Probing the Low Fill Factor of NiO p-Type Dye-Sensitized Solar Cells

p-Type dye-sensitized solar cells (p-DSCs) have attracted increasing attention recently, but they suffer from low fill factors (FFs) and unsatisfactory efficiencies. A full comprehension of the hole transport and recombination processes in the NiO p-DSC is of paramount importance for both the fundamental study and the practical device optimization. In this article, NiO p-DSCs were systematically probed under various bias and illumination conditions using electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent spectroscopy (IMPS), and intensity modulated photovoltage spectroscopy (IMVS). Under the constant 1 sun illumination, the recombination resistance (R-rec) of the cell deviates from an exponential relationship with the potential and saturates at similar to 130 Omega cm(2) under the short circuit condition, which is ascribed to the overwhelming recombination with the reduced dye anions. Such a small R-rec results in the small dc resistance, which decreases the flatness of the J-V curve. The quantitative analysis demonstrates that the FF value is largely attenuated by the recombination of holes in NiO with the reduced dyes. Our analysis also shows that if this recombination can be eliminated, then an FF value of 0.6 can be reached, which agrees with the theoretical calculation with a V-oc of 160 mV.