Deep-Blue High-Efficiency TTA OLED Using <i>Para</i>- and <i>Meta</i>-Conjugated Cyanotriphenylbenzene and Carbazole Derivatives as Emitter and Host

Abstract

Elaboration of the appropriate host materials proved to be not less important for the fabrication of a highly efficient OLED than the design of emitters. In the present work, we show how by simple variation of molecular structure both blue emitters exhibiting delayed fluorescence and ambipolar high triplet energy hosts can be obtained. The compounds with a para -junction revealed higher thermal stability ( T ID up to 480 °C), lower ionization potentials (5.51–5.60 eV), exclusively hole transport, and higher photoluminescence quantum efficiencies (0.90–0.97). Meta -linkage leads to ambipolar charge transport and higher triplet energies (2.82 eV). Introduction of the accepting nitrile groups in the para -position induces intensive delayed fluorescence via a triplet–triplet annihilation up-conversion mechanism. By utilization of the para -substituted derivative as an emitter and the meta -substituted isomer as the host, a deep-blue OLED with the external quantum efficiency of 14.1% was fabricated.