Electrochemical Impedance Spectroscopy Analysis on Dye-sensitized Solar Cells Employing (102) and (100) Dominant ZnO Nanocrystals

摘要

We carried out electrochemical impedance spectroscopy (EIS) measurement to investigate the transport and back reaction kinetics in dye-sensitized solar cells (DSSCs) employing three different kinds of ZnO nanoparticles with different crystal facets prepared based on our previous work. They were synthesized using microwave assistant hydrothermal synthesis, and named hexagonal bipyramidal (HBP) and nanosheets (NS) with predominantly (102) and (100) facets, respectively, and commercial nanoparticles (MZ) with random facets exposed was used for comparison. The order of recombination resistance MZ > HBP > NS revealed from EIS did not coincide with the order NS > MZ > HBP of the open circuit voltage (V_(OC)) of the DSSCs. Chemical capacitance indicated the most negatively lying conduction band edge for NS, that accounts for the higher V_(OC) despite lower recombination resistance. On the other hand, transport resistance indicates faster electron transport for well-crystallized hydrothermally synthesized HBP and NS than for the randomly structured commercial MZ. That of MZ, however, was still sufficiently fast compared to the electron lifetime to ensure a good collection efficiency, leading to almost constant short circuit current density (J_(SC)) among MZ, NS and HBP.