Material comprising a compound A of a formula where the following applies to the variables occurring: Z is equal to CR 1; Ar 1 is on each occurrence, identically or differently, an aromatic ring system having 6 to 30 aromatic ring atoms, which may be substituted by one or more radicals R 1, or a heteroaromatic ring system having 5 to 30 aromatic ring atoms, which may be substituted by one or more radicals R 1, where groups Ar 1 may be connected to one another via radicals R 1 verbunden sein; R 1 is selected on each occurrence, identically or differently, from H, D, F, C(=O)R 2, CN, Si(R 2) 3, P(=O)(R 2) 2, OR 2, S(=O)R 2, S(=O) 2 R 2, straight-chain alkyl or alkoxy groups having 1 to 20 C atoms, branched or cyclic alkyl or alkoxy groups having 3 to 20 C atoms, alkenyl or alkynyl groups having 2 to 20 C atoms, aromatic ring systems having 6 to 30 aromatic ring atoms, and heteroaromatic ring systems having 5 to 30 aromatic ring atoms; where two or more radicals R 1 may be linked to one another and may form a ring; where the said alkyl, alkoxy, alkenyl and alkynyl groups and the said aromatic ring systems and heteroaromatic ring systems may in each case be substituted by one or more radicals R 2; and where one or more CH 2 groups in the said alkyl, alkoxy, alkenyl and alkynyl groups may be replaced by -R 2 C=CR 2 -, -C≡C-, Si(R 2) 2, C=O, C=NR 2, -C(=O)O-, -C(=O)NR 2 -, P(=O)(R 2), -O-, -S-, SO or SO 2; R 2 is selected on each occurrence, identically or differently, from H, D, F, CN, alkyl groups having 1 to 20 C atoms, aromatic ring systems having 6 to 30 aromatic ring atoms and heteroaromatic ring systems having 5 to 30 aromatic ring atoms; where two or more radicals R 2 may be linked to one another and may form a ring; and where the said alkyl groups, aromatic ring systems and heteroaromatic ring systems may be substituted by F or CN; characterised in that a compound P which is a complex of bismuth is additionally present. Z is equal to CR 1; Ar 1 is on each occurrence, identically or differently, an aromatic ring system having 6 to 30 aromatic ring atoms, which may be substituted by one or more radicals R 1, or a heteroaromatic ring system having 5 to 30 aromatic ring atoms, which may be substituted by one or more radicals R 1, where groups Ar 1 may be connected to one another via radicals R 1 verbunden sein; R 1 is selected on each occurrence, identically or differently, from H, D, F, C(=O)R 2, CN, Si(R 2) 3, P(=O)(R 2) 2, OR 2, S(=O)R 2, S(=O) 2 R 2, straight-chain alkyl or alkoxy groups having 1 to 20 C atoms, branched or cyclic alkyl or alkoxy groups having 3 to 20 C atoms, alkenyl or alkynyl groups having 2 to 20 C atoms, aromatic ring systems having 6 to 30 aromatic ring atoms, and heteroaromatic ring systems having 5 to 30 aromatic ring atoms; where two or more radicals R 1 may be linked to one another and may form a ring; where the said alkyl, alkoxy, alkenyl and alkynyl groups and the said aromatic ring systems and heteroaromatic ring systems may in each case be substituted by one or more radicals R 2; and where one or more CH 2 groups in the said alkyl, alkoxy, alkenyl and alkynyl groups may be replaced by -R 2 C=CR 2 -, -C≡C-, Si(R 2) 2, C=O, C=NR 2, -C(=O)O-, -C(=O)NR 2 -, P(=O)(R 2), -O-, -S-, SO or SO 2; R 2 is selected on each occurrence, identically or differently, from H, D, F, CN, alkyl groups having 1 to 20 C atoms, aromatic ring systems having 6 to 30 aromatic ring atoms and heteroaromatic ring systems having 5 to 30 aromatic ring atoms; where two or more radicals R 2 may be linked to one another and may form a ring; and where the said alkyl groups, aromatic ring systems and heteroaromatic ring systems may be substituted by F or CN;