Analysis of Charge Transport and Recombination Studied by Electrochemical Impedance Spectroscopy for Dye-sensitized Solar Cells With Atomic Layer Deposited Metal Oxide Treatment on TiO2 Surface

The performance of dye-sensitized solar cells (DSSCs) is limited by the back-reaction of photogenerated electrons from the porous titanium oxide (TiO2) nanoparticles back into the electrolyte solution, which occurs almost exclusively through the interface. This and the fact that DSSCs have a very large interfacial area makes their performance greatly dependant on the density and activity of TiO2 surface states. Thus, effectively engineering the TiO2/dye/electrolyte interface to reduce carrier losses is critically important for improving the photovoltaic performance of the solar cell. Atomic layer deposition (ALD), which uses high purity gas precursors that can rapidly diffuse through the porous network, was used to grow a conformal and controllable aluminum oxide (Al2O3) and hafnium oxide (HfO2) ultra thin layer on the TiO2 surface. The effects of this interfacial treatment on the DSSC performance was studied with dark and illuminated current-voltage and electrochemical impedance spectroscopy (EIS) measurements.