Characteristics of charge transport in nano-sized TiO2 particles/submicron spheres multilayer thin-film electrode

Abstract

In this work, we design the nano-sized TiO2 particles/submicron spheres multilayer structured photoanode, based on the fact of stronger light scattering properties of TiO2 submicron spheres. Effect of TiO2 submicron-spheres on the charge transport and interfacial properties in multilayer thin-film electrodes are investigated in detail using intensity-modulated photocurrent spectroscopy (IMPS), electrochemical impedance spectroscopy (EIS) and incident photon-to-current conversion efficiency (IPCE). Results obtained from IMPS for dye-sensitized solar cells (DSCs) indicate that submicron-spheres have fewer defects, but the poor contact at the interfaces between submicron spheres hinders the electron transport and makes the transit time longer. EIS results show that there are no obvious differences in interface recombination between the designed electrodes. It is interesting to find that the bottom section of the photoanode composed of nano-sized TiO2 thin film has a higher light utilization efficiency than that composed of submicron-spheres; meanwhile, the Fermi level of TiO2 and the photovoltaic properties of DSCs have been extended. Our results may provide an experiment basis for structure design of high-efficiency DSC photoanode.