The inventions describe disclosed and described herein relate to ambipolar small molecule host materials for guest phosphorescent metal complexes. Methods of making the ambipolar small molecules are also described. These ambipolar small molecules, which comprise both an oxadiazole and one or more carbazole groups, can be used to make the emission layers of unexpectedly efficient OLED devices containing the materials of the inventions, wherein (I) at least one of the R1, R2 and R3 groups is an optionally substituted carbazole group.