A cross-linkable triphenylamine derivative as a hole injection/transporting material in organic light-emitting diodes

Abstract

We have synthesized TPABZ, a new thermally cross-linkable triphenylamine derivative containing a benzoxazine functional group, for application in organic light-emitting diodes (OLEDs). We used differential scanning calorimetry, thermogravimetric analysis, UV–Vis spectroscopy, and cyclic voltammetry to investigate the thermal, physical, and electrochemical properties of TPABZ, which is readily polymerized, through ring-opening polymerization of its benzoxazine unit, upon heating at 220 °C for 30 min. The cured TPABZ (P-TPABZ) is suitable for use as a hole injection/transport material in OLEDs because it has an appropriate HOMO energy level (−5.16 eV) to form a stepwise energy ladder and a high LUMO energy level (−1.68 eV) with great potential for electron blocking. We fabricated multilayered OLEDs (ITO/TPABZ or P-TPABZ/NPB/Alq₃/LiF/Al) through successive spin-coating and vacuum deposition processes; the device incorporating P-TPABZ exhibited good performance (EQE: 2.44%; LE_max: 8.42 cd A⁻¹; PE_max: 4.34 lm W⁻¹).