An OLED device comprises a cathode, a light emitting layer and an anode, in that order, and, having located between the cathode and the light emitting layer, a further layer containing; (a) 10 vol % or more of a carbocyclic fused ring aromatic compound, and (b) a cyclometallated complex represented by Formula (4′) wherein: Z and the dashed arc represent two or three atoms and the bonds necessary to complete a 5- or 6-membered ring with M; each A represents H or a substituent and each B represents an independently selected substituent on the Z atoms, provided that two or more substituents may combine to form a fused ring or a fused ring system; j is 0-3 and k is 1 or 2; M represents a Group IA, IIA, IIIA and IIB element of the Periodic Table; and m and n are independently selected integers selected to provide a neutral charge on the complex; and provided that the complex does not contain the 8-hydroxyquinolate ligand. Such devices exhibit reduce drive voltage while maintaining good luminance.