Cu2O based junctions (both Schottky and ZnO/Cu2O heterojunctions) exhibit a metastable capacitance increase after illumination or reverse bias application. We show that this effect is related to the persistent photoconductivity in Cu2O substrates. To obtain a quantitative evaluation of defect properties we have measured conductivity vs T, Capacitance-Voltage, persistent photoconductivity decay and capacitance transient at different temperatures. We show that it is impossible to explain these data using an electronic mechanism only. A new model which includes the formation-dissociation of intrinsic defect complexes (V-cu-V-O) can give instead a better agreement with the experimental data. (C) 2008 Elsevier B.V. All rights reserved.