from multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters have attracted much attention owing to their potential in developing high-resolution organic light-emitting diode (OLED) displays. However, host materials used for MR-TADF emitters are mainly focused on small molecules that are relying on vacuum deposition for device fabrication. Here, we demonstrate the design of novel host materials with dendritic structures consisting of a non-conjugated adamantane core and four alkoxy-capped carbazole dendrons in periphery for solution-processed MR-TADF OLEDs with highly efficient narrowband electroluminescence. By introducing electron-donating n-butoxy capping groups to carbazole units and using the second-generation dendrons instead of the first-generation ones, triplet energies for the dendritic hosts are kept at higher than 2.80 eV, but the highest occupied molecular orbital (HOMO) levels can be considerably elevated from −5.51 to −5.19 eV, leading to barrier-free hole injection from anode to emissive layer. Solution-processed OLEDs based on the alkoxy-capped dendritic host and B,N-containing MR-TADF emitter reveal narrowband emission with full-width at half-maximum of 42 nm, together with low turn-on voltage of 2.8 V, maximum external quantum efficiency of 24.2% and power efficiency of 95.0 lm W−1, which represent the promising device efficiencies for narrowband electroluminescence by solution process.