TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The organic light-emitting diode comprises an anode and a cathode and a light-emitting layer arranged between the anode and the cathode, and optionally at least one further layer including group consisting of at least one blocking layer for electrons/excitons, a blocking layer for holes/excitons, a hole injection layer, a hole conductor layer, a electron injection layer or a electron conductor layer, where (A) is present in the light-emitting layer and/or in the at least one further layer. (A) is present in the light-emitting layer as a matrix material together with at least one emitter material. The emitter material used in the light-emitting layer is at least one carbene complex of formula (((carbene)qM1(L)r-(K1)o)(p+) pW1) (IV). The organic light-emitting diode comprises as at least one further layer and a blocking layer for holes, where the blocking layer for holes comprises at least one heterocyclic compounds of formula (V).M1 = metal including metals of group IB, IIB, NIB, IVB, VB, VIB, VIIB, the lanthanides or IIIA in any oxidation state possible for the particular metal atom;carbene = carbene ligand (optionally uncharged, monoanionic, or mono-, bi- or tridentate, where the carbene ligand is optionally a bis- or tris-carbene ligand);L = mono- or dianionic ligand, preferably monoanionic ligand (optionally mono- or bidentate);K1 = uncharged mono- or bidentate ligand;q = number of carbene ligands (where, when q is greater than 1, n is at least 1);r = number of ligands L (where, when r is greater than 1, m is 0 or greater than or equal to 1);o = number of ligands K1 (where is 0 or greater than 1);p = charge of the complex including 0-4, preferably 0;W1 = monoanionic counterion, (where the sum of q, r o and the charge p depends on the oxidation state and coordination number of the metal atom used, the charge of the complex and the denticity of the carbene, L and K1 ligands, and on the charge of the carbene and L ligands, with the condition that n is at least 1);A1 = NR12, S or O;R12 = 1-20C alkyl, 6-30C aryl or heteroaryl having 5-30 ring atoms (all optionally substituted);R9-R11 = 1-20C alkyl, 6-30C aryl (both optionally substituted) or heterocyclic moiety of formula (a);R1a, R1b = 1-20C alkyl, 6-30C aryl, heteroaryl having 5-30 ring atoms (all optionally substituted) or substituent with donor or acceptor action (including 1-20C alkoxy, 6-30C aryloxy, 1-20C alkylthio, 6-30C arylthio, SiR12R13R14, halo, halogenated 1-20C alkyl, -CO(R12), -C=O(SR12), -C=O(OR12), -OC=O(R12), -SC=O(R12), -NR12R13, OH, pseudohalo, -C=O(NR12), -NR12C=O(R13), -P(O) (OR12)2, -OP(O)(OR12)2, -PR12R13, -P(O)(R12)2), -OS(O)2OR12, -S(O)R12, -S(O)2OR12, -S(O)2R12, -S(O)2NR12R13), NO2, -OB(OR12)2, -C=NR12R13, boranyl, stannyl, hydrazinyl, hydrazonyl, oxime, nitroso, diazo, vinyl, sulfoximines, alanes, germanes, boroximes or borazines;R12-R14 = 1-20C alkyl or 6-30C aryl; ands, t = 0-3 (where, when q or r is 0, all substitutable positions of the aryl are substituted by H). Preferred Definitions:    R1, R3 = phenyl (optionally substituted), CH3, C2H5, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, fluorenyl, SiR6R7R8 or -NR6R7;    R4, R5 = phenyl, SiR6R7R8-substituted phenyl; and    R6-R8 = phenyl (optionally substituted), CH3, C2H5, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl or tert-butyl.    EXAMPLE - 4-Bromophenylhydrazine hydrochloride (10.44 g) was introduced into a solution of 1,2-cyclohexadione (5.4 g) in absolute ethanol (50 ml). Then glacial acetic acid (20 drops) was added and the reaction mixture was stirred at room temperature for 1 hour and then at 80 degrees C for 4 hours. 4-Bromophenylhydrazine hydrochloride (5.3 g, 99%) was added to the reaction mixture and, after a further 6 hour at 80 degrees C, 4-bromophenylhydrazine hydrochloride (5.3 g 99%) was added. The reaction mixture was stirred overnight for 22 hours. Absolute ethanol (150 ml) was added to the viscous reaction mixture and further 4-bromophenylhydrazine hydrochloride (3 g, 99%) was added. Then solvent was distilled off and the residue was introduced gradually into polyphosphoric acid (50 g), heated to 120 degrees C and stirred for 1 hour. The reaction product was added cautiously to ice-water and neutralized with sodium hydroxide (2M). The precipitate was filtered off and washed with distilled water. The residue was dried under reduced pressure and recrystallized to obtain 3,8-dibromo-11H,12H-indol(2,3-a)carbazole (5.8 g).