A compound having the formula [L A] 3-n Ir[L B] n; wherein, n is 1 or 2; L A is a ligand of Formula I A is a fused ring structure comprising a chemical group selected from the group consisting of dibenzofuran, dibenzothiophene, carbazole, anthracene, phenanthrene and triphenylene; Z 1 to Z 4 are each independently C or N; R 1 and R 2 each independently represent mono to the maximum number of allowable substitutions, or no substitution; if there are two L A ligands, they can be the same or different; L B is a ligand of Formula II R 3 and R 4 each independently represent mono to the maximum number of allowable substitutions, or no substitution; each R 1, R 2, R 3, and R 4 is independently a hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, boryl, and combinations thereof; L 1 is a substituent of Formula III and L 2 is hydrogen or alkyl group; each R W and R Y is independently a hydrogen or a substituent selected from the group consisting of deuterium, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, aryl, and combinations thereof; R X is selected from the group consisting of hydrogen, deuterium, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, and combinations thereof; each R v and R z is independently a substituent selected from the group consisting of alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, aryl, and combinations thereof; if there are two L B ligands, they can be the same or different; in at least one ligand L B, R V, R X and R Z collectively comprise six or more carbon atoms; and any two substituents can be joined or fused together to form a ring, with the proviso that L 1 does not join with R 3 to form a ring, and L 2 does not join with R 4 to form a ring. n is 1 or 2; L A is a ligand of Formula I A is a fused ring structure comprising a chemical group selected from the group consisting of dibenzofuran, dibenzothiophene, carbazole, anthracene, phenanthrene and triphenylene; Z 1 to Z 4 are each independently C or N; R 1 and R 2 each independently represent mono to the maximum number of allowable substitutions, or no substitution; if there are two L A ligands, they can be the same or different; L B is a ligand of Formula II R 3 and R 4 each independently represent mono to the maximum number of allowable substitutions, or no substitution; each R 1, R 2, R 3, and R 4 is independently a hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, boryl, and combinations thereof; L 1 is a substituent of Formula III and L 2 is hydrogen or alkyl group; each R W and R Y is independently a hydrogen or a substituent selected from the group consisting of deuterium, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, aryl, and combinations thereof; R X is selected from the group consisting of hydrogen, deuterium, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, and combinations thereof; each R v and R z is independently a substituent selected from the group consisting of alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, aryl, and combinations thereof; if there are two L B ligands, they can be the same or different; in at least one ligand L B, R V, R X and R Z collectively comprise six or more carbon atoms; and any two substituents can be joined or fused together to form a ring, with the proviso that L 1 does not join with R 3 to form a ring, and L 2 does not join with R 4 to form a ring.