Aluminum chelate complex compounds with two substituted 8-hydroxyquinoline ligand and one dibenzothiophene, dibenzofuran or dibenzoselenophene ligands or aza-analogs of these molecules, attached directly or through an aromatic spacer to the oxygen atom is provided to improve lifetime, operating voltage and efficiency of an OLED. Additional substitution of dibenzothiophene or dibenzofuran ring may also provide charge delocalization, HOMO modification and higher Tg.