New hole transporting materials based on hexaarylbenzene and aromatic amine moiety for organic light-emitting diodes

Three different new hole transport compounds, namely DPAP-TB, 1-PNAP-TB and 2-PNAP-TB, were synthesized by Sonogashira coupling and Diels-Alder reaction. Synthesized materials exhibited high Tg in the range of 118 to 133 °C. These values are higher than that of NPB, which is commonly used as a hole transporting material. OLED devices were fabricated by the synthesized compounds using the solution process as a hole transporting layer. Device structure was ITO/PEDOT:PSS (40 nm)/synthesized compounds or NPB (20 nm)/Alq3 (70 nm)/LiF/Al. Luminance efficiencies and external quantum efficiencies of DPAP-TB, 1-PNAP-TB and 2-PNAP-TB devices were 3.98, 4.62, 4.22 cd/A, and 1.35, 1.56, 1.43% at 20 mA/cm2, respectively. In luminance efficiency and external quantum efficiency, 1-PNAP-TB especially had superior property to NPB.