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 Nd3þ-complex with thenoyltrifluoroacetone and 1,10-phe- nanthroline ligands. The NIR-emitting complex was blended into an exciplex-forming co-host system comprising 2,7-bis(diphe- nylphosphoryl)-9,90-spirobifluorene as the electron transport material and 4,40,400-tris(carbazol-9-yl)triphenylamine as the hole transport material in solution-processed small molecule organic light-emitting diodes (OLEDs). This binary ambipolar host sys- tem favors direct charge trapping and exciton formation on the Nd3þ-complex molecules. Efficient energy transfer from the sin- glet and triplet exciplexes formed between the host molecules to the Nd3þ ions contributes to the enhanced luminescence efficiency. The photoluminescence quantum yield of this blend is 1.2%, and the optimized OLED shows a maximum electrolumi- nescence external quantum efficiency of 0.034%. The device also exhibits a low efficiency roll-off of only 12% over a current den- sity range of 100 mA/cm2, due to the reduced triplet-polaron annihilation.