Polymer which contains 1 to 100 mol% of at least one recurring unit of the following formula (Ia): where A is a polycyclic, aromatic or heteroaromatic ring system having 10 to 30 aromatic or heteroaromatic ring atoms, which may be substituted by one or more radicals R, B is a mono- or polycyclic, aromatic or heteroaromatic ring system having 5 to 10 aromatic or heteroaromatic ring atoms, which may be substituted by one or more radicals R, where the number of aromatic or heteroaromatic ring atoms of A is greater than the number of aromatic or heteroaromatic ring atoms of B, Ar 1, Ar 2, Ar 3 and Ar 4 are on each occurrence, in each case identically or differently, a mono- or polycyclic, aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R, s and t are, in each case identically or differently, 0 or 1, R is on each occurrence, identically or differently, H, a straightchain alkyl or alkoxy group having 1 to 10 C atoms or an alkenyl or alkynyl group having 2 to 10 C atoms or a branched or cyclic alkyl or alkoxy group having 3 to 10 C atoms, which may in each case be substituted by one or more radicals R 1, where one or more non-adjacent CH 2 groups may be replaced by R 1 C=CR 1, C=O, C=NR 1, NR 1, O or CONR 1, or an aromatic or heteroaromatic ring system having 5 to 20 aromatic ring atoms, which may in each case be substituted by one or more radicals R 1, or an aryloxy or heteroaryloxy group having 5 to 20 aromatic ring atoms, which may be substituted by one or more radicals R 1, or an aralkyl or heteroaralkyl group having 5 to 20 aromatic ring atoms, which may be substituted by one or more radicals R 1, or a diarylamino group, diheteroarylamino group or arylheteroarylamino group having 10 to 20 aromatic ring atoms, which may be substituted by one or more radicals R 1, or a crosslinkable group Q, where two or more radicals R may also form a mono- or polycyclic, aliphatic, aromatic and/or benzo-fused ring system with one another; R 1 is on each occurrence, identically or differently, H, D, F or an aliphatic hydrocarbon radical having 1 to 20 C atoms, an aromatic and/or heteroaromatic hydrocarbon radical having 5 to 20 C atoms, in which, in addition, one or more H atoms may be replaced by F; where two or more substituents R 1 may also form a mono- or polycyclic, aliphatic, aromatic or heteroaromatic ring system with one another; Q is a terminal or cyclic alkenyl group, a terminal dienyl or alkynyl group, an alkenyloxy, dienyloxy or alkynyloxy group, an acrylic acid group, an oxetane or oxirane group, a silane group or a cyclobutane group, and the dashed lines represent bonds to adjacent recurring units in the polymer. A is a polycyclic, aromatic or heteroaromatic ring system having 10 to 30 aromatic or heteroaromatic ring atoms, which may be substituted by one or more radicals R, B is a mono- or polycyclic, aromatic or heteroaromatic ring system having 5 to 10 aromatic or heteroaromatic ring atoms, which may be substituted by one or more radicals R, where the number of aromatic or heteroaromatic ring atoms of A is greater than the number of aromatic or heteroaromatic ring atoms of B, Ar 1, Ar 2, Ar 3 and Ar 4 are on each occurrence, in each case identically or differently, a mono- or polycyclic, aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R, s and t are, in each case identically or differently, 0 or 1, R is on each occurrence, identically or differently, H, a straightchain alkyl or alkoxy group having 1 to 10 C atoms or an alkenyl or alkynyl group having 2 to 10 C atoms or a branched or cyclic alkyl or alkoxy group having 3 to 10 C atoms, which may in each case be substituted by one or more radicals R 1, where one or more non-adjacent CH 2 groups may be replaced by R 1 C=CR 1, C=O, C=NR 1, NR 1, O or CONR 1, or an aromatic or heteroaromatic ring system having 5 to 20 aromatic ring atoms, which may in each case be substituted by one or more radicals R 1, or an aryloxy or heteroaryloxy group having 5 to 20 aromatic ring atoms, which may be substituted by one or more radicals R 1, or an aralkyl or heteroaralkyl group having 5 to 20 aromatic ring atoms, which may be substituted by one or more radicals R 1, or a diarylamino group, diheteroarylamino group or arylheteroarylamino group having 10 to 20 aromatic ring atoms, which may be substituted by one or more radicals R 1, or a crosslinkable group Q, where two or more radicals R may also form a mono- or polycyclic, aliphatic, aromatic and/or benzo-fused ring system with one another; R 1 is on each occurrence, identically or differently, H, D, F or an aliphatic hydrocarbon radical having 1 to 20 C atoms, an aromatic and/or heteroaromatic hydrocarbon radical having 5 to 20 C atoms, in which, in addition, one or more H atoms may be replaced by F; where two or more substituents R 1 may also form a mono- or polycyclic, aliphatic, aromatic or heteroaromatic ring system with one another; Q is a terminal or cyclic alkenyl group, a terminal dienyl or alkynyl group, an alkenyloxy, dienyloxy or alkynyloxy group, an acrylic acid group, an oxetane or oxirane group, a silane group or a cyclobutane group, and