Low driving voltage organic light emitting diode using phenanthrene oligomers as electron transport layer

We demonstrate that an electron transport material, 2-(phenanthren-10-yl)-7 -(phenanthren-9-yl)phenanthrene (Phen-A), significantly lowers the driving voltage in organic light emitting diodes. In a device structure of indium tin oxides (110 nm)/N,N'-di(α-naphtyl)-N,N'-diphenyl-benzidine (50 nm)/ tris–(8-hydroxy quinoline)aluminum (20 nm)/Phen-A (30 nm)/MgAg (100 nm)/Ag (10 nm), a very low driving voltage of 5.8 V was obtained at a current density of 100 mA/cm2. We clarified that Phen-A has a preferred the lowest unoccupied molecular orbital level and a characteristic polycrystalline texture, which are ascribed to the reason for the improved electron injection efficiency at the Phen-A/cathode interface.