Voltage bias dependency of the space charge capacitance of wet chemically grown ZnO nanorods employed in a dye sensitized photovoltaic cell

Arrays of ZnO nanorods were suggested recently as an alternative electrode for dye sensitized (DSSC) and extremely thin absorber solar cells. In ZnO nanorod cells the electrical response is dominated by the RC behavior of the cells interfaces, which is resulting from a space charge capacitance in the order of several μF arising at the nanorods surface. We have studied the interface capacitance of a dye sensitized solar cell made from chemically prepared ZnO nanorods by time resolved photocurrent and electrical impedance measurements. While the electrical response is in good agreement with the space charge capacitance picture, the variation of the measured capacitance with the applied bias was found to deviate significantly from the simple electrostatic model. Numerical modeling of the nanorod capacitance is presented to demonstrate this.