Organic Light-Emitting Diode Composed of an Oligomer Crystal Emission Layer

We introduced a crystal of an oligomer material for p-type emission layer into an organic light-emitting diode (OLED), and compared it with the device composed of thin films. To fabricate the devices, we laminated the oligomer crystal or deposited the oligomer thin film on a substrate covered with patterned indium tin oxide electrodes. We completed the devices by depositing an n-type material, an electron injection layer, and an Al electrode. For the current-voltage characteristics, both of the crystal and thin-film devices indicated rectification properties. At a certain current density, estimated applied electric fields for the crystal device was almost a quarter of that for the thin-film device. Both devices showed the current-injected emission. Comparison of the current-injected emission spectra to photoluminescence spectra revealed that the oligomer layers dominated emissions from the devices. The rough estimation of the input power for the current-injected emissions showed the crystal device required the lower input power than the thin-film device. These results suggest an advantage of the crystal device for current injection and light emission.