Analyzing photovoltaic effect of double-layer organic solar cells as a Maxwell-Wagner effect system by optical electric-field-induced second-harmonic generation measurement

By using time-resolved optical electric-field-induced second-harmonic generation measurement, we directly probed photo-voltage generation process in organic double-layer (pentacene/C 60 ) solar cells. Results showed that photoillumination induced negative excess charge Q s =−3.6×10 −9 C/cm 2 at the pentacene/C 60 interface, and the induced charge caused generation of the open-circuit voltage 0.26 V. Using an equivalent circuit based on a Maxwell-Wagner (MW) effect model well accounted for the excess charge accumulation process. The MW model analysis also well accounted for the open-circuit voltage, the short-circuit current, and the fill-factor of organic solar cells (OSCs). We concluded that the excess charges due to the MW effect give a significant effect on the photovoltaic effect of OSCs.