Effect of arylamino-carbazole containing hole transport materials on the device performance and lifetime of OLED

We synthesized four hyper-conjugated aromatic hole transporting materials with different molecular geometry and energy levels by attaching arylamino moiety attached to the carbazole core. A brominated carbazole moiety reacted with an arylamino moiety using a Buchwald-Hartwig reaction. The characteristics of these hole transporting materials were investigated using TGA, DSC, UV–Vis and luminescence spectroscopy. The energy levels of all materials used in this study were estimated from cyclic voltammograms and absorption spectra. The hole transporting properties of the synthesized molecules were measured using single-carrier devices. All four hole transporting materials showed similar hole mobility. The effectiveness of hole transporting materials was compared by fabricating green-emitting organic light emitting diode (OLED) devices. It turned out that the device performances were critically dependent on the relative energy levels of the hole transporting layer and emission layer. However, the molecular geometry greatly influenced the device lifetime, determining thermally induced crystallization by the heat produced during device operation.