Aryl amines selected for the hole transporting layer include molecules of the following formula ##STR4## wherein X is an alkyl group or a halogen,especially those substituents selected from the group consisting of Cl and CH.sub.3.Examples of specific aryl amines are N,N'-diphenyl-N,N'-bis(alkylphenyl)-1,1-biphenyl-4,4'-diamine wherein alkyl is selected from the group consisting of methyl, ethyl, p