Highly efficient ultraviolet organic light-emitting diodes and interface study using impedance spectroscopy

We have investigated the properties of ultraviolet organic light-emitting diodes (UV OLEDs) using an oxadiazole compound (OXD-7) as emitting materials and MoO3 as hole injection and buffer material. Results have demonstrated that the introduction of MoO3 can achieve a highly efficient UV OLED, which shows a high external quantum efficiency of 1.43% with a peak wavelength of 388 nm. The impedance spectroscopy elucidates that the hole injection voltage is about 2 V (via MoO3 interlayer) and 5 V (without MoO3 interlayer), indicating that the MoO3 interlayer is critical to promote hole injection and achieve high device efficiency.