The present invention relates to the use of copper(I) complexes of the formula I where X is nitrogen or a C—R group, R is alkyl or aryl, Ar is phenyl or naphthyl, each of which is optionally substituted by from one to three radicals selected from the group consisting of alkoxy, alkylthio, alkylamino, dialkylamino, alkoxycarbonyl, alkoxysulfonyl, halogen, cyano, carboxyl, hydroxysulfonyl and nitro, and the two optionally substituted phenyl or naphthyl radicals may be joined to one another by a chemical single bond via the carbon atoms in the α- and α′-position relative to the phosphorus atom, n is 1, 2 or 3, and Y is halogen, cyano, thiocyanato, alkoxy, aryloxy, alkylthio, arylthio, alkylamino, dialkylamino, arylamino or diarylamino, in organic light-emitting diodes (OLEDs), The present invention further relates to light-emitting layers which comprise at least one copper(I) complex of the formula I, to OLEDs which comprise at least one copper(I) complex of the formula I or an inventive light-emitting layer, and to stationary visual display units which comprise inventive OLEDs.Furthermore, the present invention relates to novel copper(I) complexes of the formula Ia and Ib where R, Ar and n are each as defined in formula I, Y in formula Ia is defined as cyano, thiocyanato, alkoxy, aryloxy, alkylthio, arylthio, alkylamino, dialkylamino, arylamino or diarylamino, and Y in formula Ib is defined as halogen, cyano, thiocyanato, alkoxy, aryloxy, alkylthio, arylthio, alkylamino, dialkylamino, arylamino or diarylamino.