Enhanced near-infrared electroluminescence from a neodymium complex in organic light-emitting diodes with a solution-processed exciplex host

Abstract

We report enhanced near-infrared (NIR) electroluminescence from a Nd3+-complex with thenoyltrifluoroacetone and 1,10-phenanthroline ligands. The NIR-emitting complex was blended into an exciplex-forming co-host system comprising 2,7-bis(diphenylphosphoryl)-9,9′-spirobifluorene as the electron transport material and 4,4′,4″-tris(carbazol-9-yl)triphenylamine as the hole transport material in solution-processed small molecule organic light-emitting diodes (OLEDs). This binary ambipolar host system favors direct charge trapping and exciton formation on the Nd3+-complex molecules. Efficient energy transfer from the singlet and triplet exciplexes formed between the host molecules to the Nd3+ ions contributes to the enhanced luminescence efficiency. The photoluminescence quantum yield of this blend is 1.2%, and the optimized OLED shows a maximum electroluminescence external quantum efficiency of 0.034%. The device also exhibits a low efficiency roll-off of only 12% over a current density range of 100 mA/cm2, due to the reduced triplet-polaron annihilation.