Influence of Crystal Facets (102) or (100) on Photoelectrochemical Kinetics of ZnO Nanocrystals in Dye-Sensitized Solar Cells

Abstract

© The Author(s) 2019. Electrochemical impedance spectroscopy (EIS) and intensity-modulated photocurrent/voltage spectroscopy (IMPS/IMVS) measurements are carried out to investigate the transport and recombination kinetics in dye-sensitized solar cells (DSSCs) employing three different kinds of ZnO nanoparticles: hexagonal bipyramidal (HBP) with predominantly (102) facets, nanosheets (NS) with predominantly (100) and commercial nanoparticles (MZ) with random facets exposed. The order of recombination resistance MZ > HBP > NS revealed from EIS and IMVS did not coincide with the order NS > MZ > HBP of the open circuit voltage (VOC) of the DSSCs. Chemical capacitance determined by EIS indicated the most negatively lying conduction band edge for NS, that accounts for the higher VOC despite lower recombination resistance. On the other hand, transport resistance from EIS and electron transit time from IMPS both indicate 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 (JSC) among MZ, NS and HBP.