We report electroabsorption (EA) studies of electric fields in bilayer molecular organic solar cells made from zinc phthalocyanine (ZnPc) and a methyl substituted perylene pigment (MPP). We have detected an electric field at the metal/organic interface which is sensitive to the external DC bias. The interface field has a different spectral signature from that of the bulk of the two layers, which we attribute to interface species such as charge transfer-induced dipoles. The electric field is proportional to the applied bias in devices containing only ZnPc or MPP, but rectifying behavior is observed in the bilayer solar cell. (C) 2000 Elsevier Science B.V. All rights reserved.