p-Type Dye-Sensitized NiO Solar Cells: A Study by Electrochemical Impedance Spectroscopy

This article presents a fundamental and systematic investigation of NiO based p-type dye-sensitized solar cells (p-DSCs) using electrochemical impedance spectroscopy (EIS). The Nyquist plot features two semicircles. By varying the electrocatalytic properties of the counter electrode and the illumination intensities, we have unambiguously assigned the two semicircles to the charge transfer process at the counter electrode/electrolyte interface and the hole recombination at the NiO/dye/electrolyte interface, respectively. Key recombination parameters, including the recombination resistance, chemical capacitance, and the hole lifetime, have been obtained under illumination and in the dark. Comparisons between the recombination process of the typical n-DSCs and p-DSCs show that the hole lifetime in our NiO p-DSCs is shorter than the electron lifetime in the TiO2 n-DSCs under the same voltages.