Analyzing Photo Induced Internal Electric Field in Pentacene/C60 Double-Layer Organic Solar Cells under Various External Voltages by Electric-Field-Induced Optical Second Harmonic Generation Measurement

By using electric-field-induced optical second-harmonic generation (EFISHG) measurement, we investigated interfacial carrier behavior in pentacene/C-60 double-layer organic solar cells (OSCs). At various external DC biasing conditions, photoinduced electric field in the OSCs was directly probed by the EFISHG measurements. A potential drop was generated by photoillumination, in a manner like a potential difference across an external resistance, while applying an external DC voltage to the OSCs enables us to examine the carrier behaviors over the entire region of the external voltage Vex. Results showed that only organic double-layer interface charging was induced under positive DC biasing by photoillumination, while interface and electrode charging were induced under negative DC biasing. Analyzing the pentacene/C-60 double layer OSCs based on a Maxwell-Wagner model, we showed that the dielectric nature of the organic layers was responsible for the asymmetric charging processes. (C) 2012 The Japan Society of Applied Physics