An OLED device comprises a cathode and an anode and has located
therebetween a light-emitting layer comprising a phosphorescent
light-emitting material and a host comprising a compound of a tetravalent
atom wherein the four groups bonded to the atom are aromatic rings, at
least one of which contains an electron-withdrawing group (EWG)
substituent comprising at least three atoms, the compound having a
triplet energy of at least 2.7 eV and a LUMO energy within 0.6 eV of the
LUMO energy of at least one material in an adjacent layer on the cathode
side of the light-emitting layer. Particular embodiments include certain
tetravalent silicon compounds. The light-emitting layer emits blue light
and provides good luminance and reduced drive voltage.