Abstract: Efficient blue phosphorescent inverted bottom-emission organic light-emitting diode(IBOLED) based on indium tin oxide(ITO) cathode has been successfully fabricated by thermal evaporation using Al(2 nm)/Li2CO3(2 nm) as the electron-injection layer. The structure of this device is ITO/Al/Li2CO3/SPPO13/SPPO13∶FIrpic/TCTA/MoO3/Al(SPPO13:2,7-bis(diphenylphosphoryl)-9,9′-spirobi[fluorene]; FIrpic:bis(4,6-difluorophenylpyridinato-N,C2)picolinatoiridium; TCTA:4,4′,4″-tri(9-carbazoyl)triphenylamine). It is found that the electron injection barrier between ITO and the organic layer can be significantly reduced with the presence of Al/Li2CO3, leading to the reduction of the turn-on voltage from 11 V to 4.2 V and the significant enhancement of efficiencies. The inverted device exhibits a maximum current efficiency of 28.2 cd/A and a maximum power efficiency of 19.6 lm/W, which are comparable with the conventional device. This suggests that Al/Li2CO3 has the potential to be used as the electron injection layer for inverted OLEDs.

Key words: organic light-emitting diodes, inverted bottom-emission, electron injection layer, indium tin oxide cathode