Highly efficient new hole injection materials for organic light emitting diodes base on phenothiazine derivatives.

New hole injection materials for OLED based on phenothiazine were synthesized, and the electro-optical properties of synthesized materials were examined by through UV-Vis. and photoluminescence spectroscopy as well as cyclic voltammetry. 1-NDD-t-BPBP and 2-NDD-t-BPBP showed Tg of 180 and 177 °C. These are higher than that (110 °C) of 2-TNATA, commercial HIL material. As for the HOMO level of the synthesized materials, 1-NDD-t-BPBP and 2-NDD-t-BPBP were 4.99 and 5.02 eV, indicating well-matched values between HOMO (4.8 eV) of ITO and HOMO (5.4 eV) of NPB, HTL material. In addition, judging from the fact that the synthesized materials both barely showed any absorption in the range of over 450 nm, the synthesized materials could be effectively used as an HIL material. The synthesized materials were used as the HIL in OLED device, yielding luminance efficiencies of 4.51 cd/A (1-NDD-t-BPBP) and 4.44 cd/A (2-NDD-t-BPBP). These results indicated that 1-NDD-t-BPBP shows more excellent luminance efficiency which is about 11% improved over 2-TNATA a commercial HIL material.