Electrochemical impedance spectroscopy of dye-sensitized solar cells with post-treated TiO2 photoelectrodes using hafnium(IV) chloride and titanium(IV) chloride

Abstract

Abstract Post-treatment of the TiO 2 photoelectrodes (PEs) of dye-sensitized solar cells (DSSCs), in which an extra thin layer of metal oxide on the TiO 2 film is deposited, has been commonly employed to develop high-efficiency DSSCs. The post-treatment with TiCl 4 , a precursor for TiO 2 , is commonly known to enhance the efficiency of DSSCs by increasing the injection efficiency as a result of moving the TiO 2 conduction band edge downward. Among the wide bandgap metal oxides, HfCl 4 derived HfO 2 found to be a promising material for post-treatment. Even though the DSSCs based on PEs post-treated with TiO 2 have been studied extensively, there is no information about the kinetics and the energetics of the HfO 2 treated PE based DSSCs. Understanding interfacial charge transfer processes and energetics of PEs is crucial to find suitable materials for post-treatment of the PEs to develop high-efficiency DSSCs. In this paper, we have fabricated DSSCs with TiO 2 films post-treated with HfCl 4 and TiCl 4 by dip-coating. The photovoltaic performances of the DSSCs were correlated to the recombination kinetics and the energetics of the DSSCs by analyzing their electrochemical impedance spectroscopy (EIS) and current density-voltage ( j-V ) data systematically. The study showed that the increase of electron injection and decrease of recombination through post-treatment of the PEs with both HfCl 4 and TiCl 4 increased the short-circuit current density ( j sc ) without affecting the fill-factor ( ff ) and the open-circuit voltage ( V oc ) that ultimately improved the efficiency of the DSSCs.