Optical electric-field-induced second-harmonic generation measurement was employed for studying interfacial processes in copper phthalocyanine (CuPc)/C-60 double-layer organic solar cells. Results suggested that interfacial charging process happened on the CuPc/C-60 interface and the applied illumination can change the polarity of the accumulated charges on the double-layer interface while the direction of conduction current is the same. The Maxwell-Wagner model analysis revealed that the photo conductance change is responsible for these converse behaviors with and without illumination. (C) 2013 Elsevier B. V. All rights reserved.