A phosphine oxide derivative as a universal electron transport material for organic light-emitting diodes

Abstract

A phosphine oxide based organic material, 2-diphenylphosphine oxide-spiro[fluorene-7,11′-benzofluorene] (SPPO2), was developed as a universal electron transport layer with a thermal stability and stable morphology for organic light-emitting diodes (OLEDs). The SPPO2 was synthesized by the reaction of 2-bromo-spiro[fluorene-7,11′-benzofluorene] with diphenyl phosphine chloride. SPPO2 showed a high glass transition temperature (Tg) of 118 °C and good film-forming properties. The SPPO2 reduced the driving voltage of the OLEDs irrespective of the energy level of the host materials due to efficient electron injection from the SPPO2 to host material. In particular, the SPPO2 reduced the driving voltage of the blue device of a wide bandgap host material by more than 3 V. Therefore, the SPPO2 can be used as a universal electron transport layer for OLEDs.