Disclosed is an electroluminescent device comprising a cathode and an anode and, located therebetween, a light-emitting layer (LEL) comprising a phosphorescent guest material, a hole- and electron-transporting host material, and an efficiency-enhancing material having an ionization potential lower than that of the host material and a triplet energy level that is lower than that of the phosphorescent guest material by no more than 0.2 eV. Such a device provides useful light emission features.